Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

43 files changed, 17534 insertions, 0 deletions

diff --git a/third_party/rust/wast/src/component.rs b/third_party/rust/wast/src/component.rs
new file mode 100644
index 0000000000..899baaa356
--- /dev/null
+++ b/third_party/rust/wast/src/component.rs
@@ -0,0 +1,28 @@
+//! Types and support for parsing the component model text format.
+
+mod alias;
+mod binary;
+mod component;
+mod custom;
+mod expand;
+mod export;
+mod func;
+mod import;
+mod instance;
+mod item_ref;
+mod module;
+mod resolve;
+mod types;
+mod wast;
+
+pub use self::alias::*;
+pub use self::component::*;
+pub use self::custom::*;
+pub use self::export::*;
+pub use self::func::*;
+pub use self::import::*;
+pub use self::instance::*;
+pub use self::item_ref::*;
+pub use self::module::*;
+pub use self::types::*;
+pub use self::wast::*;
diff --git a/third_party/rust/wast/src/component/alias.rs b/third_party/rust/wast/src/component/alias.rs
new file mode 100644
index 0000000000..3c70a2d371
--- /dev/null
+++ b/third_party/rust/wast/src/component/alias.rs
@@ -0,0 +1,253 @@
+use crate::core::ExportKind;
+use crate::kw;
+use crate::parser::{Parse, Parser, Result};
+use crate::token::{Id, Index, NameAnnotation, Span};
+
+/// A inline alias for component exported items.
+#[derive(Debug)]
+pub struct InlineExportAlias<'a> {
+    /// The instance to alias the export from.
+    pub instance: Index<'a>,
+    /// The name of the export to alias.
+    pub name: &'a str,
+}
+
+impl<'a> Parse<'a> for InlineExportAlias<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.parse::<kw::alias>()?;
+        parser.parse::<kw::export>()?;
+        let instance = parser.parse()?;
+        let name = parser.parse()?;
+        Ok(Self { instance, name })
+    }
+}
+
+/// An alias to a component item.
+#[derive(Debug)]
+pub struct Alias<'a> {
+    /// Where this `alias` was defined.
+    pub span: Span,
+    /// An identifier that this alias is resolved with (optionally) for name
+    /// resolution.
+    pub id: Option<Id<'a>>,
+    /// An optional name for this alias stored in the custom `name` section.
+    pub name: Option<NameAnnotation<'a>>,
+    /// The target of this alias.
+    pub target: AliasTarget<'a>,
+}
+
+impl<'a> Alias<'a> {
+    /// Parses only an outer type alias.
+    pub fn parse_outer_core_type_alias(parser: Parser<'a>) -> Result<Self> {
+        let span = parser.parse::<kw::alias>()?.0;
+        parser.parse::<kw::outer>()?;
+        let outer = parser.parse()?;
+        let index = parser.parse()?;
+
+        let (kind, id, name) = parser.parens(|parser| {
+            let mut kind: ComponentOuterAliasKind = parser.parse()?;
+            match kind {
+                ComponentOuterAliasKind::CoreType => {
+                    return Err(parser.error("expected type for outer alias"))
+                }
+                ComponentOuterAliasKind::Type => {
+                    kind = ComponentOuterAliasKind::CoreType;
+                }
+                _ => return Err(parser.error("expected core type or type for outer alias")),
+            }
+
+            Ok((kind, parser.parse()?, parser.parse()?))
+        })?;
+
+        Ok(Self {
+            span,
+            target: AliasTarget::Outer { outer, index, kind },
+            id,
+            name,
+        })
+    }
+}
+
+impl<'a> Parse<'a> for Alias<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let span = parser.parse::<kw::alias>()?.0;
+
+        let mut l = parser.lookahead1();
+
+        let (target, id, name) = if l.peek::<kw::outer>() {
+            parser.parse::<kw::outer>()?;
+            let outer = parser.parse()?;
+            let index = parser.parse()?;
+            let (kind, id, name) =
+                parser.parens(|parser| Ok((parser.parse()?, parser.parse()?, parser.parse()?)))?;
+
+            (AliasTarget::Outer { outer, index, kind }, id, name)
+        } else if l.peek::<kw::export>() {
+            parser.parse::<kw::export>()?;
+            let instance = parser.parse()?;
+            let export_name = parser.parse()?;
+            let (kind, id, name) =
+                parser.parens(|parser| Ok((parser.parse()?, parser.parse()?, parser.parse()?)))?;
+
+            (
+                AliasTarget::Export {
+                    instance,
+                    name: export_name,
+                    kind,
+                },
+                id,
+                name,
+            )
+        } else if l.peek::<kw::core>() {
+            parser.parse::<kw::core>()?;
+            parser.parse::<kw::export>()?;
+            let instance = parser.parse()?;
+            let export_name = parser.parse()?;
+            let (kind, id, name) = parser.parens(|parser| {
+                parser.parse::<kw::core>()?;
+                Ok((parser.parse()?, parser.parse()?, parser.parse()?))
+            })?;
+
+            (
+                AliasTarget::CoreExport {
+                    instance,
+                    name: export_name,
+                    kind,
+                },
+                id,
+                name,
+            )
+        } else {
+            return Err(l.error());
+        };
+
+        Ok(Self {
+            span,
+            target,
+            id,
+            name,
+        })
+    }
+}
+
+/// Represents the kind of instance export alias.
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+pub enum ComponentExportAliasKind {
+    /// The alias is to a core module export.
+    CoreModule,
+    /// The alias is to a function export.
+    Func,
+    /// The alias is to a value export.
+    Value,
+    /// The alias is to a type export.
+    Type,
+    /// The alias is to a component export.
+    Component,
+    /// The alias is to an instance export.
+    Instance,
+}
+
+impl<'a> Parse<'a> for ComponentExportAliasKind {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut l = parser.lookahead1();
+        if l.peek::<kw::core>() {
+            parser.parse::<kw::core>()?;
+            let mut l = parser.lookahead1();
+            if l.peek::<kw::module>() {
+                parser.parse::<kw::module>()?;
+                Ok(Self::CoreModule)
+            } else {
+                Err(l.error())
+            }
+        } else if l.peek::<kw::func>() {
+            parser.parse::<kw::func>()?;
+            Ok(Self::Func)
+        } else if l.peek::<kw::value>() {
+            parser.parse::<kw::value>()?;
+            Ok(Self::Value)
+        } else if l.peek::<kw::r#type>() {
+            parser.parse::<kw::r#type>()?;
+            Ok(Self::Type)
+        } else if l.peek::<kw::component>() {
+            parser.parse::<kw::component>()?;
+            Ok(Self::Component)
+        } else if l.peek::<kw::instance>() {
+            parser.parse::<kw::instance>()?;
+            Ok(Self::Instance)
+        } else {
+            Err(l.error())
+        }
+    }
+}
+
+/// Represents the kind of outer alias.
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+pub enum ComponentOuterAliasKind {
+    /// The alias is to an outer core module.
+    CoreModule,
+    /// The alias is to an outer core type.
+    CoreType,
+    /// The alias is to an outer type.
+    Type,
+    /// The alias is to an outer component.
+    Component,
+}
+
+impl<'a> Parse<'a> for ComponentOuterAliasKind {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut l = parser.lookahead1();
+        if l.peek::<kw::core>() {
+            parser.parse::<kw::core>()?;
+            let mut l = parser.lookahead1();
+            if l.peek::<kw::module>() {
+                parser.parse::<kw::module>()?;
+                Ok(Self::CoreModule)
+            } else if l.peek::<kw::r#type>() {
+                parser.parse::<kw::r#type>()?;
+                Ok(Self::CoreType)
+            } else {
+                Err(l.error())
+            }
+        } else if l.peek::<kw::r#type>() {
+            parser.parse::<kw::r#type>()?;
+            Ok(Self::Type)
+        } else if l.peek::<kw::component>() {
+            parser.parse::<kw::component>()?;
+            Ok(Self::Component)
+        } else {
+            Err(l.error())
+        }
+    }
+}
+
+/// The target of a component alias.
+#[derive(Debug)]
+pub enum AliasTarget<'a> {
+    /// The alias is to an export of a component instance.
+    Export {
+        /// The component instance exporting the item.
+        instance: Index<'a>,
+        /// The name of the exported item to alias.
+        name: &'a str,
+        /// The export kind of the alias.
+        kind: ComponentExportAliasKind,
+    },
+    /// The alias is to an export of a module instance.
+    CoreExport {
+        /// The module instance exporting the item.
+        instance: Index<'a>,
+        /// The name of the exported item to alias.
+        name: &'a str,
+        /// The export kind of the alias.
+        kind: ExportKind,
+    },
+    /// The alias is to an item from an outer component.
+    Outer {
+        /// The number of enclosing components to skip.
+        outer: Index<'a>,
+        /// The index of the item being aliased.
+        index: Index<'a>,
+        /// The outer alias kind.
+        kind: ComponentOuterAliasKind,
+    },
+}
diff --git a/third_party/rust/wast/src/component/binary.rs b/third_party/rust/wast/src/component/binary.rs
new file mode 100644
index 0000000000..6d57ed4380
--- /dev/null
+++ b/third_party/rust/wast/src/component/binary.rs
@@ -0,0 +1,972 @@
+use crate::component::*;
+use crate::core;
+use crate::token::{Id, Index, NameAnnotation};
+use wasm_encoder::{
+    CanonicalFunctionSection, ComponentAliasSection, ComponentDefinedTypeEncoder,
+    ComponentExportSection, ComponentImportSection, ComponentInstanceSection, ComponentNameSection,
+    ComponentSection, ComponentSectionId, ComponentStartSection, ComponentTypeEncoder,
+    ComponentTypeSection, CoreTypeEncoder, CoreTypeSection, InstanceSection, NameMap,
+    NestedComponentSection, RawSection, SectionId,
+};
+
+pub fn encode(component: &Component<'_>) -> Vec<u8> {
+    match &component.kind {
+        ComponentKind::Text(fields) => {
+            encode_fields(&component.id, &component.name, fields).finish()
+        }
+        ComponentKind::Binary(bytes) => bytes.iter().flat_map(|b| b.iter().copied()).collect(),
+    }
+}
+
+fn encode_fields(
+    // TODO: use the id and name for a future names section
+    component_id: &Option<Id<'_>>,
+    component_name: &Option<NameAnnotation<'_>>,
+    fields: &[ComponentField<'_>],
+) -> wasm_encoder::Component {
+    let mut e = Encoder::default();
+
+    for field in fields {
+        match field {
+            ComponentField::CoreModule(m) => e.encode_core_module(m),
+            ComponentField::CoreInstance(i) => e.encode_core_instance(i),
+            ComponentField::CoreType(t) => e.encode_core_type(t),
+            ComponentField::Component(c) => e.encode_component(c),
+            ComponentField::Instance(i) => e.encode_instance(i),
+            ComponentField::Alias(a) => e.encode_alias(a),
+            ComponentField::Type(t) => e.encode_type(t),
+            ComponentField::CanonicalFunc(f) => e.encode_canonical_func(f),
+            ComponentField::CoreFunc(_) | ComponentField::Func(_) => {
+                unreachable!("should be expanded already")
+            }
+            ComponentField::Start(s) => e.encode_start(s),
+            ComponentField::Import(i) => e.encode_import(i),
+            ComponentField::Export(ex) => e.encode_export(ex),
+            ComponentField::Custom(c) => e.encode_custom(c),
+        }
+    }
+
+    e.flush(None);
+    e.encode_names(component_id, component_name);
+
+    e.component
+}
+
+fn encode_core_type(encoder: CoreTypeEncoder, ty: &CoreTypeDef) {
+    match ty {
+        CoreTypeDef::Def(core::TypeDef::Func(f)) => {
+            encoder.function(
+                f.params.iter().map(|(_, _, ty)| (*ty).into()),
+                f.results.iter().copied().map(Into::into),
+            );
+        }
+        CoreTypeDef::Def(core::TypeDef::Struct(_)) | CoreTypeDef::Def(core::TypeDef::Array(_)) => {
+            todo!("encoding of GC proposal types not yet implemented")
+        }
+        CoreTypeDef::Module(t) => {
+            encoder.module(&t.into());
+        }
+    }
+}
+
+fn encode_type(encoder: ComponentTypeEncoder, ty: &TypeDef) {
+    match ty {
+        TypeDef::Defined(t) => {
+            encode_defined_type(encoder.defined_type(), t);
+        }
+        TypeDef::Func(f) => {
+            let mut encoder = encoder.function();
+            encoder.params(f.params.iter().map(|p| (p.name, &p.ty)));
+
+            if f.results.len() == 1 && f.results[0].name.is_none() {
+                encoder.result(&f.results[0].ty);
+            } else {
+                encoder.results(f.results.iter().map(|r| (r.name.unwrap_or(""), &r.ty)));
+            }
+        }
+        TypeDef::Component(c) => {
+            encoder.component(&c.into());
+        }
+        TypeDef::Instance(i) => {
+            encoder.instance(&i.into());
+        }
+    }
+}
+
+fn encode_defined_type(encoder: ComponentDefinedTypeEncoder, ty: &ComponentDefinedType) {
+    match ty {
+        ComponentDefinedType::Primitive(p) => encoder.primitive((*p).into()),
+        ComponentDefinedType::Record(r) => {
+            encoder.record(r.fields.iter().map(|f| (f.name, &f.ty)));
+        }
+        ComponentDefinedType::Variant(v) => {
+            encoder.variant(v.cases.iter().map(|c| {
+                (
+                    c.name,
+                    c.ty.as_ref().map(Into::into),
+                    c.refines.as_ref().map(Into::into),
+                )
+            }));
+        }
+        ComponentDefinedType::List(l) => {
+            encoder.list(l.element.as_ref());
+        }
+        ComponentDefinedType::Tuple(t) => {
+            encoder.tuple(t.fields.iter());
+        }
+        ComponentDefinedType::Flags(f) => {
+            encoder.flags(f.names.iter().copied());
+        }
+        ComponentDefinedType::Enum(e) => {
+            encoder.enum_type(e.names.iter().copied());
+        }
+        ComponentDefinedType::Union(u) => encoder.union(u.types.iter()),
+        ComponentDefinedType::Option(o) => {
+            encoder.option(o.element.as_ref());
+        }
+        ComponentDefinedType::Result(e) => {
+            encoder.result(
+                e.ok.as_deref().map(Into::into),
+                e.err.as_deref().map(Into::into),
+            );
+        }
+    }
+}
+
+#[derive(Default)]
+struct Encoder<'a> {
+    component: wasm_encoder::Component,
+    current_section_id: Option<u8>,
+
+    // Core sections
+    // Note: module sections are written immediately
+    core_instances: InstanceSection,
+    core_types: CoreTypeSection,
+
+    // Component sections
+    // Note: custom, component, start sections are written immediately
+    instances: ComponentInstanceSection,
+    aliases: ComponentAliasSection,
+    types: ComponentTypeSection,
+    funcs: CanonicalFunctionSection,
+    imports: ComponentImportSection,
+    exports: ComponentExportSection,
+
+    core_func_names: Vec<Option<&'a str>>,
+    core_table_names: Vec<Option<&'a str>>,
+    core_memory_names: Vec<Option<&'a str>>,
+    core_global_names: Vec<Option<&'a str>>,
+    core_type_names: Vec<Option<&'a str>>,
+    core_module_names: Vec<Option<&'a str>>,
+    core_instance_names: Vec<Option<&'a str>>,
+    func_names: Vec<Option<&'a str>>,
+    value_names: Vec<Option<&'a str>>,
+    type_names: Vec<Option<&'a str>>,
+    component_names: Vec<Option<&'a str>>,
+    instance_names: Vec<Option<&'a str>>,
+}
+
+impl<'a> Encoder<'a> {
+    fn encode_custom(&mut self, custom: &Custom) {
+        // Flush any in-progress section before encoding the customs section
+        self.flush(None);
+        self.component.section(custom);
+    }
+
+    fn encode_core_module(&mut self, module: &CoreModule<'a>) {
+        // Flush any in-progress section before encoding the module
+        self.flush(None);
+
+        self.core_module_names
+            .push(get_name(&module.id, &module.name));
+
+        match &module.kind {
+            CoreModuleKind::Import { .. } => unreachable!("should be expanded already"),
+            CoreModuleKind::Inline { fields } => {
+                // TODO: replace this with a wasm-encoder based encoding (should return `wasm_encoder::Module`)
+                let data = crate::core::binary::encode(&module.id, &module.name, fields);
+                self.component.section(&RawSection {
+                    id: ComponentSectionId::CoreModule.into(),
+                    data: &data,
+                });
+            }
+        }
+    }
+
+    fn encode_core_instance(&mut self, instance: &CoreInstance<'a>) {
+        self.core_instance_names
+            .push(get_name(&instance.id, &instance.name));
+        match &instance.kind {
+            CoreInstanceKind::Instantiate { module, args } => {
+                self.core_instances.instantiate(
+                    module.into(),
+                    args.iter().map(|arg| (arg.name, (&arg.kind).into())),
+                );
+            }
+            CoreInstanceKind::BundleOfExports(exports) => {
+                self.core_instances.export_items(exports.iter().map(|e| {
+                    let (kind, index) = (&e.item).into();
+                    (e.name, kind, index)
+                }));
+            }
+        }
+
+        self.flush(Some(self.core_instances.id()));
+    }
+
+    fn encode_core_type(&mut self, ty: &CoreType<'a>) {
+        self.core_type_names.push(get_name(&ty.id, &ty.name));
+        encode_core_type(self.core_types.ty(), &ty.def);
+        self.flush(Some(self.core_types.id()));
+    }
+
+    fn encode_component(&mut self, component: &NestedComponent<'a>) {
+        self.component_names
+            .push(get_name(&component.id, &component.name));
+        // Flush any in-progress section before encoding the component
+        self.flush(None);
+
+        match &component.kind {
+            NestedComponentKind::Import { .. } => unreachable!("should be expanded already"),
+            NestedComponentKind::Inline(fields) => {
+                self.component
+                    .section(&NestedComponentSection(&encode_fields(
+                        &component.id,
+                        &component.name,
+                        fields,
+                    )));
+            }
+        }
+    }
+
+    fn encode_instance(&mut self, instance: &Instance<'a>) {
+        self.instance_names
+            .push(get_name(&instance.id, &instance.name));
+        match &instance.kind {
+            InstanceKind::Import { .. } => unreachable!("should be expanded already"),
+            InstanceKind::Instantiate { component, args } => {
+                self.instances.instantiate(
+                    component.into(),
+                    args.iter().map(|arg| {
+                        let (kind, index) = (&arg.kind).into();
+                        (arg.name, kind, index)
+                    }),
+                );
+            }
+            InstanceKind::BundleOfExports(exports) => {
+                self.instances.export_items(exports.iter().map(|e| {
+                    let (kind, index) = (&e.kind).into();
+                    (e.name, kind, index)
+                }));
+            }
+        }
+
+        self.flush(Some(self.instances.id()));
+    }
+
+    fn encode_alias(&mut self, alias: &Alias<'a>) {
+        let name = get_name(&alias.id, &alias.name);
+        self.aliases.alias((&alias.target).into());
+        match &alias.target {
+            AliasTarget::Export { kind, .. } => {
+                self.names_for_component_export_alias(*kind).push(name);
+            }
+            AliasTarget::CoreExport { kind, .. } => {
+                self.names_for_core_export_alias(*kind).push(name);
+            }
+            AliasTarget::Outer { kind, .. } => {
+                self.names_for_component_outer_alias(*kind).push(name);
+            }
+        }
+
+        self.flush(Some(self.aliases.id()));
+    }
+
+    fn encode_start(&mut self, start: &Start) {
+        // Flush any in-progress section before encoding the start section
+        self.flush(None);
+
+        self.component.section(&ComponentStartSection {
+            function_index: start.func.into(),
+            args: start.args.iter().map(|a| a.idx.into()).collect::<Vec<_>>(),
+            results: start.results.len() as u32,
+        });
+    }
+
+    fn encode_type(&mut self, ty: &Type<'a>) {
+        self.type_names.push(get_name(&ty.id, &ty.name));
+        encode_type(self.types.ty(), &ty.def);
+        self.flush(Some(self.types.id()));
+    }
+
+    fn encode_canonical_func(&mut self, func: &CanonicalFunc<'a>) {
+        let name = get_name(&func.id, &func.name);
+        match &func.kind {
+            CanonicalFuncKind::Lift { ty, info } => {
+                self.func_names.push(name);
+                self.funcs.lift(
+                    info.func.idx.into(),
+                    ty.into(),
+                    info.opts.iter().map(Into::into),
+                );
+            }
+            CanonicalFuncKind::Lower(info) => {
+                self.core_func_names.push(name);
+                self.funcs
+                    .lower(info.func.idx.into(), info.opts.iter().map(Into::into));
+            }
+        }
+
+        self.flush(Some(self.funcs.id()));
+    }
+
+    fn encode_import(&mut self, import: &ComponentImport<'a>) {
+        let name = get_name(&import.item.id, &import.item.name);
+        self.names_for_item_kind(&import.item.kind).push(name);
+        self.imports.import(
+            import.name,
+            import.url.unwrap_or(""),
+            (&import.item.kind).into(),
+        );
+        self.flush(Some(self.imports.id()));
+    }
+
+    fn encode_export(&mut self, export: &ComponentExport<'a>) {
+        let name = get_name(&export.id, &export.debug_name);
+        let (kind, index) = (&export.kind).into();
+        self.exports.export(
+            export.name,
+            export.url.unwrap_or(""),
+            kind,
+            index,
+            export.ty.as_ref().map(|ty| (&ty.0.kind).into()),
+        );
+        match &export.kind {
+            ComponentExportKind::CoreModule(_) => self.core_module_names.push(name),
+            ComponentExportKind::Func(_) => self.func_names.push(name),
+            ComponentExportKind::Instance(_) => self.instance_names.push(name),
+            ComponentExportKind::Value(_) => self.value_names.push(name),
+            ComponentExportKind::Component(_) => self.component_names.push(name),
+            ComponentExportKind::Type(_) => self.type_names.push(name),
+        }
+        self.flush(Some(self.exports.id()));
+    }
+
+    fn flush(&mut self, section_id: Option<u8>) {
+        if self.current_section_id == section_id {
+            return;
+        }
+
+        if let Some(id) = self.current_section_id {
+            match id {
+                // 0 => custom sections are written immediately
+                // 1 => core modules sections are written immediately
+                2 => {
+                    assert_eq!(id, self.core_instances.id());
+                    self.component.section(&self.core_instances);
+                    self.core_instances = Default::default();
+                }
+                3 => {
+                    assert_eq!(id, self.core_types.id());
+                    self.component.section(&self.core_types);
+                    self.core_types = Default::default();
+                }
+                // 4 => components sections are written immediately
+                5 => {
+                    assert_eq!(id, self.instances.id());
+                    self.component.section(&self.instances);
+                    self.instances = Default::default();
+                }
+                6 => {
+                    assert_eq!(id, self.aliases.id());
+                    self.component.section(&self.aliases);
+                    self.aliases = Default::default();
+                }
+                7 => {
+                    assert_eq!(id, self.types.id());
+                    self.component.section(&self.types);
+                    self.types = Default::default();
+                }
+                8 => {
+                    assert_eq!(id, self.funcs.id());
+                    self.component.section(&self.funcs);
+                    self.funcs = Default::default();
+                }
+                // 9 => start sections are written immediately
+                10 => {
+                    assert_eq!(id, self.imports.id());
+                    self.component.section(&self.imports);
+                    self.imports = Default::default();
+                }
+                11 => {
+                    assert_eq!(id, self.exports.id());
+                    self.component.section(&self.exports);
+                    self.exports = Default::default();
+                }
+                _ => unreachable!("unknown incremental component section id: {}", id),
+            }
+        }
+
+        self.current_section_id = section_id
+    }
+
+    fn encode_names(
+        &mut self,
+        component_id: &Option<Id<'_>>,
+        component_name: &Option<NameAnnotation<'_>>,
+    ) {
+        let mut names = ComponentNameSection::new();
+        if let Some(name) = get_name(component_id, component_name) {
+            names.component(name);
+        }
+
+        let mut funcs = |list: &[Option<&str>], append: fn(&mut ComponentNameSection, &NameMap)| {
+            let mut map = NameMap::new();
+            for (i, entry) in list.iter().enumerate() {
+                if let Some(name) = entry {
+                    map.append(i as u32, name);
+                }
+            }
+            if !map.is_empty() {
+                append(&mut names, &map);
+            }
+        };
+
+        funcs(&self.core_func_names, ComponentNameSection::core_funcs);
+        funcs(&self.core_table_names, ComponentNameSection::core_tables);
+        funcs(&self.core_memory_names, ComponentNameSection::core_memories);
+        funcs(&self.core_global_names, ComponentNameSection::core_globals);
+        funcs(&self.core_type_names, ComponentNameSection::core_types);
+        funcs(&self.core_module_names, ComponentNameSection::core_modules);
+        funcs(
+            &self.core_instance_names,
+            ComponentNameSection::core_instances,
+        );
+        funcs(&self.func_names, ComponentNameSection::funcs);
+        funcs(&self.value_names, ComponentNameSection::values);
+        funcs(&self.type_names, ComponentNameSection::types);
+        funcs(&self.component_names, ComponentNameSection::components);
+        funcs(&self.instance_names, ComponentNameSection::instances);
+
+        if !names.is_empty() {
+            self.component.section(&names);
+        }
+    }
+
+    fn names_for_component_export_alias(
+        &mut self,
+        kind: ComponentExportAliasKind,
+    ) -> &mut Vec<Option<&'a str>> {
+        match kind {
+            ComponentExportAliasKind::Func => &mut self.func_names,
+            ComponentExportAliasKind::CoreModule => &mut self.core_module_names,
+            ComponentExportAliasKind::Value => &mut self.value_names,
+            ComponentExportAliasKind::Type => &mut self.type_names,
+            ComponentExportAliasKind::Component => &mut self.component_names,
+            ComponentExportAliasKind::Instance => &mut self.instance_names,
+        }
+    }
+
+    fn names_for_component_outer_alias(
+        &mut self,
+        kind: ComponentOuterAliasKind,
+    ) -> &mut Vec<Option<&'a str>> {
+        match kind {
+            ComponentOuterAliasKind::CoreModule => &mut self.core_module_names,
+            ComponentOuterAliasKind::CoreType => &mut self.core_type_names,
+            ComponentOuterAliasKind::Component => &mut self.component_names,
+            ComponentOuterAliasKind::Type => &mut self.type_names,
+        }
+    }
+
+    fn names_for_core_export_alias(&mut self, kind: core::ExportKind) -> &mut Vec<Option<&'a str>> {
+        match kind {
+            core::ExportKind::Func => &mut self.core_func_names,
+            core::ExportKind::Global => &mut self.core_global_names,
+            core::ExportKind::Table => &mut self.core_table_names,
+            core::ExportKind::Memory => &mut self.core_memory_names,
+            core::ExportKind::Tag => unimplemented!(),
+        }
+    }
+
+    fn names_for_item_kind(&mut self, kind: &ItemSigKind) -> &mut Vec<Option<&'a str>> {
+        match kind {
+            ItemSigKind::CoreModule(_) => &mut self.core_module_names,
+            ItemSigKind::Func(_) => &mut self.func_names,
+            ItemSigKind::Component(_) => &mut self.component_names,
+            ItemSigKind::Instance(_) => &mut self.instance_names,
+            ItemSigKind::Value(_) => &mut self.value_names,
+            ItemSigKind::Type(_) => &mut self.type_names,
+        }
+    }
+}
+
+fn get_name<'a>(id: &Option<Id<'a>>, name: &Option<NameAnnotation<'a>>) -> Option<&'a str> {
+    name.as_ref().map(|n| n.name).or_else(|| {
+        id.and_then(|id| {
+            if id.is_gensym() {
+                None
+            } else {
+                Some(id.name())
+            }
+        })
+    })
+}
+
+// This implementation is much like `wasm_encoder::CustomSection`, except
+// that it extends via a list of slices instead of a single slice.
+impl wasm_encoder::Encode for Custom<'_> {
+    fn encode(&self, sink: &mut Vec<u8>) {
+        let mut buf = [0u8; 5];
+        let encoded_name_len =
+            leb128::write::unsigned(&mut &mut buf[..], u64::try_from(self.name.len()).unwrap())
+                .unwrap();
+        let data_len = self.data.iter().fold(0, |acc, s| acc + s.len());
+
+        // name length
+        (encoded_name_len + self.name.len() + data_len).encode(sink);
+
+        // name
+        self.name.encode(sink);
+
+        // data
+        for s in &self.data {
+            sink.extend(*s);
+        }
+    }
+}
+
+impl wasm_encoder::ComponentSection for Custom<'_> {
+    fn id(&self) -> u8 {
+        SectionId::Custom.into()
+    }
+}
+
+// TODO: move these core conversion functions to the core module
+// once we update core encoding to use wasm-encoder.
+impl From<core::ValType<'_>> for wasm_encoder::ValType {
+    fn from(ty: core::ValType) -> Self {
+        match ty {
+            core::ValType::I32 => Self::I32,
+            core::ValType::I64 => Self::I64,
+            core::ValType::F32 => Self::F32,
+            core::ValType::F64 => Self::F64,
+            core::ValType::V128 => Self::V128,
+            core::ValType::Ref(r) => Self::Ref(r.into()),
+        }
+    }
+}
+
+impl From<core::RefType<'_>> for wasm_encoder::RefType {
+    fn from(r: core::RefType<'_>) -> Self {
+        wasm_encoder::RefType {
+            nullable: r.nullable,
+            heap_type: r.heap.into(),
+        }
+    }
+}
+
+impl From<core::HeapType<'_>> for wasm_encoder::HeapType {
+    fn from(r: core::HeapType<'_>) -> Self {
+        match r {
+            core::HeapType::Func => Self::Func,
+            core::HeapType::Extern => Self::Extern,
+            core::HeapType::Index(Index::Num(i, _)) => Self::TypedFunc(i),
+            core::HeapType::Index(_) => panic!("unresolved index"),
+            core::HeapType::Any
+            | core::HeapType::Eq
+            | core::HeapType::Struct
+            | core::HeapType::Array
+            | core::HeapType::NoFunc
+            | core::HeapType::NoExtern
+            | core::HeapType::None
+            | core::HeapType::I31 => {
+                todo!("encoding of GC proposal types not yet implemented")
+            }
+        }
+    }
+}
+
+impl From<&core::ItemKind<'_>> for wasm_encoder::EntityType {
+    fn from(kind: &core::ItemKind) -> Self {
+        match kind {
+            core::ItemKind::Func(t) => Self::Function(t.into()),
+            core::ItemKind::Table(t) => Self::Table((*t).into()),
+            core::ItemKind::Memory(t) => Self::Memory((*t).into()),
+            core::ItemKind::Global(t) => Self::Global((*t).into()),
+            core::ItemKind::Tag(t) => Self::Tag(t.into()),
+        }
+    }
+}
+
+impl From<core::TableType<'_>> for wasm_encoder::TableType {
+    fn from(ty: core::TableType) -> Self {
+        Self {
+            element_type: ty.elem.into(),
+            minimum: ty.limits.min,
+            maximum: ty.limits.max,
+        }
+    }
+}
+
+impl From<core::MemoryType> for wasm_encoder::MemoryType {
+    fn from(ty: core::MemoryType) -> Self {
+        let (minimum, maximum, memory64, shared) = match ty {
+            core::MemoryType::B32 { limits, shared } => {
+                (limits.min.into(), limits.max.map(Into::into), false, shared)
+            }
+            core::MemoryType::B64 { limits, shared } => (limits.min, limits.max, true, shared),
+        };
+
+        Self {
+            minimum,
+            maximum,
+            memory64,
+            shared,
+        }
+    }
+}
+
+impl From<core::GlobalType<'_>> for wasm_encoder::GlobalType {
+    fn from(ty: core::GlobalType) -> Self {
+        Self {
+            val_type: ty.ty.into(),
+            mutable: ty.mutable,
+        }
+    }
+}
+
+impl From<&core::TagType<'_>> for wasm_encoder::TagType {
+    fn from(ty: &core::TagType) -> Self {
+        match ty {
+            core::TagType::Exception(r) => Self {
+                kind: wasm_encoder::TagKind::Exception,
+                func_type_idx: r.into(),
+            },
+        }
+    }
+}
+
+impl<T: std::fmt::Debug> From<&core::TypeUse<'_, T>> for u32 {
+    fn from(u: &core::TypeUse<'_, T>) -> Self {
+        match &u.index {
+            Some(i) => (*i).into(),
+            None => unreachable!("unresolved type use in encoding: {:?}", u),
+        }
+    }
+}
+
+impl From<&CoreInstantiationArgKind<'_>> for wasm_encoder::ModuleArg {
+    fn from(kind: &CoreInstantiationArgKind) -> Self {
+        match kind {
+            CoreInstantiationArgKind::Instance(i) => {
+                wasm_encoder::ModuleArg::Instance(i.idx.into())
+            }
+            CoreInstantiationArgKind::BundleOfExports(..) => {
+                unreachable!("should be expanded already")
+            }
+        }
+    }
+}
+
+impl From<&CoreItemRef<'_, core::ExportKind>> for (wasm_encoder::ExportKind, u32) {
+    fn from(item: &CoreItemRef<'_, core::ExportKind>) -> Self {
+        match &item.kind {
+            core::ExportKind::Func => (wasm_encoder::ExportKind::Func, item.idx.into()),
+            core::ExportKind::Table => (wasm_encoder::ExportKind::Table, item.idx.into()),
+            core::ExportKind::Memory => (wasm_encoder::ExportKind::Memory, item.idx.into()),
+            core::ExportKind::Global => (wasm_encoder::ExportKind::Global, item.idx.into()),
+            core::ExportKind::Tag => (wasm_encoder::ExportKind::Tag, item.idx.into()),
+        }
+    }
+}
+
+impl From<core::ExportKind> for wasm_encoder::ExportKind {
+    fn from(kind: core::ExportKind) -> Self {
+        match kind {
+            core::ExportKind::Func => Self::Func,
+            core::ExportKind::Table => Self::Table,
+            core::ExportKind::Memory => Self::Memory,
+            core::ExportKind::Global => Self::Global,
+            core::ExportKind::Tag => Self::Tag,
+        }
+    }
+}
+
+impl From<Index<'_>> for u32 {
+    fn from(i: Index<'_>) -> Self {
+        match i {
+            Index::Num(i, _) => i,
+            Index::Id(_) => unreachable!("unresolved index in encoding: {:?}", i),
+        }
+    }
+}
+
+impl<T> From<&ItemRef<'_, T>> for u32 {
+    fn from(i: &ItemRef<'_, T>) -> Self {
+        assert!(i.export_names.is_empty());
+        i.idx.into()
+    }
+}
+
+impl<T> From<&CoreTypeUse<'_, T>> for u32 {
+    fn from(u: &CoreTypeUse<'_, T>) -> Self {
+        match u {
+            CoreTypeUse::Inline(_) => unreachable!("should be expanded already"),
+            CoreTypeUse::Ref(r) => r.idx.into(),
+        }
+    }
+}
+
+impl<T> From<&ComponentTypeUse<'_, T>> for u32 {
+    fn from(u: &ComponentTypeUse<'_, T>) -> Self {
+        match u {
+            ComponentTypeUse::Inline(_) => unreachable!("should be expanded already"),
+            ComponentTypeUse::Ref(r) => r.idx.into(),
+        }
+    }
+}
+
+impl From<&ComponentValType<'_>> for wasm_encoder::ComponentValType {
+    fn from(r: &ComponentValType) -> Self {
+        match r {
+            ComponentValType::Inline(ComponentDefinedType::Primitive(p)) => {
+                Self::Primitive((*p).into())
+            }
+            ComponentValType::Ref(i) => Self::Type(u32::from(*i)),
+            ComponentValType::Inline(_) => unreachable!("should be expanded by now"),
+        }
+    }
+}
+
+impl From<PrimitiveValType> for wasm_encoder::PrimitiveValType {
+    fn from(p: PrimitiveValType) -> Self {
+        match p {
+            PrimitiveValType::Bool => Self::Bool,
+            PrimitiveValType::S8 => Self::S8,
+            PrimitiveValType::U8 => Self::U8,
+            PrimitiveValType::S16 => Self::S16,
+            PrimitiveValType::U16 => Self::U16,
+            PrimitiveValType::S32 => Self::S32,
+            PrimitiveValType::U32 => Self::U32,
+            PrimitiveValType::S64 => Self::S64,
+            PrimitiveValType::U64 => Self::U64,
+            PrimitiveValType::Float32 => Self::Float32,
+            PrimitiveValType::Float64 => Self::Float64,
+            PrimitiveValType::Char => Self::Char,
+            PrimitiveValType::String => Self::String,
+        }
+    }
+}
+
+impl From<&Refinement<'_>> for u32 {
+    fn from(r: &Refinement) -> Self {
+        match r {
+            Refinement::Index(..) => unreachable!("should be resolved by now"),
+            Refinement::Resolved(i) => *i,
+        }
+    }
+}
+
+impl From<&ItemSigKind<'_>> for wasm_encoder::ComponentTypeRef {
+    fn from(k: &ItemSigKind) -> Self {
+        match k {
+            ItemSigKind::Component(c) => Self::Component(c.into()),
+            ItemSigKind::CoreModule(m) => Self::Module(m.into()),
+            ItemSigKind::Instance(i) => Self::Instance(i.into()),
+            ItemSigKind::Value(v) => Self::Value((&v.0).into()),
+            ItemSigKind::Func(f) => Self::Func(f.into()),
+            ItemSigKind::Type(TypeBounds::Eq(t)) => {
+                Self::Type(wasm_encoder::TypeBounds::Eq, (*t).into())
+            }
+        }
+    }
+}
+
+impl From<&ComponentType<'_>> for wasm_encoder::ComponentType {
+    fn from(ty: &ComponentType) -> Self {
+        let mut encoded = wasm_encoder::ComponentType::new();
+
+        for decl in &ty.decls {
+            match decl {
+                ComponentTypeDecl::CoreType(t) => {
+                    encode_core_type(encoded.core_type(), &t.def);
+                }
+                ComponentTypeDecl::Type(t) => {
+                    encode_type(encoded.ty(), &t.def);
+                }
+                ComponentTypeDecl::Alias(a) => {
+                    encoded.alias((&a.target).into());
+                }
+                ComponentTypeDecl::Import(i) => {
+                    encoded.import(i.name, i.url.unwrap_or(""), (&i.item.kind).into());
+                }
+                ComponentTypeDecl::Export(e) => {
+                    encoded.export(e.name, e.url.unwrap_or(""), (&e.item.kind).into());
+                }
+            }
+        }
+
+        encoded
+    }
+}
+
+impl From<&InstanceType<'_>> for wasm_encoder::InstanceType {
+    fn from(ty: &InstanceType) -> Self {
+        let mut encoded = wasm_encoder::InstanceType::new();
+
+        for decl in &ty.decls {
+            match decl {
+                InstanceTypeDecl::CoreType(t) => {
+                    encode_core_type(encoded.core_type(), &t.def);
+                }
+                InstanceTypeDecl::Type(t) => {
+                    encode_type(encoded.ty(), &t.def);
+                }
+                InstanceTypeDecl::Alias(a) => {
+                    encoded.alias((&a.target).into());
+                }
+                InstanceTypeDecl::Export(e) => {
+                    encoded.export(e.name, e.url.unwrap_or(""), (&e.item.kind).into());
+                }
+            }
+        }
+
+        encoded
+    }
+}
+
+impl From<&ModuleType<'_>> for wasm_encoder::ModuleType {
+    fn from(ty: &ModuleType) -> Self {
+        let mut encoded = wasm_encoder::ModuleType::new();
+
+        for decl in &ty.decls {
+            match decl {
+                ModuleTypeDecl::Type(t) => match &t.def {
+                    core::TypeDef::Func(f) => encoded.ty().function(
+                        f.params.iter().map(|(_, _, ty)| (*ty).into()),
+                        f.results.iter().copied().map(Into::into),
+                    ),
+                    core::TypeDef::Struct(_) | core::TypeDef::Array(_) => {
+                        todo!("encoding of GC proposal types not yet implemented")
+                    }
+                },
+                ModuleTypeDecl::Alias(a) => match &a.target {
+                    AliasTarget::Outer {
+                        outer,
+                        index,
+                        kind: ComponentOuterAliasKind::CoreType,
+                    } => {
+                        encoded.alias_outer_core_type(u32::from(*outer), u32::from(*index));
+                    }
+                    _ => unreachable!("only outer type aliases are supported"),
+                },
+                ModuleTypeDecl::Import(i) => {
+                    encoded.import(i.module, i.field, (&i.item.kind).into());
+                }
+                ModuleTypeDecl::Export(name, item) => {
+                    encoded.export(name, (&item.kind).into());
+                }
+            }
+        }
+
+        encoded
+    }
+}
+
+impl From<&InstantiationArgKind<'_>> for (wasm_encoder::ComponentExportKind, u32) {
+    fn from(kind: &InstantiationArgKind) -> Self {
+        match kind {
+            InstantiationArgKind::Item(i) => i.into(),
+            InstantiationArgKind::BundleOfExports(..) => unreachable!("should be expanded already"),
+        }
+    }
+}
+
+impl From<&ComponentExportKind<'_>> for (wasm_encoder::ComponentExportKind, u32) {
+    fn from(kind: &ComponentExportKind) -> Self {
+        match kind {
+            ComponentExportKind::CoreModule(m) => {
+                (wasm_encoder::ComponentExportKind::Module, m.idx.into())
+            }
+            ComponentExportKind::Func(f) => (wasm_encoder::ComponentExportKind::Func, f.idx.into()),
+            ComponentExportKind::Value(v) => {
+                (wasm_encoder::ComponentExportKind::Value, v.idx.into())
+            }
+            ComponentExportKind::Type(t) => (wasm_encoder::ComponentExportKind::Type, t.idx.into()),
+            ComponentExportKind::Component(c) => {
+                (wasm_encoder::ComponentExportKind::Component, c.idx.into())
+            }
+            ComponentExportKind::Instance(i) => {
+                (wasm_encoder::ComponentExportKind::Instance, i.idx.into())
+            }
+        }
+    }
+}
+
+impl From<ComponentOuterAliasKind> for wasm_encoder::ComponentOuterAliasKind {
+    fn from(kind: ComponentOuterAliasKind) -> Self {
+        match kind {
+            ComponentOuterAliasKind::CoreModule => Self::CoreModule,
+            ComponentOuterAliasKind::CoreType => Self::CoreType,
+            ComponentOuterAliasKind::Type => Self::Type,
+            ComponentOuterAliasKind::Component => Self::Component,
+        }
+    }
+}
+
+impl From<ComponentExportAliasKind> for wasm_encoder::ComponentExportKind {
+    fn from(kind: ComponentExportAliasKind) -> Self {
+        match kind {
+            ComponentExportAliasKind::CoreModule => Self::Module,
+            ComponentExportAliasKind::Func => Self::Func,
+            ComponentExportAliasKind::Value => Self::Value,
+            ComponentExportAliasKind::Type => Self::Type,
+            ComponentExportAliasKind::Component => Self::Component,
+            ComponentExportAliasKind::Instance => Self::Instance,
+        }
+    }
+}
+
+impl From<&CanonOpt<'_>> for wasm_encoder::CanonicalOption {
+    fn from(opt: &CanonOpt) -> Self {
+        match opt {
+            CanonOpt::StringUtf8 => Self::UTF8,
+            CanonOpt::StringUtf16 => Self::UTF16,
+            CanonOpt::StringLatin1Utf16 => Self::CompactUTF16,
+            CanonOpt::Memory(m) => Self::Memory(m.idx.into()),
+            CanonOpt::Realloc(f) => Self::Realloc(f.idx.into()),
+            CanonOpt::PostReturn(f) => Self::PostReturn(f.idx.into()),
+        }
+    }
+}
+
+impl<'a> From<&AliasTarget<'a>> for wasm_encoder::Alias<'a> {
+    fn from(target: &AliasTarget<'a>) -> Self {
+        match target {
+            AliasTarget::Export {
+                instance,
+                name,
+                kind,
+            } => wasm_encoder::Alias::InstanceExport {
+                instance: (*instance).into(),
+                kind: (*kind).into(),
+                name,
+            },
+            AliasTarget::CoreExport {
+                instance,
+                name,
+                kind,
+            } => wasm_encoder::Alias::CoreInstanceExport {
+                instance: (*instance).into(),
+                kind: (*kind).into(),
+                name,
+            },
+            AliasTarget::Outer { outer, index, kind } => wasm_encoder::Alias::Outer {
+                count: (*outer).into(),
+                kind: (*kind).into(),
+                index: (*index).into(),
+            },
+        }
+    }
+}
diff --git a/third_party/rust/wast/src/component/component.rs b/third_party/rust/wast/src/component/component.rs
new file mode 100644
index 0000000000..8424e083b8
--- /dev/null
+++ b/third_party/rust/wast/src/component/component.rs
@@ -0,0 +1,313 @@
+use crate::annotation;
+use crate::component::*;
+use crate::kw;
+use crate::parser::{Parse, Parser, Result};
+use crate::token::Index;
+use crate::token::{Id, NameAnnotation, Span};
+
+/// A parsed WebAssembly component module.
+#[derive(Debug)]
+pub struct Component<'a> {
+    /// Where this `component` was defined
+    pub span: Span,
+    /// An optional identifier this component is known by
+    pub id: Option<Id<'a>>,
+    /// An optional `@name` annotation for this component
+    pub name: Option<NameAnnotation<'a>>,
+    /// What kind of component this was parsed as.
+    pub kind: ComponentKind<'a>,
+}
+
+/// The different kinds of ways to define a component.
+#[derive(Debug)]
+pub enum ComponentKind<'a> {
+    /// A component defined in the textual s-expression format.
+    Text(Vec<ComponentField<'a>>),
+    /// A component that had its raw binary bytes defined via the `binary`
+    /// directive.
+    Binary(Vec<&'a [u8]>),
+}
+
+impl<'a> Component<'a> {
+    /// Performs a name resolution pass on this [`Component`], resolving all
+    /// symbolic names to indices.
+    ///
+    /// The WAT format contains a number of shorthands to make it easier to
+    /// write, such as inline exports, inline imports, inline type definitions,
+    /// etc. Additionally it allows using symbolic names such as `$foo` instead
+    /// of using indices. This module will postprocess an AST to remove all of
+    /// this syntactic sugar, preparing the AST for binary emission.  This is
+    /// where expansion and name resolution happens.
+    ///
+    /// This function will mutate the AST of this [`Component`] and replace all
+    /// [`Index`](crate::token::Index) arguments with `Index::Num`. This will
+    /// also expand inline exports/imports listed on fields and handle various
+    /// other shorthands of the text format.
+    ///
+    /// If successful the AST was modified to be ready for binary encoding.
+    ///
+    /// # Errors
+    ///
+    /// If an error happens during resolution, such a name resolution error or
+    /// items are found in the wrong order, then an error is returned.
+    pub fn resolve(&mut self) -> std::result::Result<(), crate::Error> {
+        match &mut self.kind {
+            ComponentKind::Text(fields) => {
+                crate::component::expand::expand(fields);
+            }
+            ComponentKind::Binary(_) => {}
+        }
+        crate::component::resolve::resolve(self)
+    }
+
+    /// Encodes this [`Component`] to its binary form.
+    ///
+    /// This function will take the textual representation in [`Component`] and
+    /// perform all steps necessary to convert it to a binary WebAssembly
+    /// component, suitable for writing to a `*.wasm` file. This function may
+    /// internally modify the [`Component`], for example:
+    ///
+    /// * Name resolution is performed to ensure that `Index::Id` isn't present
+    ///   anywhere in the AST.
+    ///
+    /// * Inline shorthands such as imports/exports/types are all expanded to be
+    ///   dedicated fields of the component.
+    ///
+    /// * Component fields may be shuffled around to preserve index ordering from
+    ///   expansions.
+    ///
+    /// After all of this expansion has happened the component will be converted to
+    /// its binary form and returned as a `Vec<u8>`. This is then suitable to
+    /// hand off to other wasm runtimes and such.
+    ///
+    /// # Errors
+    ///
+    /// This function can return an error for name resolution errors and other
+    /// expansion-related errors.
+    pub fn encode(&mut self) -> std::result::Result<Vec<u8>, crate::Error> {
+        self.resolve()?;
+        Ok(crate::component::binary::encode(self))
+    }
+
+    pub(crate) fn validate(&self, parser: Parser<'_>) -> Result<()> {
+        let mut starts = 0;
+        if let ComponentKind::Text(fields) = &self.kind {
+            for item in fields.iter() {
+                if let ComponentField::Start(_) = item {
+                    starts += 1;
+                }
+            }
+        }
+        if starts > 1 {
+            return Err(parser.error("multiple start sections found"));
+        }
+        Ok(())
+    }
+}
+
+impl<'a> Parse<'a> for Component<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let _r = parser.register_annotation("custom");
+
+        let span = parser.parse::<kw::component>()?.0;
+        let id = parser.parse()?;
+        let name = parser.parse()?;
+
+        let kind = if parser.peek::<kw::binary>() {
+            parser.parse::<kw::binary>()?;
+            let mut data = Vec::new();
+            while !parser.is_empty() {
+                data.push(parser.parse()?);
+            }
+            ComponentKind::Binary(data)
+        } else {
+            ComponentKind::Text(ComponentField::parse_remaining(parser)?)
+        };
+        Ok(Component {
+            span,
+            id,
+            name,
+            kind,
+        })
+    }
+}
+
+/// A listing of all possible fields that can make up a WebAssembly component.
+#[allow(missing_docs)]
+#[derive(Debug)]
+pub enum ComponentField<'a> {
+    CoreModule(CoreModule<'a>),
+    CoreInstance(CoreInstance<'a>),
+    CoreType(CoreType<'a>),
+    Component(NestedComponent<'a>),
+    Instance(Instance<'a>),
+    Alias(Alias<'a>),
+    Type(Type<'a>),
+    CanonicalFunc(CanonicalFunc<'a>),
+    CoreFunc(CoreFunc<'a>), // Supports inverted forms of other items
+    Func(Func<'a>),         // Supports inverted forms of other items
+    Start(Start<'a>),
+    Import(ComponentImport<'a>),
+    Export(ComponentExport<'a>),
+    Custom(Custom<'a>),
+}
+
+impl<'a> ComponentField<'a> {
+    fn parse_remaining(parser: Parser<'a>) -> Result<Vec<ComponentField>> {
+        let mut fields = Vec::new();
+        while !parser.is_empty() {
+            fields.push(parser.parens(ComponentField::parse)?);
+        }
+        Ok(fields)
+    }
+}
+
+impl<'a> Parse<'a> for ComponentField<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        if parser.peek::<kw::core>() {
+            if parser.peek2::<kw::module>() {
+                return Ok(Self::CoreModule(parser.parse()?));
+            }
+            if parser.peek2::<kw::instance>() {
+                return Ok(Self::CoreInstance(parser.parse()?));
+            }
+            if parser.peek2::<kw::r#type>() {
+                return Ok(Self::CoreType(parser.parse()?));
+            }
+            if parser.peek2::<kw::func>() {
+                return Ok(Self::CoreFunc(parser.parse()?));
+            }
+        } else {
+            if parser.peek::<kw::component>() {
+                return Ok(Self::Component(parser.parse()?));
+            }
+            if parser.peek::<kw::instance>() {
+                return Ok(Self::Instance(parser.parse()?));
+            }
+            if parser.peek::<kw::alias>() {
+                return Ok(Self::Alias(parser.parse()?));
+            }
+            if parser.peek::<kw::r#type>() {
+                return Ok(Self::Type(parser.parse()?));
+            }
+            if parser.peek::<kw::import>() {
+                return Ok(Self::Import(parser.parse()?));
+            }
+            if parser.peek::<kw::func>() {
+                return Ok(Self::Func(parser.parse()?));
+            }
+            if parser.peek::<kw::export>() {
+                return Ok(Self::Export(parser.parse()?));
+            }
+            if parser.peek::<kw::start>() {
+                return Ok(Self::Start(parser.parse()?));
+            }
+            if parser.peek::<annotation::custom>() {
+                return Ok(Self::Custom(parser.parse()?));
+            }
+        }
+        Err(parser.error("expected valid component field"))
+    }
+}
+
+/// A function to call at instantiation time.
+#[derive(Debug)]
+pub struct Start<'a> {
+    /// The function to call.
+    pub func: Index<'a>,
+    /// The arguments to pass to the function.
+    pub args: Vec<ItemRef<'a, kw::value>>,
+    /// Names of the result values.
+    pub results: Vec<Option<Id<'a>>>,
+}
+
+impl<'a> Parse<'a> for Start<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.parse::<kw::start>()?;
+        let func = parser.parse()?;
+        let mut args = Vec::new();
+        while !parser.is_empty() && !parser.peek2::<kw::result>() {
+            args.push(parser.parens(|parser| parser.parse())?);
+        }
+
+        let mut results = Vec::new();
+        while !parser.is_empty() && parser.peek2::<kw::result>() {
+            results.push(parser.parens(|parser| {
+                parser.parse::<kw::result>()?;
+                parser.parens(|parser| {
+                    parser.parse::<kw::value>()?;
+                    parser.parse()
+                })
+            })?);
+        }
+
+        Ok(Start {
+            func,
+            args,
+            results,
+        })
+    }
+}
+
+/// A nested WebAssembly component.
+#[derive(Debug)]
+pub struct NestedComponent<'a> {
+    /// Where this `component` was defined
+    pub span: Span,
+    /// An optional identifier this component is known by
+    pub id: Option<Id<'a>>,
+    /// An optional `@name` annotation for this component
+    pub name: Option<NameAnnotation<'a>>,
+    /// If present, inline export annotations which indicate names this
+    /// definition should be exported under.
+    pub exports: InlineExport<'a>,
+    /// What kind of component this was parsed as.
+    pub kind: NestedComponentKind<'a>,
+}
+
+/// The different kinds of ways to define a nested component.
+#[derive(Debug)]
+pub enum NestedComponentKind<'a> {
+    /// This is actually an inline import of a component
+    Import {
+        /// The information about where this is being imported from.
+        import: InlineImport<'a>,
+        /// The type of component being imported.
+        ty: ComponentTypeUse<'a, ComponentType<'a>>,
+    },
+    /// The component is defined inline as a local definition with its fields
+    /// listed here.
+    Inline(Vec<ComponentField<'a>>),
+}
+
+impl<'a> Parse<'a> for NestedComponent<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.depth_check()?;
+
+        let span = parser.parse::<kw::component>()?.0;
+        let id = parser.parse()?;
+        let name = parser.parse()?;
+        let exports = parser.parse()?;
+
+        let kind = if let Some(import) = parser.parse()? {
+            NestedComponentKind::Import {
+                import,
+                ty: parser.parse()?,
+            }
+        } else {
+            let mut fields = Vec::new();
+            while !parser.is_empty() {
+                fields.push(parser.parens(|p| p.parse())?);
+            }
+            NestedComponentKind::Inline(fields)
+        };
+
+        Ok(NestedComponent {
+            span,
+            id,
+            name,
+            exports,
+            kind,
+        })
+    }
+}
diff --git a/third_party/rust/wast/src/component/custom.rs b/third_party/rust/wast/src/component/custom.rs
new file mode 100644
index 0000000000..b17a7fafb4
--- /dev/null
+++ b/third_party/rust/wast/src/component/custom.rs
@@ -0,0 +1,28 @@
+use crate::annotation;
+use crate::parser::{Parse, Parser, Result};
+use crate::token::Span;
+
+/// A custom section within a component.
+#[derive(Debug)]
+pub struct Custom<'a> {
+    /// Where this `@custom` was defined.
+    pub span: Span,
+
+    /// Name of the custom section.
+    pub name: &'a str,
+
+    /// Payload of this custom section.
+    pub data: Vec<&'a [u8]>,
+}
+
+impl<'a> Parse<'a> for Custom<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let span = parser.parse::<annotation::custom>()?.0;
+        let name = parser.parse()?;
+        let mut data = Vec::new();
+        while !parser.is_empty() {
+            data.push(parser.parse()?);
+        }
+        Ok(Self { span, name, data })
+    }
+}
diff --git a/third_party/rust/wast/src/component/expand.rs b/third_party/rust/wast/src/component/expand.rs
new file mode 100644
index 0000000000..2bf0b529e4
--- /dev/null
+++ b/third_party/rust/wast/src/component/expand.rs
@@ -0,0 +1,859 @@
+use crate::component::*;
+use crate::core;
+use crate::gensym;
+use crate::kw;
+use crate::token::Id;
+use crate::token::{Index, Span};
+use std::collections::HashMap;
+use std::mem;
+
+/// Performs an AST "expansion" pass over the component fields provided.
+///
+/// This expansion is intended to desugar the AST from various parsed constructs
+/// to bits and bobs amenable for name resolution as well as binary encoding.
+/// For example `(import "i" (func))` is split into a type definition followed by
+/// the import referencing that type definition.
+///
+/// Most forms of AST expansion happen in this file and afterwards the AST will
+/// be handed to the name resolution pass which will convert `Index::Id` to
+/// `Index::Num` wherever it's found.
+pub fn expand(fields: &mut Vec<ComponentField<'_>>) {
+    Expander::default().expand_component_fields(fields)
+}
+
+enum AnyType<'a> {
+    Core(CoreType<'a>),
+    Component(Type<'a>),
+}
+
+impl<'a> From<AnyType<'a>> for ComponentTypeDecl<'a> {
+    fn from(t: AnyType<'a>) -> Self {
+        match t {
+            AnyType::Core(t) => Self::CoreType(t),
+            AnyType::Component(t) => Self::Type(t),
+        }
+    }
+}
+
+impl<'a> From<AnyType<'a>> for InstanceTypeDecl<'a> {
+    fn from(t: AnyType<'a>) -> Self {
+        match t {
+            AnyType::Core(t) => Self::CoreType(t),
+            AnyType::Component(t) => Self::Type(t),
+        }
+    }
+}
+
+impl<'a> From<AnyType<'a>> for ComponentField<'a> {
+    fn from(t: AnyType<'a>) -> Self {
+        match t {
+            AnyType::Core(t) => Self::CoreType(t),
+            AnyType::Component(t) => Self::Type(t),
+        }
+    }
+}
+
+#[derive(Default)]
+struct Expander<'a> {
+    /// Fields, during processing, which should be prepended to the
+    /// currently-being-processed field. This should always be empty after
+    /// processing is complete.
+    types_to_prepend: Vec<AnyType<'a>>,
+    component_fields_to_prepend: Vec<ComponentField<'a>>,
+
+    /// Fields that are appended to the end of the module once everything has
+    /// finished.
+    component_fields_to_append: Vec<ComponentField<'a>>,
+}
+
+impl<'a> Expander<'a> {
+    fn expand_component_fields(&mut self, fields: &mut Vec<ComponentField<'a>>) {
+        let mut cur = 0;
+        while cur < fields.len() {
+            self.expand_field(&mut fields[cur]);
+            let amt = self.types_to_prepend.len() + self.component_fields_to_prepend.len();
+            fields.splice(cur..cur, self.component_fields_to_prepend.drain(..));
+            fields.splice(cur..cur, self.types_to_prepend.drain(..).map(Into::into));
+            cur += 1 + amt;
+        }
+        fields.append(&mut self.component_fields_to_append);
+    }
+
+    fn expand_decls<T>(&mut self, decls: &mut Vec<T>, expand: fn(&mut Self, &mut T))
+    where
+        T: From<AnyType<'a>>,
+    {
+        let mut cur = 0;
+        while cur < decls.len() {
+            expand(self, &mut decls[cur]);
+            assert!(self.component_fields_to_prepend.is_empty());
+            assert!(self.component_fields_to_append.is_empty());
+            let amt = self.types_to_prepend.len();
+            decls.splice(cur..cur, self.types_to_prepend.drain(..).map(From::from));
+            cur += 1 + amt;
+        }
+    }
+
+    fn expand_field(&mut self, item: &mut ComponentField<'a>) {
+        let expanded = match item {
+            ComponentField::CoreModule(m) => self.expand_core_module(m),
+            ComponentField::CoreInstance(i) => {
+                self.expand_core_instance(i);
+                None
+            }
+            ComponentField::CoreType(t) => {
+                self.expand_core_type(t);
+                None
+            }
+            ComponentField::Component(c) => self.expand_nested_component(c),
+            ComponentField::Instance(i) => self.expand_instance(i),
+            ComponentField::Type(t) => {
+                self.expand_type(t);
+                None
+            }
+            ComponentField::CanonicalFunc(f) => {
+                self.expand_canonical_func(f);
+                None
+            }
+            ComponentField::CoreFunc(f) => self.expand_core_func(f),
+            ComponentField::Func(f) => self.expand_func(f),
+            ComponentField::Import(i) => {
+                self.expand_item_sig(&mut i.item);
+                None
+            }
+            ComponentField::Export(e) => {
+                if let Some(sig) = &mut e.ty {
+                    self.expand_item_sig(&mut sig.0);
+                }
+                None
+            }
+            ComponentField::Start(_) | ComponentField::Alias(_) | ComponentField::Custom(_) => None,
+        };
+
+        if let Some(expanded) = expanded {
+            *item = expanded;
+        }
+    }
+
+    fn expand_core_module(&mut self, module: &mut CoreModule<'a>) -> Option<ComponentField<'a>> {
+        for (name, url) in module.exports.names.drain(..) {
+            let id = gensym::fill(module.span, &mut module.id);
+            self.component_fields_to_append
+                .push(ComponentField::Export(ComponentExport {
+                    span: module.span,
+                    id: None,
+                    debug_name: None,
+                    name,
+                    url,
+                    kind: ComponentExportKind::module(module.span, id),
+                    ty: None,
+                }));
+        }
+        match &mut module.kind {
+            // inline modules are expanded later during resolution
+            CoreModuleKind::Inline { .. } => None,
+            CoreModuleKind::Import { import, ty } => {
+                let idx = self.expand_core_type_use(ty);
+                Some(ComponentField::Import(ComponentImport {
+                    span: module.span,
+                    name: import.name,
+                    url: import.url,
+                    item: ItemSig {
+                        span: module.span,
+                        id: module.id,
+                        name: None,
+                        kind: ItemSigKind::CoreModule(CoreTypeUse::Ref(idx)),
+                    },
+                }))
+            }
+        }
+    }
+
+    fn expand_core_instance(&mut self, instance: &mut CoreInstance<'a>) {
+        match &mut instance.kind {
+            CoreInstanceKind::Instantiate { args, .. } => {
+                for arg in args {
+                    self.expand_core_instantiation_arg(&mut arg.kind);
+                }
+            }
+            CoreInstanceKind::BundleOfExports { .. } => {}
+        }
+    }
+
+    fn expand_nested_component(
+        &mut self,
+        component: &mut NestedComponent<'a>,
+    ) -> Option<ComponentField<'a>> {
+        for (name, url) in component.exports.names.drain(..) {
+            let id = gensym::fill(component.span, &mut component.id);
+            self.component_fields_to_append
+                .push(ComponentField::Export(ComponentExport {
+                    span: component.span,
+                    id: None,
+                    debug_name: None,
+                    name,
+                    url,
+                    kind: ComponentExportKind::component(component.span, id),
+                    ty: None,
+                }));
+        }
+        match &mut component.kind {
+            NestedComponentKind::Inline(fields) => {
+                expand(fields);
+                None
+            }
+            NestedComponentKind::Import { import, ty } => {
+                let idx = self.expand_component_type_use(ty);
+                Some(ComponentField::Import(ComponentImport {
+                    span: component.span,
+                    name: import.name,
+                    url: import.url,
+                    item: ItemSig {
+                        span: component.span,
+                        id: component.id,
+                        name: None,
+                        kind: ItemSigKind::Component(ComponentTypeUse::Ref(idx)),
+                    },
+                }))
+            }
+        }
+    }
+
+    fn expand_instance(&mut self, instance: &mut Instance<'a>) -> Option<ComponentField<'a>> {
+        for (name, url) in instance.exports.names.drain(..) {
+            let id = gensym::fill(instance.span, &mut instance.id);
+            self.component_fields_to_append
+                .push(ComponentField::Export(ComponentExport {
+                    span: instance.span,
+                    id: None,
+                    debug_name: None,
+                    name,
+                    url,
+                    kind: ComponentExportKind::instance(instance.span, id),
+                    ty: None,
+                }));
+        }
+        match &mut instance.kind {
+            InstanceKind::Import { import, ty } => {
+                let idx = self.expand_component_type_use(ty);
+                Some(ComponentField::Import(ComponentImport {
+                    span: instance.span,
+                    name: import.name,
+                    url: import.url,
+                    item: ItemSig {
+                        span: instance.span,
+                        id: instance.id,
+                        name: None,
+                        kind: ItemSigKind::Instance(ComponentTypeUse::Ref(idx)),
+                    },
+                }))
+            }
+            InstanceKind::Instantiate { args, .. } => {
+                for arg in args {
+                    self.expand_instantiation_arg(&mut arg.kind);
+                }
+                None
+            }
+            InstanceKind::BundleOfExports { .. } => None,
+        }
+    }
+
+    fn expand_canonical_func(&mut self, func: &mut CanonicalFunc<'a>) {
+        match &mut func.kind {
+            CanonicalFuncKind::Lift { ty, .. } => {
+                self.expand_component_type_use(ty);
+            }
+            CanonicalFuncKind::Lower(_) => {}
+        }
+    }
+
+    fn expand_core_func(&mut self, func: &mut CoreFunc<'a>) -> Option<ComponentField<'a>> {
+        match &mut func.kind {
+            CoreFuncKind::Alias(a) => Some(ComponentField::Alias(Alias {
+                span: func.span,
+                id: func.id,
+                name: func.name,
+                target: AliasTarget::CoreExport {
+                    instance: a.instance,
+                    name: a.name,
+                    kind: core::ExportKind::Func,
+                },
+            })),
+            CoreFuncKind::Lower(info) => Some(ComponentField::CanonicalFunc(CanonicalFunc {
+                span: func.span,
+                id: func.id,
+                name: func.name,
+                kind: CanonicalFuncKind::Lower(mem::take(info)),
+            })),
+        }
+    }
+
+    fn expand_func(&mut self, func: &mut Func<'a>) -> Option<ComponentField<'a>> {
+        for (name, url) in func.exports.names.drain(..) {
+            let id = gensym::fill(func.span, &mut func.id);
+            self.component_fields_to_append
+                .push(ComponentField::Export(ComponentExport {
+                    span: func.span,
+                    id: None,
+                    debug_name: None,
+                    name,
+                    url,
+                    kind: ComponentExportKind::func(func.span, id),
+                    ty: None,
+                }));
+        }
+        match &mut func.kind {
+            FuncKind::Import { import, ty } => {
+                let idx = self.expand_component_type_use(ty);
+                Some(ComponentField::Import(ComponentImport {
+                    span: func.span,
+                    name: import.name,
+                    url: import.url,
+                    item: ItemSig {
+                        span: func.span,
+                        id: func.id,
+                        name: None,
+                        kind: ItemSigKind::Func(ComponentTypeUse::Ref(idx)),
+                    },
+                }))
+            }
+            FuncKind::Lift { ty, info } => {
+                let idx = self.expand_component_type_use(ty);
+                Some(ComponentField::CanonicalFunc(CanonicalFunc {
+                    span: func.span,
+                    id: func.id,
+                    name: func.name,
+                    kind: CanonicalFuncKind::Lift {
+                        ty: ComponentTypeUse::Ref(idx),
+                        info: mem::take(info),
+                    },
+                }))
+            }
+            FuncKind::Alias(a) => Some(ComponentField::Alias(Alias {
+                span: func.span,
+                id: func.id,
+                name: func.name,
+                target: AliasTarget::Export {
+                    instance: a.instance,
+                    name: a.name,
+                    kind: ComponentExportAliasKind::Func,
+                },
+            })),
+        }
+    }
+
+    fn expand_core_type(&mut self, field: &mut CoreType<'a>) {
+        match &mut field.def {
+            CoreTypeDef::Def(_) => {}
+            CoreTypeDef::Module(m) => self.expand_module_ty(m),
+        }
+
+        let id = gensym::fill(field.span, &mut field.id);
+        let index = Index::Id(id);
+        match &field.def {
+            CoreTypeDef::Def(_) => {}
+            CoreTypeDef::Module(t) => t.key().insert(self, index),
+        }
+    }
+
+    fn expand_type(&mut self, field: &mut Type<'a>) {
+        match &mut field.def {
+            TypeDef::Defined(d) => self.expand_defined_ty(d),
+            TypeDef::Func(f) => self.expand_func_ty(f),
+            TypeDef::Component(c) => self.expand_component_ty(c),
+            TypeDef::Instance(i) => self.expand_instance_ty(i),
+        }
+
+        let id = gensym::fill(field.span, &mut field.id);
+        let index = Index::Id(id);
+        match &field.def {
+            TypeDef::Defined(t) => t.key().insert(self, index),
+            TypeDef::Func(t) => t.key().insert(self, index),
+            TypeDef::Component(t) => t.key().insert(self, index),
+            TypeDef::Instance(t) => t.key().insert(self, index),
+        }
+        for (name, url) in field.exports.names.drain(..) {
+            self.component_fields_to_append
+                .push(ComponentField::Export(ComponentExport {
+                    span: field.span,
+                    id: None,
+                    debug_name: None,
+                    name,
+                    url,
+                    kind: ComponentExportKind::ty(field.span, id),
+                    ty: None,
+                }));
+        }
+    }
+
+    fn expand_func_ty(&mut self, ty: &mut ComponentFunctionType<'a>) {
+        for param in ty.params.iter_mut() {
+            self.expand_component_val_ty(&mut param.ty);
+        }
+
+        for result in ty.results.iter_mut() {
+            self.expand_component_val_ty(&mut result.ty);
+        }
+    }
+
+    fn expand_module_ty(&mut self, ty: &mut ModuleType<'a>) {
+        use crate::core::resolve::types::{FuncKey, TypeKey, TypeReference};
+
+        // Note that this is a custom implementation from everything else in
+        // this file since this is using core wasm types instead of component
+        // types, so a small part of the core wasm expansion process is
+        // inlined here to handle the `TypeUse` from core wasm.
+
+        let mut func_type_to_idx = HashMap::new();
+        let mut to_prepend = Vec::new();
+        let mut i = 0;
+        while i < ty.decls.len() {
+            match &mut ty.decls[i] {
+                ModuleTypeDecl::Type(ty) => match &ty.def {
+                    core::TypeDef::Func(f) => {
+                        let id = gensym::fill(ty.span, &mut ty.id);
+                        func_type_to_idx.insert(f.key(), Index::Id(id));
+                    }
+                    core::TypeDef::Struct(_) => {}
+                    core::TypeDef::Array(_) => {}
+                },
+                ModuleTypeDecl::Alias(_) => {}
+                ModuleTypeDecl::Import(ty) => {
+                    expand_sig(&mut ty.item, &mut to_prepend, &mut func_type_to_idx);
+                }
+                ModuleTypeDecl::Export(_, item) => {
+                    expand_sig(item, &mut to_prepend, &mut func_type_to_idx);
+                }
+            }
+            ty.decls.splice(i..i, to_prepend.drain(..));
+            i += 1;
+        }
+
+        fn expand_sig<'a>(
+            item: &mut core::ItemSig<'a>,
+            to_prepend: &mut Vec<ModuleTypeDecl<'a>>,
+            func_type_to_idx: &mut HashMap<FuncKey<'a>, Index<'a>>,
+        ) {
+            match &mut item.kind {
+                core::ItemKind::Func(t) | core::ItemKind::Tag(core::TagType::Exception(t)) => {
+                    // If the index is already filled in then this is skipped
+                    if t.index.is_some() {
+                        return;
+                    }
+
+                    // Otherwise the inline type information is used to
+                    // generate a type into this module if necessary. If the
+                    // function type already exists we reuse the same key,
+                    // otherwise a fresh type definition is created and we use
+                    // that one instead.
+                    let ty = t.inline.take().unwrap_or_default();
+                    let key = ty.key();
+                    if let Some(idx) = func_type_to_idx.get(&key) {
+                        t.index = Some(*idx);
+                        return;
+                    }
+                    let id = gensym::gen(item.span);
+                    to_prepend.push(ModuleTypeDecl::Type(core::Type {
+                        span: item.span,
+                        id: Some(id),
+                        name: None,
+                        def: key.to_def(item.span),
+                        parent: None,
+                    }));
+                    let idx = Index::Id(id);
+                    t.index = Some(idx);
+                }
+                core::ItemKind::Global(_)
+                | core::ItemKind::Table(_)
+                | core::ItemKind::Memory(_) => {}
+            }
+        }
+    }
+
+    fn expand_component_ty(&mut self, ty: &mut ComponentType<'a>) {
+        Expander::default().expand_decls(&mut ty.decls, |e, decl| match decl {
+            ComponentTypeDecl::CoreType(t) => e.expand_core_type(t),
+            ComponentTypeDecl::Type(t) => e.expand_type(t),
+            ComponentTypeDecl::Alias(_) => {}
+            ComponentTypeDecl::Export(t) => e.expand_item_sig(&mut t.item),
+            ComponentTypeDecl::Import(t) => e.expand_item_sig(&mut t.item),
+        })
+    }
+
+    fn expand_instance_ty(&mut self, ty: &mut InstanceType<'a>) {
+        Expander::default().expand_decls(&mut ty.decls, |e, decl| match decl {
+            InstanceTypeDecl::CoreType(t) => e.expand_core_type(t),
+            InstanceTypeDecl::Type(t) => e.expand_type(t),
+            InstanceTypeDecl::Alias(_) => {}
+            InstanceTypeDecl::Export(t) => e.expand_item_sig(&mut t.item),
+        })
+    }
+
+    fn expand_item_sig(&mut self, ext: &mut ItemSig<'a>) {
+        match &mut ext.kind {
+            ItemSigKind::CoreModule(t) => {
+                self.expand_core_type_use(t);
+            }
+            ItemSigKind::Func(t) => {
+                self.expand_component_type_use(t);
+            }
+            ItemSigKind::Component(t) => {
+                self.expand_component_type_use(t);
+            }
+            ItemSigKind::Instance(t) => {
+                self.expand_component_type_use(t);
+            }
+            ItemSigKind::Value(t) => {
+                self.expand_component_val_ty(&mut t.0);
+            }
+            ItemSigKind::Type(_) => {}
+        }
+    }
+
+    fn expand_defined_ty(&mut self, ty: &mut ComponentDefinedType<'a>) {
+        match ty {
+            ComponentDefinedType::Primitive(_)
+            | ComponentDefinedType::Flags(_)
+            | ComponentDefinedType::Enum(_) => {}
+            ComponentDefinedType::Record(r) => {
+                for field in r.fields.iter_mut() {
+                    self.expand_component_val_ty(&mut field.ty);
+                }
+            }
+            ComponentDefinedType::Variant(v) => {
+                for case in v.cases.iter_mut() {
+                    if let Some(ty) = &mut case.ty {
+                        self.expand_component_val_ty(ty);
+                    }
+                }
+            }
+            ComponentDefinedType::List(t) => {
+                self.expand_component_val_ty(&mut t.element);
+            }
+            ComponentDefinedType::Tuple(t) => {
+                for field in t.fields.iter_mut() {
+                    self.expand_component_val_ty(field);
+                }
+            }
+            ComponentDefinedType::Union(u) => {
+                for ty in u.types.iter_mut() {
+                    self.expand_component_val_ty(ty);
+                }
+            }
+            ComponentDefinedType::Option(t) => {
+                self.expand_component_val_ty(&mut t.element);
+            }
+            ComponentDefinedType::Result(r) => {
+                if let Some(ty) = &mut r.ok {
+                    self.expand_component_val_ty(ty);
+                }
+
+                if let Some(ty) = &mut r.err {
+                    self.expand_component_val_ty(ty);
+                }
+            }
+        }
+    }
+
+    fn expand_component_val_ty(&mut self, ty: &mut ComponentValType<'a>) {
+        let inline = match ty {
+            ComponentValType::Inline(ComponentDefinedType::Primitive(_))
+            | ComponentValType::Ref(_) => return,
+            ComponentValType::Inline(inline) => {
+                self.expand_defined_ty(inline);
+                mem::take(inline)
+            }
+        };
+        // If this inline type has already been defined within this context
+        // then reuse the previously defined type to avoid injecting too many
+        // types into the type index space.
+        if let Some(idx) = inline.key().lookup(self) {
+            *ty = ComponentValType::Ref(idx);
+            return;
+        }
+
+        // And if this type isn't already defined we append it to the index
+        // space with a fresh and unique name.
+        let span = Span::from_offset(0); // FIXME(#613): don't manufacture
+        let id = gensym::gen(span);
+
+        self.types_to_prepend.push(inline.into_any_type(span, id));
+
+        let idx = Index::Id(id);
+        *ty = ComponentValType::Ref(idx);
+    }
+
+    fn expand_core_type_use<T>(
+        &mut self,
+        item: &mut CoreTypeUse<'a, T>,
+    ) -> CoreItemRef<'a, kw::r#type>
+    where
+        T: TypeReference<'a>,
+    {
+        let span = Span::from_offset(0); // FIXME(#613): don't manufacture
+        let mut inline = match mem::take(item) {
+            // If this type-use was already a reference to an existing type
+            // then we put it back the way it was and return the corresponding
+            // index.
+            CoreTypeUse::Ref(idx) => {
+                *item = CoreTypeUse::Ref(idx.clone());
+                return idx;
+            }
+
+            // ... otherwise with an inline type definition we go into
+            // processing below.
+            CoreTypeUse::Inline(inline) => inline,
+        };
+        inline.expand(self);
+
+        // If this inline type has already been defined within this context
+        // then reuse the previously defined type to avoid injecting too many
+        // types into the type index space.
+        if let Some(idx) = inline.key().lookup(self) {
+            let ret = CoreItemRef {
+                idx,
+                kind: kw::r#type(span),
+                export_name: None,
+            };
+            *item = CoreTypeUse::Ref(ret.clone());
+            return ret;
+        }
+
+        // And if this type isn't already defined we append it to the index
+        // space with a fresh and unique name.
+        let id = gensym::gen(span);
+
+        self.types_to_prepend.push(inline.into_any_type(span, id));
+
+        let idx = Index::Id(id);
+        let ret = CoreItemRef {
+            idx,
+            kind: kw::r#type(span),
+            export_name: None,
+        };
+
+        *item = CoreTypeUse::Ref(ret.clone());
+        ret
+    }
+
+    fn expand_component_type_use<T>(
+        &mut self,
+        item: &mut ComponentTypeUse<'a, T>,
+    ) -> ItemRef<'a, kw::r#type>
+    where
+        T: TypeReference<'a>,
+    {
+        let span = Span::from_offset(0); // FIXME(#613): don't manufacture
+        let mut inline = match mem::take(item) {
+            // If this type-use was already a reference to an existing type
+            // then we put it back the way it was and return the corresponding
+            // index.
+            ComponentTypeUse::Ref(idx) => {
+                *item = ComponentTypeUse::Ref(idx.clone());
+                return idx;
+            }
+
+            // ... otherwise with an inline type definition we go into
+            // processing below.
+            ComponentTypeUse::Inline(inline) => inline,
+        };
+        inline.expand(self);
+
+        // If this inline type has already been defined within this context
+        // then reuse the previously defined type to avoid injecting too many
+        // types into the type index space.
+        if let Some(idx) = inline.key().lookup(self) {
+            let ret = ItemRef {
+                idx,
+                kind: kw::r#type(span),
+                export_names: Vec::new(),
+            };
+            *item = ComponentTypeUse::Ref(ret.clone());
+            return ret;
+        }
+
+        // And if this type isn't already defined we append it to the index
+        // space with a fresh and unique name.
+        let id = gensym::gen(span);
+
+        self.types_to_prepend.push(inline.into_any_type(span, id));
+
+        let idx = Index::Id(id);
+        let ret = ItemRef {
+            idx,
+            kind: kw::r#type(span),
+            export_names: Vec::new(),
+        };
+
+        *item = ComponentTypeUse::Ref(ret.clone());
+        ret
+    }
+
+    fn expand_core_instantiation_arg(&mut self, arg: &mut CoreInstantiationArgKind<'a>) {
+        let (span, exports) = match arg {
+            CoreInstantiationArgKind::Instance(_) => return,
+            CoreInstantiationArgKind::BundleOfExports(span, exports) => (*span, mem::take(exports)),
+        };
+        let id = gensym::gen(span);
+        self.component_fields_to_prepend
+            .push(ComponentField::CoreInstance(CoreInstance {
+                span,
+                id: Some(id),
+                name: None,
+                kind: CoreInstanceKind::BundleOfExports(exports),
+            }));
+        *arg = CoreInstantiationArgKind::Instance(CoreItemRef {
+            kind: kw::instance(span),
+            idx: Index::Id(id),
+            export_name: None,
+        });
+    }
+
+    fn expand_instantiation_arg(&mut self, arg: &mut InstantiationArgKind<'a>) {
+        let (span, exports) = match arg {
+            InstantiationArgKind::Item(_) => return,
+            InstantiationArgKind::BundleOfExports(span, exports) => (*span, mem::take(exports)),
+        };
+        let id = gensym::gen(span);
+        self.component_fields_to_prepend
+            .push(ComponentField::Instance(Instance {
+                span,
+                id: Some(id),
+                name: None,
+                exports: Default::default(),
+                kind: InstanceKind::BundleOfExports(exports),
+            }));
+        *arg = InstantiationArgKind::Item(ComponentExportKind::instance(span, id));
+    }
+}
+
+trait TypeReference<'a> {
+    type Key: TypeKey<'a>;
+    fn key(&self) -> Self::Key;
+    fn expand(&mut self, cx: &mut Expander<'a>);
+    fn into_any_type(self, span: Span, id: Id<'a>) -> AnyType<'a>;
+}
+
+impl<'a> TypeReference<'a> for ComponentDefinedType<'a> {
+    type Key = Todo; // FIXME(#598): should implement this
+
+    fn key(&self) -> Self::Key {
+        Todo
+    }
+
+    fn expand(&mut self, cx: &mut Expander<'a>) {
+        cx.expand_defined_ty(self)
+    }
+
+    fn into_any_type(self, span: Span, id: Id<'a>) -> AnyType<'a> {
+        AnyType::Component(Type {
+            span,
+            id: Some(id),
+            name: None,
+            exports: Default::default(),
+            def: TypeDef::Defined(self),
+        })
+    }
+}
+
+impl<'a> TypeReference<'a> for ComponentType<'a> {
+    type Key = Todo; // FIXME(#598): should implement this
+
+    fn key(&self) -> Self::Key {
+        Todo
+    }
+
+    fn expand(&mut self, cx: &mut Expander<'a>) {
+        cx.expand_component_ty(self)
+    }
+
+    fn into_any_type(self, span: Span, id: Id<'a>) -> AnyType<'a> {
+        AnyType::Component(Type {
+            span,
+            id: Some(id),
+            name: None,
+            exports: Default::default(),
+            def: TypeDef::Component(self),
+        })
+    }
+}
+
+impl<'a> TypeReference<'a> for ModuleType<'a> {
+    type Key = Todo; // FIXME(#598): should implement this
+
+    fn key(&self) -> Self::Key {
+        Todo
+    }
+
+    fn expand(&mut self, cx: &mut Expander<'a>) {
+        cx.expand_module_ty(self)
+    }
+
+    fn into_any_type(self, span: Span, id: Id<'a>) -> AnyType<'a> {
+        AnyType::Core(CoreType {
+            span,
+            id: Some(id),
+            name: None,
+            def: CoreTypeDef::Module(self),
+        })
+    }
+}
+
+impl<'a> TypeReference<'a> for InstanceType<'a> {
+    type Key = Todo; // FIXME(#598): should implement this
+
+    fn key(&self) -> Self::Key {
+        Todo
+    }
+
+    fn expand(&mut self, cx: &mut Expander<'a>) {
+        cx.expand_instance_ty(self)
+    }
+
+    fn into_any_type(self, span: Span, id: Id<'a>) -> AnyType<'a> {
+        AnyType::Component(Type {
+            span,
+            id: Some(id),
+            name: None,
+            exports: Default::default(),
+            def: TypeDef::Instance(self),
+        })
+    }
+}
+
+impl<'a> TypeReference<'a> for ComponentFunctionType<'a> {
+    type Key = Todo; // FIXME(#598): should implement this
+
+    fn key(&self) -> Self::Key {
+        Todo
+    }
+
+    fn expand(&mut self, cx: &mut Expander<'a>) {
+        cx.expand_func_ty(self)
+    }
+
+    fn into_any_type(self, span: Span, id: Id<'a>) -> AnyType<'a> {
+        AnyType::Component(Type {
+            span,
+            id: Some(id),
+            name: None,
+            exports: Default::default(),
+            def: TypeDef::Func(self),
+        })
+    }
+}
+
+trait TypeKey<'a> {
+    fn lookup(&self, cx: &Expander<'a>) -> Option<Index<'a>>;
+    fn insert(&self, cx: &mut Expander<'a>, index: Index<'a>);
+}
+
+struct Todo;
+
+impl<'a> TypeKey<'a> for Todo {
+    fn lookup(&self, _cx: &Expander<'a>) -> Option<Index<'a>> {
+        None
+    }
+
+    fn insert(&self, _cx: &mut Expander<'a>, _index: Index<'a>) {}
+}
diff --git a/third_party/rust/wast/src/component/export.rs b/third_party/rust/wast/src/component/export.rs
new file mode 100644
index 0000000000..ce9baaf453
--- /dev/null
+++ b/third_party/rust/wast/src/component/export.rs
@@ -0,0 +1,221 @@
+use super::{ItemRef, ItemSigNoName};
+use crate::kw;
+use crate::parser::{Cursor, Parse, Parser, Peek, Result};
+use crate::token::{Id, Index, NameAnnotation, Span};
+
+/// An entry in a WebAssembly component's export section.
+#[derive(Debug)]
+pub struct ComponentExport<'a> {
+    /// Where this export was defined.
+    pub span: Span,
+    /// Optional identifier bound to this export.
+    pub id: Option<Id<'a>>,
+    /// An optional name for this instance stored in the custom `name` section.
+    pub debug_name: Option<NameAnnotation<'a>>,
+    /// The name of this export from the component.
+    pub name: &'a str,
+    /// The URL of the export.
+    pub url: Option<&'a str>,
+    /// The kind of export.
+    pub kind: ComponentExportKind<'a>,
+    /// The kind of export.
+    pub ty: Option<ItemSigNoName<'a>>,
+}
+
+impl<'a> Parse<'a> for ComponentExport<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let span = parser.parse::<kw::export>()?.0;
+        let id = parser.parse()?;
+        let debug_name = parser.parse()?;
+        let name = parser.parse()?;
+        let url = parser.parse()?;
+        let kind = parser.parse()?;
+        let ty = if !parser.is_empty() {
+            Some(parser.parens(|p| p.parse())?)
+        } else {
+            None
+        };
+        Ok(ComponentExport {
+            span,
+            id,
+            debug_name,
+            name,
+            url,
+            kind,
+            ty,
+        })
+    }
+}
+
+impl<'a> Parse<'a> for Vec<ComponentExport<'a>> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut exports = Vec::new();
+        while !parser.is_empty() {
+            exports.push(parser.parens(|parser| parser.parse())?);
+        }
+        Ok(exports)
+    }
+}
+
+/// The kind of exported item.
+#[derive(Debug)]
+pub enum ComponentExportKind<'a> {
+    /// The export is a core module.
+    ///
+    /// Note this isn't a core item ref as currently only
+    /// components can export core modules.
+    CoreModule(ItemRef<'a, kw::module>),
+    /// The export is a function.
+    Func(ItemRef<'a, kw::func>),
+    /// The export is a value.
+    Value(ItemRef<'a, kw::value>),
+    /// The export is a type.
+    Type(ItemRef<'a, kw::r#type>),
+    /// The export is a component.
+    Component(ItemRef<'a, kw::component>),
+    /// The export is an instance.
+    Instance(ItemRef<'a, kw::instance>),
+}
+
+impl<'a> ComponentExportKind<'a> {
+    pub(crate) fn module(span: Span, id: Id<'a>) -> Self {
+        Self::CoreModule(ItemRef {
+            kind: kw::module(span),
+            idx: Index::Id(id),
+            export_names: Default::default(),
+        })
+    }
+
+    pub(crate) fn component(span: Span, id: Id<'a>) -> Self {
+        Self::Component(ItemRef {
+            kind: kw::component(span),
+            idx: Index::Id(id),
+            export_names: Default::default(),
+        })
+    }
+
+    pub(crate) fn instance(span: Span, id: Id<'a>) -> Self {
+        Self::Instance(ItemRef {
+            kind: kw::instance(span),
+            idx: Index::Id(id),
+            export_names: Default::default(),
+        })
+    }
+
+    pub(crate) fn func(span: Span, id: Id<'a>) -> Self {
+        Self::Func(ItemRef {
+            kind: kw::func(span),
+            idx: Index::Id(id),
+            export_names: Default::default(),
+        })
+    }
+
+    pub(crate) fn ty(span: Span, id: Id<'a>) -> Self {
+        Self::Type(ItemRef {
+            kind: kw::r#type(span),
+            idx: Index::Id(id),
+            export_names: Default::default(),
+        })
+    }
+}
+
+impl<'a> Parse<'a> for ComponentExportKind<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.parens(|parser| {
+            let mut l = parser.lookahead1();
+            if l.peek::<kw::core>() {
+                // Remove core prefix
+                parser.parse::<kw::core>()?;
+                Ok(Self::CoreModule(parser.parse()?))
+            } else if l.peek::<kw::func>() {
+                Ok(Self::Func(parser.parse()?))
+            } else if l.peek::<kw::value>() {
+                Ok(Self::Value(parser.parse()?))
+            } else if l.peek::<kw::r#type>() {
+                Ok(Self::Type(parser.parse()?))
+            } else if l.peek::<kw::component>() {
+                Ok(Self::Component(parser.parse()?))
+            } else if l.peek::<kw::instance>() {
+                Ok(Self::Instance(parser.parse()?))
+            } else {
+                Err(l.error())
+            }
+        })
+    }
+}
+
+impl Peek for ComponentExportKind<'_> {
+    fn peek(cursor: Cursor) -> bool {
+        let cursor = match cursor.lparen() {
+            Some(c) => c,
+            None => return false,
+        };
+
+        let cursor = match cursor.keyword() {
+            Some(("core", c)) => match c.keyword() {
+                Some(("module", c)) => c,
+                _ => return false,
+            },
+            Some(("func", c))
+            | Some(("value", c))
+            | Some(("type", c))
+            | Some(("component", c))
+            | Some(("instance", c)) => c,
+            _ => return false,
+        };
+
+        Index::peek(cursor)
+    }
+
+    fn display() -> &'static str {
+        "component export"
+    }
+}
+
+/// A listing of inline `(export "foo" <url>)` statements on a WebAssembly
+/// component item in its textual format.
+#[derive(Debug, Default)]
+pub struct InlineExport<'a> {
+    /// The extra names to export an item as, if any.
+    pub names: Vec<(&'a str, Option<&'a str>)>,
+}
+
+impl<'a> Parse<'a> for InlineExport<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut names = Vec::new();
+        while parser.peek::<Self>() {
+            names.push(parser.parens(|p| {
+                p.parse::<kw::export>()?;
+                Ok((p.parse()?, p.parse()?))
+            })?);
+        }
+        Ok(InlineExport { names })
+    }
+}
+
+impl Peek for InlineExport<'_> {
+    fn peek(cursor: Cursor<'_>) -> bool {
+        let cursor = match cursor.lparen() {
+            Some(cursor) => cursor,
+            None => return false,
+        };
+        let cursor = match cursor.keyword() {
+            Some(("export", cursor)) => cursor,
+            _ => return false,
+        };
+        // Name
+        let mut cursor = match cursor.string() {
+            Some((_, cursor)) => cursor,
+            None => return false,
+        };
+        // Optional URL
+        if let Some((_, c)) = cursor.string() {
+            cursor = c;
+        }
+        cursor.rparen().is_some()
+    }
+
+    fn display() -> &'static str {
+        "inline export"
+    }
+}
diff --git a/third_party/rust/wast/src/component/func.rs b/third_party/rust/wast/src/component/func.rs
new file mode 100644
index 0000000000..4edbc63171
--- /dev/null
+++ b/third_party/rust/wast/src/component/func.rs
@@ -0,0 +1,372 @@
+use crate::component::*;
+use crate::kw;
+use crate::parser::{Parse, Parser, Result};
+use crate::token::{Id, Index, LParen, NameAnnotation, Span};
+
+/// A declared core function.
+///
+/// This is a member of both the core alias and canon sections.
+#[derive(Debug)]
+pub struct CoreFunc<'a> {
+    /// Where this `core func` was defined.
+    pub span: Span,
+    /// An identifier that this function is resolved with (optionally) for name
+    /// resolution.
+    pub id: Option<Id<'a>>,
+    /// An optional name for this function stored in the custom `name` section.
+    pub name: Option<NameAnnotation<'a>>,
+    /// The kind of core function.
+    pub kind: CoreFuncKind<'a>,
+}
+
+impl<'a> Parse<'a> for CoreFunc<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let span = parser.parse::<kw::core>()?.0;
+        parser.parse::<kw::func>()?;
+        let id = parser.parse()?;
+        let name = parser.parse()?;
+        let kind = parser.parse()?;
+
+        Ok(Self {
+            span,
+            id,
+            name,
+            kind,
+        })
+    }
+}
+
+/// Represents the kind of core functions.
+#[derive(Debug)]
+pub enum CoreFuncKind<'a> {
+    /// The core function is defined in terms of lowering a component function.
+    ///
+    /// The core function is actually a member of the canon section.
+    Lower(CanonLower<'a>),
+    /// The core function is defined in terms of aliasing a module instance export.
+    ///
+    /// The core function is actually a member of the core alias section.
+    Alias(InlineExportAlias<'a>),
+}
+
+impl<'a> Parse<'a> for CoreFuncKind<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.parens(|parser| {
+            let mut l = parser.lookahead1();
+            if l.peek::<kw::canon>() {
+                parser.parse::<kw::canon>()?;
+                Ok(Self::Lower(parser.parse()?))
+            } else if l.peek::<kw::alias>() {
+                Ok(Self::Alias(parser.parse()?))
+            } else {
+                Err(l.error())
+            }
+        })
+    }
+}
+
+/// A declared component function.
+///
+/// This may be a member of the import, alias, or canon sections.
+#[derive(Debug)]
+pub struct Func<'a> {
+    /// Where this `func` was defined.
+    pub span: Span,
+    /// An identifier that this function is resolved with (optionally) for name
+    /// resolution.
+    pub id: Option<Id<'a>>,
+    /// An optional name for this function stored in the custom `name` section.
+    pub name: Option<NameAnnotation<'a>>,
+    /// If present, inline export annotations which indicate names this
+    /// definition should be exported under.
+    pub exports: InlineExport<'a>,
+    /// The kind of function.
+    pub kind: FuncKind<'a>,
+}
+
+impl<'a> Parse<'a> for Func<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let span = parser.parse::<kw::func>()?.0;
+        let id = parser.parse()?;
+        let name = parser.parse()?;
+        let exports = parser.parse()?;
+        let kind = parser.parse()?;
+
+        Ok(Self {
+            span,
+            id,
+            name,
+            exports,
+            kind,
+        })
+    }
+}
+
+/// Represents the kind of component functions.
+#[derive(Debug)]
+pub enum FuncKind<'a> {
+    /// A function which is actually defined as an import, such as:
+    ///
+    /// ```text
+    /// (func (import "foo") (param string))
+    /// ```
+    Import {
+        /// The import name of this import.
+        import: InlineImport<'a>,
+        /// The type that this function will have.
+        ty: ComponentTypeUse<'a, ComponentFunctionType<'a>>,
+    },
+    /// The function is defined in terms of lifting a core function.
+    ///
+    /// The function is actually a member of the canon section.
+    Lift {
+        /// The lifted function's type.
+        ty: ComponentTypeUse<'a, ComponentFunctionType<'a>>,
+        /// Information relating to the lifting of the core function.
+        info: CanonLift<'a>,
+    },
+    /// The function is defined in terms of aliasing a component instance export.
+    ///
+    /// The function is actually a member of the alias section.
+    Alias(InlineExportAlias<'a>),
+}
+
+impl<'a> Parse<'a> for FuncKind<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        if let Some(import) = parser.parse()? {
+            Ok(Self::Import {
+                import,
+                ty: parser.parse()?,
+            })
+        } else if parser.peek::<LParen>() && parser.peek2::<kw::alias>() {
+            parser.parens(|parser| Ok(Self::Alias(parser.parse()?)))
+        } else {
+            Ok(Self::Lift {
+                ty: parser.parse()?,
+                info: parser.parens(|parser| {
+                    parser.parse::<kw::canon>()?;
+                    parser.parse()
+                })?,
+            })
+        }
+    }
+}
+
+/// A WebAssembly canonical function to be inserted into a component.
+///
+/// This is a member of the canonical section.
+#[derive(Debug)]
+pub struct CanonicalFunc<'a> {
+    /// Where this `func` was defined.
+    pub span: Span,
+    /// An identifier that this function is resolved with (optionally) for name
+    /// resolution.
+    pub id: Option<Id<'a>>,
+    /// An optional name for this function stored in the custom `name` section.
+    pub name: Option<NameAnnotation<'a>>,
+    /// What kind of function this is, be it a lowered or lifted function.
+    pub kind: CanonicalFuncKind<'a>,
+}
+
+impl<'a> Parse<'a> for CanonicalFunc<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let span = parser.parse::<kw::canon>()?.0;
+
+        if parser.peek::<kw::lift>() {
+            let info = parser.parse()?;
+            let (id, name, ty) = parser.parens(|parser| {
+                parser.parse::<kw::func>()?;
+                let id = parser.parse()?;
+                let name = parser.parse()?;
+                let ty = parser.parse()?;
+                Ok((id, name, ty))
+            })?;
+
+            Ok(Self {
+                span,
+                id,
+                name,
+                kind: CanonicalFuncKind::Lift { info, ty },
+            })
+        } else if parser.peek::<kw::lower>() {
+            let info = parser.parse()?;
+            let (id, name) = parser.parens(|parser| {
+                parser.parse::<kw::core>()?;
+                parser.parse::<kw::func>()?;
+                let id = parser.parse()?;
+                let name = parser.parse()?;
+                Ok((id, name))
+            })?;
+
+            Ok(Self {
+                span,
+                id,
+                name,
+                kind: CanonicalFuncKind::Lower(info),
+            })
+        } else {
+            Err(parser.error("expected `canon lift` or `canon lower`"))
+        }
+    }
+}
+
+/// Possible ways to define a canonical function in the text format.
+#[derive(Debug)]
+pub enum CanonicalFuncKind<'a> {
+    /// A canonical function that is defined in terms of lifting a core function.
+    Lift {
+        /// The lifted function's type.
+        ty: ComponentTypeUse<'a, ComponentFunctionType<'a>>,
+        /// Information relating to the lifting of the core function.
+        info: CanonLift<'a>,
+    },
+    /// A canonical function that is defined in terms of lowering a component function.
+    Lower(CanonLower<'a>),
+}
+
+/// Information relating to lifting a core function.
+#[derive(Debug)]
+pub struct CanonLift<'a> {
+    /// The core function being lifted.
+    pub func: CoreItemRef<'a, kw::func>,
+    /// The canonical options for the lifting.
+    pub opts: Vec<CanonOpt<'a>>,
+}
+
+impl<'a> Parse<'a> for CanonLift<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.parse::<kw::lift>()?;
+
+        Ok(Self {
+            func: parser.parens(|parser| {
+                parser.parse::<kw::core>()?;
+                parser.parse()
+            })?,
+            opts: parser.parse()?,
+        })
+    }
+}
+
+impl Default for CanonLift<'_> {
+    fn default() -> Self {
+        let span = Span::from_offset(0);
+        Self {
+            func: CoreItemRef {
+                kind: kw::func(span),
+                idx: Index::Num(0, span),
+                export_name: None,
+            },
+            opts: Vec::new(),
+        }
+    }
+}
+
+/// Information relating to lowering a component function.
+#[derive(Debug)]
+pub struct CanonLower<'a> {
+    /// The function being lowered.
+    pub func: ItemRef<'a, kw::func>,
+    /// The canonical options for the lowering.
+    pub opts: Vec<CanonOpt<'a>>,
+}
+
+impl<'a> Parse<'a> for CanonLower<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.parse::<kw::lower>()?;
+
+        Ok(Self {
+            func: parser.parens(|parser| parser.parse())?,
+            opts: parser.parse()?,
+        })
+    }
+}
+
+impl Default for CanonLower<'_> {
+    fn default() -> Self {
+        let span = Span::from_offset(0);
+        Self {
+            func: ItemRef {
+                kind: kw::func(span),
+                idx: Index::Num(0, span),
+                export_names: Vec::new(),
+            },
+            opts: Vec::new(),
+        }
+    }
+}
+
+#[derive(Debug)]
+/// Canonical ABI options.
+pub enum CanonOpt<'a> {
+    /// Encode strings as UTF-8.
+    StringUtf8,
+    /// Encode strings as UTF-16.
+    StringUtf16,
+    /// Encode strings as "compact UTF-16".
+    StringLatin1Utf16,
+    /// Use the specified memory for canonical ABI memory access.
+    Memory(CoreItemRef<'a, kw::memory>),
+    /// Use the specified reallocation function for memory allocations.
+    Realloc(CoreItemRef<'a, kw::func>),
+    /// Call the specified function after the lifted function has returned.
+    PostReturn(CoreItemRef<'a, kw::func>),
+}
+
+impl<'a> Parse<'a> for CanonOpt<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut l = parser.lookahead1();
+        if l.peek::<kw::string_utf8>() {
+            parser.parse::<kw::string_utf8>()?;
+            Ok(Self::StringUtf8)
+        } else if l.peek::<kw::string_utf16>() {
+            parser.parse::<kw::string_utf16>()?;
+            Ok(Self::StringUtf16)
+        } else if l.peek::<kw::string_latin1_utf16>() {
+            parser.parse::<kw::string_latin1_utf16>()?;
+            Ok(Self::StringLatin1Utf16)
+        } else if l.peek::<LParen>() {
+            parser.parens(|parser| {
+                let mut l = parser.lookahead1();
+                if l.peek::<kw::memory>() {
+                    let span = parser.parse::<kw::memory>()?.0;
+                    Ok(CanonOpt::Memory(parse_trailing_item_ref(
+                        kw::memory(span),
+                        parser,
+                    )?))
+                } else if l.peek::<kw::realloc>() {
+                    parser.parse::<kw::realloc>()?;
+                    Ok(CanonOpt::Realloc(
+                        parser.parse::<IndexOrCoreRef<'_, _>>()?.0,
+                    ))
+                } else if l.peek::<kw::post_return>() {
+                    parser.parse::<kw::post_return>()?;
+                    Ok(CanonOpt::PostReturn(
+                        parser.parse::<IndexOrCoreRef<'_, _>>()?.0,
+                    ))
+                } else {
+                    Err(l.error())
+                }
+            })
+        } else {
+            Err(l.error())
+        }
+    }
+}
+
+fn parse_trailing_item_ref<T>(kind: T, parser: Parser) -> Result<CoreItemRef<T>> {
+    Ok(CoreItemRef {
+        kind,
+        idx: parser.parse()?,
+        export_name: parser.parse()?,
+    })
+}
+
+impl<'a> Parse<'a> for Vec<CanonOpt<'a>> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut funcs = Vec::new();
+        while !parser.is_empty() {
+            funcs.push(parser.parse()?);
+        }
+        Ok(funcs)
+    }
+}
diff --git a/third_party/rust/wast/src/component/import.rs b/third_party/rust/wast/src/component/import.rs
new file mode 100644
index 0000000000..98fec55aa7
--- /dev/null
+++ b/third_party/rust/wast/src/component/import.rs
@@ -0,0 +1,176 @@
+use crate::component::*;
+use crate::kw;
+use crate::parser::{Cursor, Parse, Parser, Peek, Result};
+use crate::token::Index;
+use crate::token::{Id, NameAnnotation, Span};
+
+/// An `import` statement and entry in a WebAssembly component.
+#[derive(Debug)]
+pub struct ComponentImport<'a> {
+    /// Where this `import` was defined
+    pub span: Span,
+    /// The name of the item to import.
+    pub name: &'a str,
+    /// The optional URL of the import.
+    pub url: Option<&'a str>,
+    /// The item that's being imported.
+    pub item: ItemSig<'a>,
+}
+
+impl<'a> Parse<'a> for ComponentImport<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let span = parser.parse::<kw::import>()?.0;
+        let name = parser.parse()?;
+        let url = parser.parse()?;
+        let item = parser.parens(|p| p.parse())?;
+        Ok(ComponentImport {
+            span,
+            name,
+            url,
+            item,
+        })
+    }
+}
+
+/// An item signature for imported items.
+#[derive(Debug)]
+pub struct ItemSig<'a> {
+    /// Where this item is defined in the source.
+    pub span: Span,
+    /// An optional identifier used during name resolution to refer to this item
+    /// from the rest of the component.
+    pub id: Option<Id<'a>>,
+    /// An optional name which, for functions, will be stored in the
+    /// custom `name` section.
+    pub name: Option<NameAnnotation<'a>>,
+    /// What kind of item this is.
+    pub kind: ItemSigKind<'a>,
+}
+
+impl<'a> Parse<'a> for ItemSig<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parse_item_sig(parser, true)
+    }
+}
+
+/// An item signature for imported items.
+#[derive(Debug)]
+pub struct ItemSigNoName<'a>(pub ItemSig<'a>);
+
+impl<'a> Parse<'a> for ItemSigNoName<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        Ok(ItemSigNoName(parse_item_sig(parser, false)?))
+    }
+}
+
+fn parse_item_sig<'a>(parser: Parser<'a>, name: bool) -> Result<ItemSig<'a>> {
+    let mut l = parser.lookahead1();
+    let (span, parse_kind): (_, fn(Parser<'a>) -> Result<ItemSigKind>) = if l.peek::<kw::core>() {
+        let span = parser.parse::<kw::core>()?.0;
+        parser.parse::<kw::module>()?;
+        (span, |parser| Ok(ItemSigKind::CoreModule(parser.parse()?)))
+    } else if l.peek::<kw::func>() {
+        let span = parser.parse::<kw::func>()?.0;
+        (span, |parser| Ok(ItemSigKind::Func(parser.parse()?)))
+    } else if l.peek::<kw::component>() {
+        let span = parser.parse::<kw::component>()?.0;
+        (span, |parser| Ok(ItemSigKind::Component(parser.parse()?)))
+    } else if l.peek::<kw::instance>() {
+        let span = parser.parse::<kw::instance>()?.0;
+        (span, |parser| Ok(ItemSigKind::Instance(parser.parse()?)))
+    } else if l.peek::<kw::value>() {
+        let span = parser.parse::<kw::value>()?.0;
+        (span, |parser| Ok(ItemSigKind::Value(parser.parse()?)))
+    } else if l.peek::<kw::r#type>() {
+        let span = parser.parse::<kw::r#type>()?.0;
+        (span, |parser| {
+            Ok(ItemSigKind::Type(parser.parens(|parser| parser.parse())?))
+        })
+    } else {
+        return Err(l.error());
+    };
+    Ok(ItemSig {
+        span,
+        id: if name { parser.parse()? } else { None },
+        name: if name { parser.parse()? } else { None },
+        kind: parse_kind(parser)?,
+    })
+}
+
+/// The kind of signatures for imported items.
+#[derive(Debug)]
+pub enum ItemSigKind<'a> {
+    /// The item signature is for a core module.
+    CoreModule(CoreTypeUse<'a, ModuleType<'a>>),
+    /// The item signature is for a function.
+    Func(ComponentTypeUse<'a, ComponentFunctionType<'a>>),
+    /// The item signature is for a component.
+    Component(ComponentTypeUse<'a, ComponentType<'a>>),
+    /// The item signature is for an instance.
+    Instance(ComponentTypeUse<'a, InstanceType<'a>>),
+    /// The item signature is for a value.
+    Value(ComponentValTypeUse<'a>),
+    /// The item signature is for a type.
+    Type(TypeBounds<'a>),
+}
+
+/// Represents the bounds applied to types being imported.
+#[derive(Debug)]
+pub enum TypeBounds<'a> {
+    /// The equality type bounds.
+    Eq(Index<'a>),
+}
+
+impl<'a> Parse<'a> for TypeBounds<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        // Currently this is the only supported type bounds.
+        parser.parse::<kw::eq>()?;
+        Ok(Self::Eq(parser.parse()?))
+    }
+}
+
+/// A listing of a inline `(import "foo")` statement.
+///
+/// This is the same as `core::InlineImport` except only one string import is
+/// required.
+#[derive(Debug, Clone)]
+pub struct InlineImport<'a> {
+    /// The name of the item being imported.
+    pub name: &'a str,
+    /// The optional URL of the item being imported.
+    pub url: Option<&'a str>,
+}
+
+impl<'a> Parse<'a> for InlineImport<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.parens(|p| {
+            p.parse::<kw::import>()?;
+            Ok(InlineImport {
+                name: p.parse()?,
+                url: p.parse()?,
+            })
+        })
+    }
+}
+
+impl Peek for InlineImport<'_> {
+    fn peek(cursor: Cursor<'_>) -> bool {
+        let cursor = match cursor.lparen() {
+            Some(cursor) => cursor,
+            None => return false,
+        };
+        let cursor = match cursor.keyword() {
+            Some(("import", cursor)) => cursor,
+            _ => return false,
+        };
+        let cursor = match cursor.string() {
+            Some((_, cursor)) => cursor,
+            None => return false,
+        };
+        cursor.rparen().is_some()
+    }
+
+    fn display() -> &'static str {
+        "inline import"
+    }
+}
diff --git a/third_party/rust/wast/src/component/instance.rs b/third_party/rust/wast/src/component/instance.rs
new file mode 100644
index 0000000000..888f4ee9f9
--- /dev/null
+++ b/third_party/rust/wast/src/component/instance.rs
@@ -0,0 +1,296 @@
+use crate::component::*;
+use crate::core;
+use crate::kw;
+use crate::parser::{Parse, Parser, Result};
+use crate::token::{Id, LParen, NameAnnotation, Span};
+
+/// A core instance defined by instantiation or exporting core items.
+#[derive(Debug)]
+pub struct CoreInstance<'a> {
+    /// Where this `core instance` was defined.
+    pub span: Span,
+    /// An identifier that this instance is resolved with (optionally) for name
+    /// resolution.
+    pub id: Option<Id<'a>>,
+    /// An optional name for this instance stored in the custom `name` section.
+    pub name: Option<NameAnnotation<'a>>,
+    /// What kind of instance this is.
+    pub kind: CoreInstanceKind<'a>,
+}
+
+impl<'a> Parse<'a> for CoreInstance<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let span = parser.parse::<kw::core>()?.0;
+        parser.parse::<kw::instance>()?;
+        let id = parser.parse()?;
+        let name = parser.parse()?;
+        let kind = parser.parse()?;
+
+        Ok(Self {
+            span,
+            id,
+            name,
+            kind,
+        })
+    }
+}
+
+/// The kinds of core instances in the text format.
+#[derive(Debug)]
+pub enum CoreInstanceKind<'a> {
+    /// Instantiate a core module.
+    Instantiate {
+        /// The module being instantiated.
+        module: ItemRef<'a, kw::module>,
+        /// Arguments used to instantiate the instance.
+        args: Vec<CoreInstantiationArg<'a>>,
+    },
+    /// The instance is defined by exporting local items as an instance.
+    BundleOfExports(Vec<CoreInstanceExport<'a>>),
+}
+
+impl<'a> Parse<'a> for CoreInstanceKind<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        if parser.peek::<LParen>() && parser.peek2::<kw::instantiate>() {
+            parser.parens(|parser| {
+                parser.parse::<kw::instantiate>()?;
+                Ok(Self::Instantiate {
+                    module: parser.parse::<IndexOrRef<'_, _>>()?.0,
+                    args: parser.parse()?,
+                })
+            })
+        } else {
+            Ok(Self::BundleOfExports(parser.parse()?))
+        }
+    }
+}
+
+impl Default for kw::module {
+    fn default() -> kw::module {
+        kw::module(Span::from_offset(0))
+    }
+}
+
+/// An argument to instantiate a core module.
+#[derive(Debug)]
+pub struct CoreInstantiationArg<'a> {
+    /// The name of the instantiation argument.
+    pub name: &'a str,
+    /// The kind of core instantiation argument.
+    pub kind: CoreInstantiationArgKind<'a>,
+}
+
+impl<'a> Parse<'a> for CoreInstantiationArg<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.parse::<kw::with>()?;
+        Ok(Self {
+            name: parser.parse()?,
+            kind: parser.parse()?,
+        })
+    }
+}
+
+impl<'a> Parse<'a> for Vec<CoreInstantiationArg<'a>> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut args = Vec::new();
+        while !parser.is_empty() {
+            args.push(parser.parens(|parser| parser.parse())?);
+        }
+        Ok(args)
+    }
+}
+
+/// The kind of core instantiation argument.
+#[derive(Debug)]
+pub enum CoreInstantiationArgKind<'a> {
+    /// The argument is a reference to an instance.
+    Instance(CoreItemRef<'a, kw::instance>),
+    /// The argument is an instance created from local exported core items.
+    ///
+    /// This is syntactic sugar for defining a core instance and also using it
+    /// as an instantiation argument.
+    BundleOfExports(Span, Vec<CoreInstanceExport<'a>>),
+}
+
+impl<'a> Parse<'a> for CoreInstantiationArgKind<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.parens(|parser| {
+            if let Some(r) = parser.parse()? {
+                Ok(Self::Instance(r))
+            } else {
+                let span = parser.parse::<kw::instance>()?.0;
+                Ok(Self::BundleOfExports(span, parser.parse()?))
+            }
+        })
+    }
+}
+
+/// An exported item as part of a core instance.
+#[derive(Debug)]
+pub struct CoreInstanceExport<'a> {
+    /// Where this export was defined.
+    pub span: Span,
+    /// The name of this export from the instance.
+    pub name: &'a str,
+    /// What's being exported from the instance.
+    pub item: CoreItemRef<'a, core::ExportKind>,
+}
+
+impl<'a> Parse<'a> for CoreInstanceExport<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        Ok(Self {
+            span: parser.parse::<kw::export>()?.0,
+            name: parser.parse()?,
+            item: parser.parens(|parser| parser.parse())?,
+        })
+    }
+}
+
+impl<'a> Parse<'a> for Vec<CoreInstanceExport<'a>> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut exports = Vec::new();
+        while !parser.is_empty() {
+            exports.push(parser.parens(|parser| parser.parse())?);
+        }
+        Ok(exports)
+    }
+}
+
+/// A component instance defined by instantiation or exporting items.
+#[derive(Debug)]
+pub struct Instance<'a> {
+    /// Where this `instance` was defined.
+    pub span: Span,
+    /// An identifier that this instance is resolved with (optionally) for name
+    /// resolution.
+    pub id: Option<Id<'a>>,
+    /// An optional name for this instance stored in the custom `name` section.
+    pub name: Option<NameAnnotation<'a>>,
+    /// If present, inline export annotations which indicate names this
+    /// definition should be exported under.
+    pub exports: InlineExport<'a>,
+    /// What kind of instance this is.
+    pub kind: InstanceKind<'a>,
+}
+
+impl<'a> Parse<'a> for Instance<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let span = parser.parse::<kw::instance>()?.0;
+        let id = parser.parse()?;
+        let name = parser.parse()?;
+        let exports = parser.parse()?;
+        let kind = parser.parse()?;
+
+        Ok(Self {
+            span,
+            id,
+            name,
+            exports,
+            kind,
+        })
+    }
+}
+
+/// The kinds of instances in the text format.
+#[derive(Debug)]
+pub enum InstanceKind<'a> {
+    /// The `(instance (import "x"))` sugar syntax
+    Import {
+        /// The name of the import
+        import: InlineImport<'a>,
+        /// The type of the instance being imported
+        ty: ComponentTypeUse<'a, InstanceType<'a>>,
+    },
+    /// Instantiate a component.
+    Instantiate {
+        /// The component being instantiated.
+        component: ItemRef<'a, kw::component>,
+        /// Arguments used to instantiate the instance.
+        args: Vec<InstantiationArg<'a>>,
+    },
+    /// The instance is defined by exporting local items as an instance.
+    BundleOfExports(Vec<ComponentExport<'a>>),
+}
+
+impl<'a> Parse<'a> for InstanceKind<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        if let Some(import) = parser.parse()? {
+            return Ok(Self::Import {
+                import,
+                ty: parser.parse()?,
+            });
+        }
+
+        if parser.peek::<LParen>() && parser.peek2::<kw::instantiate>() {
+            parser.parens(|parser| {
+                parser.parse::<kw::instantiate>()?;
+                Ok(Self::Instantiate {
+                    component: parser.parse::<IndexOrRef<'_, _>>()?.0,
+                    args: parser.parse()?,
+                })
+            })
+        } else {
+            Ok(Self::BundleOfExports(parser.parse()?))
+        }
+    }
+}
+
+impl Default for kw::component {
+    fn default() -> kw::component {
+        kw::component(Span::from_offset(0))
+    }
+}
+
+/// An argument to instantiate a component.
+#[derive(Debug)]
+pub struct InstantiationArg<'a> {
+    /// The name of the instantiation argument.
+    pub name: &'a str,
+    /// The kind of instantiation argument.
+    pub kind: InstantiationArgKind<'a>,
+}
+
+impl<'a> Parse<'a> for InstantiationArg<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.parse::<kw::with>()?;
+        Ok(Self {
+            name: parser.parse()?,
+            kind: parser.parse()?,
+        })
+    }
+}
+
+impl<'a> Parse<'a> for Vec<InstantiationArg<'a>> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut args = Vec::new();
+        while !parser.is_empty() {
+            args.push(parser.parens(|parser| parser.parse())?);
+        }
+        Ok(args)
+    }
+}
+
+/// The kind of instantiation argument.
+#[derive(Debug)]
+pub enum InstantiationArgKind<'a> {
+    /// The argument is a reference to a component item.
+    Item(ComponentExportKind<'a>),
+    /// The argument is an instance created from local exported items.
+    ///
+    /// This is syntactic sugar for defining an instance and also using it
+    /// as an instantiation argument.
+    BundleOfExports(Span, Vec<ComponentExport<'a>>),
+}
+
+impl<'a> Parse<'a> for InstantiationArgKind<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        if let Some(item) = parser.parse()? {
+            Ok(Self::Item(item))
+        } else {
+            parser.parens(|parser| {
+                let span = parser.parse::<kw::instance>()?.0;
+                Ok(Self::BundleOfExports(span, parser.parse()?))
+            })
+        }
+    }
+}
diff --git a/third_party/rust/wast/src/component/item_ref.rs b/third_party/rust/wast/src/component/item_ref.rs
new file mode 100644
index 0000000000..c3bbf2f9f4
--- /dev/null
+++ b/third_party/rust/wast/src/component/item_ref.rs
@@ -0,0 +1,154 @@
+use crate::parser::{Cursor, Parse, Parser, Peek, Result};
+use crate::token::Index;
+
+fn peek<K: Peek>(cursor: Cursor) -> bool {
+    // This is a little fancy because when parsing something like:
+    //
+    //      (type (component (type $foo)))
+    //
+    // we need to disambiguate that from
+    //
+    //      (type (component (type $foo (func))))
+    //
+    // where the first is a type reference and the second is an inline
+    // component type defining a type internally. The peek here not only
+    // peeks for `K` but also for the index and possibly trailing
+    // strings.
+
+    // Peek for the given keyword type
+    if !K::peek(cursor) {
+        return false;
+    }
+
+    // Move past the given keyword
+    let cursor = match cursor.keyword() {
+        Some((_, c)) => c,
+        _ => return false,
+    };
+
+    // Peek an id or integer index, followed by `)` or string to disambiguate
+    match cursor
+        .id()
+        .map(|p| p.1)
+        .or_else(|| cursor.integer().map(|p| p.1))
+    {
+        Some(cursor) => cursor.rparen().is_some() || cursor.string().is_some(),
+        None => false,
+    }
+}
+
+/// Parses core item references.
+#[derive(Clone, Debug)]
+pub struct CoreItemRef<'a, K> {
+    /// The item kind being parsed.
+    pub kind: K,
+    /// The item or instance reference.
+    pub idx: Index<'a>,
+    /// Export name to resolve the item from.
+    pub export_name: Option<&'a str>,
+}
+
+impl<'a, K: Parse<'a>> Parse<'a> for CoreItemRef<'a, K> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        // This does not parse the surrounding `(` and `)` because
+        // core prefix is context dependent and only the caller knows if it should be
+        // present for core references; therefore, the caller parses the parens and any core prefix
+        let kind = parser.parse::<K>()?;
+        let idx = parser.parse()?;
+        let export_name = parser.parse()?;
+        Ok(Self {
+            kind,
+            idx,
+            export_name,
+        })
+    }
+}
+
+impl<'a, K: Peek> Peek for CoreItemRef<'a, K> {
+    fn peek(cursor: Cursor<'_>) -> bool {
+        peek::<K>(cursor)
+    }
+
+    fn display() -> &'static str {
+        "a core item reference"
+    }
+}
+
+/// Parses component item references.
+#[derive(Clone, Debug)]
+pub struct ItemRef<'a, K> {
+    /// The item kind being parsed.
+    pub kind: K,
+    /// The item or instance reference.
+    pub idx: Index<'a>,
+    /// Export names to resolve the item from.
+    pub export_names: Vec<&'a str>,
+}
+
+impl<'a, K: Parse<'a>> Parse<'a> for ItemRef<'a, K> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let kind = parser.parse::<K>()?;
+        let idx = parser.parse()?;
+        let mut export_names = Vec::new();
+        while !parser.is_empty() {
+            export_names.push(parser.parse()?);
+        }
+        Ok(Self {
+            kind,
+            idx,
+            export_names,
+        })
+    }
+}
+
+impl<'a, K: Peek> Peek for ItemRef<'a, K> {
+    fn peek(cursor: Cursor<'_>) -> bool {
+        peek::<K>(cursor)
+    }
+
+    fn display() -> &'static str {
+        "a component item reference"
+    }
+}
+
+/// Convenience structure to parse `$f` or `(item $f)`.
+#[derive(Clone, Debug)]
+pub struct IndexOrRef<'a, K>(pub ItemRef<'a, K>);
+
+impl<'a, K> Parse<'a> for IndexOrRef<'a, K>
+where
+    K: Parse<'a> + Default,
+{
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        if parser.peek::<Index<'_>>() {
+            Ok(IndexOrRef(ItemRef {
+                kind: K::default(),
+                idx: parser.parse()?,
+                export_names: Vec::new(),
+            }))
+        } else {
+            Ok(IndexOrRef(parser.parens(|p| p.parse())?))
+        }
+    }
+}
+
+/// Convenience structure to parse `$f` or `(item $f)`.
+#[derive(Clone, Debug)]
+pub struct IndexOrCoreRef<'a, K>(pub CoreItemRef<'a, K>);
+
+impl<'a, K> Parse<'a> for IndexOrCoreRef<'a, K>
+where
+    K: Parse<'a> + Default,
+{
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        if parser.peek::<Index<'_>>() {
+            Ok(IndexOrCoreRef(CoreItemRef {
+                kind: K::default(),
+                idx: parser.parse()?,
+                export_name: None,
+            }))
+        } else {
+            Ok(IndexOrCoreRef(parser.parens(|p| p.parse())?))
+        }
+    }
+}
diff --git a/third_party/rust/wast/src/component/module.rs b/third_party/rust/wast/src/component/module.rs
new file mode 100644
index 0000000000..6871af8d4c
--- /dev/null
+++ b/third_party/rust/wast/src/component/module.rs
@@ -0,0 +1,75 @@
+use crate::component::*;
+use crate::core;
+use crate::kw;
+use crate::parser::{Parse, Parser, Result};
+use crate::token::{Id, NameAnnotation, Span};
+
+/// A core WebAssembly module to be created as part of a component.
+///
+/// This is a member of the core module section.
+#[derive(Debug)]
+pub struct CoreModule<'a> {
+    /// Where this `core module` was defined.
+    pub span: Span,
+    /// An identifier that this module is resolved with (optionally) for name
+    /// resolution.
+    pub id: Option<Id<'a>>,
+    /// An optional name for this module stored in the custom `name` section.
+    pub name: Option<NameAnnotation<'a>>,
+    /// If present, inline export annotations which indicate names this
+    /// definition should be exported under.
+    pub exports: InlineExport<'a>,
+    /// What kind of module this is, be it an inline-defined or imported one.
+    pub kind: CoreModuleKind<'a>,
+}
+
+/// Possible ways to define a core module in the text format.
+#[derive(Debug)]
+pub enum CoreModuleKind<'a> {
+    /// A core module which is actually defined as an import
+    Import {
+        /// Where this core module is imported from
+        import: InlineImport<'a>,
+        /// The type that this core module will have.
+        ty: CoreTypeUse<'a, ModuleType<'a>>,
+    },
+
+    /// Modules that are defined inline.
+    Inline {
+        /// Fields in the core module.
+        fields: Vec<core::ModuleField<'a>>,
+    },
+}
+
+impl<'a> Parse<'a> for CoreModule<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.depth_check()?;
+
+        let span = parser.parse::<kw::core>()?.0;
+        parser.parse::<kw::module>()?;
+        let id = parser.parse()?;
+        let name = parser.parse()?;
+        let exports = parser.parse()?;
+
+        let kind = if let Some(import) = parser.parse()? {
+            CoreModuleKind::Import {
+                import,
+                ty: parser.parse()?,
+            }
+        } else {
+            let mut fields = Vec::new();
+            while !parser.is_empty() {
+                fields.push(parser.parens(|p| p.parse())?);
+            }
+            CoreModuleKind::Inline { fields }
+        };
+
+        Ok(Self {
+            span,
+            id,
+            name,
+            exports,
+            kind,
+        })
+    }
+}
diff --git a/third_party/rust/wast/src/component/resolve.rs b/third_party/rust/wast/src/component/resolve.rs
new file mode 100644
index 0000000000..e87350e329
--- /dev/null
+++ b/third_party/rust/wast/src/component/resolve.rs
@@ -0,0 +1,973 @@
+use crate::component::*;
+use crate::core;
+use crate::kw;
+use crate::names::Namespace;
+use crate::token::Span;
+use crate::token::{Id, Index};
+use crate::Error;
+
+/// Resolve the fields of a component and everything nested within it, changing
+/// `Index::Id` to `Index::Num` and expanding alias syntax sugar.
+pub fn resolve(component: &mut Component<'_>) -> Result<(), Error> {
+    let fields = match &mut component.kind {
+        ComponentKind::Text(fields) => fields,
+        ComponentKind::Binary(_) => return Ok(()),
+    };
+    let mut resolver = Resolver::default();
+    resolver.fields(component.id, fields)
+}
+
+impl<'a> From<Alias<'a>> for ComponentField<'a> {
+    fn from(a: Alias<'a>) -> Self {
+        Self::Alias(a)
+    }
+}
+
+impl<'a> From<Alias<'a>> for ModuleTypeDecl<'a> {
+    fn from(a: Alias<'a>) -> Self {
+        Self::Alias(a)
+    }
+}
+
+impl<'a> From<Alias<'a>> for ComponentTypeDecl<'a> {
+    fn from(a: Alias<'a>) -> Self {
+        Self::Alias(a)
+    }
+}
+
+impl<'a> From<Alias<'a>> for InstanceTypeDecl<'a> {
+    fn from(a: Alias<'a>) -> Self {
+        Self::Alias(a)
+    }
+}
+
+#[derive(Default)]
+struct Resolver<'a> {
+    stack: Vec<ComponentState<'a>>,
+
+    // When a name refers to a definition in an outer scope, we'll need to
+    // insert an outer alias before it. This collects the aliases to be
+    // inserted during resolution.
+    aliases_to_insert: Vec<Alias<'a>>,
+}
+
+/// Context structure used to perform name resolution.
+#[derive(Default)]
+struct ComponentState<'a> {
+    id: Option<Id<'a>>,
+
+    // Namespaces within each component. Note that each namespace carries
+    // with it information about the signature of the item in that namespace.
+    // The signature is later used to synthesize the type of a component and
+    // inject type annotations if necessary.
+    core_funcs: Namespace<'a>,
+    core_globals: Namespace<'a>,
+    core_tables: Namespace<'a>,
+    core_memories: Namespace<'a>,
+    core_types: Namespace<'a>,
+    core_tags: Namespace<'a>,
+    core_instances: Namespace<'a>,
+    core_modules: Namespace<'a>,
+
+    funcs: Namespace<'a>,
+    types: Namespace<'a>,
+    instances: Namespace<'a>,
+    components: Namespace<'a>,
+    values: Namespace<'a>,
+}
+
+impl<'a> ComponentState<'a> {
+    fn new(id: Option<Id<'a>>) -> ComponentState<'a> {
+        ComponentState {
+            id,
+            ..ComponentState::default()
+        }
+    }
+
+    fn register_item_sig(&mut self, sig: &ItemSig<'a>) -> Result<u32, Error> {
+        match &sig.kind {
+            ItemSigKind::CoreModule(_) => self.core_modules.register(sig.id, "core module"),
+            ItemSigKind::Func(_) => self.funcs.register(sig.id, "func"),
+            ItemSigKind::Component(_) => self.components.register(sig.id, "component"),
+            ItemSigKind::Instance(_) => self.instances.register(sig.id, "instance"),
+            ItemSigKind::Value(_) => self.values.register(sig.id, "value"),
+            ItemSigKind::Type(_) => self.types.register(sig.id, "type"),
+        }
+    }
+}
+
+impl<'a> Resolver<'a> {
+    fn current(&mut self) -> &mut ComponentState<'a> {
+        self.stack
+            .last_mut()
+            .expect("should have at least one component state")
+    }
+
+    fn fields(
+        &mut self,
+        id: Option<Id<'a>>,
+        fields: &mut Vec<ComponentField<'a>>,
+    ) -> Result<(), Error> {
+        self.stack.push(ComponentState::new(id));
+        self.resolve_prepending_aliases(fields, Resolver::field, ComponentState::register)?;
+        self.stack.pop();
+        Ok(())
+    }
+
+    fn resolve_prepending_aliases<T>(
+        &mut self,
+        fields: &mut Vec<T>,
+        resolve: fn(&mut Self, &mut T) -> Result<(), Error>,
+        register: fn(&mut ComponentState<'a>, &T) -> Result<(), Error>,
+    ) -> Result<(), Error>
+    where
+        T: From<Alias<'a>>,
+    {
+        assert!(self.aliases_to_insert.is_empty());
+
+        // Iterate through the fields of the component. We use an index
+        // instead of an iterator because we'll be inserting aliases
+        // as we go.
+        let mut i = 0;
+        while i < fields.len() {
+            // Resolve names within the field.
+            resolve(self, &mut fields[i])?;
+
+            // Name resolution may have emitted some aliases. Insert them before
+            // the current definition.
+            let amt = self.aliases_to_insert.len();
+            fields.splice(i..i, self.aliases_to_insert.drain(..).map(T::from));
+            i += amt;
+
+            // Definitions can't refer to themselves or to definitions that appear
+            // later in the format. Now that we're done resolving this field,
+            // assign it an index for later definitions to refer to.
+            register(self.current(), &fields[i])?;
+
+            i += 1;
+        }
+
+        Ok(())
+    }
+
+    fn field(&mut self, field: &mut ComponentField<'a>) -> Result<(), Error> {
+        match field {
+            ComponentField::CoreModule(m) => self.core_module(m),
+            ComponentField::CoreInstance(i) => self.core_instance(i),
+            ComponentField::CoreType(t) => self.core_ty(t),
+            ComponentField::Component(c) => self.component(c),
+            ComponentField::Instance(i) => self.instance(i),
+            ComponentField::Alias(a) => self.alias(a, false),
+            ComponentField::Type(t) => self.ty(t),
+            ComponentField::CanonicalFunc(f) => self.canonical_func(f),
+            ComponentField::CoreFunc(_) => unreachable!("should be expanded already"),
+            ComponentField::Func(_) => unreachable!("should be expanded already"),
+            ComponentField::Start(s) => self.start(s),
+            ComponentField::Import(i) => self.item_sig(&mut i.item),
+            ComponentField::Export(e) => {
+                if let Some(ty) = &mut e.ty {
+                    self.item_sig(&mut ty.0)?;
+                }
+                self.export(&mut e.kind)
+            }
+            ComponentField::Custom(_) => Ok(()),
+        }
+    }
+
+    fn core_module(&mut self, module: &mut CoreModule) -> Result<(), Error> {
+        match &mut module.kind {
+            CoreModuleKind::Inline { fields } => {
+                crate::core::resolve::resolve(fields)?;
+            }
+
+            CoreModuleKind::Import { .. } => {
+                unreachable!("should be expanded already")
+            }
+        }
+
+        Ok(())
+    }
+
+    fn component(&mut self, component: &mut NestedComponent<'a>) -> Result<(), Error> {
+        match &mut component.kind {
+            NestedComponentKind::Import { .. } => unreachable!("should be expanded already"),
+            NestedComponentKind::Inline(fields) => self.fields(component.id, fields),
+        }
+    }
+
+    fn core_instance(&mut self, instance: &mut CoreInstance<'a>) -> Result<(), Error> {
+        match &mut instance.kind {
+            CoreInstanceKind::Instantiate { module, args } => {
+                self.component_item_ref(module)?;
+                for arg in args {
+                    match &mut arg.kind {
+                        CoreInstantiationArgKind::Instance(i) => {
+                            self.core_item_ref(i)?;
+                        }
+                        CoreInstantiationArgKind::BundleOfExports(..) => {
+                            unreachable!("should be expanded already");
+                        }
+                    }
+                }
+            }
+            CoreInstanceKind::BundleOfExports(exports) => {
+                for export in exports {
+                    self.core_item_ref(&mut export.item)?;
+                }
+            }
+        }
+        Ok(())
+    }
+
+    fn instance(&mut self, instance: &mut Instance<'a>) -> Result<(), Error> {
+        match &mut instance.kind {
+            InstanceKind::Instantiate { component, args } => {
+                self.component_item_ref(component)?;
+                for arg in args {
+                    match &mut arg.kind {
+                        InstantiationArgKind::Item(e) => {
+                            self.export(e)?;
+                        }
+                        InstantiationArgKind::BundleOfExports(..) => {
+                            unreachable!("should be expanded already")
+                        }
+                    }
+                }
+            }
+            InstanceKind::BundleOfExports(exports) => {
+                for export in exports {
+                    self.export(&mut export.kind)?;
+                }
+            }
+            InstanceKind::Import { .. } => {
+                unreachable!("should be expanded already")
+            }
+        }
+        Ok(())
+    }
+
+    fn item_sig(&mut self, item: &mut ItemSig<'a>) -> Result<(), Error> {
+        match &mut item.kind {
+            // Here we must be explicit otherwise the module type reference will
+            // be assumed to be in the component type namespace
+            ItemSigKind::CoreModule(t) => self.core_type_use(t),
+            ItemSigKind::Func(t) => self.component_type_use(t),
+            ItemSigKind::Component(t) => self.component_type_use(t),
+            ItemSigKind::Instance(t) => self.component_type_use(t),
+            ItemSigKind::Value(t) => self.component_val_type(&mut t.0),
+            ItemSigKind::Type(b) => match b {
+                TypeBounds::Eq(i) => self.resolve_ns(i, Ns::Type),
+            },
+        }
+    }
+
+    fn export(&mut self, kind: &mut ComponentExportKind<'a>) -> Result<(), Error> {
+        match kind {
+            // Here we do *not* have to be explicit as the item ref is to a core module
+            ComponentExportKind::CoreModule(r) => self.component_item_ref(r),
+            ComponentExportKind::Func(r) => self.component_item_ref(r),
+            ComponentExportKind::Value(r) => self.component_item_ref(r),
+            ComponentExportKind::Type(r) => self.component_item_ref(r),
+            ComponentExportKind::Component(r) => self.component_item_ref(r),
+            ComponentExportKind::Instance(r) => self.component_item_ref(r),
+        }
+    }
+
+    fn start(&mut self, start: &mut Start<'a>) -> Result<(), Error> {
+        self.resolve_ns(&mut start.func, Ns::Func)?;
+        for arg in start.args.iter_mut() {
+            self.component_item_ref(arg)?;
+        }
+        Ok(())
+    }
+
+    fn outer_alias<T: Into<Ns>>(
+        &mut self,
+        outer: &mut Index<'a>,
+        index: &mut Index<'a>,
+        kind: T,
+        span: Span,
+        enclosing_only: bool,
+    ) -> Result<(), Error> {
+        // Short-circuit when both indices are already resolved as this
+        // helps to write tests for invalid modules where wasmparser should
+        // be the one returning the error.
+        if let Index::Num(..) = outer {
+            if let Index::Num(..) = index {
+                return Ok(());
+            }
+        }
+
+        // Resolve `outer`, and compute the depth at which to look up
+        // `index`.
+        let depth = match outer {
+            Index::Id(id) => {
+                let mut depth = 0;
+                for resolver in self.stack.iter().rev() {
+                    if resolver.id == Some(*id) {
+                        break;
+                    }
+                    depth += 1;
+                }
+                if depth as usize == self.stack.len() {
+                    return Err(Error::new(
+                        span,
+                        format!("outer component `{}` not found", id.name()),
+                    ));
+                }
+                depth
+            }
+            Index::Num(n, _span) => *n,
+        };
+
+        if depth as usize >= self.stack.len() {
+            return Err(Error::new(
+                span,
+                format!("outer count of `{}` is too large", depth),
+            ));
+        }
+
+        if enclosing_only && depth > 1 {
+            return Err(Error::new(
+                span,
+                "only the local or enclosing scope can be aliased".to_string(),
+            ));
+        }
+
+        *outer = Index::Num(depth, span);
+
+        // Resolve `index` within the computed scope depth.
+        let computed = self.stack.len() - 1 - depth as usize;
+        self.stack[computed].resolve(kind.into(), index)?;
+
+        Ok(())
+    }
+
+    fn alias(&mut self, alias: &mut Alias<'a>, enclosing_only: bool) -> Result<(), Error> {
+        match &mut alias.target {
+            AliasTarget::Export {
+                instance,
+                name: _,
+                kind: _,
+            } => self.resolve_ns(instance, Ns::Instance),
+            AliasTarget::CoreExport {
+                instance,
+                name: _,
+                kind: _,
+            } => self.resolve_ns(instance, Ns::CoreInstance),
+            AliasTarget::Outer { outer, index, kind } => {
+                self.outer_alias(outer, index, *kind, alias.span, enclosing_only)
+            }
+        }
+    }
+
+    fn canonical_func(&mut self, func: &mut CanonicalFunc<'a>) -> Result<(), Error> {
+        let opts = match &mut func.kind {
+            CanonicalFuncKind::Lift { ty, info } => {
+                self.component_type_use(ty)?;
+                self.core_item_ref(&mut info.func)?;
+                &mut info.opts
+            }
+            CanonicalFuncKind::Lower(info) => {
+                self.component_item_ref(&mut info.func)?;
+                &mut info.opts
+            }
+        };
+
+        for opt in opts {
+            match opt {
+                CanonOpt::StringUtf8 | CanonOpt::StringUtf16 | CanonOpt::StringLatin1Utf16 => {}
+                CanonOpt::Memory(r) => self.core_item_ref(r)?,
+                CanonOpt::Realloc(r) | CanonOpt::PostReturn(r) => self.core_item_ref(r)?,
+            }
+        }
+
+        Ok(())
+    }
+
+    fn core_type_use<T>(&mut self, ty: &mut CoreTypeUse<'a, T>) -> Result<(), Error> {
+        let item = match ty {
+            CoreTypeUse::Ref(r) => r,
+            CoreTypeUse::Inline(_) => {
+                unreachable!("inline type-use should be expanded by now")
+            }
+        };
+        self.core_item_ref(item)
+    }
+
+    fn component_type_use<T>(&mut self, ty: &mut ComponentTypeUse<'a, T>) -> Result<(), Error> {
+        let item = match ty {
+            ComponentTypeUse::Ref(r) => r,
+            ComponentTypeUse::Inline(_) => {
+                unreachable!("inline type-use should be expanded by now")
+            }
+        };
+        self.component_item_ref(item)
+    }
+
+    fn defined_type(&mut self, ty: &mut ComponentDefinedType<'a>) -> Result<(), Error> {
+        match ty {
+            ComponentDefinedType::Primitive(_) => {}
+            ComponentDefinedType::Flags(_) => {}
+            ComponentDefinedType::Enum(_) => {}
+            ComponentDefinedType::Record(r) => {
+                for field in r.fields.iter_mut() {
+                    self.component_val_type(&mut field.ty)?;
+                }
+            }
+            ComponentDefinedType::Variant(v) => {
+                // Namespace for case identifier resolution
+                let mut ns = Namespace::default();
+                for case in v.cases.iter_mut() {
+                    let index = ns.register(case.id, "variant case")?;
+
+                    if let Some(ty) = &mut case.ty {
+                        self.component_val_type(ty)?;
+                    }
+
+                    if let Some(refines) = &mut case.refines {
+                        if let Refinement::Index(span, idx) = refines {
+                            let resolved = ns.resolve(idx, "variant case")?;
+                            if resolved == index {
+                                return Err(Error::new(
+                                    *span,
+                                    "variant case cannot refine itself".to_string(),
+                                ));
+                            }
+
+                            *refines = Refinement::Resolved(resolved);
+                        }
+                    }
+                }
+            }
+            ComponentDefinedType::List(l) => {
+                self.component_val_type(&mut l.element)?;
+            }
+            ComponentDefinedType::Tuple(t) => {
+                for field in t.fields.iter_mut() {
+                    self.component_val_type(field)?;
+                }
+            }
+            ComponentDefinedType::Union(t) => {
+                for ty in t.types.iter_mut() {
+                    self.component_val_type(ty)?;
+                }
+            }
+            ComponentDefinedType::Option(o) => {
+                self.component_val_type(&mut o.element)?;
+            }
+            ComponentDefinedType::Result(r) => {
+                if let Some(ty) = &mut r.ok {
+                    self.component_val_type(ty)?;
+                }
+
+                if let Some(ty) = &mut r.err {
+                    self.component_val_type(ty)?;
+                }
+            }
+        }
+        Ok(())
+    }
+
+    fn component_val_type(&mut self, ty: &mut ComponentValType<'a>) -> Result<(), Error> {
+        match ty {
+            ComponentValType::Ref(idx) => self.resolve_ns(idx, Ns::Type),
+            ComponentValType::Inline(ComponentDefinedType::Primitive(_)) => Ok(()),
+            ComponentValType::Inline(_) => unreachable!("should be expanded by now"),
+        }
+    }
+
+    fn core_ty(&mut self, field: &mut CoreType<'a>) -> Result<(), Error> {
+        match &mut field.def {
+            CoreTypeDef::Def(_) => {}
+            CoreTypeDef::Module(t) => {
+                self.stack.push(ComponentState::new(field.id));
+                self.module_type(t)?;
+                self.stack.pop();
+            }
+        }
+        Ok(())
+    }
+
+    fn ty(&mut self, field: &mut Type<'a>) -> Result<(), Error> {
+        match &mut field.def {
+            TypeDef::Defined(t) => {
+                self.defined_type(t)?;
+            }
+            TypeDef::Func(f) => {
+                for param in f.params.iter_mut() {
+                    self.component_val_type(&mut param.ty)?;
+                }
+
+                for result in f.results.iter_mut() {
+                    self.component_val_type(&mut result.ty)?;
+                }
+            }
+            TypeDef::Component(c) => {
+                self.stack.push(ComponentState::new(field.id));
+                self.component_type(c)?;
+                self.stack.pop();
+            }
+            TypeDef::Instance(i) => {
+                self.stack.push(ComponentState::new(field.id));
+                self.instance_type(i)?;
+                self.stack.pop();
+            }
+        }
+        Ok(())
+    }
+
+    fn component_type(&mut self, c: &mut ComponentType<'a>) -> Result<(), Error> {
+        self.resolve_prepending_aliases(
+            &mut c.decls,
+            |resolver, decl| match decl {
+                ComponentTypeDecl::Alias(alias) => resolver.alias(alias, false),
+                ComponentTypeDecl::CoreType(ty) => resolver.core_ty(ty),
+                ComponentTypeDecl::Type(ty) => resolver.ty(ty),
+                ComponentTypeDecl::Import(import) => resolver.item_sig(&mut import.item),
+                ComponentTypeDecl::Export(export) => resolver.item_sig(&mut export.item),
+            },
+            |state, decl| {
+                match decl {
+                    ComponentTypeDecl::Alias(alias) => {
+                        state.register_alias(alias)?;
+                    }
+                    ComponentTypeDecl::CoreType(ty) => {
+                        state.core_types.register(ty.id, "core type")?;
+                    }
+                    ComponentTypeDecl::Type(ty) => {
+                        state.types.register(ty.id, "type")?;
+                    }
+                    ComponentTypeDecl::Export(e) => {
+                        state.register_item_sig(&e.item)?;
+                    }
+                    ComponentTypeDecl::Import(i) => {
+                        state.register_item_sig(&i.item)?;
+                    }
+                }
+                Ok(())
+            },
+        )
+    }
+
+    fn instance_type(&mut self, c: &mut InstanceType<'a>) -> Result<(), Error> {
+        self.resolve_prepending_aliases(
+            &mut c.decls,
+            |resolver, decl| match decl {
+                InstanceTypeDecl::Alias(alias) => resolver.alias(alias, false),
+                InstanceTypeDecl::CoreType(ty) => resolver.core_ty(ty),
+                InstanceTypeDecl::Type(ty) => resolver.ty(ty),
+                InstanceTypeDecl::Export(export) => resolver.item_sig(&mut export.item),
+            },
+            |state, decl| {
+                match decl {
+                    InstanceTypeDecl::Alias(alias) => {
+                        state.register_alias(alias)?;
+                    }
+                    InstanceTypeDecl::CoreType(ty) => {
+                        state.core_types.register(ty.id, "core type")?;
+                    }
+                    InstanceTypeDecl::Type(ty) => {
+                        state.types.register(ty.id, "type")?;
+                    }
+                    InstanceTypeDecl::Export(export) => {
+                        state.register_item_sig(&export.item)?;
+                    }
+                }
+                Ok(())
+            },
+        )
+    }
+
+    fn core_item_ref<K>(&mut self, item: &mut CoreItemRef<'a, K>) -> Result<(), Error>
+    where
+        K: CoreItem + Copy,
+    {
+        // Check for not being an instance export reference
+        if item.export_name.is_none() {
+            self.resolve_ns(&mut item.idx, item.kind.ns())?;
+            return Ok(());
+        }
+
+        // This is a reference to a core instance export
+        let mut index = item.idx;
+        self.resolve_ns(&mut index, Ns::CoreInstance)?;
+
+        // Record an alias to reference the export
+        let span = item.idx.span();
+        let alias = Alias {
+            span,
+            id: None,
+            name: None,
+            target: AliasTarget::CoreExport {
+                instance: index,
+                name: item.export_name.unwrap(),
+                kind: item.kind.ns().into(),
+            },
+        };
+
+        index = Index::Num(self.current().register_alias(&alias)?, span);
+        self.aliases_to_insert.push(alias);
+
+        item.idx = index;
+        item.export_name = None;
+
+        Ok(())
+    }
+
+    fn component_item_ref<K>(&mut self, item: &mut ItemRef<'a, K>) -> Result<(), Error>
+    where
+        K: ComponentItem + Copy,
+    {
+        // Check for not being an instance export reference
+        if item.export_names.is_empty() {
+            self.resolve_ns(&mut item.idx, item.kind.ns())?;
+            return Ok(());
+        }
+
+        // This is a reference to an instance export
+        let mut index = item.idx;
+        self.resolve_ns(&mut index, Ns::Instance)?;
+
+        let span = item.idx.span();
+        for (pos, export_name) in item.export_names.iter().enumerate() {
+            // Record an alias to reference the export
+            let alias = Alias {
+                span,
+                id: None,
+                name: None,
+                target: AliasTarget::Export {
+                    instance: index,
+                    name: export_name,
+                    kind: if pos == item.export_names.len() - 1 {
+                        item.kind.ns().into()
+                    } else {
+                        ComponentExportAliasKind::Instance
+                    },
+                },
+            };
+
+            index = Index::Num(self.current().register_alias(&alias)?, span);
+            self.aliases_to_insert.push(alias);
+        }
+
+        item.idx = index;
+        item.export_names = Vec::new();
+
+        Ok(())
+    }
+
+    fn resolve_ns(&mut self, idx: &mut Index<'a>, ns: Ns) -> Result<(), Error> {
+        // Perform resolution on a local clone walking up the stack of components
+        // that we have. Note that a local clone is used since we don't want to use
+        // the parent's resolved index if a parent matches, instead we want to use
+        // the index of the alias that we will automatically insert.
+        let mut idx_clone = *idx;
+        for (depth, resolver) in self.stack.iter_mut().rev().enumerate() {
+            let depth = depth as u32;
+            let found = match resolver.resolve(ns, &mut idx_clone) {
+                Ok(idx) => idx,
+                // Try the next parent
+                Err(_) => continue,
+            };
+
+            // If this is the current component then no extra alias is necessary, so
+            // return success.
+            if depth == 0 {
+                *idx = idx_clone;
+                return Ok(());
+            }
+            let id = match idx {
+                Index::Id(id) => *id,
+                Index::Num(..) => unreachable!(),
+            };
+
+            // When resolution succeeds in a parent then an outer alias is
+            // automatically inserted here in this component.
+            let span = idx.span();
+            let alias = Alias {
+                span,
+                id: Some(id),
+                name: None,
+                target: AliasTarget::Outer {
+                    outer: Index::Num(depth, span),
+                    index: Index::Num(found, span),
+                    kind: ns.into(),
+                },
+            };
+            let local_index = self.current().register_alias(&alias)?;
+            self.aliases_to_insert.push(alias);
+            *idx = Index::Num(local_index, span);
+            return Ok(());
+        }
+
+        // If resolution in any parent failed then simply return the error from our
+        // local namespace
+        self.current().resolve(ns, idx)?;
+        unreachable!()
+    }
+
+    fn module_type(&mut self, ty: &mut ModuleType<'a>) -> Result<(), Error> {
+        return self.resolve_prepending_aliases(
+            &mut ty.decls,
+            |resolver, decl| match decl {
+                ModuleTypeDecl::Alias(alias) => resolver.alias(alias, true),
+                ModuleTypeDecl::Type(_) => Ok(()),
+                ModuleTypeDecl::Import(import) => resolve_item_sig(resolver, &mut import.item),
+                ModuleTypeDecl::Export(_, item) => resolve_item_sig(resolver, item),
+            },
+            |state, decl| {
+                match decl {
+                    ModuleTypeDecl::Alias(alias) => {
+                        state.register_alias(alias)?;
+                    }
+                    ModuleTypeDecl::Type(ty) => {
+                        state.core_types.register(ty.id, "type")?;
+                    }
+                    // Only the type namespace is populated within the module type
+                    // namespace so these are ignored here.
+                    ModuleTypeDecl::Import(_) | ModuleTypeDecl::Export(..) => {}
+                }
+                Ok(())
+            },
+        );
+
+        fn resolve_item_sig<'a>(
+            resolver: &Resolver<'a>,
+            sig: &mut core::ItemSig<'a>,
+        ) -> Result<(), Error> {
+            match &mut sig.kind {
+                core::ItemKind::Func(ty) | core::ItemKind::Tag(core::TagType::Exception(ty)) => {
+                    let idx = ty.index.as_mut().expect("index should be filled in");
+                    resolver
+                        .stack
+                        .last()
+                        .unwrap()
+                        .core_types
+                        .resolve(idx, "type")?;
+                }
+                core::ItemKind::Memory(_)
+                | core::ItemKind::Global(_)
+                | core::ItemKind::Table(_) => {}
+            }
+            Ok(())
+        }
+    }
+}
+
+impl<'a> ComponentState<'a> {
+    fn resolve(&mut self, ns: Ns, idx: &mut Index<'a>) -> Result<u32, Error> {
+        match ns {
+            Ns::CoreFunc => self.core_funcs.resolve(idx, "core func"),
+            Ns::CoreGlobal => self.core_globals.resolve(idx, "core global"),
+            Ns::CoreTable => self.core_tables.resolve(idx, "core table"),
+            Ns::CoreMemory => self.core_memories.resolve(idx, "core memory"),
+            Ns::CoreType => self.core_types.resolve(idx, "core type"),
+            Ns::CoreTag => self.core_tags.resolve(idx, "core tag"),
+            Ns::CoreInstance => self.core_instances.resolve(idx, "core instance"),
+            Ns::CoreModule => self.core_modules.resolve(idx, "core module"),
+            Ns::Func => self.funcs.resolve(idx, "func"),
+            Ns::Type => self.types.resolve(idx, "type"),
+            Ns::Instance => self.instances.resolve(idx, "instance"),
+            Ns::Component => self.components.resolve(idx, "component"),
+            Ns::Value => self.values.resolve(idx, "value"),
+        }
+    }
+
+    /// Assign an index to the given field.
+    fn register(&mut self, item: &ComponentField<'a>) -> Result<(), Error> {
+        match item {
+            ComponentField::CoreModule(m) => self.core_modules.register(m.id, "core module")?,
+            ComponentField::CoreInstance(i) => {
+                self.core_instances.register(i.id, "core instance")?
+            }
+            ComponentField::CoreType(t) => self.core_types.register(t.id, "core type")?,
+            ComponentField::Component(c) => self.components.register(c.id, "component")?,
+            ComponentField::Instance(i) => self.instances.register(i.id, "instance")?,
+            ComponentField::Alias(a) => self.register_alias(a)?,
+            ComponentField::Type(t) => self.types.register(t.id, "type")?,
+            ComponentField::CanonicalFunc(f) => match &f.kind {
+                CanonicalFuncKind::Lift { .. } => self.funcs.register(f.id, "func")?,
+                CanonicalFuncKind::Lower(_) => self.core_funcs.register(f.id, "core func")?,
+            },
+            ComponentField::CoreFunc(_) | ComponentField::Func(_) => {
+                unreachable!("should be expanded already")
+            }
+            ComponentField::Start(s) => {
+                for r in &s.results {
+                    self.values.register(*r, "value")?;
+                }
+                return Ok(());
+            }
+            ComponentField::Import(i) => self.register_item_sig(&i.item)?,
+            ComponentField::Export(e) => match &e.kind {
+                ComponentExportKind::CoreModule(_) => {
+                    self.core_modules.register(e.id, "core module")?
+                }
+                ComponentExportKind::Func(_) => self.funcs.register(e.id, "func")?,
+                ComponentExportKind::Instance(_) => self.instances.register(e.id, "instance")?,
+                ComponentExportKind::Value(_) => self.values.register(e.id, "value")?,
+                ComponentExportKind::Component(_) => self.components.register(e.id, "component")?,
+                ComponentExportKind::Type(_) => self.types.register(e.id, "type")?,
+            },
+            ComponentField::Custom(_) => return Ok(()),
+        };
+
+        Ok(())
+    }
+
+    fn register_alias(&mut self, alias: &Alias<'a>) -> Result<u32, Error> {
+        match alias.target {
+            AliasTarget::Export { kind, .. } => match kind {
+                ComponentExportAliasKind::CoreModule => {
+                    self.core_modules.register(alias.id, "core module")
+                }
+                ComponentExportAliasKind::Func => self.funcs.register(alias.id, "func"),
+                ComponentExportAliasKind::Value => self.values.register(alias.id, "value"),
+                ComponentExportAliasKind::Type => self.types.register(alias.id, "type"),
+                ComponentExportAliasKind::Component => {
+                    self.components.register(alias.id, "component")
+                }
+                ComponentExportAliasKind::Instance => self.instances.register(alias.id, "instance"),
+            },
+            AliasTarget::CoreExport { kind, .. } => match kind {
+                core::ExportKind::Func => self.core_funcs.register(alias.id, "core func"),
+                core::ExportKind::Table => self.core_tables.register(alias.id, "core table"),
+                core::ExportKind::Memory => self.core_memories.register(alias.id, "core memory"),
+                core::ExportKind::Global => self.core_globals.register(alias.id, "core global"),
+                core::ExportKind::Tag => self.core_tags.register(alias.id, "core tag"),
+            },
+            AliasTarget::Outer { kind, .. } => match kind {
+                ComponentOuterAliasKind::CoreModule => {
+                    self.core_modules.register(alias.id, "core module")
+                }
+                ComponentOuterAliasKind::CoreType => {
+                    self.core_types.register(alias.id, "core type")
+                }
+                ComponentOuterAliasKind::Type => self.types.register(alias.id, "type"),
+                ComponentOuterAliasKind::Component => {
+                    self.components.register(alias.id, "component")
+                }
+            },
+        }
+    }
+}
+
+#[derive(PartialEq, Eq, Hash, Copy, Clone, Debug)]
+enum Ns {
+    CoreFunc,
+    CoreGlobal,
+    CoreTable,
+    CoreMemory,
+    CoreType,
+    CoreTag,
+    CoreInstance,
+    CoreModule,
+    Func,
+    Type,
+    Instance,
+    Component,
+    Value,
+}
+
+trait ComponentItem {
+    fn ns(&self) -> Ns;
+}
+
+trait CoreItem {
+    fn ns(&self) -> Ns;
+}
+
+macro_rules! component_item {
+    ($kw:path, $kind:ident) => {
+        impl ComponentItem for $kw {
+            fn ns(&self) -> Ns {
+                Ns::$kind
+            }
+        }
+    };
+}
+
+macro_rules! core_item {
+    ($kw:path, $kind:ident) => {
+        impl CoreItem for $kw {
+            fn ns(&self) -> Ns {
+                Ns::$kind
+            }
+        }
+    };
+}
+
+component_item!(kw::func, Func);
+component_item!(kw::r#type, Type);
+component_item!(kw::r#instance, Instance);
+component_item!(kw::component, Component);
+component_item!(kw::value, Value);
+component_item!(kw::module, CoreModule);
+
+core_item!(kw::func, CoreFunc);
+core_item!(kw::memory, CoreMemory);
+core_item!(kw::r#type, CoreType);
+core_item!(kw::r#instance, CoreInstance);
+
+impl From<Ns> for ComponentExportAliasKind {
+    fn from(ns: Ns) -> Self {
+        match ns {
+            Ns::CoreModule => Self::CoreModule,
+            Ns::Func => Self::Func,
+            Ns::Type => Self::Type,
+            Ns::Instance => Self::Instance,
+            Ns::Component => Self::Component,
+            Ns::Value => Self::Value,
+            _ => unreachable!("not a component exportable namespace"),
+        }
+    }
+}
+
+impl From<Ns> for ComponentOuterAliasKind {
+    fn from(ns: Ns) -> Self {
+        match ns {
+            Ns::CoreModule => Self::CoreModule,
+            Ns::CoreType => Self::CoreType,
+            Ns::Type => Self::Type,
+            Ns::Component => Self::Component,
+            _ => unreachable!("not an outer alias namespace"),
+        }
+    }
+}
+
+impl From<Ns> for core::ExportKind {
+    fn from(ns: Ns) -> Self {
+        match ns {
+            Ns::CoreFunc => Self::Func,
+            Ns::CoreTable => Self::Table,
+            Ns::CoreGlobal => Self::Global,
+            Ns::CoreMemory => Self::Memory,
+            Ns::CoreTag => Self::Tag,
+            _ => unreachable!("not a core exportable namespace"),
+        }
+    }
+}
+
+impl From<ComponentOuterAliasKind> for Ns {
+    fn from(kind: ComponentOuterAliasKind) -> Self {
+        match kind {
+            ComponentOuterAliasKind::CoreModule => Self::CoreModule,
+            ComponentOuterAliasKind::CoreType => Self::CoreType,
+            ComponentOuterAliasKind::Type => Self::Type,
+            ComponentOuterAliasKind::Component => Self::Component,
+        }
+    }
+}
+
+impl CoreItem for core::ExportKind {
+    fn ns(&self) -> Ns {
+        match self {
+            Self::Func => Ns::CoreFunc,
+            Self::Table => Ns::CoreTable,
+            Self::Global => Ns::CoreGlobal,
+            Self::Memory => Ns::CoreMemory,
+            Self::Tag => Ns::CoreTag,
+        }
+    }
+}
diff --git a/third_party/rust/wast/src/component/types.rs b/third_party/rust/wast/src/component/types.rs
new file mode 100644
index 0000000000..0ff8cc0183
--- /dev/null
+++ b/third_party/rust/wast/src/component/types.rs
@@ -0,0 +1,965 @@
+use crate::component::*;
+use crate::core;
+use crate::kw;
+use crate::parser::Lookahead1;
+use crate::parser::Peek;
+use crate::parser::{Parse, Parser, Result};
+use crate::token::Index;
+use crate::token::LParen;
+use crate::token::{Id, NameAnnotation, Span};
+
+/// A core type declaration.
+#[derive(Debug)]
+pub struct CoreType<'a> {
+    /// Where this type was defined.
+    pub span: Span,
+    /// An optional identifier to refer to this `core type` by as part of name
+    /// resolution.
+    pub id: Option<Id<'a>>,
+    /// An optional name for this type stored in the custom `name` section.
+    pub name: Option<NameAnnotation<'a>>,
+    /// The core type's definition.
+    pub def: CoreTypeDef<'a>,
+}
+
+impl<'a> Parse<'a> for CoreType<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let span = parser.parse::<kw::core>()?.0;
+        parser.parse::<kw::r#type>()?;
+        let id = parser.parse()?;
+        let name = parser.parse()?;
+        let def = parser.parens(|p| p.parse())?;
+
+        Ok(Self {
+            span,
+            id,
+            name,
+            def,
+        })
+    }
+}
+
+/// Represents a core type definition.
+///
+/// In the future this may be removed when module types are a part of
+/// a core module.
+#[derive(Debug)]
+pub enum CoreTypeDef<'a> {
+    /// The type definition is one of the core types.
+    Def(core::TypeDef<'a>),
+    /// The type definition is a module type.
+    Module(ModuleType<'a>),
+}
+
+impl<'a> Parse<'a> for CoreTypeDef<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        if parser.peek::<kw::module>() {
+            parser.parse::<kw::module>()?;
+            Ok(Self::Module(parser.parse()?))
+        } else {
+            Ok(Self::Def(parser.parse()?))
+        }
+    }
+}
+
+/// A type definition for a core module.
+#[derive(Debug)]
+pub struct ModuleType<'a> {
+    /// The declarations of the module type.
+    pub decls: Vec<ModuleTypeDecl<'a>>,
+}
+
+impl<'a> Parse<'a> for ModuleType<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.depth_check()?;
+        Ok(Self {
+            decls: parser.parse()?,
+        })
+    }
+}
+
+/// The declarations of a [`ModuleType`].
+#[derive(Debug)]
+pub enum ModuleTypeDecl<'a> {
+    /// A core type.
+    Type(core::Type<'a>),
+    /// An alias local to the component type.
+    Alias(Alias<'a>),
+    /// An import.
+    Import(core::Import<'a>),
+    /// An export.
+    Export(&'a str, core::ItemSig<'a>),
+}
+
+impl<'a> Parse<'a> for ModuleTypeDecl<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut l = parser.lookahead1();
+        if l.peek::<kw::r#type>() {
+            Ok(Self::Type(parser.parse()?))
+        } else if l.peek::<kw::alias>() {
+            Ok(Self::Alias(Alias::parse_outer_core_type_alias(parser)?))
+        } else if l.peek::<kw::import>() {
+            Ok(Self::Import(parser.parse()?))
+        } else if l.peek::<kw::export>() {
+            parser.parse::<kw::export>()?;
+            let name = parser.parse()?;
+            let et = parser.parens(|parser| parser.parse())?;
+            Ok(Self::Export(name, et))
+        } else {
+            Err(l.error())
+        }
+    }
+}
+
+impl<'a> Parse<'a> for Vec<ModuleTypeDecl<'a>> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut decls = Vec::new();
+        while !parser.is_empty() {
+            decls.push(parser.parens(|parser| parser.parse())?);
+        }
+        Ok(decls)
+    }
+}
+
+/// A type declaration in a component.
+#[derive(Debug)]
+pub struct Type<'a> {
+    /// Where this type was defined.
+    pub span: Span,
+    /// An optional identifier to refer to this `type` by as part of name
+    /// resolution.
+    pub id: Option<Id<'a>>,
+    /// An optional name for this type stored in the custom `name` section.
+    pub name: Option<NameAnnotation<'a>>,
+    /// If present, inline export annotations which indicate names this
+    /// definition should be exported under.
+    pub exports: InlineExport<'a>,
+    /// The type definition.
+    pub def: TypeDef<'a>,
+}
+
+impl<'a> Parse<'a> for Type<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let span = parser.parse::<kw::r#type>()?.0;
+        let id = parser.parse()?;
+        let name = parser.parse()?;
+        let exports = parser.parse()?;
+        let def = parser.parse()?;
+
+        Ok(Self {
+            span,
+            id,
+            name,
+            exports,
+            def,
+        })
+    }
+}
+
+/// A definition of a component type.
+#[derive(Debug)]
+pub enum TypeDef<'a> {
+    /// A defined value type.
+    Defined(ComponentDefinedType<'a>),
+    /// A component function type.
+    Func(ComponentFunctionType<'a>),
+    /// A component type.
+    Component(ComponentType<'a>),
+    /// An instance type.
+    Instance(InstanceType<'a>),
+}
+
+impl<'a> Parse<'a> for TypeDef<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        if parser.peek::<LParen>() {
+            parser.parens(|parser| {
+                let mut l = parser.lookahead1();
+                if l.peek::<kw::func>() {
+                    parser.parse::<kw::func>()?;
+                    Ok(Self::Func(parser.parse()?))
+                } else if l.peek::<kw::component>() {
+                    parser.parse::<kw::component>()?;
+                    Ok(Self::Component(parser.parse()?))
+                } else if l.peek::<kw::instance>() {
+                    parser.parse::<kw::instance>()?;
+                    Ok(Self::Instance(parser.parse()?))
+                } else {
+                    Ok(Self::Defined(ComponentDefinedType::parse_non_primitive(
+                        parser, l,
+                    )?))
+                }
+            })
+        } else {
+            // Only primitive types have no parens
+            Ok(Self::Defined(ComponentDefinedType::Primitive(
+                parser.parse()?,
+            )))
+        }
+    }
+}
+
+/// A primitive value type.
+#[allow(missing_docs)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum PrimitiveValType {
+    Bool,
+    S8,
+    U8,
+    S16,
+    U16,
+    S32,
+    U32,
+    S64,
+    U64,
+    Float32,
+    Float64,
+    Char,
+    String,
+}
+
+impl<'a> Parse<'a> for PrimitiveValType {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut l = parser.lookahead1();
+        if l.peek::<kw::bool_>() {
+            parser.parse::<kw::bool_>()?;
+            Ok(Self::Bool)
+        } else if l.peek::<kw::s8>() {
+            parser.parse::<kw::s8>()?;
+            Ok(Self::S8)
+        } else if l.peek::<kw::u8>() {
+            parser.parse::<kw::u8>()?;
+            Ok(Self::U8)
+        } else if l.peek::<kw::s16>() {
+            parser.parse::<kw::s16>()?;
+            Ok(Self::S16)
+        } else if l.peek::<kw::u16>() {
+            parser.parse::<kw::u16>()?;
+            Ok(Self::U16)
+        } else if l.peek::<kw::s32>() {
+            parser.parse::<kw::s32>()?;
+            Ok(Self::S32)
+        } else if l.peek::<kw::u32>() {
+            parser.parse::<kw::u32>()?;
+            Ok(Self::U32)
+        } else if l.peek::<kw::s64>() {
+            parser.parse::<kw::s64>()?;
+            Ok(Self::S64)
+        } else if l.peek::<kw::u64>() {
+            parser.parse::<kw::u64>()?;
+            Ok(Self::U64)
+        } else if l.peek::<kw::float32>() {
+            parser.parse::<kw::float32>()?;
+            Ok(Self::Float32)
+        } else if l.peek::<kw::float64>() {
+            parser.parse::<kw::float64>()?;
+            Ok(Self::Float64)
+        } else if l.peek::<kw::char>() {
+            parser.parse::<kw::char>()?;
+            Ok(Self::Char)
+        } else if l.peek::<kw::string>() {
+            parser.parse::<kw::string>()?;
+            Ok(Self::String)
+        } else {
+            Err(l.error())
+        }
+    }
+}
+
+impl Peek for PrimitiveValType {
+    fn peek(cursor: crate::parser::Cursor<'_>) -> bool {
+        matches!(
+            cursor.keyword(),
+            Some(("bool", _))
+                | Some(("s8", _))
+                | Some(("u8", _))
+                | Some(("s16", _))
+                | Some(("u16", _))
+                | Some(("s32", _))
+                | Some(("u32", _))
+                | Some(("s64", _))
+                | Some(("u64", _))
+                | Some(("float32", _))
+                | Some(("float64", _))
+                | Some(("char", _))
+                | Some(("string", _))
+        )
+    }
+
+    fn display() -> &'static str {
+        "primitive value type"
+    }
+}
+
+/// A component value type.
+#[allow(missing_docs)]
+#[derive(Debug)]
+pub enum ComponentValType<'a> {
+    /// The value type is an inline defined type.
+    Inline(ComponentDefinedType<'a>),
+    /// The value type is an index reference to a defined type.
+    Ref(Index<'a>),
+}
+
+impl<'a> Parse<'a> for ComponentValType<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        if parser.peek::<Index<'_>>() {
+            Ok(Self::Ref(parser.parse()?))
+        } else {
+            Ok(Self::Inline(InlineComponentValType::parse(parser)?.0))
+        }
+    }
+}
+
+impl Peek for ComponentValType<'_> {
+    fn peek(cursor: crate::parser::Cursor<'_>) -> bool {
+        Index::peek(cursor) || ComponentDefinedType::peek(cursor)
+    }
+
+    fn display() -> &'static str {
+        "component value type"
+    }
+}
+
+/// An inline-only component value type.
+///
+/// This variation does not parse type indexes.
+#[allow(missing_docs)]
+#[derive(Debug)]
+pub struct InlineComponentValType<'a>(ComponentDefinedType<'a>);
+
+impl<'a> Parse<'a> for InlineComponentValType<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        if parser.peek::<LParen>() {
+            parser.parens(|parser| {
+                Ok(Self(ComponentDefinedType::parse_non_primitive(
+                    parser,
+                    parser.lookahead1(),
+                )?))
+            })
+        } else {
+            Ok(Self(ComponentDefinedType::Primitive(parser.parse()?)))
+        }
+    }
+}
+
+// A component defined type.
+#[allow(missing_docs)]
+#[derive(Debug)]
+pub enum ComponentDefinedType<'a> {
+    Primitive(PrimitiveValType),
+    Record(Record<'a>),
+    Variant(Variant<'a>),
+    List(List<'a>),
+    Tuple(Tuple<'a>),
+    Flags(Flags<'a>),
+    Enum(Enum<'a>),
+    Union(Union<'a>),
+    Option(OptionType<'a>),
+    Result(ResultType<'a>),
+}
+
+impl<'a> ComponentDefinedType<'a> {
+    fn parse_non_primitive(parser: Parser<'a>, mut l: Lookahead1<'a>) -> Result<Self> {
+        parser.depth_check()?;
+        if l.peek::<kw::record>() {
+            Ok(Self::Record(parser.parse()?))
+        } else if l.peek::<kw::variant>() {
+            Ok(Self::Variant(parser.parse()?))
+        } else if l.peek::<kw::list>() {
+            Ok(Self::List(parser.parse()?))
+        } else if l.peek::<kw::tuple>() {
+            Ok(Self::Tuple(parser.parse()?))
+        } else if l.peek::<kw::flags>() {
+            Ok(Self::Flags(parser.parse()?))
+        } else if l.peek::<kw::enum_>() {
+            Ok(Self::Enum(parser.parse()?))
+        } else if l.peek::<kw::union>() {
+            Ok(Self::Union(parser.parse()?))
+        } else if l.peek::<kw::option>() {
+            Ok(Self::Option(parser.parse()?))
+        } else if l.peek::<kw::result>() {
+            Ok(Self::Result(parser.parse()?))
+        } else {
+            Err(l.error())
+        }
+    }
+}
+
+impl Default for ComponentDefinedType<'_> {
+    fn default() -> Self {
+        Self::Primitive(PrimitiveValType::Bool)
+    }
+}
+
+impl Peek for ComponentDefinedType<'_> {
+    fn peek(cursor: crate::parser::Cursor<'_>) -> bool {
+        if PrimitiveValType::peek(cursor) {
+            return true;
+        }
+
+        match cursor.lparen() {
+            Some(cursor) => matches!(
+                cursor.keyword(),
+                Some(("record", _))
+                    | Some(("variant", _))
+                    | Some(("list", _))
+                    | Some(("tuple", _))
+                    | Some(("flags", _))
+                    | Some(("enum", _))
+                    | Some(("union", _))
+                    | Some(("option", _))
+                    | Some(("result", _))
+            ),
+            None => false,
+        }
+    }
+
+    fn display() -> &'static str {
+        "component defined type"
+    }
+}
+
+/// A record defined type.
+#[derive(Debug)]
+pub struct Record<'a> {
+    /// The fields of the record.
+    pub fields: Vec<RecordField<'a>>,
+}
+
+impl<'a> Parse<'a> for Record<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.parse::<kw::record>()?;
+        let mut fields = Vec::new();
+        while !parser.is_empty() {
+            fields.push(parser.parens(|p| p.parse())?);
+        }
+        Ok(Self { fields })
+    }
+}
+
+/// A record type field.
+#[derive(Debug)]
+pub struct RecordField<'a> {
+    /// The name of the field.
+    pub name: &'a str,
+    /// The type of the field.
+    pub ty: ComponentValType<'a>,
+}
+
+impl<'a> Parse<'a> for RecordField<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.parse::<kw::field>()?;
+        Ok(Self {
+            name: parser.parse()?,
+            ty: parser.parse()?,
+        })
+    }
+}
+
+/// A variant defined type.
+#[derive(Debug)]
+pub struct Variant<'a> {
+    /// The cases of the variant type.
+    pub cases: Vec<VariantCase<'a>>,
+}
+
+impl<'a> Parse<'a> for Variant<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.parse::<kw::variant>()?;
+        let mut cases = Vec::new();
+        while !parser.is_empty() {
+            cases.push(parser.parens(|p| p.parse())?);
+        }
+        Ok(Self { cases })
+    }
+}
+
+/// A case of a variant type.
+#[derive(Debug)]
+pub struct VariantCase<'a> {
+    /// Where this `case` was defined
+    pub span: Span,
+    /// An optional identifier to refer to this case by as part of name
+    /// resolution.
+    pub id: Option<Id<'a>>,
+    /// The name of the case.
+    pub name: &'a str,
+    /// The optional type of the case.
+    pub ty: Option<ComponentValType<'a>>,
+    /// The optional refinement.
+    pub refines: Option<Refinement<'a>>,
+}
+
+impl<'a> Parse<'a> for VariantCase<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let span = parser.parse::<kw::case>()?.0;
+        let id = parser.parse()?;
+        let name = parser.parse()?;
+        let ty = parser.parse()?;
+        let refines = if !parser.is_empty() {
+            Some(parser.parse()?)
+        } else {
+            None
+        };
+        Ok(Self {
+            span,
+            id,
+            name,
+            ty,
+            refines,
+        })
+    }
+}
+
+/// A refinement for a variant case.
+#[derive(Debug)]
+pub enum Refinement<'a> {
+    /// The refinement is referenced by index.
+    Index(Span, Index<'a>),
+    /// The refinement has been resolved to an index into
+    /// the cases of the variant.
+    Resolved(u32),
+}
+
+impl<'a> Parse<'a> for Refinement<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.parens(|parser| {
+            let span = parser.parse::<kw::refines>()?.0;
+            let id = parser.parse()?;
+            Ok(Self::Index(span, id))
+        })
+    }
+}
+
+/// A list type.
+#[derive(Debug)]
+pub struct List<'a> {
+    /// The element type of the array.
+    pub element: Box<ComponentValType<'a>>,
+}
+
+impl<'a> Parse<'a> for List<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.parse::<kw::list>()?;
+        Ok(Self {
+            element: Box::new(parser.parse()?),
+        })
+    }
+}
+
+/// A tuple type.
+#[derive(Debug)]
+pub struct Tuple<'a> {
+    /// The types of the fields of the tuple.
+    pub fields: Vec<ComponentValType<'a>>,
+}
+
+impl<'a> Parse<'a> for Tuple<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.parse::<kw::tuple>()?;
+        let mut fields = Vec::new();
+        while !parser.is_empty() {
+            fields.push(parser.parse()?);
+        }
+        Ok(Self { fields })
+    }
+}
+
+/// A flags type.
+#[derive(Debug)]
+pub struct Flags<'a> {
+    /// The names of the individual flags.
+    pub names: Vec<&'a str>,
+}
+
+impl<'a> Parse<'a> for Flags<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.parse::<kw::flags>()?;
+        let mut names = Vec::new();
+        while !parser.is_empty() {
+            names.push(parser.parse()?);
+        }
+        Ok(Self { names })
+    }
+}
+
+/// An enum type.
+#[derive(Debug)]
+pub struct Enum<'a> {
+    /// The tag names of the enum.
+    pub names: Vec<&'a str>,
+}
+
+impl<'a> Parse<'a> for Enum<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.parse::<kw::enum_>()?;
+        let mut names = Vec::new();
+        while !parser.is_empty() {
+            names.push(parser.parse()?);
+        }
+        Ok(Self { names })
+    }
+}
+
+/// A union type.
+#[derive(Debug)]
+pub struct Union<'a> {
+    /// The types of the union.
+    pub types: Vec<ComponentValType<'a>>,
+}
+
+impl<'a> Parse<'a> for Union<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.parse::<kw::union>()?;
+        let mut types = Vec::new();
+        while !parser.is_empty() {
+            types.push(parser.parse()?);
+        }
+        Ok(Self { types })
+    }
+}
+
+/// An optional type.
+#[derive(Debug)]
+pub struct OptionType<'a> {
+    /// The type of the value, when a value is present.
+    pub element: Box<ComponentValType<'a>>,
+}
+
+impl<'a> Parse<'a> for OptionType<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.parse::<kw::option>()?;
+        Ok(Self {
+            element: Box::new(parser.parse()?),
+        })
+    }
+}
+
+/// A result type.
+#[derive(Debug)]
+pub struct ResultType<'a> {
+    /// The type on success.
+    pub ok: Option<Box<ComponentValType<'a>>>,
+    /// The type on failure.
+    pub err: Option<Box<ComponentValType<'a>>>,
+}
+
+impl<'a> Parse<'a> for ResultType<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.parse::<kw::result>()?;
+
+        let ok: Option<ComponentValType> = parser.parse()?;
+        let err: Option<ComponentValType> = if parser.peek::<LParen>() {
+            Some(parser.parens(|parser| {
+                parser.parse::<kw::error>()?;
+                parser.parse()
+            })?)
+        } else {
+            None
+        };
+
+        Ok(Self {
+            ok: ok.map(Box::new),
+            err: err.map(Box::new),
+        })
+    }
+}
+
+/// A component function type with parameters and result.
+#[derive(Debug)]
+pub struct ComponentFunctionType<'a> {
+    /// The parameters of a function, optionally each having an identifier for
+    /// name resolution and a name for the custom `name` section.
+    pub params: Box<[ComponentFunctionParam<'a>]>,
+    /// The result of a function, optionally each having an identifier for
+    /// name resolution and a name for the custom `name` section.
+    pub results: Box<[ComponentFunctionResult<'a>]>,
+}
+
+impl<'a> Parse<'a> for ComponentFunctionType<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut params: Vec<ComponentFunctionParam> = Vec::new();
+        while parser.peek2::<kw::param>() {
+            params.push(parser.parens(|p| p.parse())?);
+        }
+
+        let mut results: Vec<ComponentFunctionResult> = Vec::new();
+        while parser.peek2::<kw::result>() {
+            results.push(parser.parens(|p| p.parse())?);
+        }
+
+        Ok(Self {
+            params: params.into(),
+            results: results.into(),
+        })
+    }
+}
+
+/// A parameter of a [`ComponentFunctionType`].
+#[derive(Debug)]
+pub struct ComponentFunctionParam<'a> {
+    /// The name of the parameter
+    pub name: &'a str,
+    /// The type of the parameter.
+    pub ty: ComponentValType<'a>,
+}
+
+impl<'a> Parse<'a> for ComponentFunctionParam<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.parse::<kw::param>()?;
+        Ok(Self {
+            name: parser.parse()?,
+            ty: parser.parse()?,
+        })
+    }
+}
+
+/// A result of a [`ComponentFunctionType`].
+#[derive(Debug)]
+pub struct ComponentFunctionResult<'a> {
+    /// An optionally-specified name of this result
+    pub name: Option<&'a str>,
+    /// The type of the result.
+    pub ty: ComponentValType<'a>,
+}
+
+impl<'a> Parse<'a> for ComponentFunctionResult<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.parse::<kw::result>()?;
+        Ok(Self {
+            name: parser.parse()?,
+            ty: parser.parse()?,
+        })
+    }
+}
+
+/// The type of an exported item from an component or instance type.
+#[derive(Debug)]
+pub struct ComponentExportType<'a> {
+    /// Where this export was defined.
+    pub span: Span,
+    /// The name of this export.
+    pub name: &'a str,
+    /// The optional URL of this export.
+    pub url: Option<&'a str>,
+    /// The signature of the item.
+    pub item: ItemSig<'a>,
+}
+
+impl<'a> Parse<'a> for ComponentExportType<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let span = parser.parse::<kw::export>()?.0;
+        let id = parser.parse()?;
+        let debug_name = parser.parse()?;
+        let name = parser.parse()?;
+        let url = parser.parse()?;
+        let item = parser.parens(|p| {
+            let mut item = p.parse::<ItemSigNoName<'_>>()?.0;
+            item.id = id;
+            item.name = debug_name;
+            Ok(item)
+        })?;
+        Ok(Self {
+            span,
+            name,
+            url,
+            item,
+        })
+    }
+}
+
+/// A type definition for a component type.
+#[derive(Debug, Default)]
+pub struct ComponentType<'a> {
+    /// The declarations of the component type.
+    pub decls: Vec<ComponentTypeDecl<'a>>,
+}
+
+impl<'a> Parse<'a> for ComponentType<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.depth_check()?;
+        Ok(Self {
+            decls: parser.parse()?,
+        })
+    }
+}
+
+/// A declaration of a component type.
+#[derive(Debug)]
+pub enum ComponentTypeDecl<'a> {
+    /// A core type definition local to the component type.
+    CoreType(CoreType<'a>),
+    /// A type definition local to the component type.
+    Type(Type<'a>),
+    /// An alias local to the component type.
+    Alias(Alias<'a>),
+    /// An import of the component type.
+    Import(ComponentImport<'a>),
+    /// An export of the component type.
+    Export(ComponentExportType<'a>),
+}
+
+impl<'a> Parse<'a> for ComponentTypeDecl<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut l = parser.lookahead1();
+        if l.peek::<kw::core>() {
+            Ok(Self::CoreType(parser.parse()?))
+        } else if l.peek::<kw::r#type>() {
+            Ok(Self::Type(parser.parse()?))
+        } else if l.peek::<kw::alias>() {
+            Ok(Self::Alias(parser.parse()?))
+        } else if l.peek::<kw::import>() {
+            Ok(Self::Import(parser.parse()?))
+        } else if l.peek::<kw::export>() {
+            Ok(Self::Export(parser.parse()?))
+        } else {
+            Err(l.error())
+        }
+    }
+}
+
+impl<'a> Parse<'a> for Vec<ComponentTypeDecl<'a>> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut decls = Vec::new();
+        while !parser.is_empty() {
+            decls.push(parser.parens(|parser| parser.parse())?);
+        }
+        Ok(decls)
+    }
+}
+
+/// A type definition for an instance type.
+#[derive(Debug)]
+pub struct InstanceType<'a> {
+    /// The declarations of the instance type.
+    pub decls: Vec<InstanceTypeDecl<'a>>,
+}
+
+impl<'a> Parse<'a> for InstanceType<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.depth_check()?;
+        Ok(Self {
+            decls: parser.parse()?,
+        })
+    }
+}
+
+/// A declaration of an instance type.
+#[derive(Debug)]
+pub enum InstanceTypeDecl<'a> {
+    /// A core type definition local to the component type.
+    CoreType(CoreType<'a>),
+    /// A type definition local to the instance type.
+    Type(Type<'a>),
+    /// An alias local to the instance type.
+    Alias(Alias<'a>),
+    /// An export of the instance type.
+    Export(ComponentExportType<'a>),
+}
+
+impl<'a> Parse<'a> for InstanceTypeDecl<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut l = parser.lookahead1();
+        if l.peek::<kw::core>() {
+            Ok(Self::CoreType(parser.parse()?))
+        } else if l.peek::<kw::r#type>() {
+            Ok(Self::Type(parser.parse()?))
+        } else if l.peek::<kw::alias>() {
+            Ok(Self::Alias(parser.parse()?))
+        } else if l.peek::<kw::export>() {
+            Ok(Self::Export(parser.parse()?))
+        } else {
+            Err(l.error())
+        }
+    }
+}
+
+impl<'a> Parse<'a> for Vec<InstanceTypeDecl<'a>> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut decls = Vec::new();
+        while !parser.is_empty() {
+            decls.push(parser.parens(|parser| parser.parse())?);
+        }
+        Ok(decls)
+    }
+}
+
+/// A value type declaration used for values in import signatures.
+#[derive(Debug)]
+pub struct ComponentValTypeUse<'a>(pub ComponentValType<'a>);
+
+impl<'a> Parse<'a> for ComponentValTypeUse<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        match ComponentTypeUse::<'a, InlineComponentValType<'a>>::parse(parser)? {
+            ComponentTypeUse::Ref(i) => Ok(Self(ComponentValType::Ref(i.idx))),
+            ComponentTypeUse::Inline(t) => Ok(Self(ComponentValType::Inline(t.0))),
+        }
+    }
+}
+
+/// A reference to a core type defined in this component.
+///
+/// This is the same as `TypeUse`, but accepts `$T` as shorthand for
+/// `(type $T)`.
+#[derive(Debug, Clone)]
+pub enum CoreTypeUse<'a, T> {
+    /// The type that we're referencing.
+    Ref(CoreItemRef<'a, kw::r#type>),
+    /// The inline type.
+    Inline(T),
+}
+
+impl<'a, T: Parse<'a>> Parse<'a> for CoreTypeUse<'a, T> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        // Here the core context is assumed, so no core prefix is expected
+        if parser.peek::<LParen>() && parser.peek2::<CoreItemRef<'a, kw::r#type>>() {
+            Ok(Self::Ref(parser.parens(|parser| parser.parse())?))
+        } else {
+            Ok(Self::Inline(parser.parse()?))
+        }
+    }
+}
+
+impl<T> Default for CoreTypeUse<'_, T> {
+    fn default() -> Self {
+        let span = Span::from_offset(0);
+        Self::Ref(CoreItemRef {
+            idx: Index::Num(0, span),
+            kind: kw::r#type(span),
+            export_name: None,
+        })
+    }
+}
+
+/// A reference to a type defined in this component.
+///
+/// This is the same as `TypeUse`, but accepts `$T` as shorthand for
+/// `(type $T)`.
+#[derive(Debug, Clone)]
+pub enum ComponentTypeUse<'a, T> {
+    /// The type that we're referencing.
+    Ref(ItemRef<'a, kw::r#type>),
+    /// The inline type.
+    Inline(T),
+}
+
+impl<'a, T: Parse<'a>> Parse<'a> for ComponentTypeUse<'a, T> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        if parser.peek::<LParen>() && parser.peek2::<ItemRef<'a, kw::r#type>>() {
+            Ok(Self::Ref(parser.parens(|parser| parser.parse())?))
+        } else {
+            Ok(Self::Inline(parser.parse()?))
+        }
+    }
+}
+
+impl<T> Default for ComponentTypeUse<'_, T> {
+    fn default() -> Self {
+        let span = Span::from_offset(0);
+        Self::Ref(ItemRef {
+            idx: Index::Num(0, span),
+            kind: kw::r#type(span),
+            export_names: Vec::new(),
+        })
+    }
+}
diff --git a/third_party/rust/wast/src/component/wast.rs b/third_party/rust/wast/src/component/wast.rs
new file mode 100644
index 0000000000..8409a6c969
--- /dev/null
+++ b/third_party/rust/wast/src/component/wast.rs
@@ -0,0 +1,166 @@
+use crate::kw;
+use crate::parser::{Cursor, Parse, Parser, Peek, Result};
+use crate::token::{Float32, Float64};
+
+/// Expression that can be used inside of `invoke` expressions for core wasm
+/// functions.
+#[derive(Debug)]
+#[allow(missing_docs)]
+pub enum WastVal<'a> {
+    Bool(bool),
+    U8(u8),
+    S8(i8),
+    U16(u16),
+    S16(i16),
+    U32(u32),
+    S32(i32),
+    U64(u64),
+    S64(i64),
+    Float32(Float32),
+    Float64(Float64),
+    Char(char),
+    String(&'a str),
+    List(Vec<WastVal<'a>>),
+    Record(Vec<(&'a str, WastVal<'a>)>),
+    Tuple(Vec<WastVal<'a>>),
+    Variant(&'a str, Option<Box<WastVal<'a>>>),
+    Enum(&'a str),
+    Union(u32, Box<WastVal<'a>>),
+    Option(Option<Box<WastVal<'a>>>),
+    Result(Result<Option<Box<WastVal<'a>>>, Option<Box<WastVal<'a>>>>),
+    Flags(Vec<&'a str>),
+}
+
+static CASES: &[(&str, fn(Parser<'_>) -> Result<WastVal<'_>>)] = {
+    use WastVal::*;
+    &[
+        ("bool.const", |p| {
+            let mut l = p.lookahead1();
+            if l.peek::<kw::true_>() {
+                p.parse::<kw::true_>()?;
+                Ok(Bool(true))
+            } else if l.peek::<kw::false_>() {
+                p.parse::<kw::false_>()?;
+                Ok(Bool(false))
+            } else {
+                Err(l.error())
+            }
+        }),
+        ("u8.const", |p| Ok(U8(p.parse()?))),
+        ("s8.const", |p| Ok(S8(p.parse()?))),
+        ("u16.const", |p| Ok(U16(p.parse()?))),
+        ("s16.const", |p| Ok(S16(p.parse()?))),
+        ("u32.const", |p| Ok(U32(p.parse()?))),
+        ("s32.const", |p| Ok(S32(p.parse()?))),
+        ("u64.const", |p| Ok(U64(p.parse()?))),
+        ("s64.const", |p| Ok(S64(p.parse()?))),
+        ("f32.const", |p| Ok(Float32(p.parse()?))),
+        ("f64.const", |p| Ok(Float64(p.parse()?))),
+        ("char.const", |p| {
+            let s = p.parse::<&str>()?;
+            let mut ch = s.chars();
+            let ret = match ch.next() {
+                Some(c) => c,
+                None => return Err(p.error("empty string")),
+            };
+            if ch.next().is_some() {
+                return Err(p.error("more than one character"));
+            }
+            Ok(Char(ret))
+        }),
+        ("str.const", |p| Ok(String(p.parse()?))),
+        ("list.const", |p| {
+            let mut ret = Vec::new();
+            while !p.is_empty() {
+                ret.push(p.parens(|p| p.parse())?);
+            }
+            Ok(List(ret))
+        }),
+        ("record.const", |p| {
+            let mut ret = Vec::new();
+            while !p.is_empty() {
+                ret.push(p.parens(|p| {
+                    p.parse::<kw::field>()?;
+                    Ok((p.parse()?, p.parse()?))
+                })?);
+            }
+            Ok(Record(ret))
+        }),
+        ("tuple.const", |p| {
+            let mut ret = Vec::new();
+            while !p.is_empty() {
+                ret.push(p.parens(|p| p.parse())?);
+            }
+            Ok(Tuple(ret))
+        }),
+        ("variant.const", |p| {
+            let name = p.parse()?;
+            let payload = if p.is_empty() {
+                None
+            } else {
+                Some(Box::new(p.parens(|p| p.parse())?))
+            };
+            Ok(Variant(name, payload))
+        }),
+        ("enum.const", |p| Ok(Enum(p.parse()?))),
+        ("union.const", |p| {
+            let num = p.parse()?;
+            let payload = Box::new(p.parens(|p| p.parse())?);
+            Ok(Union(num, payload))
+        }),
+        ("option.none", |_| Ok(Option(None))),
+        ("option.some", |p| {
+            Ok(Option(Some(Box::new(p.parens(|p| p.parse())?))))
+        }),
+        ("result.ok", |p| {
+            Ok(Result(Ok(if p.is_empty() {
+                None
+            } else {
+                Some(Box::new(p.parens(|p| p.parse())?))
+            })))
+        }),
+        ("result.err", |p| {
+            Ok(Result(Err(if p.is_empty() {
+                None
+            } else {
+                Some(Box::new(p.parens(|p| p.parse())?))
+            })))
+        }),
+        ("flags.const", |p| {
+            let mut ret = Vec::new();
+            while !p.is_empty() {
+                ret.push(p.parse()?);
+            }
+            Ok(Flags(ret))
+        }),
+    ]
+};
+
+impl<'a> Parse<'a> for WastVal<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.depth_check()?;
+        let parse = parser.step(|c| {
+            if let Some((kw, rest)) = c.keyword() {
+                if let Some(i) = CASES.iter().position(|(name, _)| *name == kw) {
+                    return Ok((CASES[i].1, rest));
+                }
+            }
+            Err(c.error("expected a [type].const expression"))
+        })?;
+        parse(parser)
+    }
+}
+
+impl Peek for WastVal<'_> {
+    fn peek(cursor: Cursor<'_>) -> bool {
+        let kw = match cursor.keyword() {
+            Some((kw, _)) => kw,
+            None => return false,
+        };
+        CASES.iter().any(|(name, _)| *name == kw)
+    }
+
+    fn display() -> &'static str {
+        "core wasm argument"
+    }
+}
diff --git a/third_party/rust/wast/src/core.rs b/third_party/rust/wast/src/core.rs
new file mode 100644
index 0000000000..785a081853
--- /dev/null
+++ b/third_party/rust/wast/src/core.rs
@@ -0,0 +1,29 @@
+//! Types and support for parsing the core wasm text format.
+
+mod custom;
+mod export;
+mod expr;
+mod func;
+mod global;
+mod import;
+mod memory;
+mod module;
+mod table;
+mod tag;
+mod types;
+mod wast;
+pub use self::custom::*;
+pub use self::export::*;
+pub use self::expr::*;
+pub use self::func::*;
+pub use self::global::*;
+pub use self::import::*;
+pub use self::memory::*;
+pub use self::module::*;
+pub use self::table::*;
+pub use self::tag::*;
+pub use self::types::*;
+pub use self::wast::*;
+
+pub(crate) mod binary;
+pub(crate) mod resolve;
diff --git a/third_party/rust/wast/src/core/binary.rs b/third_party/rust/wast/src/core/binary.rs
new file mode 100644
index 0000000000..5ae4752349
--- /dev/null
+++ b/third_party/rust/wast/src/core/binary.rs
@@ -0,0 +1,1180 @@
+use crate::core::*;
+use crate::encode::Encode;
+use crate::token::*;
+
+pub fn encode(
+    module_id: &Option<Id<'_>>,
+    module_name: &Option<NameAnnotation<'_>>,
+    fields: &[ModuleField<'_>],
+) -> Vec<u8> {
+    use CustomPlace::*;
+    use CustomPlaceAnchor::*;
+
+    let mut types = Vec::new();
+    let mut imports = Vec::new();
+    let mut funcs = Vec::new();
+    let mut tables = Vec::new();
+    let mut memories = Vec::new();
+    let mut globals = Vec::new();
+    let mut exports = Vec::new();
+    let mut start = Vec::new();
+    let mut elem = Vec::new();
+    let mut data = Vec::new();
+    let mut tags = Vec::new();
+    let mut customs = Vec::new();
+    for field in fields {
+        match field {
+            ModuleField::Type(i) => types.push(RecOrType::Type(i)),
+            ModuleField::Rec(i) => types.push(RecOrType::Rec(i)),
+            ModuleField::Import(i) => imports.push(i),
+            ModuleField::Func(i) => funcs.push(i),
+            ModuleField::Table(i) => tables.push(i),
+            ModuleField::Memory(i) => memories.push(i),
+            ModuleField::Global(i) => globals.push(i),
+            ModuleField::Export(i) => exports.push(i),
+            ModuleField::Start(i) => start.push(i),
+            ModuleField::Elem(i) => elem.push(i),
+            ModuleField::Data(i) => data.push(i),
+            ModuleField::Tag(i) => tags.push(i),
+            ModuleField::Custom(i) => customs.push(i),
+        }
+    }
+
+    let mut e = Encoder {
+        wasm: Vec::new(),
+        tmp: Vec::new(),
+        customs: &customs,
+    };
+    e.wasm.extend(b"\0asm");
+    e.wasm.extend(b"\x01\0\0\0");
+
+    e.custom_sections(BeforeFirst);
+
+    e.section_list(1, Type, &types);
+    e.section_list(2, Import, &imports);
+
+    let functys = funcs.iter().map(|f| &f.ty).collect::<Vec<_>>();
+    e.section_list(3, Func, &functys);
+    e.section_list(4, Table, &tables);
+    e.section_list(5, Memory, &memories);
+    e.section_list(13, Tag, &tags);
+    e.section_list(6, Global, &globals);
+    e.section_list(7, Export, &exports);
+    e.custom_sections(Before(Start));
+    if let Some(start) = start.get(0) {
+        e.section(8, start);
+    }
+    e.custom_sections(After(Start));
+    e.section_list(9, Elem, &elem);
+    if needs_data_count(&funcs) {
+        e.section(12, &data.len());
+    }
+    e.section_list(10, Code, &funcs);
+    e.section_list(11, Data, &data);
+
+    let names = find_names(module_id, module_name, fields);
+    if !names.is_empty() {
+        e.section(0, &("name", names));
+    }
+    e.custom_sections(AfterLast);
+
+    return e.wasm;
+
+    fn needs_data_count(funcs: &[&crate::core::Func<'_>]) -> bool {
+        funcs
+            .iter()
+            .filter_map(|f| match &f.kind {
+                FuncKind::Inline { expression, .. } => Some(expression),
+                _ => None,
+            })
+            .flat_map(|e| e.instrs.iter())
+            .any(|i| i.needs_data_count())
+    }
+}
+
+struct Encoder<'a> {
+    wasm: Vec<u8>,
+    tmp: Vec<u8>,
+    customs: &'a [&'a Custom<'a>],
+}
+
+impl Encoder<'_> {
+    fn section(&mut self, id: u8, section: &dyn Encode) {
+        self.tmp.truncate(0);
+        section.encode(&mut self.tmp);
+        self.wasm.push(id);
+        self.tmp.encode(&mut self.wasm);
+    }
+
+    fn custom_sections(&mut self, place: CustomPlace) {
+        for entry in self.customs.iter() {
+            if entry.place == place {
+                self.section(0, &(entry.name, entry));
+            }
+        }
+    }
+
+    fn section_list(&mut self, id: u8, anchor: CustomPlaceAnchor, list: &[impl Encode]) {
+        self.custom_sections(CustomPlace::Before(anchor));
+        if !list.is_empty() {
+            self.section(id, &list)
+        }
+        self.custom_sections(CustomPlace::After(anchor));
+    }
+}
+
+impl Encode for FunctionType<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.params.len().encode(e);
+        for (_, _, ty) in self.params.iter() {
+            ty.encode(e);
+        }
+        self.results.encode(e);
+    }
+}
+
+impl Encode for StructType<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.fields.len().encode(e);
+        for field in self.fields.iter() {
+            field.ty.encode(e);
+            (field.mutable as i32).encode(e);
+        }
+    }
+}
+
+impl Encode for ArrayType<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.ty.encode(e);
+        (self.mutable as i32).encode(e);
+    }
+}
+
+impl Encode for ExportType<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.name.encode(e);
+        self.item.encode(e);
+    }
+}
+
+enum RecOrType<'a> {
+    Type(&'a Type<'a>),
+    Rec(&'a Rec<'a>),
+}
+
+impl Encode for RecOrType<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        match self {
+            RecOrType::Type(ty) => ty.encode(e),
+            RecOrType::Rec(rec) => rec.encode(e),
+        }
+    }
+}
+
+impl Encode for Type<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        if let Some(parent) = &self.parent {
+            e.push(0x50);
+            (1 as usize).encode(e);
+            parent.encode(e);
+        }
+        match &self.def {
+            TypeDef::Func(func) => {
+                e.push(0x60);
+                func.encode(e)
+            }
+            TypeDef::Struct(r#struct) => {
+                e.push(0x5f);
+                r#struct.encode(e)
+            }
+            TypeDef::Array(array) => {
+                e.push(0x5e);
+                array.encode(e)
+            }
+        }
+    }
+}
+
+impl Encode for Rec<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        if self.types.len() == 1 {
+            self.types[0].encode(e);
+            return;
+        }
+
+        e.push(0x4f);
+        self.types.len().encode(e);
+        for ty in &self.types {
+            ty.encode(e);
+        }
+    }
+}
+
+impl Encode for Option<Id<'_>> {
+    fn encode(&self, _e: &mut Vec<u8>) {
+        // used for parameters in the tuple impl as well as instruction labels
+    }
+}
+
+impl<'a> Encode for ValType<'a> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        match self {
+            ValType::I32 => e.push(0x7f),
+            ValType::I64 => e.push(0x7e),
+            ValType::F32 => e.push(0x7d),
+            ValType::F64 => e.push(0x7c),
+            ValType::V128 => e.push(0x7b),
+            ValType::Ref(ty) => {
+                ty.encode(e);
+            }
+        }
+    }
+}
+
+impl<'a> Encode for HeapType<'a> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        match self {
+            HeapType::Func => e.push(0x70),
+            HeapType::Extern => e.push(0x6f),
+            HeapType::Any => e.push(0x6e),
+            HeapType::Eq => e.push(0x6d),
+            HeapType::Struct => e.push(0x67),
+            HeapType::Array => e.push(0x66),
+            HeapType::I31 => e.push(0x6a),
+            HeapType::NoFunc => e.push(0x68),
+            HeapType::NoExtern => e.push(0x69),
+            HeapType::None => e.push(0x65),
+            // Note that this is encoded as a signed leb128 so be sure to cast
+            // to an i64 first
+            HeapType::Index(Index::Num(n, _)) => i64::from(*n).encode(e),
+            HeapType::Index(Index::Id(n)) => {
+                panic!("unresolved index in emission: {:?}", n)
+            }
+        }
+    }
+}
+
+impl<'a> Encode for RefType<'a> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        match self {
+            // The 'funcref' binary abbreviation
+            RefType {
+                nullable: true,
+                heap: HeapType::Func,
+            } => e.push(0x70),
+            // The 'externref' binary abbreviation
+            RefType {
+                nullable: true,
+                heap: HeapType::Extern,
+            } => e.push(0x6f),
+            // The 'eqref' binary abbreviation
+            RefType {
+                nullable: true,
+                heap: HeapType::Eq,
+            } => e.push(0x6d),
+            // The 'structref' binary abbreviation
+            RefType {
+                nullable: true,
+                heap: HeapType::Struct,
+            } => e.push(0x67),
+            // The 'i31ref' binary abbreviation
+            RefType {
+                nullable: true,
+                heap: HeapType::I31,
+            } => e.push(0x6a),
+            // The 'nullfuncref' binary abbreviation
+            RefType {
+                nullable: true,
+                heap: HeapType::NoFunc,
+            } => e.push(0x68),
+            // The 'nullexternref' binary abbreviation
+            RefType {
+                nullable: true,
+                heap: HeapType::NoExtern,
+            } => e.push(0x69),
+            // The 'nullref' binary abbreviation
+            RefType {
+                nullable: true,
+                heap: HeapType::None,
+            } => e.push(0x65),
+
+            // Generic 'ref null <heaptype>' encoding
+            RefType {
+                nullable: true,
+                heap,
+            } => {
+                e.push(0x6c);
+                heap.encode(e);
+            }
+            // Generic 'ref <heaptype>' encoding
+            RefType {
+                nullable: false,
+                heap,
+            } => {
+                e.push(0x6b);
+                heap.encode(e);
+            }
+        }
+    }
+}
+
+impl<'a> Encode for StorageType<'a> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        match self {
+            StorageType::I8 => e.push(0x7a),
+            StorageType::I16 => e.push(0x79),
+            StorageType::Val(ty) => {
+                ty.encode(e);
+            }
+        }
+    }
+}
+
+impl Encode for Import<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.module.encode(e);
+        self.field.encode(e);
+        self.item.encode(e);
+    }
+}
+
+impl Encode for ItemSig<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        match &self.kind {
+            ItemKind::Func(f) => {
+                e.push(0x00);
+                f.encode(e);
+            }
+            ItemKind::Table(f) => {
+                e.push(0x01);
+                f.encode(e);
+            }
+            ItemKind::Memory(f) => {
+                e.push(0x02);
+                f.encode(e);
+            }
+            ItemKind::Global(f) => {
+                e.push(0x03);
+                f.encode(e);
+            }
+            ItemKind::Tag(f) => {
+                e.push(0x04);
+                f.encode(e);
+            }
+        }
+    }
+}
+
+impl<T> Encode for TypeUse<'_, T> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.index
+            .as_ref()
+            .expect("TypeUse should be filled in by this point")
+            .encode(e)
+    }
+}
+
+impl Encode for Index<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        match self {
+            Index::Num(n, _) => n.encode(e),
+            Index::Id(n) => panic!("unresolved index in emission: {:?}", n),
+        }
+    }
+}
+
+impl<'a> Encode for TableType<'a> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.elem.encode(e);
+        self.limits.encode(e);
+    }
+}
+
+impl Encode for Limits {
+    fn encode(&self, e: &mut Vec<u8>) {
+        match self.max {
+            Some(max) => {
+                e.push(0x01);
+                self.min.encode(e);
+                max.encode(e);
+            }
+            None => {
+                e.push(0x00);
+                self.min.encode(e);
+            }
+        }
+    }
+}
+
+impl Encode for MemoryType {
+    fn encode(&self, e: &mut Vec<u8>) {
+        match self {
+            MemoryType::B32 { limits, shared } => {
+                let flag_max = limits.max.is_some() as u8;
+                let flag_shared = *shared as u8;
+                let flags = flag_max | (flag_shared << 1);
+                e.push(flags);
+                limits.min.encode(e);
+                if let Some(max) = limits.max {
+                    max.encode(e);
+                }
+            }
+            MemoryType::B64 { limits, shared } => {
+                let flag_max = limits.max.is_some() as u8;
+                let flag_shared = *shared as u8;
+                let flags = flag_max | (flag_shared << 1) | 0x04;
+                e.push(flags);
+                limits.min.encode(e);
+                if let Some(max) = limits.max {
+                    max.encode(e);
+                }
+            }
+        }
+    }
+}
+
+impl<'a> Encode for GlobalType<'a> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.ty.encode(e);
+        if self.mutable {
+            e.push(0x01);
+        } else {
+            e.push(0x00);
+        }
+    }
+}
+
+impl Encode for Table<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        assert!(self.exports.names.is_empty());
+        match &self.kind {
+            TableKind::Normal {
+                ty,
+                init_expr: None,
+            } => ty.encode(e),
+            TableKind::Normal {
+                ty,
+                init_expr: Some(init_expr),
+            } => {
+                e.push(0x40);
+                e.push(0x00);
+                ty.encode(e);
+                init_expr.encode(e);
+            }
+            _ => panic!("TableKind should be normal during encoding"),
+        }
+    }
+}
+
+impl Encode for Memory<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        assert!(self.exports.names.is_empty());
+        match &self.kind {
+            MemoryKind::Normal(t) => t.encode(e),
+            _ => panic!("MemoryKind should be normal during encoding"),
+        }
+    }
+}
+
+impl Encode for Global<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        assert!(self.exports.names.is_empty());
+        self.ty.encode(e);
+        match &self.kind {
+            GlobalKind::Inline(expr) => expr.encode(e),
+            _ => panic!("GlobalKind should be inline during encoding"),
+        }
+    }
+}
+
+impl Encode for Export<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.name.encode(e);
+        self.kind.encode(e);
+        self.item.encode(e);
+    }
+}
+
+impl Encode for ExportKind {
+    fn encode(&self, e: &mut Vec<u8>) {
+        match self {
+            ExportKind::Func => e.push(0x00),
+            ExportKind::Table => e.push(0x01),
+            ExportKind::Memory => e.push(0x02),
+            ExportKind::Global => e.push(0x03),
+            ExportKind::Tag => e.push(0x04),
+        }
+    }
+}
+
+impl Encode for Elem<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        match (&self.kind, &self.payload) {
+            (
+                ElemKind::Active {
+                    table: Index::Num(0, _),
+                    offset,
+                },
+                ElemPayload::Indices(_),
+            ) => {
+                e.push(0x00);
+                offset.encode(e);
+            }
+            (ElemKind::Passive, ElemPayload::Indices(_)) => {
+                e.push(0x01); // flags
+                e.push(0x00); // extern_kind
+            }
+            (ElemKind::Active { table, offset }, ElemPayload::Indices(_)) => {
+                e.push(0x02); // flags
+                table.encode(e);
+                offset.encode(e);
+                e.push(0x00); // extern_kind
+            }
+            (
+                ElemKind::Active {
+                    table: Index::Num(0, _),
+                    offset,
+                },
+                ElemPayload::Exprs {
+                    ty:
+                        RefType {
+                            nullable: true,
+                            heap: HeapType::Func,
+                        },
+                    ..
+                },
+            ) => {
+                e.push(0x04);
+                offset.encode(e);
+            }
+            (ElemKind::Passive, ElemPayload::Exprs { ty, .. }) => {
+                e.push(0x05);
+                ty.encode(e);
+            }
+            (ElemKind::Active { table, offset }, ElemPayload::Exprs { ty, .. }) => {
+                e.push(0x06);
+                table.encode(e);
+                offset.encode(e);
+                ty.encode(e);
+            }
+            (ElemKind::Declared, ElemPayload::Indices(_)) => {
+                e.push(0x03); // flags
+                e.push(0x00); // extern_kind
+            }
+            (ElemKind::Declared, ElemPayload::Exprs { ty, .. }) => {
+                e.push(0x07); // flags
+                ty.encode(e);
+            }
+        }
+
+        self.payload.encode(e);
+    }
+}
+
+impl Encode for ElemPayload<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        match self {
+            ElemPayload::Indices(v) => v.encode(e),
+            ElemPayload::Exprs { exprs, ty: _ } => {
+                exprs.len().encode(e);
+                for expr in exprs {
+                    expr.encode(e);
+                }
+            }
+        }
+    }
+}
+
+impl Encode for Data<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        match &self.kind {
+            DataKind::Passive => e.push(0x01),
+            DataKind::Active {
+                memory: Index::Num(0, _),
+                offset,
+            } => {
+                e.push(0x00);
+                offset.encode(e);
+            }
+            DataKind::Active { memory, offset } => {
+                e.push(0x02);
+                memory.encode(e);
+                offset.encode(e);
+            }
+        }
+        self.data.iter().map(|l| l.len()).sum::<usize>().encode(e);
+        for val in self.data.iter() {
+            val.push_onto(e);
+        }
+    }
+}
+
+impl Encode for Func<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        assert!(self.exports.names.is_empty());
+        let mut tmp = Vec::new();
+        let (expr, locals) = match &self.kind {
+            FuncKind::Inline { expression, locals } => (expression, locals),
+            _ => panic!("should only have inline functions in emission"),
+        };
+
+        locals.encode(&mut tmp);
+        expr.encode(&mut tmp);
+
+        tmp.len().encode(e);
+        e.extend_from_slice(&tmp);
+    }
+}
+
+impl Encode for Vec<Local<'_>> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        let mut locals_compressed = Vec::<(u32, ValType)>::new();
+        for local in self {
+            if let Some((cnt, prev)) = locals_compressed.last_mut() {
+                if *prev == local.ty {
+                    *cnt += 1;
+                    continue;
+                }
+            }
+            locals_compressed.push((1, local.ty));
+        }
+        locals_compressed.encode(e);
+    }
+}
+
+impl Encode for Expression<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        for instr in self.instrs.iter() {
+            instr.encode(e);
+        }
+        e.push(0x0b);
+    }
+}
+
+impl Encode for BlockType<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        // block types using an index are encoded as an sleb, not a uleb
+        if let Some(Index::Num(n, _)) = &self.ty.index {
+            return i64::from(*n).encode(e);
+        }
+        let ty = self
+            .ty
+            .inline
+            .as_ref()
+            .expect("function type not filled in");
+        if ty.params.is_empty() && ty.results.is_empty() {
+            return e.push(0x40);
+        }
+        if ty.params.is_empty() && ty.results.len() == 1 {
+            return ty.results[0].encode(e);
+        }
+        panic!("multi-value block types should have an index");
+    }
+}
+
+impl Encode for FuncBindType<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.ty.encode(e);
+    }
+}
+
+impl Encode for LetType<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.block.encode(e);
+        self.locals.encode(e);
+    }
+}
+
+impl Encode for LaneArg {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.lane.encode(e);
+    }
+}
+
+impl Encode for MemArg<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        match &self.memory {
+            Index::Num(0, _) => {
+                self.align.trailing_zeros().encode(e);
+                self.offset.encode(e);
+            }
+            _ => {
+                (self.align.trailing_zeros() | (1 << 6)).encode(e);
+                self.memory.encode(e);
+                self.offset.encode(e);
+            }
+        }
+    }
+}
+
+impl Encode for LoadOrStoreLane<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.memarg.encode(e);
+        self.lane.encode(e);
+    }
+}
+
+impl Encode for CallIndirect<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.ty.encode(e);
+        self.table.encode(e);
+    }
+}
+
+impl Encode for TableInit<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.elem.encode(e);
+        self.table.encode(e);
+    }
+}
+
+impl Encode for TableCopy<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.dst.encode(e);
+        self.src.encode(e);
+    }
+}
+
+impl Encode for TableArg<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.dst.encode(e);
+    }
+}
+
+impl Encode for MemoryArg<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.mem.encode(e);
+    }
+}
+
+impl Encode for MemoryInit<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.data.encode(e);
+        self.mem.encode(e);
+    }
+}
+
+impl Encode for MemoryCopy<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.dst.encode(e);
+        self.src.encode(e);
+    }
+}
+
+impl Encode for BrTableIndices<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.labels.encode(e);
+        self.default.encode(e);
+    }
+}
+
+impl Encode for Float32 {
+    fn encode(&self, e: &mut Vec<u8>) {
+        e.extend_from_slice(&self.bits.to_le_bytes());
+    }
+}
+
+impl Encode for Float64 {
+    fn encode(&self, e: &mut Vec<u8>) {
+        e.extend_from_slice(&self.bits.to_le_bytes());
+    }
+}
+
+#[derive(Default)]
+struct Names<'a> {
+    module: Option<&'a str>,
+    funcs: Vec<(u32, &'a str)>,
+    func_idx: u32,
+    locals: Vec<(u32, Vec<(u32, &'a str)>)>,
+    labels: Vec<(u32, Vec<(u32, &'a str)>)>,
+    globals: Vec<(u32, &'a str)>,
+    global_idx: u32,
+    memories: Vec<(u32, &'a str)>,
+    memory_idx: u32,
+    tables: Vec<(u32, &'a str)>,
+    table_idx: u32,
+    tags: Vec<(u32, &'a str)>,
+    tag_idx: u32,
+    types: Vec<(u32, &'a str)>,
+    type_idx: u32,
+    data: Vec<(u32, &'a str)>,
+    data_idx: u32,
+    elems: Vec<(u32, &'a str)>,
+    elem_idx: u32,
+}
+
+fn find_names<'a>(
+    module_id: &Option<Id<'a>>,
+    module_name: &Option<NameAnnotation<'a>>,
+    fields: &[ModuleField<'a>],
+) -> Names<'a> {
+    fn get_name<'a>(id: &Option<Id<'a>>, name: &Option<NameAnnotation<'a>>) -> Option<&'a str> {
+        name.as_ref().map(|n| n.name).or(id.and_then(|id| {
+            if id.is_gensym() {
+                None
+            } else {
+                Some(id.name())
+            }
+        }))
+    }
+
+    enum Name {
+        Type,
+        Global,
+        Func,
+        Memory,
+        Table,
+        Tag,
+        Elem,
+        Data,
+    }
+
+    let mut ret = Names::default();
+    ret.module = get_name(module_id, module_name);
+    let mut names = Vec::new();
+    for field in fields {
+        // Extract the kind/id/name from whatever kind of field this is...
+        let (kind, id, name) = match field {
+            ModuleField::Import(i) => (
+                match i.item.kind {
+                    ItemKind::Func(_) => Name::Func,
+                    ItemKind::Table(_) => Name::Table,
+                    ItemKind::Memory(_) => Name::Memory,
+                    ItemKind::Global(_) => Name::Global,
+                    ItemKind::Tag(_) => Name::Tag,
+                },
+                &i.item.id,
+                &i.item.name,
+            ),
+            ModuleField::Global(g) => (Name::Global, &g.id, &g.name),
+            ModuleField::Table(t) => (Name::Table, &t.id, &t.name),
+            ModuleField::Memory(m) => (Name::Memory, &m.id, &m.name),
+            ModuleField::Tag(t) => (Name::Tag, &t.id, &t.name),
+            ModuleField::Type(t) => (Name::Type, &t.id, &t.name),
+            ModuleField::Rec(r) => {
+                for ty in &r.types {
+                    names.push((Name::Type, &ty.id, &ty.name, field));
+                }
+                continue;
+            }
+            ModuleField::Elem(e) => (Name::Elem, &e.id, &e.name),
+            ModuleField::Data(d) => (Name::Data, &d.id, &d.name),
+            ModuleField::Func(f) => (Name::Func, &f.id, &f.name),
+            ModuleField::Export(_) | ModuleField::Start(_) | ModuleField::Custom(_) => continue,
+        };
+        names.push((kind, id, name, field));
+    }
+
+    for (kind, id, name, field) in names {
+        // .. and using the kind we can figure out where to place this name
+        let (list, idx) = match kind {
+            Name::Func => (&mut ret.funcs, &mut ret.func_idx),
+            Name::Table => (&mut ret.tables, &mut ret.table_idx),
+            Name::Memory => (&mut ret.memories, &mut ret.memory_idx),
+            Name::Global => (&mut ret.globals, &mut ret.global_idx),
+            Name::Tag => (&mut ret.tags, &mut ret.tag_idx),
+            Name::Type => (&mut ret.types, &mut ret.type_idx),
+            Name::Elem => (&mut ret.elems, &mut ret.elem_idx),
+            Name::Data => (&mut ret.data, &mut ret.data_idx),
+        };
+        if let Some(name) = get_name(id, name) {
+            list.push((*idx, name));
+        }
+
+        // Handle module locals separately from above
+        if let ModuleField::Func(f) = field {
+            let mut local_names = Vec::new();
+            let mut label_names = Vec::new();
+            let mut local_idx = 0;
+            let mut label_idx = 0;
+
+            // Consult the inline type listed for local names of parameters.
+            // This is specifically preserved during the name resolution
+            // pass, but only for functions, so here we can look at the
+            // original source's names.
+            if let Some(ty) = &f.ty.inline {
+                for (id, name, _) in ty.params.iter() {
+                    if let Some(name) = get_name(id, name) {
+                        local_names.push((local_idx, name));
+                    }
+                    local_idx += 1;
+                }
+            }
+            if let FuncKind::Inline {
+                locals, expression, ..
+            } = &f.kind
+            {
+                for local in locals {
+                    if let Some(name) = get_name(&local.id, &local.name) {
+                        local_names.push((local_idx, name));
+                    }
+                    local_idx += 1;
+                }
+
+                for i in expression.instrs.iter() {
+                    match i {
+                        Instruction::If(block)
+                        | Instruction::Block(block)
+                        | Instruction::Loop(block)
+                        | Instruction::Try(block)
+                        | Instruction::Let(LetType { block, .. }) => {
+                            if let Some(name) = get_name(&block.label, &block.label_name) {
+                                label_names.push((label_idx, name));
+                            }
+                            label_idx += 1;
+                        }
+                        _ => {}
+                    }
+                }
+            }
+            if local_names.len() > 0 {
+                ret.locals.push((*idx, local_names));
+            }
+            if label_names.len() > 0 {
+                ret.labels.push((*idx, label_names));
+            }
+        }
+
+        *idx += 1;
+    }
+
+    return ret;
+}
+
+impl Names<'_> {
+    fn is_empty(&self) -> bool {
+        self.module.is_none()
+            && self.funcs.is_empty()
+            && self.locals.is_empty()
+            && self.labels.is_empty()
+            && self.globals.is_empty()
+            && self.memories.is_empty()
+            && self.tables.is_empty()
+            && self.types.is_empty()
+            && self.data.is_empty()
+            && self.elems.is_empty()
+        // NB: specifically don't check tags/modules/instances since they're
+        // not encoded for now.
+    }
+}
+
+impl Encode for Names<'_> {
+    fn encode(&self, dst: &mut Vec<u8>) {
+        let mut tmp = Vec::new();
+
+        let mut subsec = |id: u8, data: &mut Vec<u8>| {
+            dst.push(id);
+            data.encode(dst);
+            data.truncate(0);
+        };
+
+        if let Some(id) = self.module {
+            id.encode(&mut tmp);
+            subsec(0, &mut tmp);
+        }
+        if self.funcs.len() > 0 {
+            self.funcs.encode(&mut tmp);
+            subsec(1, &mut tmp);
+        }
+        if self.locals.len() > 0 {
+            self.locals.encode(&mut tmp);
+            subsec(2, &mut tmp);
+        }
+        if self.labels.len() > 0 {
+            self.labels.encode(&mut tmp);
+            subsec(3, &mut tmp);
+        }
+        if self.types.len() > 0 {
+            self.types.encode(&mut tmp);
+            subsec(4, &mut tmp);
+        }
+        if self.tables.len() > 0 {
+            self.tables.encode(&mut tmp);
+            subsec(5, &mut tmp);
+        }
+        if self.memories.len() > 0 {
+            self.memories.encode(&mut tmp);
+            subsec(6, &mut tmp);
+        }
+        if self.globals.len() > 0 {
+            self.globals.encode(&mut tmp);
+            subsec(7, &mut tmp);
+        }
+        if self.elems.len() > 0 {
+            self.elems.encode(&mut tmp);
+            subsec(8, &mut tmp);
+        }
+        if self.data.len() > 0 {
+            self.data.encode(&mut tmp);
+            subsec(9, &mut tmp);
+        }
+    }
+}
+
+impl Encode for Id<'_> {
+    fn encode(&self, dst: &mut Vec<u8>) {
+        assert!(!self.is_gensym());
+        self.name().encode(dst);
+    }
+}
+
+impl Encode for V128Const {
+    fn encode(&self, dst: &mut Vec<u8>) {
+        dst.extend_from_slice(&self.to_le_bytes());
+    }
+}
+
+impl Encode for I8x16Shuffle {
+    fn encode(&self, dst: &mut Vec<u8>) {
+        dst.extend_from_slice(&self.lanes);
+    }
+}
+
+impl<'a> Encode for SelectTypes<'a> {
+    fn encode(&self, dst: &mut Vec<u8>) {
+        match &self.tys {
+            Some(list) => {
+                dst.push(0x1c);
+                list.encode(dst);
+            }
+            None => dst.push(0x1b),
+        }
+    }
+}
+
+impl Encode for Custom<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        for list in self.data.iter() {
+            e.extend_from_slice(list);
+        }
+    }
+}
+
+impl Encode for Tag<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.ty.encode(e);
+        match &self.kind {
+            TagKind::Inline() => {}
+            _ => panic!("TagKind should be inline during encoding"),
+        }
+    }
+}
+
+impl Encode for TagType<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        match self {
+            TagType::Exception(ty) => {
+                e.push(0x00);
+                ty.encode(e);
+            }
+        }
+    }
+}
+
+impl Encode for StructAccess<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.r#struct.encode(e);
+        self.field.encode(e);
+    }
+}
+
+impl Encode for ArrayFill<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.array.encode(e);
+    }
+}
+
+impl Encode for ArrayCopy<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.dest_array.encode(e);
+        self.src_array.encode(e);
+    }
+}
+
+impl Encode for ArrayInit<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.array.encode(e);
+        self.segment.encode(e);
+    }
+}
+
+impl Encode for ArrayNewFixed<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.array.encode(e);
+        self.length.encode(e);
+    }
+}
+
+impl Encode for ArrayNewData<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.array.encode(e);
+        self.data_idx.encode(e);
+    }
+}
+
+impl Encode for ArrayNewElem<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.array.encode(e);
+        self.elem_idx.encode(e);
+    }
+}
+
+impl Encode for RefTest<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        e.push(0xfb);
+        if self.r#type.nullable {
+            e.push(0x48);
+        } else {
+            e.push(0x40);
+        }
+        self.r#type.heap.encode(e);
+    }
+}
+
+impl Encode for RefCast<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        e.push(0xfb);
+        if self.r#type.nullable {
+            e.push(0x49);
+        } else {
+            e.push(0x41);
+        }
+        self.r#type.heap.encode(e);
+    }
+}
+
+fn br_on_cast_flags(on_fail: bool, from_nullable: bool, to_nullable: bool) -> u8 {
+    let mut flag = 0;
+    if from_nullable {
+        flag |= 1 << 0;
+    }
+    if to_nullable {
+        flag |= 1 << 1;
+    }
+    if on_fail {
+        flag |= 1 << 2;
+    }
+    flag
+}
+
+impl Encode for BrOnCast<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        e.push(0xfb);
+        e.push(0x4f);
+        e.push(br_on_cast_flags(false, self.from_type.nullable, self.to_type.nullable));
+        self.label.encode(e);
+        self.from_type.heap.encode(e);
+        self.to_type.heap.encode(e);
+    }
+}
+
+impl Encode for BrOnCastFail<'_> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        e.push(0xfb);
+        e.push(0x4f);
+        e.push(br_on_cast_flags(true, self.from_type.nullable, self.to_type.nullable));
+        self.label.encode(e);
+        self.from_type.heap.encode(e);
+        self.to_type.heap.encode(e);
+    }
+}
diff --git a/third_party/rust/wast/src/core/custom.rs b/third_party/rust/wast/src/core/custom.rs
new file mode 100644
index 0000000000..40c20b1cc7
--- /dev/null
+++ b/third_party/rust/wast/src/core/custom.rs
@@ -0,0 +1,151 @@
+use crate::parser::{Parse, Parser, Result};
+use crate::token::{self, Span};
+use crate::{annotation, kw};
+
+/// A wasm custom section within a module.
+#[derive(Debug)]
+pub struct Custom<'a> {
+    /// Where this `@custom` was defined.
+    pub span: Span,
+
+    /// Name of the custom section.
+    pub name: &'a str,
+
+    /// Where the custom section is being placed,
+    pub place: CustomPlace,
+
+    /// Payload of this custom section.
+    pub data: Vec<&'a [u8]>,
+}
+
+/// Possible locations to place a custom section within a module.
+#[derive(Debug, PartialEq, Copy, Clone)]
+pub enum CustomPlace {
+    /// This custom section will appear before the first section in the module.
+    BeforeFirst,
+    /// This custom section will be placed just before a known section.
+    Before(CustomPlaceAnchor),
+    /// This custom section will be placed just after a known section.
+    After(CustomPlaceAnchor),
+    /// This custom section will appear after the last section in the module.
+    AfterLast,
+}
+
+/// Known sections that custom sections can be placed relative to.
+#[derive(Debug, PartialEq, Eq, Copy, Clone)]
+#[allow(missing_docs)]
+pub enum CustomPlaceAnchor {
+    Type,
+    Import,
+    Func,
+    Table,
+    Memory,
+    Global,
+    Export,
+    Start,
+    Elem,
+    Code,
+    Data,
+    Tag,
+}
+
+impl<'a> Parse<'a> for Custom<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let span = parser.parse::<annotation::custom>()?.0;
+        let name = parser.parse()?;
+        let place = if parser.peek::<token::LParen>() {
+            parser.parens(|p| p.parse())?
+        } else {
+            CustomPlace::AfterLast
+        };
+        let mut data = Vec::new();
+        while !parser.is_empty() {
+            data.push(parser.parse()?);
+        }
+        Ok(Custom {
+            span,
+            name,
+            place,
+            data,
+        })
+    }
+}
+
+impl<'a> Parse<'a> for CustomPlace {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut l = parser.lookahead1();
+        let ctor = if l.peek::<kw::before>() {
+            parser.parse::<kw::before>()?;
+            if l.peek::<kw::first>() {
+                parser.parse::<kw::first>()?;
+                return Ok(CustomPlace::BeforeFirst);
+            }
+            CustomPlace::Before as fn(CustomPlaceAnchor) -> _
+        } else if l.peek::<kw::after>() {
+            parser.parse::<kw::after>()?;
+            if l.peek::<kw::last>() {
+                parser.parse::<kw::last>()?;
+                return Ok(CustomPlace::AfterLast);
+            }
+            CustomPlace::After
+        } else {
+            return Err(l.error());
+        };
+        Ok(ctor(parser.parse()?))
+    }
+}
+
+impl<'a> Parse<'a> for CustomPlaceAnchor {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        if parser.peek::<kw::r#type>() {
+            parser.parse::<kw::r#type>()?;
+            return Ok(CustomPlaceAnchor::Type);
+        }
+        if parser.peek::<kw::import>() {
+            parser.parse::<kw::import>()?;
+            return Ok(CustomPlaceAnchor::Import);
+        }
+        if parser.peek::<kw::func>() {
+            parser.parse::<kw::func>()?;
+            return Ok(CustomPlaceAnchor::Func);
+        }
+        if parser.peek::<kw::table>() {
+            parser.parse::<kw::table>()?;
+            return Ok(CustomPlaceAnchor::Table);
+        }
+        if parser.peek::<kw::memory>() {
+            parser.parse::<kw::memory>()?;
+            return Ok(CustomPlaceAnchor::Memory);
+        }
+        if parser.peek::<kw::global>() {
+            parser.parse::<kw::global>()?;
+            return Ok(CustomPlaceAnchor::Global);
+        }
+        if parser.peek::<kw::export>() {
+            parser.parse::<kw::export>()?;
+            return Ok(CustomPlaceAnchor::Export);
+        }
+        if parser.peek::<kw::start>() {
+            parser.parse::<kw::start>()?;
+            return Ok(CustomPlaceAnchor::Start);
+        }
+        if parser.peek::<kw::elem>() {
+            parser.parse::<kw::elem>()?;
+            return Ok(CustomPlaceAnchor::Elem);
+        }
+        if parser.peek::<kw::code>() {
+            parser.parse::<kw::code>()?;
+            return Ok(CustomPlaceAnchor::Code);
+        }
+        if parser.peek::<kw::data>() {
+            parser.parse::<kw::data>()?;
+            return Ok(CustomPlaceAnchor::Data);
+        }
+        if parser.peek::<kw::tag>() {
+            parser.parse::<kw::tag>()?;
+            return Ok(CustomPlaceAnchor::Tag);
+        }
+
+        Err(parser.error("expected a valid section name"))
+    }
+}
diff --git a/third_party/rust/wast/src/core/export.rs b/third_party/rust/wast/src/core/export.rs
new file mode 100644
index 0000000000..66354d0546
--- /dev/null
+++ b/third_party/rust/wast/src/core/export.rs
@@ -0,0 +1,146 @@
+use crate::kw;
+use crate::parser::{Cursor, Parse, Parser, Peek, Result};
+use crate::token::{Index, Span};
+
+/// A entry in a WebAssembly module's export section.
+#[derive(Debug)]
+pub struct Export<'a> {
+    /// Where this export was defined.
+    pub span: Span,
+    /// The name of this export from the module.
+    pub name: &'a str,
+    /// The kind of item being exported.
+    pub kind: ExportKind,
+    /// What's being exported from the module.
+    pub item: Index<'a>,
+}
+
+/// Different kinds of elements that can be exported from a WebAssembly module,
+/// contained in an [`Export`].
+#[derive(Debug, Clone, Copy, Hash, Eq, PartialEq)]
+#[allow(missing_docs)]
+pub enum ExportKind {
+    Func,
+    Table,
+    Memory,
+    Global,
+    Tag,
+}
+
+impl<'a> Parse<'a> for Export<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let span = parser.parse::<kw::export>()?.0;
+        let name = parser.parse()?;
+        let (kind, item) = parser.parens(|p| Ok((p.parse()?, p.parse()?)))?;
+        Ok(Export {
+            span,
+            name,
+            kind,
+            item,
+        })
+    }
+}
+
+impl<'a> Parse<'a> for ExportKind {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut l = parser.lookahead1();
+        if l.peek::<kw::func>() {
+            parser.parse::<kw::func>()?;
+            Ok(ExportKind::Func)
+        } else if l.peek::<kw::table>() {
+            parser.parse::<kw::table>()?;
+            Ok(ExportKind::Table)
+        } else if l.peek::<kw::memory>() {
+            parser.parse::<kw::memory>()?;
+            Ok(ExportKind::Memory)
+        } else if l.peek::<kw::global>() {
+            parser.parse::<kw::global>()?;
+            Ok(ExportKind::Global)
+        } else if l.peek::<kw::tag>() {
+            parser.parse::<kw::tag>()?;
+            Ok(ExportKind::Tag)
+        } else {
+            Err(l.error())
+        }
+    }
+}
+
+impl Peek for ExportKind {
+    fn peek(cursor: Cursor<'_>) -> bool {
+        kw::func::peek(cursor)
+            || kw::table::peek(cursor)
+            || kw::memory::peek(cursor)
+            || kw::global::peek(cursor)
+            || kw::tag::peek(cursor)
+    }
+    fn display() -> &'static str {
+        "export kind"
+    }
+}
+
+macro_rules! kw_conversions {
+    ($($kw:ident => $kind:ident)*) => ($(
+        impl From<kw::$kw> for ExportKind {
+            fn from(_: kw::$kw) -> ExportKind {
+                ExportKind::$kind
+            }
+        }
+
+        impl Default for kw::$kw {
+            fn default() -> kw::$kw {
+                kw::$kw(Span::from_offset(0))
+            }
+        }
+    )*);
+}
+
+kw_conversions! {
+    func => Func
+    table => Table
+    global => Global
+    tag => Tag
+    memory => Memory
+}
+
+/// A listing of inline `(export "foo")` statements on a WebAssembly item in
+/// its textual format.
+#[derive(Debug, Default)]
+pub struct InlineExport<'a> {
+    /// The extra names to export an item as, if any.
+    pub names: Vec<&'a str>,
+}
+
+impl<'a> Parse<'a> for InlineExport<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut names = Vec::new();
+        while parser.peek::<Self>() {
+            names.push(parser.parens(|p| {
+                p.parse::<kw::export>()?;
+                p.parse::<&str>()
+            })?);
+        }
+        Ok(InlineExport { names })
+    }
+}
+
+impl Peek for InlineExport<'_> {
+    fn peek(cursor: Cursor<'_>) -> bool {
+        let cursor = match cursor.lparen() {
+            Some(cursor) => cursor,
+            None => return false,
+        };
+        let cursor = match cursor.keyword() {
+            Some(("export", cursor)) => cursor,
+            _ => return false,
+        };
+        let cursor = match cursor.string() {
+            Some((_, cursor)) => cursor,
+            None => return false,
+        };
+        cursor.rparen().is_some()
+    }
+
+    fn display() -> &'static str {
+        "inline export"
+    }
+}
diff --git a/third_party/rust/wast/src/core/expr.rs b/third_party/rust/wast/src/core/expr.rs
new file mode 100644
index 0000000000..14d309fc0d
--- /dev/null
+++ b/third_party/rust/wast/src/core/expr.rs
@@ -0,0 +1,1960 @@
+use crate::core::*;
+use crate::encode::Encode;
+use crate::kw;
+use crate::parser::{Cursor, Parse, Parser, Result};
+use crate::token::*;
+use std::mem;
+
+/// An expression, or a list of instructions, in the WebAssembly text format.
+///
+/// This expression type will parse s-expression-folded instructions into a flat
+/// list of instructions for emission later on. The implicit `end` instruction
+/// at the end of an expression is not included in the `instrs` field.
+#[derive(Debug)]
+#[allow(missing_docs)]
+pub struct Expression<'a> {
+    pub instrs: Box<[Instruction<'a>]>,
+}
+
+impl<'a> Parse<'a> for Expression<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut exprs = ExpressionParser::default();
+        exprs.parse(parser)?;
+        Ok(Expression {
+            instrs: exprs.instrs.into(),
+        })
+    }
+}
+
+/// Helper struct used to parse an `Expression` with helper methods and such.
+///
+/// The primary purpose of this is to avoid defining expression parsing as a
+/// call-thread-stack recursive function. Since we're parsing user input that
+/// runs the risk of blowing the call stack, so we want to be sure to use a heap
+/// stack structure wherever possible.
+#[derive(Default)]
+struct ExpressionParser<'a> {
+    /// The flat list of instructions that we've parsed so far, and will
+    /// eventually become the final `Expression`.
+    instrs: Vec<Instruction<'a>>,
+
+    /// Descriptor of all our nested s-expr blocks. This only happens when
+    /// instructions themselves are nested.
+    stack: Vec<Level<'a>>,
+}
+
+enum Paren {
+    None,
+    Left,
+    Right,
+}
+
+/// A "kind" of nested block that we can be parsing inside of.
+enum Level<'a> {
+    /// This is a normal `block` or `loop` or similar, where the instruction
+    /// payload here is pushed when the block is exited.
+    EndWith(Instruction<'a>),
+
+    /// This is a pretty special variant which means that we're parsing an `if`
+    /// statement, and the state of the `if` parsing is tracked internally in
+    /// the payload.
+    If(If<'a>),
+
+    /// This means we're either parsing inside of `(then ...)` or `(else ...)`
+    /// which don't correspond to terminating instructions, we're just in a
+    /// nested block.
+    IfArm,
+
+    /// Similar to `If` but for `Try` statements, which has simpler parsing
+    /// state to track.
+    Try(Try<'a>),
+
+    /// Similar to `IfArm` but for `(do ...)` and `(catch ...)` blocks.
+    TryArm,
+}
+
+/// Possible states of "what should be parsed next?" in an `if` expression.
+enum If<'a> {
+    /// Only the `if` has been parsed, next thing to parse is the clause, if
+    /// any, of the `if` instruction.
+    Clause(Instruction<'a>),
+    /// Next thing to parse is the `then` block
+    Then(Instruction<'a>),
+    /// Next thing to parse is the `else` block
+    Else,
+    /// This `if` statement has finished parsing and if anything remains it's a
+    /// syntax error.
+    End,
+}
+
+/// Possible state of "what should be parsed next?" in a `try` expression.
+enum Try<'a> {
+    /// Next thing to parse is the `do` block.
+    Do(Instruction<'a>),
+    /// Next thing to parse is `catch`/`catch_all`, or `delegate`.
+    CatchOrDelegate,
+    /// Next thing to parse is a `catch` block or `catch_all`.
+    Catch,
+    /// Finished parsing like the `End` case, but does not push `end` opcode.
+    Delegate,
+    /// This `try` statement has finished parsing and if anything remains it's a
+    /// syntax error.
+    End,
+}
+
+impl<'a> ExpressionParser<'a> {
+    fn parse(&mut self, parser: Parser<'a>) -> Result<()> {
+        // Here we parse instructions in a loop, and we do not recursively
+        // invoke this parse function to avoid blowing the stack on
+        // deeply-recursive parses.
+        //
+        // Our loop generally only finishes once there's no more input left int
+        // the `parser`. If there's some unclosed delimiters though (on our
+        // `stack`), then we also keep parsing to generate error messages if
+        // there's no input left.
+        while !parser.is_empty() || !self.stack.is_empty() {
+            // As a small ease-of-life adjustment here, if we're parsing inside
+            // of an `if block then we require that all sub-components are
+            // s-expressions surrounded by `(` and `)`, so verify that here.
+            if let Some(Level::If(_)) | Some(Level::Try(_)) = self.stack.last() {
+                if !parser.is_empty() && !parser.peek::<LParen>() {
+                    return Err(parser.error("expected `(`"));
+                }
+            }
+
+            match self.paren(parser)? {
+                // No parenthesis seen? Then we just parse the next instruction
+                // and move on.
+                Paren::None => self.instrs.push(parser.parse()?),
+
+                // If we see a left-parenthesis then things are a little
+                // special. We handle block-like instructions specially
+                // (`block`, `loop`, and `if`), and otherwise all other
+                // instructions simply get appended once we reach the end of the
+                // s-expression.
+                //
+                // In all cases here we push something onto the `stack` to get
+                // popped when the `)` character is seen.
+                Paren::Left => {
+                    // First up is handling `if` parsing, which is funky in a
+                    // whole bunch of ways. See the method internally for more
+                    // information.
+                    if self.handle_if_lparen(parser)? {
+                        continue;
+                    }
+                    // Second, we handle `try` parsing, which is simpler than
+                    // `if` but more complicated than, e.g., `block`.
+                    if self.handle_try_lparen(parser)? {
+                        continue;
+                    }
+                    match parser.parse()? {
+                        // If block/loop show up then we just need to be sure to
+                        // push an `end` instruction whenever the `)` token is
+                        // seen
+                        i @ Instruction::Block(_)
+                        | i @ Instruction::Loop(_)
+                        | i @ Instruction::Let(_) => {
+                            self.instrs.push(i);
+                            self.stack.push(Level::EndWith(Instruction::End(None)));
+                        }
+
+                        // Parsing an `if` instruction is super tricky, so we
+                        // push an `If` scope and we let all our scope-based
+                        // parsing handle the remaining items.
+                        i @ Instruction::If(_) => {
+                            self.stack.push(Level::If(If::Clause(i)));
+                        }
+
+                        // Parsing a `try` is easier than `if` but we also push
+                        // a `Try` scope to handle the required nested blocks.
+                        i @ Instruction::Try(_) => {
+                            self.stack.push(Level::Try(Try::Do(i)));
+                        }
+
+                        // Anything else means that we're parsing a nested form
+                        // such as `(i32.add ...)` which means that the
+                        // instruction we parsed will be coming at the end.
+                        other => self.stack.push(Level::EndWith(other)),
+                    }
+                }
+
+                // If we registered a `)` token as being seen, then we're
+                // guaranteed there's an item in the `stack` stack for us to
+                // pop. We peel that off and take a look at what it says to do.
+                Paren::Right => match self.stack.pop().unwrap() {
+                    Level::EndWith(i) => self.instrs.push(i),
+                    Level::IfArm => {}
+                    Level::TryArm => {}
+
+                    // If an `if` statement hasn't parsed the clause or `then`
+                    // block, then that's an error because there weren't enough
+                    // items in the `if` statement. Otherwise we're just careful
+                    // to terminate with an `end` instruction.
+                    Level::If(If::Clause(_)) => {
+                        return Err(parser.error("previous `if` had no clause"));
+                    }
+                    Level::If(If::Then(_)) => {
+                        return Err(parser.error("previous `if` had no `then`"));
+                    }
+                    Level::If(_) => {
+                        self.instrs.push(Instruction::End(None));
+                    }
+
+                    // The `do` clause is required in a `try` statement, so
+                    // we will signal that error here. Otherwise, terminate with
+                    // an `end` or `delegate` instruction.
+                    Level::Try(Try::Do(_)) => {
+                        return Err(parser.error("previous `try` had no `do`"));
+                    }
+                    Level::Try(Try::Delegate) => {}
+                    Level::Try(_) => {
+                        self.instrs.push(Instruction::End(None));
+                    }
+                },
+            }
+        }
+
+        Ok(())
+    }
+
+    /// Parses either `(`, `)`, or nothing.
+    fn paren(&self, parser: Parser<'a>) -> Result<Paren> {
+        parser.step(|cursor| {
+            Ok(match cursor.lparen() {
+                Some(rest) => (Paren::Left, rest),
+                None if self.stack.is_empty() => (Paren::None, cursor),
+                None => match cursor.rparen() {
+                    Some(rest) => (Paren::Right, rest),
+                    None => (Paren::None, cursor),
+                },
+            })
+        })
+    }
+
+    /// Handles all parsing of an `if` statement.
+    ///
+    /// The syntactical form of an `if` stament looks like:
+    ///
+    /// ```wat
+    /// (if $clause (then $then) (else $else))
+    /// ```
+    ///
+    /// but it turns out we practically see a few things in the wild:
+    ///
+    /// * inside the `(if ...)` every sub-thing is surrounded by parens
+    /// * The `then` and `else` keywords are optional
+    /// * The `$then` and `$else` blocks don't need to be surrounded by parens
+    ///
+    /// That's all attempted to be handled here. The part about all sub-parts
+    /// being surrounded by `(` and `)` means that we hook into the `LParen`
+    /// parsing above to call this method there unconditionally.
+    ///
+    /// Returns `true` if the rest of the arm above should be skipped, or
+    /// `false` if we should parse the next item as an instruction (because we
+    /// didn't handle the lparen here).
+    fn handle_if_lparen(&mut self, parser: Parser<'a>) -> Result<bool> {
+        // Only execute the code below if there's an `If` listed last.
+        let i = match self.stack.last_mut() {
+            Some(Level::If(i)) => i,
+            _ => return Ok(false),
+        };
+
+        // The first thing parsed in an `if` statement is the clause. If the
+        // clause starts with `then`, however, then we know to skip the clause
+        // and fall through to below.
+        if let If::Clause(if_instr) = i {
+            let instr = mem::replace(if_instr, Instruction::End(None));
+            *i = If::Then(instr);
+            if !parser.peek::<kw::then>() {
+                return Ok(false);
+            }
+        }
+
+        // All `if` statements are required to have a `then`. This is either the
+        // second s-expr (with or without a leading `then`) or the first s-expr
+        // with a leading `then`. The optionality of `then` isn't strictly what
+        // the text spec says but it matches wabt for now.
+        //
+        // Note that when we see the `then`, that's when we actually add the
+        // original `if` instruction to the stream.
+        if let If::Then(if_instr) = i {
+            let instr = mem::replace(if_instr, Instruction::End(None));
+            self.instrs.push(instr);
+            *i = If::Else;
+            if parser.parse::<Option<kw::then>>()?.is_some() {
+                self.stack.push(Level::IfArm);
+                return Ok(true);
+            }
+            return Ok(false);
+        }
+
+        // effectively the same as the `then` parsing above
+        if let If::Else = i {
+            self.instrs.push(Instruction::Else(None));
+            if parser.parse::<Option<kw::r#else>>()?.is_some() {
+                if parser.is_empty() {
+                    self.instrs.pop();
+                }
+                self.stack.push(Level::IfArm);
+                return Ok(true);
+            }
+            *i = If::End;
+            return Ok(false);
+        }
+
+        // If we made it this far then we're at `If::End` which means that there
+        // were too many s-expressions inside the `(if)` and we don't want to
+        // parse anything else.
+        Err(parser.error("unexpected token: too many payloads inside of `(if)`"))
+    }
+
+    /// Handles parsing of a `try` statement. A `try` statement is simpler
+    /// than an `if` as the syntactic form is:
+    ///
+    /// ```wat
+    /// (try (do $do) (catch $tag $catch))
+    /// ```
+    ///
+    /// where the `do` and `catch` keywords are mandatory, even for an empty
+    /// $do or $catch.
+    ///
+    /// Returns `true` if the rest of the arm above should be skipped, or
+    /// `false` if we should parse the next item as an instruction (because we
+    /// didn't handle the lparen here).
+    fn handle_try_lparen(&mut self, parser: Parser<'a>) -> Result<bool> {
+        // Only execute the code below if there's a `Try` listed last.
+        let i = match self.stack.last_mut() {
+            Some(Level::Try(i)) => i,
+            _ => return Ok(false),
+        };
+
+        // Try statements must start with a `do` block.
+        if let Try::Do(try_instr) = i {
+            let instr = mem::replace(try_instr, Instruction::End(None));
+            self.instrs.push(instr);
+            if parser.parse::<Option<kw::r#do>>()?.is_some() {
+                // The state is advanced here only if the parse succeeds in
+                // order to strictly require the keyword.
+                *i = Try::CatchOrDelegate;
+                self.stack.push(Level::TryArm);
+                return Ok(true);
+            }
+            // We return here and continue parsing instead of raising an error
+            // immediately because the missing keyword will be caught more
+            // generally in the `Paren::Right` case in `parse`.
+            return Ok(false);
+        }
+
+        // After a try's `do`, there are several possible kinds of handlers.
+        if let Try::CatchOrDelegate = i {
+            // `catch` may be followed by more `catch`s or `catch_all`.
+            if parser.parse::<Option<kw::catch>>()?.is_some() {
+                let evt = parser.parse::<Index<'a>>()?;
+                self.instrs.push(Instruction::Catch(evt));
+                *i = Try::Catch;
+                self.stack.push(Level::TryArm);
+                return Ok(true);
+            }
+            // `catch_all` can only come at the end and has no argument.
+            if parser.parse::<Option<kw::catch_all>>()?.is_some() {
+                self.instrs.push(Instruction::CatchAll);
+                *i = Try::End;
+                self.stack.push(Level::TryArm);
+                return Ok(true);
+            }
+            // `delegate` has an index, and also ends the block like `end`.
+            if parser.parse::<Option<kw::delegate>>()?.is_some() {
+                let depth = parser.parse::<Index<'a>>()?;
+                self.instrs.push(Instruction::Delegate(depth));
+                *i = Try::Delegate;
+                match self.paren(parser)? {
+                    Paren::Left | Paren::None => return Ok(false),
+                    Paren::Right => return Ok(true),
+                }
+            }
+            return Err(parser.error("expected a `catch`, `catch_all`, or `delegate`"));
+        }
+
+        if let Try::Catch = i {
+            if parser.parse::<Option<kw::catch>>()?.is_some() {
+                let evt = parser.parse::<Index<'a>>()?;
+                self.instrs.push(Instruction::Catch(evt));
+                *i = Try::Catch;
+                self.stack.push(Level::TryArm);
+                return Ok(true);
+            }
+            if parser.parse::<Option<kw::catch_all>>()?.is_some() {
+                self.instrs.push(Instruction::CatchAll);
+                *i = Try::End;
+                self.stack.push(Level::TryArm);
+                return Ok(true);
+            }
+            return Err(parser.error("unexpected items after `catch`"));
+        }
+
+        Err(parser.error("unexpected token: too many payloads inside of `(try)`"))
+    }
+}
+
+// TODO: document this obscenity
+macro_rules! instructions {
+    (pub enum Instruction<'a> {
+        $(
+            $(#[$doc:meta])*
+            $name:ident $(($($arg:tt)*))? : [$($binary:tt)*] : $instr:tt $( | $deprecated:tt )?,
+        )*
+    }) => (
+        /// A listing of all WebAssembly instructions that can be in a module
+        /// that this crate currently parses.
+        #[derive(Debug)]
+        #[allow(missing_docs)]
+        pub enum Instruction<'a> {
+            $(
+                $(#[$doc])*
+                $name $(( instructions!(@ty $($arg)*) ))?,
+            )*
+        }
+
+        #[allow(non_snake_case)]
+        impl<'a> Parse<'a> for Instruction<'a> {
+            fn parse(parser: Parser<'a>) -> Result<Self> {
+                $(
+                    fn $name<'a>(_parser: Parser<'a>) -> Result<Instruction<'a>> {
+                        Ok(Instruction::$name $((
+                            instructions!(@parse _parser $($arg)*)?
+                        ))?)
+                    }
+                )*
+                let parse_remainder = parser.step(|c| {
+                    let (kw, rest) = match c.keyword() {
+                        Some(pair) => pair,
+                        None => return Err(c.error("expected an instruction")),
+                    };
+                    match kw {
+                        $($instr $( | $deprecated )?=> Ok(($name as fn(_) -> _, rest)),)*
+                        _ => return Err(c.error("unknown operator or unexpected token")),
+                    }
+                })?;
+                parse_remainder(parser)
+            }
+        }
+
+        impl Encode for Instruction<'_> {
+            #[allow(non_snake_case)]
+            fn encode(&self, v: &mut Vec<u8>) {
+                match self {
+                    $(
+                        Instruction::$name $((instructions!(@first x $($arg)*)))? => {
+                            fn encode<'a>($(arg: &instructions!(@ty $($arg)*),)? v: &mut Vec<u8>) {
+                                instructions!(@encode v $($binary)*);
+                                $(<instructions!(@ty $($arg)*) as Encode>::encode(arg, v);)?
+                            }
+                            encode($( instructions!(@first x $($arg)*), )? v)
+                        }
+                    )*
+                }
+            }
+        }
+
+        impl<'a> Instruction<'a> {
+            /// Returns the associated [`MemArg`] if one is available for this
+            /// instruction.
+            #[allow(unused_variables, non_snake_case)]
+            pub fn memarg_mut(&mut self) -> Option<&mut MemArg<'a>> {
+                match self {
+                    $(
+                        Instruction::$name $((instructions!(@memarg_binding a $($arg)*)))? => {
+                            instructions!(@get_memarg a $($($arg)*)?)
+                        }
+                    )*
+                }
+            }
+        }
+    );
+
+    (@ty MemArg<$amt:tt>) => (MemArg<'a>);
+    (@ty LoadOrStoreLane<$amt:tt>) => (LoadOrStoreLane<'a>);
+    (@ty $other:ty) => ($other);
+
+    (@first $first:ident $($t:tt)*) => ($first);
+
+    (@parse $parser:ident MemArg<$amt:tt>) => (MemArg::parse($parser, $amt));
+    (@parse $parser:ident MemArg) => (compile_error!("must specify `MemArg` default"));
+    (@parse $parser:ident LoadOrStoreLane<$amt:tt>) => (LoadOrStoreLane::parse($parser, $amt));
+    (@parse $parser:ident LoadOrStoreLane) => (compile_error!("must specify `LoadOrStoreLane` default"));
+    (@parse $parser:ident $other:ty) => ($parser.parse::<$other>());
+
+    // simd opcodes prefixed with `0xfd` get a varuint32 encoding for their payload
+    (@encode $dst:ident 0xfd, $simd:tt) => ({
+        $dst.push(0xfd);
+        <u32 as Encode>::encode(&$simd, $dst);
+    });
+    (@encode $dst:ident $($bytes:tt)*) => ($dst.extend_from_slice(&[$($bytes)*]););
+
+    (@get_memarg $name:ident MemArg<$amt:tt>) => (Some($name));
+    (@get_memarg $name:ident LoadOrStoreLane<$amt:tt>) => (Some(&mut $name.memarg));
+    (@get_memarg $($other:tt)*) => (None);
+
+    (@memarg_binding $name:ident MemArg<$amt:tt>) => ($name);
+    (@memarg_binding $name:ident LoadOrStoreLane<$amt:tt>) => ($name);
+    (@memarg_binding $name:ident $other:ty) => (_);
+}
+
+instructions! {
+    pub enum Instruction<'a> {
+        Block(BlockType<'a>) : [0x02] : "block",
+        If(BlockType<'a>) : [0x04] : "if",
+        Else(Option<Id<'a>>) : [0x05] : "else",
+        Loop(BlockType<'a>) : [0x03] : "loop",
+        End(Option<Id<'a>>) : [0x0b] : "end",
+
+        Unreachable : [0x00] : "unreachable",
+        Nop : [0x01] : "nop",
+        Br(Index<'a>) : [0x0c] : "br",
+        BrIf(Index<'a>) : [0x0d] : "br_if",
+        BrTable(BrTableIndices<'a>) : [0x0e] : "br_table",
+        Return : [0x0f] : "return",
+        Call(Index<'a>) : [0x10] : "call",
+        CallIndirect(CallIndirect<'a>) : [0x11] : "call_indirect",
+
+        // tail-call proposal
+        ReturnCall(Index<'a>) : [0x12] : "return_call",
+        ReturnCallIndirect(CallIndirect<'a>) : [0x13] : "return_call_indirect",
+
+        // function-references proposal
+        CallRef(HeapType<'a>) : [0x14] : "call_ref",
+        ReturnCallRef(HeapType<'a>) : [0x15] : "return_call_ref",
+        FuncBind(FuncBindType<'a>) : [0x16] : "func.bind",
+        Let(LetType<'a>) : [0x17] : "let",
+
+        Drop : [0x1a] : "drop",
+        Select(SelectTypes<'a>) : [] : "select",
+        LocalGet(Index<'a>) : [0x20] : "local.get" | "get_local",
+        LocalSet(Index<'a>) : [0x21] : "local.set" | "set_local",
+        LocalTee(Index<'a>) : [0x22] : "local.tee" | "tee_local",
+        GlobalGet(Index<'a>) : [0x23] : "global.get" | "get_global",
+        GlobalSet(Index<'a>) : [0x24] : "global.set" | "set_global",
+
+        TableGet(TableArg<'a>) : [0x25] : "table.get",
+        TableSet(TableArg<'a>) : [0x26] : "table.set",
+
+        I32Load(MemArg<4>) : [0x28] : "i32.load",
+        I64Load(MemArg<8>) : [0x29] : "i64.load",
+        F32Load(MemArg<4>) : [0x2a] : "f32.load",
+        F64Load(MemArg<8>) : [0x2b] : "f64.load",
+        I32Load8s(MemArg<1>) : [0x2c] : "i32.load8_s",
+        I32Load8u(MemArg<1>) : [0x2d] : "i32.load8_u",
+        I32Load16s(MemArg<2>) : [0x2e] : "i32.load16_s",
+        I32Load16u(MemArg<2>) : [0x2f] : "i32.load16_u",
+        I64Load8s(MemArg<1>) : [0x30] : "i64.load8_s",
+        I64Load8u(MemArg<1>) : [0x31] : "i64.load8_u",
+        I64Load16s(MemArg<2>) : [0x32] : "i64.load16_s",
+        I64Load16u(MemArg<2>) : [0x33] : "i64.load16_u",
+        I64Load32s(MemArg<4>) : [0x34] : "i64.load32_s",
+        I64Load32u(MemArg<4>) : [0x35] : "i64.load32_u",
+        I32Store(MemArg<4>) : [0x36] : "i32.store",
+        I64Store(MemArg<8>) : [0x37] : "i64.store",
+        F32Store(MemArg<4>) : [0x38] : "f32.store",
+        F64Store(MemArg<8>) : [0x39] : "f64.store",
+        I32Store8(MemArg<1>) : [0x3a] : "i32.store8",
+        I32Store16(MemArg<2>) : [0x3b] : "i32.store16",
+        I64Store8(MemArg<1>) : [0x3c] : "i64.store8",
+        I64Store16(MemArg<2>) : [0x3d] : "i64.store16",
+        I64Store32(MemArg<4>) : [0x3e] : "i64.store32",
+
+        // Lots of bulk memory proposal here as well
+        MemorySize(MemoryArg<'a>) : [0x3f] : "memory.size" | "current_memory",
+        MemoryGrow(MemoryArg<'a>) : [0x40] : "memory.grow" | "grow_memory",
+        MemoryInit(MemoryInit<'a>) : [0xfc, 0x08] : "memory.init",
+        MemoryCopy(MemoryCopy<'a>) : [0xfc, 0x0a] : "memory.copy",
+        MemoryFill(MemoryArg<'a>) : [0xfc, 0x0b] : "memory.fill",
+        MemoryDiscard(MemoryArg<'a>) : [0xfc, 0x12] : "memory.discard",
+        DataDrop(Index<'a>) : [0xfc, 0x09] : "data.drop",
+        ElemDrop(Index<'a>) : [0xfc, 0x0d] : "elem.drop",
+        TableInit(TableInit<'a>) : [0xfc, 0x0c] : "table.init",
+        TableCopy(TableCopy<'a>) : [0xfc, 0x0e] : "table.copy",
+        TableFill(TableArg<'a>) : [0xfc, 0x11] : "table.fill",
+        TableSize(TableArg<'a>) : [0xfc, 0x10] : "table.size",
+        TableGrow(TableArg<'a>) : [0xfc, 0x0f] : "table.grow",
+
+        RefNull(HeapType<'a>) : [0xd0] : "ref.null",
+        RefIsNull : [0xd1] : "ref.is_null",
+        RefFunc(Index<'a>) : [0xd2] : "ref.func",
+
+        // function-references proposal
+        RefAsNonNull : [0xd3] : "ref.as_non_null",
+        BrOnNull(Index<'a>) : [0xd4] : "br_on_null",
+        BrOnNonNull(Index<'a>) : [0xd6] : "br_on_non_null",
+
+        // gc proposal: eqref
+        RefEq : [0xd5] : "ref.eq",
+
+        // gc proposal: struct
+        StructNew(Index<'a>) : [0xfb, 0x07] : "struct.new",
+        StructNewDefault(Index<'a>) : [0xfb, 0x08] : "struct.new_default",
+        StructGet(StructAccess<'a>) : [0xfb, 0x03] : "struct.get",
+        StructGetS(StructAccess<'a>) : [0xfb, 0x04] : "struct.get_s",
+        StructGetU(StructAccess<'a>) : [0xfb, 0x05] : "struct.get_u",
+        StructSet(StructAccess<'a>) : [0xfb, 0x06] : "struct.set",
+
+        // gc proposal: array
+        ArrayNew(Index<'a>) : [0xfb, 0x1b] : "array.new",
+        ArrayNewDefault(Index<'a>) : [0xfb, 0x1c] : "array.new_default",
+        ArrayNewFixed(ArrayNewFixed<'a>) : [0xfb, 0x1a] : "array.new_fixed",
+        ArrayNewData(ArrayNewData<'a>) : [0xfb, 0x1d] : "array.new_data",
+        ArrayNewElem(ArrayNewElem<'a>) : [0xfb, 0x1f] : "array.new_elem",
+        ArrayGet(Index<'a>) : [0xfb, 0x13] : "array.get",
+        ArrayGetS(Index<'a>) : [0xfb, 0x14] : "array.get_s",
+        ArrayGetU(Index<'a>) : [0xfb, 0x15] : "array.get_u",
+        ArraySet(Index<'a>) : [0xfb, 0x16] : "array.set",
+        ArrayLen : [0xfb, 0x19] : "array.len",
+        ArrayFill(ArrayFill<'a>) : [0xfb, 0x0f] : "array.fill",
+        ArrayCopy(ArrayCopy<'a>) : [0xfb, 0x18] : "array.copy",
+        ArrayInitData(ArrayInit<'a>) : [0xfb, 0x54] : "array.init_data",
+        ArrayInitElem(ArrayInit<'a>) : [0xfb, 0x55] : "array.init_elem",
+
+        // gc proposal, i31
+        I31New : [0xfb, 0x20] : "i31.new",
+        I31GetS : [0xfb, 0x21] : "i31.get_s",
+        I31GetU : [0xfb, 0x22] : "i31.get_u",
+
+        // gc proposal, concrete casting
+        RefTest(RefTest<'a>) : [] : "ref.test",
+        RefCast(RefCast<'a>) : [] : "ref.cast",
+        BrOnCast(BrOnCast<'a>) : [] : "br_on_cast",
+        BrOnCastFail(BrOnCastFail<'a>) : [] : "br_on_cast_fail",
+
+        // gc proposal extern/any coercion operations
+        ExternInternalize : [0xfb, 0x70] : "extern.internalize",
+        ExternExternalize : [0xfb, 0x71] : "extern.externalize",
+
+        I32Const(i32) : [0x41] : "i32.const",
+        I64Const(i64) : [0x42] : "i64.const",
+        F32Const(Float32) : [0x43] : "f32.const",
+        F64Const(Float64) : [0x44] : "f64.const",
+
+        I32Clz : [0x67] : "i32.clz",
+        I32Ctz : [0x68] : "i32.ctz",
+        I32Popcnt : [0x69] : "i32.popcnt",
+        I32Add : [0x6a] : "i32.add",
+        I32Sub : [0x6b] : "i32.sub",
+        I32Mul : [0x6c] : "i32.mul",
+        I32DivS : [0x6d] : "i32.div_s",
+        I32DivU : [0x6e] : "i32.div_u",
+        I32RemS : [0x6f] : "i32.rem_s",
+        I32RemU : [0x70] : "i32.rem_u",
+        I32And : [0x71] : "i32.and",
+        I32Or : [0x72] : "i32.or",
+        I32Xor : [0x73] : "i32.xor",
+        I32Shl : [0x74] : "i32.shl",
+        I32ShrS : [0x75] : "i32.shr_s",
+        I32ShrU : [0x76] : "i32.shr_u",
+        I32Rotl : [0x77] : "i32.rotl",
+        I32Rotr : [0x78] : "i32.rotr",
+
+        I64Clz : [0x79] : "i64.clz",
+        I64Ctz : [0x7a] : "i64.ctz",
+        I64Popcnt : [0x7b] : "i64.popcnt",
+        I64Add : [0x7c] : "i64.add",
+        I64Sub : [0x7d] : "i64.sub",
+        I64Mul : [0x7e] : "i64.mul",
+        I64DivS : [0x7f] : "i64.div_s",
+        I64DivU : [0x80] : "i64.div_u",
+        I64RemS : [0x81] : "i64.rem_s",
+        I64RemU : [0x82] : "i64.rem_u",
+        I64And : [0x83] : "i64.and",
+        I64Or : [0x84] : "i64.or",
+        I64Xor : [0x85] : "i64.xor",
+        I64Shl : [0x86] : "i64.shl",
+        I64ShrS : [0x87] : "i64.shr_s",
+        I64ShrU : [0x88] : "i64.shr_u",
+        I64Rotl : [0x89] : "i64.rotl",
+        I64Rotr : [0x8a] : "i64.rotr",
+
+        F32Abs : [0x8b] : "f32.abs",
+        F32Neg : [0x8c] : "f32.neg",
+        F32Ceil : [0x8d] : "f32.ceil",
+        F32Floor : [0x8e] : "f32.floor",
+        F32Trunc : [0x8f] : "f32.trunc",
+        F32Nearest : [0x90] : "f32.nearest",
+        F32Sqrt : [0x91] : "f32.sqrt",
+        F32Add : [0x92] : "f32.add",
+        F32Sub : [0x93] : "f32.sub",
+        F32Mul : [0x94] : "f32.mul",
+        F32Div : [0x95] : "f32.div",
+        F32Min : [0x96] : "f32.min",
+        F32Max : [0x97] : "f32.max",
+        F32Copysign : [0x98] : "f32.copysign",
+
+        F64Abs : [0x99] : "f64.abs",
+        F64Neg : [0x9a] : "f64.neg",
+        F64Ceil : [0x9b] : "f64.ceil",
+        F64Floor : [0x9c] : "f64.floor",
+        F64Trunc : [0x9d] : "f64.trunc",
+        F64Nearest : [0x9e] : "f64.nearest",
+        F64Sqrt : [0x9f] : "f64.sqrt",
+        F64Add : [0xa0] : "f64.add",
+        F64Sub : [0xa1] : "f64.sub",
+        F64Mul : [0xa2] : "f64.mul",
+        F64Div : [0xa3] : "f64.div",
+        F64Min : [0xa4] : "f64.min",
+        F64Max : [0xa5] : "f64.max",
+        F64Copysign : [0xa6] : "f64.copysign",
+
+        I32Eqz : [0x45] : "i32.eqz",
+        I32Eq : [0x46] : "i32.eq",
+        I32Ne : [0x47] : "i32.ne",
+        I32LtS : [0x48] : "i32.lt_s",
+        I32LtU : [0x49] : "i32.lt_u",
+        I32GtS : [0x4a] : "i32.gt_s",
+        I32GtU : [0x4b] : "i32.gt_u",
+        I32LeS : [0x4c] : "i32.le_s",
+        I32LeU : [0x4d] : "i32.le_u",
+        I32GeS : [0x4e] : "i32.ge_s",
+        I32GeU : [0x4f] : "i32.ge_u",
+
+        I64Eqz : [0x50] : "i64.eqz",
+        I64Eq : [0x51] : "i64.eq",
+        I64Ne : [0x52] : "i64.ne",
+        I64LtS : [0x53] : "i64.lt_s",
+        I64LtU : [0x54] : "i64.lt_u",
+        I64GtS : [0x55] : "i64.gt_s",
+        I64GtU : [0x56] : "i64.gt_u",
+        I64LeS : [0x57] : "i64.le_s",
+        I64LeU : [0x58] : "i64.le_u",
+        I64GeS : [0x59] : "i64.ge_s",
+        I64GeU : [0x5a] : "i64.ge_u",
+
+        F32Eq : [0x5b] : "f32.eq",
+        F32Ne : [0x5c] : "f32.ne",
+        F32Lt : [0x5d] : "f32.lt",
+        F32Gt : [0x5e] : "f32.gt",
+        F32Le : [0x5f] : "f32.le",
+        F32Ge : [0x60] : "f32.ge",
+
+        F64Eq : [0x61] : "f64.eq",
+        F64Ne : [0x62] : "f64.ne",
+        F64Lt : [0x63] : "f64.lt",
+        F64Gt : [0x64] : "f64.gt",
+        F64Le : [0x65] : "f64.le",
+        F64Ge : [0x66] : "f64.ge",
+
+        I32WrapI64 : [0xa7] : "i32.wrap_i64" | "i32.wrap/i64",
+        I32TruncF32S : [0xa8] : "i32.trunc_f32_s" | "i32.trunc_s/f32",
+        I32TruncF32U : [0xa9] : "i32.trunc_f32_u" | "i32.trunc_u/f32",
+        I32TruncF64S : [0xaa] : "i32.trunc_f64_s" | "i32.trunc_s/f64",
+        I32TruncF64U : [0xab] : "i32.trunc_f64_u" | "i32.trunc_u/f64",
+        I64ExtendI32S : [0xac] : "i64.extend_i32_s" | "i64.extend_s/i32",
+        I64ExtendI32U : [0xad] : "i64.extend_i32_u" | "i64.extend_u/i32",
+        I64TruncF32S : [0xae] : "i64.trunc_f32_s" | "i64.trunc_s/f32",
+        I64TruncF32U : [0xaf] : "i64.trunc_f32_u" | "i64.trunc_u/f32",
+        I64TruncF64S : [0xb0] : "i64.trunc_f64_s" | "i64.trunc_s/f64",
+        I64TruncF64U : [0xb1] : "i64.trunc_f64_u" | "i64.trunc_u/f64",
+        F32ConvertI32S : [0xb2] : "f32.convert_i32_s" | "f32.convert_s/i32",
+        F32ConvertI32U : [0xb3] : "f32.convert_i32_u" | "f32.convert_u/i32",
+        F32ConvertI64S : [0xb4] : "f32.convert_i64_s" | "f32.convert_s/i64",
+        F32ConvertI64U : [0xb5] : "f32.convert_i64_u" | "f32.convert_u/i64",
+        F32DemoteF64 : [0xb6] : "f32.demote_f64" | "f32.demote/f64",
+        F64ConvertI32S : [0xb7] : "f64.convert_i32_s" | "f64.convert_s/i32",
+        F64ConvertI32U : [0xb8] : "f64.convert_i32_u" | "f64.convert_u/i32",
+        F64ConvertI64S : [0xb9] : "f64.convert_i64_s" | "f64.convert_s/i64",
+        F64ConvertI64U : [0xba] : "f64.convert_i64_u" | "f64.convert_u/i64",
+        F64PromoteF32 : [0xbb] : "f64.promote_f32" | "f64.promote/f32",
+        I32ReinterpretF32 : [0xbc] : "i32.reinterpret_f32" | "i32.reinterpret/f32",
+        I64ReinterpretF64 : [0xbd] : "i64.reinterpret_f64" | "i64.reinterpret/f64",
+        F32ReinterpretI32 : [0xbe] : "f32.reinterpret_i32" | "f32.reinterpret/i32",
+        F64ReinterpretI64 : [0xbf] : "f64.reinterpret_i64" | "f64.reinterpret/i64",
+
+        // non-trapping float to int
+        I32TruncSatF32S : [0xfc, 0x00] : "i32.trunc_sat_f32_s" | "i32.trunc_s:sat/f32",
+        I32TruncSatF32U : [0xfc, 0x01] : "i32.trunc_sat_f32_u" | "i32.trunc_u:sat/f32",
+        I32TruncSatF64S : [0xfc, 0x02] : "i32.trunc_sat_f64_s" | "i32.trunc_s:sat/f64",
+        I32TruncSatF64U : [0xfc, 0x03] : "i32.trunc_sat_f64_u" | "i32.trunc_u:sat/f64",
+        I64TruncSatF32S : [0xfc, 0x04] : "i64.trunc_sat_f32_s" | "i64.trunc_s:sat/f32",
+        I64TruncSatF32U : [0xfc, 0x05] : "i64.trunc_sat_f32_u" | "i64.trunc_u:sat/f32",
+        I64TruncSatF64S : [0xfc, 0x06] : "i64.trunc_sat_f64_s" | "i64.trunc_s:sat/f64",
+        I64TruncSatF64U : [0xfc, 0x07] : "i64.trunc_sat_f64_u" | "i64.trunc_u:sat/f64",
+
+        // sign extension proposal
+        I32Extend8S : [0xc0] : "i32.extend8_s",
+        I32Extend16S : [0xc1] : "i32.extend16_s",
+        I64Extend8S : [0xc2] : "i64.extend8_s",
+        I64Extend16S : [0xc3] : "i64.extend16_s",
+        I64Extend32S : [0xc4] : "i64.extend32_s",
+
+        // atomics proposal
+        MemoryAtomicNotify(MemArg<4>) : [0xfe, 0x00] : "memory.atomic.notify" | "atomic.notify",
+        MemoryAtomicWait32(MemArg<4>) : [0xfe, 0x01] : "memory.atomic.wait32" | "i32.atomic.wait",
+        MemoryAtomicWait64(MemArg<8>) : [0xfe, 0x02] : "memory.atomic.wait64" | "i64.atomic.wait",
+        AtomicFence : [0xfe, 0x03, 0x00] : "atomic.fence",
+
+        I32AtomicLoad(MemArg<4>) : [0xfe, 0x10] : "i32.atomic.load",
+        I64AtomicLoad(MemArg<8>) : [0xfe, 0x11] : "i64.atomic.load",
+        I32AtomicLoad8u(MemArg<1>) : [0xfe, 0x12] : "i32.atomic.load8_u",
+        I32AtomicLoad16u(MemArg<2>) : [0xfe, 0x13] : "i32.atomic.load16_u",
+        I64AtomicLoad8u(MemArg<1>) : [0xfe, 0x14] : "i64.atomic.load8_u",
+        I64AtomicLoad16u(MemArg<2>) : [0xfe, 0x15] : "i64.atomic.load16_u",
+        I64AtomicLoad32u(MemArg<4>) : [0xfe, 0x16] : "i64.atomic.load32_u",
+        I32AtomicStore(MemArg<4>) : [0xfe, 0x17] : "i32.atomic.store",
+        I64AtomicStore(MemArg<8>) : [0xfe, 0x18] : "i64.atomic.store",
+        I32AtomicStore8(MemArg<1>) : [0xfe, 0x19] : "i32.atomic.store8",
+        I32AtomicStore16(MemArg<2>) : [0xfe, 0x1a] : "i32.atomic.store16",
+        I64AtomicStore8(MemArg<1>) : [0xfe, 0x1b] : "i64.atomic.store8",
+        I64AtomicStore16(MemArg<2>) : [0xfe, 0x1c] : "i64.atomic.store16",
+        I64AtomicStore32(MemArg<4>) : [0xfe, 0x1d] : "i64.atomic.store32",
+
+        I32AtomicRmwAdd(MemArg<4>) : [0xfe, 0x1e] : "i32.atomic.rmw.add",
+        I64AtomicRmwAdd(MemArg<8>) : [0xfe, 0x1f] : "i64.atomic.rmw.add",
+        I32AtomicRmw8AddU(MemArg<1>) : [0xfe, 0x20] : "i32.atomic.rmw8.add_u",
+        I32AtomicRmw16AddU(MemArg<2>) : [0xfe, 0x21] : "i32.atomic.rmw16.add_u",
+        I64AtomicRmw8AddU(MemArg<1>) : [0xfe, 0x22] : "i64.atomic.rmw8.add_u",
+        I64AtomicRmw16AddU(MemArg<2>) : [0xfe, 0x23] : "i64.atomic.rmw16.add_u",
+        I64AtomicRmw32AddU(MemArg<4>) : [0xfe, 0x24] : "i64.atomic.rmw32.add_u",
+
+        I32AtomicRmwSub(MemArg<4>) : [0xfe, 0x25] : "i32.atomic.rmw.sub",
+        I64AtomicRmwSub(MemArg<8>) : [0xfe, 0x26] : "i64.atomic.rmw.sub",
+        I32AtomicRmw8SubU(MemArg<1>) : [0xfe, 0x27] : "i32.atomic.rmw8.sub_u",
+        I32AtomicRmw16SubU(MemArg<2>) : [0xfe, 0x28] : "i32.atomic.rmw16.sub_u",
+        I64AtomicRmw8SubU(MemArg<1>) : [0xfe, 0x29] : "i64.atomic.rmw8.sub_u",
+        I64AtomicRmw16SubU(MemArg<2>) : [0xfe, 0x2a] : "i64.atomic.rmw16.sub_u",
+        I64AtomicRmw32SubU(MemArg<4>) : [0xfe, 0x2b] : "i64.atomic.rmw32.sub_u",
+
+        I32AtomicRmwAnd(MemArg<4>) : [0xfe, 0x2c] : "i32.atomic.rmw.and",
+        I64AtomicRmwAnd(MemArg<8>) : [0xfe, 0x2d] : "i64.atomic.rmw.and",
+        I32AtomicRmw8AndU(MemArg<1>) : [0xfe, 0x2e] : "i32.atomic.rmw8.and_u",
+        I32AtomicRmw16AndU(MemArg<2>) : [0xfe, 0x2f] : "i32.atomic.rmw16.and_u",
+        I64AtomicRmw8AndU(MemArg<1>) : [0xfe, 0x30] : "i64.atomic.rmw8.and_u",
+        I64AtomicRmw16AndU(MemArg<2>) : [0xfe, 0x31] : "i64.atomic.rmw16.and_u",
+        I64AtomicRmw32AndU(MemArg<4>) : [0xfe, 0x32] : "i64.atomic.rmw32.and_u",
+
+        I32AtomicRmwOr(MemArg<4>) : [0xfe, 0x33] : "i32.atomic.rmw.or",
+        I64AtomicRmwOr(MemArg<8>) : [0xfe, 0x34] : "i64.atomic.rmw.or",
+        I32AtomicRmw8OrU(MemArg<1>) : [0xfe, 0x35] : "i32.atomic.rmw8.or_u",
+        I32AtomicRmw16OrU(MemArg<2>) : [0xfe, 0x36] : "i32.atomic.rmw16.or_u",
+        I64AtomicRmw8OrU(MemArg<1>) : [0xfe, 0x37] : "i64.atomic.rmw8.or_u",
+        I64AtomicRmw16OrU(MemArg<2>) : [0xfe, 0x38] : "i64.atomic.rmw16.or_u",
+        I64AtomicRmw32OrU(MemArg<4>) : [0xfe, 0x39] : "i64.atomic.rmw32.or_u",
+
+        I32AtomicRmwXor(MemArg<4>) : [0xfe, 0x3a] : "i32.atomic.rmw.xor",
+        I64AtomicRmwXor(MemArg<8>) : [0xfe, 0x3b] : "i64.atomic.rmw.xor",
+        I32AtomicRmw8XorU(MemArg<1>) : [0xfe, 0x3c] : "i32.atomic.rmw8.xor_u",
+        I32AtomicRmw16XorU(MemArg<2>) : [0xfe, 0x3d] : "i32.atomic.rmw16.xor_u",
+        I64AtomicRmw8XorU(MemArg<1>) : [0xfe, 0x3e] : "i64.atomic.rmw8.xor_u",
+        I64AtomicRmw16XorU(MemArg<2>) : [0xfe, 0x3f] : "i64.atomic.rmw16.xor_u",
+        I64AtomicRmw32XorU(MemArg<4>) : [0xfe, 0x40] : "i64.atomic.rmw32.xor_u",
+
+        I32AtomicRmwXchg(MemArg<4>) : [0xfe, 0x41] : "i32.atomic.rmw.xchg",
+        I64AtomicRmwXchg(MemArg<8>) : [0xfe, 0x42] : "i64.atomic.rmw.xchg",
+        I32AtomicRmw8XchgU(MemArg<1>) : [0xfe, 0x43] : "i32.atomic.rmw8.xchg_u",
+        I32AtomicRmw16XchgU(MemArg<2>) : [0xfe, 0x44] : "i32.atomic.rmw16.xchg_u",
+        I64AtomicRmw8XchgU(MemArg<1>) : [0xfe, 0x45] : "i64.atomic.rmw8.xchg_u",
+        I64AtomicRmw16XchgU(MemArg<2>) : [0xfe, 0x46] : "i64.atomic.rmw16.xchg_u",
+        I64AtomicRmw32XchgU(MemArg<4>) : [0xfe, 0x47] : "i64.atomic.rmw32.xchg_u",
+
+        I32AtomicRmwCmpxchg(MemArg<4>) : [0xfe, 0x48] : "i32.atomic.rmw.cmpxchg",
+        I64AtomicRmwCmpxchg(MemArg<8>) : [0xfe, 0x49] : "i64.atomic.rmw.cmpxchg",
+        I32AtomicRmw8CmpxchgU(MemArg<1>) : [0xfe, 0x4a] : "i32.atomic.rmw8.cmpxchg_u",
+        I32AtomicRmw16CmpxchgU(MemArg<2>) : [0xfe, 0x4b] : "i32.atomic.rmw16.cmpxchg_u",
+        I64AtomicRmw8CmpxchgU(MemArg<1>) : [0xfe, 0x4c] : "i64.atomic.rmw8.cmpxchg_u",
+        I64AtomicRmw16CmpxchgU(MemArg<2>) : [0xfe, 0x4d] : "i64.atomic.rmw16.cmpxchg_u",
+        I64AtomicRmw32CmpxchgU(MemArg<4>) : [0xfe, 0x4e] : "i64.atomic.rmw32.cmpxchg_u",
+
+        // proposal: simd
+        //
+        // https://webassembly.github.io/simd/core/binary/instructions.html
+        V128Load(MemArg<16>) : [0xfd, 0] : "v128.load",
+        V128Load8x8S(MemArg<8>) : [0xfd, 1] : "v128.load8x8_s",
+        V128Load8x8U(MemArg<8>) : [0xfd, 2] : "v128.load8x8_u",
+        V128Load16x4S(MemArg<8>) : [0xfd, 3] : "v128.load16x4_s",
+        V128Load16x4U(MemArg<8>) : [0xfd, 4] : "v128.load16x4_u",
+        V128Load32x2S(MemArg<8>) : [0xfd, 5] : "v128.load32x2_s",
+        V128Load32x2U(MemArg<8>) : [0xfd, 6] : "v128.load32x2_u",
+        V128Load8Splat(MemArg<1>) : [0xfd, 7] : "v128.load8_splat",
+        V128Load16Splat(MemArg<2>) : [0xfd, 8] : "v128.load16_splat",
+        V128Load32Splat(MemArg<4>) : [0xfd, 9] : "v128.load32_splat",
+        V128Load64Splat(MemArg<8>) : [0xfd, 10] : "v128.load64_splat",
+        V128Load32Zero(MemArg<4>) : [0xfd, 92] : "v128.load32_zero",
+        V128Load64Zero(MemArg<8>) : [0xfd, 93] : "v128.load64_zero",
+        V128Store(MemArg<16>) : [0xfd, 11] : "v128.store",
+
+        V128Load8Lane(LoadOrStoreLane<1>) : [0xfd, 84] : "v128.load8_lane",
+        V128Load16Lane(LoadOrStoreLane<2>) : [0xfd, 85] : "v128.load16_lane",
+        V128Load32Lane(LoadOrStoreLane<4>) : [0xfd, 86] : "v128.load32_lane",
+        V128Load64Lane(LoadOrStoreLane<8>): [0xfd, 87] : "v128.load64_lane",
+        V128Store8Lane(LoadOrStoreLane<1>) : [0xfd, 88] : "v128.store8_lane",
+        V128Store16Lane(LoadOrStoreLane<2>) : [0xfd, 89] : "v128.store16_lane",
+        V128Store32Lane(LoadOrStoreLane<4>) : [0xfd, 90] : "v128.store32_lane",
+        V128Store64Lane(LoadOrStoreLane<8>) : [0xfd, 91] : "v128.store64_lane",
+
+        V128Const(V128Const) : [0xfd, 12] : "v128.const",
+        I8x16Shuffle(I8x16Shuffle) : [0xfd, 13] : "i8x16.shuffle",
+
+        I8x16ExtractLaneS(LaneArg) : [0xfd, 21] : "i8x16.extract_lane_s",
+        I8x16ExtractLaneU(LaneArg) : [0xfd, 22] : "i8x16.extract_lane_u",
+        I8x16ReplaceLane(LaneArg) : [0xfd, 23] : "i8x16.replace_lane",
+        I16x8ExtractLaneS(LaneArg) : [0xfd, 24] : "i16x8.extract_lane_s",
+        I16x8ExtractLaneU(LaneArg) : [0xfd, 25] : "i16x8.extract_lane_u",
+        I16x8ReplaceLane(LaneArg) : [0xfd, 26] : "i16x8.replace_lane",
+        I32x4ExtractLane(LaneArg) : [0xfd, 27] : "i32x4.extract_lane",
+        I32x4ReplaceLane(LaneArg) : [0xfd, 28] : "i32x4.replace_lane",
+        I64x2ExtractLane(LaneArg) : [0xfd, 29] : "i64x2.extract_lane",
+        I64x2ReplaceLane(LaneArg) : [0xfd, 30] : "i64x2.replace_lane",
+        F32x4ExtractLane(LaneArg) : [0xfd, 31] : "f32x4.extract_lane",
+        F32x4ReplaceLane(LaneArg) : [0xfd, 32] : "f32x4.replace_lane",
+        F64x2ExtractLane(LaneArg) : [0xfd, 33] : "f64x2.extract_lane",
+        F64x2ReplaceLane(LaneArg) : [0xfd, 34] : "f64x2.replace_lane",
+
+        I8x16Swizzle : [0xfd, 14] : "i8x16.swizzle",
+        I8x16Splat : [0xfd, 15] : "i8x16.splat",
+        I16x8Splat : [0xfd, 16] : "i16x8.splat",
+        I32x4Splat : [0xfd, 17] : "i32x4.splat",
+        I64x2Splat : [0xfd, 18] : "i64x2.splat",
+        F32x4Splat : [0xfd, 19] : "f32x4.splat",
+        F64x2Splat : [0xfd, 20] : "f64x2.splat",
+
+        I8x16Eq : [0xfd, 35] : "i8x16.eq",
+        I8x16Ne : [0xfd, 36] : "i8x16.ne",
+        I8x16LtS : [0xfd, 37] : "i8x16.lt_s",
+        I8x16LtU : [0xfd, 38] : "i8x16.lt_u",
+        I8x16GtS : [0xfd, 39] : "i8x16.gt_s",
+        I8x16GtU : [0xfd, 40] : "i8x16.gt_u",
+        I8x16LeS : [0xfd, 41] : "i8x16.le_s",
+        I8x16LeU : [0xfd, 42] : "i8x16.le_u",
+        I8x16GeS : [0xfd, 43] : "i8x16.ge_s",
+        I8x16GeU : [0xfd, 44] : "i8x16.ge_u",
+
+        I16x8Eq : [0xfd, 45] : "i16x8.eq",
+        I16x8Ne : [0xfd, 46] : "i16x8.ne",
+        I16x8LtS : [0xfd, 47] : "i16x8.lt_s",
+        I16x8LtU : [0xfd, 48] : "i16x8.lt_u",
+        I16x8GtS : [0xfd, 49] : "i16x8.gt_s",
+        I16x8GtU : [0xfd, 50] : "i16x8.gt_u",
+        I16x8LeS : [0xfd, 51] : "i16x8.le_s",
+        I16x8LeU : [0xfd, 52] : "i16x8.le_u",
+        I16x8GeS : [0xfd, 53] : "i16x8.ge_s",
+        I16x8GeU : [0xfd, 54] : "i16x8.ge_u",
+
+        I32x4Eq : [0xfd, 55] : "i32x4.eq",
+        I32x4Ne : [0xfd, 56] : "i32x4.ne",
+        I32x4LtS : [0xfd, 57] : "i32x4.lt_s",
+        I32x4LtU : [0xfd, 58] : "i32x4.lt_u",
+        I32x4GtS : [0xfd, 59] : "i32x4.gt_s",
+        I32x4GtU : [0xfd, 60] : "i32x4.gt_u",
+        I32x4LeS : [0xfd, 61] : "i32x4.le_s",
+        I32x4LeU : [0xfd, 62] : "i32x4.le_u",
+        I32x4GeS : [0xfd, 63] : "i32x4.ge_s",
+        I32x4GeU : [0xfd, 64] : "i32x4.ge_u",
+
+        I64x2Eq : [0xfd, 214] : "i64x2.eq",
+        I64x2Ne : [0xfd, 215] : "i64x2.ne",
+        I64x2LtS : [0xfd, 216] : "i64x2.lt_s",
+        I64x2GtS : [0xfd, 217] : "i64x2.gt_s",
+        I64x2LeS : [0xfd, 218] : "i64x2.le_s",
+        I64x2GeS : [0xfd, 219] : "i64x2.ge_s",
+
+        F32x4Eq : [0xfd, 65] : "f32x4.eq",
+        F32x4Ne : [0xfd, 66] : "f32x4.ne",
+        F32x4Lt : [0xfd, 67] : "f32x4.lt",
+        F32x4Gt : [0xfd, 68] : "f32x4.gt",
+        F32x4Le : [0xfd, 69] : "f32x4.le",
+        F32x4Ge : [0xfd, 70] : "f32x4.ge",
+
+        F64x2Eq : [0xfd, 71] : "f64x2.eq",
+        F64x2Ne : [0xfd, 72] : "f64x2.ne",
+        F64x2Lt : [0xfd, 73] : "f64x2.lt",
+        F64x2Gt : [0xfd, 74] : "f64x2.gt",
+        F64x2Le : [0xfd, 75] : "f64x2.le",
+        F64x2Ge : [0xfd, 76] : "f64x2.ge",
+
+        V128Not : [0xfd, 77] : "v128.not",
+        V128And : [0xfd, 78] : "v128.and",
+        V128Andnot : [0xfd, 79] : "v128.andnot",
+        V128Or : [0xfd, 80] : "v128.or",
+        V128Xor : [0xfd, 81] : "v128.xor",
+        V128Bitselect : [0xfd, 82] : "v128.bitselect",
+        V128AnyTrue : [0xfd, 83] : "v128.any_true",
+
+        I8x16Abs : [0xfd, 96] : "i8x16.abs",
+        I8x16Neg : [0xfd, 97] : "i8x16.neg",
+        I8x16Popcnt : [0xfd, 98] : "i8x16.popcnt",
+        I8x16AllTrue : [0xfd, 99] : "i8x16.all_true",
+        I8x16Bitmask : [0xfd, 100] : "i8x16.bitmask",
+        I8x16NarrowI16x8S : [0xfd, 101] : "i8x16.narrow_i16x8_s",
+        I8x16NarrowI16x8U : [0xfd, 102] : "i8x16.narrow_i16x8_u",
+        I8x16Shl : [0xfd, 107] : "i8x16.shl",
+        I8x16ShrS : [0xfd, 108] : "i8x16.shr_s",
+        I8x16ShrU : [0xfd, 109] : "i8x16.shr_u",
+        I8x16Add : [0xfd, 110] : "i8x16.add",
+        I8x16AddSatS : [0xfd, 111] : "i8x16.add_sat_s",
+        I8x16AddSatU : [0xfd, 112] : "i8x16.add_sat_u",
+        I8x16Sub : [0xfd, 113] : "i8x16.sub",
+        I8x16SubSatS : [0xfd, 114] : "i8x16.sub_sat_s",
+        I8x16SubSatU : [0xfd, 115] : "i8x16.sub_sat_u",
+        I8x16MinS : [0xfd, 118] : "i8x16.min_s",
+        I8x16MinU : [0xfd, 119] : "i8x16.min_u",
+        I8x16MaxS : [0xfd, 120] : "i8x16.max_s",
+        I8x16MaxU : [0xfd, 121] : "i8x16.max_u",
+        I8x16AvgrU : [0xfd, 123] : "i8x16.avgr_u",
+
+        I16x8ExtAddPairwiseI8x16S : [0xfd, 124] : "i16x8.extadd_pairwise_i8x16_s",
+        I16x8ExtAddPairwiseI8x16U : [0xfd, 125] : "i16x8.extadd_pairwise_i8x16_u",
+        I16x8Abs : [0xfd, 128] : "i16x8.abs",
+        I16x8Neg : [0xfd, 129] : "i16x8.neg",
+        I16x8Q15MulrSatS : [0xfd, 130] : "i16x8.q15mulr_sat_s",
+        I16x8AllTrue : [0xfd, 131] : "i16x8.all_true",
+        I16x8Bitmask : [0xfd, 132] : "i16x8.bitmask",
+        I16x8NarrowI32x4S : [0xfd, 133] : "i16x8.narrow_i32x4_s",
+        I16x8NarrowI32x4U : [0xfd, 134] : "i16x8.narrow_i32x4_u",
+        I16x8ExtendLowI8x16S : [0xfd, 135] : "i16x8.extend_low_i8x16_s",
+        I16x8ExtendHighI8x16S : [0xfd, 136] : "i16x8.extend_high_i8x16_s",
+        I16x8ExtendLowI8x16U : [0xfd, 137] : "i16x8.extend_low_i8x16_u",
+        I16x8ExtendHighI8x16u : [0xfd, 138] : "i16x8.extend_high_i8x16_u",
+        I16x8Shl : [0xfd, 139] : "i16x8.shl",
+        I16x8ShrS : [0xfd, 140] : "i16x8.shr_s",
+        I16x8ShrU : [0xfd, 141] : "i16x8.shr_u",
+        I16x8Add : [0xfd, 142] : "i16x8.add",
+        I16x8AddSatS : [0xfd, 143] : "i16x8.add_sat_s",
+        I16x8AddSatU : [0xfd, 144] : "i16x8.add_sat_u",
+        I16x8Sub : [0xfd, 145] : "i16x8.sub",
+        I16x8SubSatS : [0xfd, 146] : "i16x8.sub_sat_s",
+        I16x8SubSatU : [0xfd, 147] : "i16x8.sub_sat_u",
+        I16x8Mul : [0xfd, 149] : "i16x8.mul",
+        I16x8MinS : [0xfd, 150] : "i16x8.min_s",
+        I16x8MinU : [0xfd, 151] : "i16x8.min_u",
+        I16x8MaxS : [0xfd, 152] : "i16x8.max_s",
+        I16x8MaxU : [0xfd, 153] : "i16x8.max_u",
+        I16x8AvgrU : [0xfd, 155] : "i16x8.avgr_u",
+        I16x8ExtMulLowI8x16S : [0xfd, 156] : "i16x8.extmul_low_i8x16_s",
+        I16x8ExtMulHighI8x16S : [0xfd, 157] : "i16x8.extmul_high_i8x16_s",
+        I16x8ExtMulLowI8x16U : [0xfd, 158] : "i16x8.extmul_low_i8x16_u",
+        I16x8ExtMulHighI8x16U : [0xfd, 159] : "i16x8.extmul_high_i8x16_u",
+
+        I32x4ExtAddPairwiseI16x8S : [0xfd, 126] : "i32x4.extadd_pairwise_i16x8_s",
+        I32x4ExtAddPairwiseI16x8U : [0xfd, 127] : "i32x4.extadd_pairwise_i16x8_u",
+        I32x4Abs : [0xfd, 160] : "i32x4.abs",
+        I32x4Neg : [0xfd, 161] : "i32x4.neg",
+        I32x4AllTrue : [0xfd, 163] : "i32x4.all_true",
+        I32x4Bitmask : [0xfd, 164] : "i32x4.bitmask",
+        I32x4ExtendLowI16x8S : [0xfd, 167] : "i32x4.extend_low_i16x8_s",
+        I32x4ExtendHighI16x8S : [0xfd, 168] : "i32x4.extend_high_i16x8_s",
+        I32x4ExtendLowI16x8U : [0xfd, 169] : "i32x4.extend_low_i16x8_u",
+        I32x4ExtendHighI16x8U : [0xfd, 170] : "i32x4.extend_high_i16x8_u",
+        I32x4Shl : [0xfd, 171] : "i32x4.shl",
+        I32x4ShrS : [0xfd, 172] : "i32x4.shr_s",
+        I32x4ShrU : [0xfd, 173] : "i32x4.shr_u",
+        I32x4Add : [0xfd, 174] : "i32x4.add",
+        I32x4Sub : [0xfd, 177] : "i32x4.sub",
+        I32x4Mul : [0xfd, 181] : "i32x4.mul",
+        I32x4MinS : [0xfd, 182] : "i32x4.min_s",
+        I32x4MinU : [0xfd, 183] : "i32x4.min_u",
+        I32x4MaxS : [0xfd, 184] : "i32x4.max_s",
+        I32x4MaxU : [0xfd, 185] : "i32x4.max_u",
+        I32x4DotI16x8S : [0xfd, 186] : "i32x4.dot_i16x8_s",
+        I32x4ExtMulLowI16x8S : [0xfd, 188] : "i32x4.extmul_low_i16x8_s",
+        I32x4ExtMulHighI16x8S : [0xfd, 189] : "i32x4.extmul_high_i16x8_s",
+        I32x4ExtMulLowI16x8U : [0xfd, 190] : "i32x4.extmul_low_i16x8_u",
+        I32x4ExtMulHighI16x8U : [0xfd, 191] : "i32x4.extmul_high_i16x8_u",
+
+        I64x2Abs : [0xfd, 192] : "i64x2.abs",
+        I64x2Neg : [0xfd, 193] : "i64x2.neg",
+        I64x2AllTrue : [0xfd, 195] : "i64x2.all_true",
+        I64x2Bitmask : [0xfd, 196] : "i64x2.bitmask",
+        I64x2ExtendLowI32x4S : [0xfd, 199] : "i64x2.extend_low_i32x4_s",
+        I64x2ExtendHighI32x4S : [0xfd, 200] : "i64x2.extend_high_i32x4_s",
+        I64x2ExtendLowI32x4U : [0xfd, 201] : "i64x2.extend_low_i32x4_u",
+        I64x2ExtendHighI32x4U : [0xfd, 202] : "i64x2.extend_high_i32x4_u",
+        I64x2Shl : [0xfd, 203] : "i64x2.shl",
+        I64x2ShrS : [0xfd, 204] : "i64x2.shr_s",
+        I64x2ShrU : [0xfd, 205] : "i64x2.shr_u",
+        I64x2Add : [0xfd, 206] : "i64x2.add",
+        I64x2Sub : [0xfd, 209] : "i64x2.sub",
+        I64x2Mul : [0xfd, 213] : "i64x2.mul",
+        I64x2ExtMulLowI32x4S : [0xfd, 220] : "i64x2.extmul_low_i32x4_s",
+        I64x2ExtMulHighI32x4S : [0xfd, 221] : "i64x2.extmul_high_i32x4_s",
+        I64x2ExtMulLowI32x4U : [0xfd, 222] : "i64x2.extmul_low_i32x4_u",
+        I64x2ExtMulHighI32x4U : [0xfd, 223] : "i64x2.extmul_high_i32x4_u",
+
+        F32x4Ceil : [0xfd, 103] : "f32x4.ceil",
+        F32x4Floor : [0xfd, 104] : "f32x4.floor",
+        F32x4Trunc : [0xfd, 105] : "f32x4.trunc",
+        F32x4Nearest : [0xfd, 106] : "f32x4.nearest",
+        F32x4Abs : [0xfd, 224] : "f32x4.abs",
+        F32x4Neg : [0xfd, 225] : "f32x4.neg",
+        F32x4Sqrt : [0xfd, 227] : "f32x4.sqrt",
+        F32x4Add : [0xfd, 228] : "f32x4.add",
+        F32x4Sub : [0xfd, 229] : "f32x4.sub",
+        F32x4Mul : [0xfd, 230] : "f32x4.mul",
+        F32x4Div : [0xfd, 231] : "f32x4.div",
+        F32x4Min : [0xfd, 232] : "f32x4.min",
+        F32x4Max : [0xfd, 233] : "f32x4.max",
+        F32x4PMin : [0xfd, 234] : "f32x4.pmin",
+        F32x4PMax : [0xfd, 235] : "f32x4.pmax",
+
+        F64x2Ceil : [0xfd, 116] : "f64x2.ceil",
+        F64x2Floor : [0xfd, 117] : "f64x2.floor",
+        F64x2Trunc : [0xfd, 122] : "f64x2.trunc",
+        F64x2Nearest : [0xfd, 148] : "f64x2.nearest",
+        F64x2Abs : [0xfd, 236] : "f64x2.abs",
+        F64x2Neg : [0xfd, 237] : "f64x2.neg",
+        F64x2Sqrt : [0xfd, 239] : "f64x2.sqrt",
+        F64x2Add : [0xfd, 240] : "f64x2.add",
+        F64x2Sub : [0xfd, 241] : "f64x2.sub",
+        F64x2Mul : [0xfd, 242] : "f64x2.mul",
+        F64x2Div : [0xfd, 243] : "f64x2.div",
+        F64x2Min : [0xfd, 244] : "f64x2.min",
+        F64x2Max : [0xfd, 245] : "f64x2.max",
+        F64x2PMin : [0xfd, 246] : "f64x2.pmin",
+        F64x2PMax : [0xfd, 247] : "f64x2.pmax",
+
+        I32x4TruncSatF32x4S : [0xfd, 248] : "i32x4.trunc_sat_f32x4_s",
+        I32x4TruncSatF32x4U : [0xfd, 249] : "i32x4.trunc_sat_f32x4_u",
+        F32x4ConvertI32x4S : [0xfd, 250] : "f32x4.convert_i32x4_s",
+        F32x4ConvertI32x4U : [0xfd, 251] : "f32x4.convert_i32x4_u",
+        I32x4TruncSatF64x2SZero : [0xfd, 252] : "i32x4.trunc_sat_f64x2_s_zero",
+        I32x4TruncSatF64x2UZero : [0xfd, 253] : "i32x4.trunc_sat_f64x2_u_zero",
+        F64x2ConvertLowI32x4S : [0xfd, 254] : "f64x2.convert_low_i32x4_s",
+        F64x2ConvertLowI32x4U : [0xfd, 255] : "f64x2.convert_low_i32x4_u",
+        F32x4DemoteF64x2Zero : [0xfd, 94] : "f32x4.demote_f64x2_zero",
+        F64x2PromoteLowF32x4 : [0xfd, 95] : "f64x2.promote_low_f32x4",
+
+        // Exception handling proposal
+        Try(BlockType<'a>) : [0x06] : "try",
+        Catch(Index<'a>) : [0x07] : "catch",
+        Throw(Index<'a>) : [0x08] : "throw",
+        Rethrow(Index<'a>) : [0x09] : "rethrow",
+        Delegate(Index<'a>) : [0x18] : "delegate",
+        CatchAll : [0x19] : "catch_all",
+
+        // Relaxed SIMD proposal
+        I8x16RelaxedSwizzle : [0xfd, 0x100]: "i8x16.relaxed_swizzle",
+        I32x4RelaxedTruncF32x4S : [0xfd, 0x101]: "i32x4.relaxed_trunc_f32x4_s",
+        I32x4RelaxedTruncF32x4U : [0xfd, 0x102]: "i32x4.relaxed_trunc_f32x4_u",
+        I32x4RelaxedTruncF64x2SZero : [0xfd, 0x103]: "i32x4.relaxed_trunc_f64x2_s_zero",
+        I32x4RelaxedTruncF64x2UZero : [0xfd, 0x104]: "i32x4.relaxed_trunc_f64x2_u_zero",
+        F32x4RelaxedMadd : [0xfd, 0x105]: "f32x4.relaxed_madd",
+        F32x4RelaxedNmadd : [0xfd, 0x106]: "f32x4.relaxed_nmadd",
+        F64x2RelaxedMadd : [0xfd, 0x107]: "f64x2.relaxed_madd",
+        F64x2RelaxedNmadd : [0xfd, 0x108]: "f64x2.relaxed_nmadd",
+        I8x16RelaxedLaneselect : [0xfd, 0x109]: "i8x16.relaxed_laneselect",
+        I16x8RelaxedLaneselect : [0xfd, 0x10A]: "i16x8.relaxed_laneselect",
+        I32x4RelaxedLaneselect : [0xfd, 0x10B]: "i32x4.relaxed_laneselect",
+        I64x2RelaxedLaneselect : [0xfd, 0x10C]: "i64x2.relaxed_laneselect",
+        F32x4RelaxedMin : [0xfd, 0x10D]: "f32x4.relaxed_min",
+        F32x4RelaxedMax : [0xfd, 0x10E]: "f32x4.relaxed_max",
+        F64x2RelaxedMin : [0xfd, 0x10F]: "f64x2.relaxed_min",
+        F64x2RelaxedMax : [0xfd, 0x110]: "f64x2.relaxed_max",
+        I16x8RelaxedQ15mulrS: [0xfd, 0x111]: "i16x8.relaxed_q15mulr_s",
+        I16x8RelaxedDotI8x16I7x16S: [0xfd, 0x112]: "i16x8.relaxed_dot_i8x16_i7x16_s",
+        I32x4RelaxedDotI8x16I7x16AddS: [0xfd, 0x113]: "i32x4.relaxed_dot_i8x16_i7x16_add_s",
+    }
+}
+
+impl<'a> Instruction<'a> {
+    pub(crate) fn needs_data_count(&self) -> bool {
+        match self {
+            Instruction::MemoryInit(_)
+            | Instruction::DataDrop(_)
+            | Instruction::ArrayNewData(_) => true,
+            _ => false,
+        }
+    }
+}
+
+/// Extra information associated with block-related instructions.
+///
+/// This is used to label blocks and also annotate what types are expected for
+/// the block.
+#[derive(Debug)]
+#[allow(missing_docs)]
+pub struct BlockType<'a> {
+    pub label: Option<Id<'a>>,
+    pub label_name: Option<NameAnnotation<'a>>,
+    pub ty: TypeUse<'a, FunctionType<'a>>,
+}
+
+impl<'a> Parse<'a> for BlockType<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        Ok(BlockType {
+            label: parser.parse()?,
+            label_name: parser.parse()?,
+            ty: parser
+                .parse::<TypeUse<'a, FunctionTypeNoNames<'a>>>()?
+                .into(),
+        })
+    }
+}
+
+/// Extra information associated with the func.bind instruction.
+#[derive(Debug)]
+#[allow(missing_docs)]
+pub struct FuncBindType<'a> {
+    pub ty: TypeUse<'a, FunctionType<'a>>,
+}
+
+impl<'a> Parse<'a> for FuncBindType<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        Ok(FuncBindType {
+            ty: parser
+                .parse::<TypeUse<'a, FunctionTypeNoNames<'a>>>()?
+                .into(),
+        })
+    }
+}
+
+/// Extra information associated with the let instruction.
+#[derive(Debug)]
+#[allow(missing_docs)]
+pub struct LetType<'a> {
+    pub block: BlockType<'a>,
+    pub locals: Vec<Local<'a>>,
+}
+
+impl<'a> Parse<'a> for LetType<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        Ok(LetType {
+            block: parser.parse()?,
+            locals: Local::parse_remainder(parser)?,
+        })
+    }
+}
+
+/// Extra information associated with the `br_table` instruction.
+#[allow(missing_docs)]
+#[derive(Debug)]
+pub struct BrTableIndices<'a> {
+    pub labels: Vec<Index<'a>>,
+    pub default: Index<'a>,
+}
+
+impl<'a> Parse<'a> for BrTableIndices<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut labels = vec![parser.parse()?];
+        while parser.peek::<Index>() {
+            labels.push(parser.parse()?);
+        }
+        let default = labels.pop().unwrap();
+        Ok(BrTableIndices { labels, default })
+    }
+}
+
+/// Payload for lane-related instructions. Unsigned with no + prefix.
+#[derive(Debug)]
+pub struct LaneArg {
+    /// The lane argument.
+    pub lane: u8,
+}
+
+impl<'a> Parse<'a> for LaneArg {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let lane = parser.step(|c| {
+            if let Some((i, rest)) = c.integer() {
+                if i.sign() == None {
+                    let (src, radix) = i.val();
+                    let val = u8::from_str_radix(src, radix)
+                        .map_err(|_| c.error("malformed lane index"))?;
+                    Ok((val, rest))
+                } else {
+                    Err(c.error("unexpected token"))
+                }
+            } else {
+                Err(c.error("expected a lane index"))
+            }
+        })?;
+        Ok(LaneArg { lane })
+    }
+}
+
+/// Payload for memory-related instructions indicating offset/alignment of
+/// memory accesses.
+#[derive(Debug)]
+pub struct MemArg<'a> {
+    /// The alignment of this access.
+    ///
+    /// This is not stored as a log, this is the actual alignment (e.g. 1, 2, 4,
+    /// 8, etc).
+    pub align: u32,
+    /// The offset, in bytes of this access.
+    pub offset: u64,
+    /// The memory index we're accessing
+    pub memory: Index<'a>,
+}
+
+impl<'a> MemArg<'a> {
+    fn parse(parser: Parser<'a>, default_align: u32) -> Result<Self> {
+        fn parse_field<T>(
+            name: &str,
+            parser: Parser<'_>,
+            f: impl FnOnce(Cursor<'_>, &str, u32) -> Result<T>,
+        ) -> Result<Option<T>> {
+            parser.step(|c| {
+                let (kw, rest) = match c.keyword() {
+                    Some(p) => p,
+                    None => return Ok((None, c)),
+                };
+                if !kw.starts_with(name) {
+                    return Ok((None, c));
+                }
+                let kw = &kw[name.len()..];
+                if !kw.starts_with('=') {
+                    return Ok((None, c));
+                }
+                let num = &kw[1..];
+                let num = if let Some(stripped) = num.strip_prefix("0x") {
+                    f(c, stripped, 16)?
+                } else {
+                    f(c, num, 10)?
+                };
+
+                Ok((Some(num), rest))
+            })
+        }
+
+        fn parse_u32(name: &str, parser: Parser<'_>) -> Result<Option<u32>> {
+            parse_field(name, parser, |c, num, radix| {
+                u32::from_str_radix(num, radix).map_err(|_| c.error("i32 constant out of range"))
+            })
+        }
+
+        fn parse_u64(name: &str, parser: Parser<'_>) -> Result<Option<u64>> {
+            parse_field(name, parser, |c, num, radix| {
+                u64::from_str_radix(num, radix).map_err(|_| c.error("i64 constant out of range"))
+            })
+        }
+
+        let memory = parser
+            .parse::<Option<_>>()?
+            .unwrap_or_else(|| Index::Num(0, parser.prev_span()));
+        let offset = parse_u64("offset", parser)?.unwrap_or(0);
+        let align = match parse_u32("align", parser)? {
+            Some(n) if !n.is_power_of_two() => {
+                return Err(parser.error("alignment must be a power of two"))
+            }
+            n => n.unwrap_or(default_align),
+        };
+
+        Ok(MemArg {
+            offset,
+            align,
+            memory,
+        })
+    }
+}
+
+/// Extra data associated with the `loadN_lane` and `storeN_lane` instructions.
+#[derive(Debug)]
+pub struct LoadOrStoreLane<'a> {
+    /// The memory argument for this instruction.
+    pub memarg: MemArg<'a>,
+    /// The lane argument for this instruction.
+    pub lane: LaneArg,
+}
+
+impl<'a> LoadOrStoreLane<'a> {
+    fn parse(parser: Parser<'a>, default_align: u32) -> Result<Self> {
+        // This is sort of funky. The first integer we see could be the lane
+        // index, but it could also be the memory index. To determine what it is
+        // then if we see a second integer we need to look further.
+        let has_memarg = parser.step(|c| match c.integer() {
+            Some((_, after_int)) => {
+                // Two integers in a row? That means that the first one is the
+                // memory index and the second must be the lane index.
+                if after_int.integer().is_some() {
+                    return Ok((true, c));
+                }
+
+                // If the first integer is trailed by `offset=...` or
+                // `align=...` then this is definitely a memarg.
+                if let Some((kw, _)) = after_int.keyword() {
+                    if kw.starts_with("offset=") || kw.starts_with("align=") {
+                        return Ok((true, c));
+                    }
+                }
+
+                // Otherwise the first integer was trailed by something that
+                // didn't look like a memarg, so this must be the lane index.
+                Ok((false, c))
+            }
+
+            // Not an integer here? That must mean that this must be the memarg
+            // first followed by the trailing index.
+            None => Ok((true, c)),
+        })?;
+        Ok(LoadOrStoreLane {
+            memarg: if has_memarg {
+                MemArg::parse(parser, default_align)?
+            } else {
+                MemArg {
+                    align: default_align,
+                    offset: 0,
+                    memory: Index::Num(0, parser.prev_span()),
+                }
+            },
+            lane: LaneArg::parse(parser)?,
+        })
+    }
+}
+
+/// Extra data associated with the `call_indirect` instruction.
+#[derive(Debug)]
+pub struct CallIndirect<'a> {
+    /// The table that this call is going to be indexing.
+    pub table: Index<'a>,
+    /// Type type signature that this `call_indirect` instruction is using.
+    pub ty: TypeUse<'a, FunctionType<'a>>,
+}
+
+impl<'a> Parse<'a> for CallIndirect<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let prev_span = parser.prev_span();
+        let table: Option<_> = parser.parse()?;
+        let ty = parser.parse::<TypeUse<'a, FunctionTypeNoNames<'a>>>()?;
+        Ok(CallIndirect {
+            table: table.unwrap_or(Index::Num(0, prev_span)),
+            ty: ty.into(),
+        })
+    }
+}
+
+/// Extra data associated with the `table.init` instruction
+#[derive(Debug)]
+pub struct TableInit<'a> {
+    /// The index of the table we're copying into.
+    pub table: Index<'a>,
+    /// The index of the element segment we're copying into a table.
+    pub elem: Index<'a>,
+}
+
+impl<'a> Parse<'a> for TableInit<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let prev_span = parser.prev_span();
+        let (elem, table) = if parser.peek2::<Index>() {
+            let table = parser.parse()?;
+            (parser.parse()?, table)
+        } else {
+            (parser.parse()?, Index::Num(0, prev_span))
+        };
+        Ok(TableInit { table, elem })
+    }
+}
+
+/// Extra data associated with the `table.copy` instruction.
+#[derive(Debug)]
+pub struct TableCopy<'a> {
+    /// The index of the destination table to copy into.
+    pub dst: Index<'a>,
+    /// The index of the source table to copy from.
+    pub src: Index<'a>,
+}
+
+impl<'a> Parse<'a> for TableCopy<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let (dst, src) = match parser.parse::<Option<_>>()? {
+            Some(dst) => (dst, parser.parse()?),
+            None => (
+                Index::Num(0, parser.prev_span()),
+                Index::Num(0, parser.prev_span()),
+            ),
+        };
+        Ok(TableCopy { dst, src })
+    }
+}
+
+/// Extra data associated with unary table instructions.
+#[derive(Debug)]
+pub struct TableArg<'a> {
+    /// The index of the table argument.
+    pub dst: Index<'a>,
+}
+
+impl<'a> Parse<'a> for TableArg<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let dst = if let Some(dst) = parser.parse()? {
+            dst
+        } else {
+            Index::Num(0, parser.prev_span())
+        };
+        Ok(TableArg { dst })
+    }
+}
+
+/// Extra data associated with unary memory instructions.
+#[derive(Debug)]
+pub struct MemoryArg<'a> {
+    /// The index of the memory space.
+    pub mem: Index<'a>,
+}
+
+impl<'a> Parse<'a> for MemoryArg<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mem = if let Some(mem) = parser.parse()? {
+            mem
+        } else {
+            Index::Num(0, parser.prev_span())
+        };
+        Ok(MemoryArg { mem })
+    }
+}
+
+/// Extra data associated with the `memory.init` instruction
+#[derive(Debug)]
+pub struct MemoryInit<'a> {
+    /// The index of the data segment we're copying into memory.
+    pub data: Index<'a>,
+    /// The index of the memory we're copying into,
+    pub mem: Index<'a>,
+}
+
+impl<'a> Parse<'a> for MemoryInit<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let prev_span = parser.prev_span();
+        let (data, mem) = if parser.peek2::<Index>() {
+            let memory = parser.parse()?;
+            (parser.parse()?, memory)
+        } else {
+            (parser.parse()?, Index::Num(0, prev_span))
+        };
+        Ok(MemoryInit { data, mem })
+    }
+}
+
+/// Extra data associated with the `memory.copy` instruction
+#[derive(Debug)]
+pub struct MemoryCopy<'a> {
+    /// The index of the memory we're copying from.
+    pub src: Index<'a>,
+    /// The index of the memory we're copying to.
+    pub dst: Index<'a>,
+}
+
+impl<'a> Parse<'a> for MemoryCopy<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let (src, dst) = match parser.parse()? {
+            Some(dst) => (parser.parse()?, dst),
+            None => (
+                Index::Num(0, parser.prev_span()),
+                Index::Num(0, parser.prev_span()),
+            ),
+        };
+        Ok(MemoryCopy { src, dst })
+    }
+}
+
+/// Extra data associated with the `struct.get/set` instructions
+#[derive(Debug)]
+pub struct StructAccess<'a> {
+    /// The index of the struct type we're accessing.
+    pub r#struct: Index<'a>,
+    /// The index of the field of the struct we're accessing
+    pub field: Index<'a>,
+}
+
+impl<'a> Parse<'a> for StructAccess<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        Ok(StructAccess {
+            r#struct: parser.parse()?,
+            field: parser.parse()?,
+        })
+    }
+}
+
+/// Extra data associated with the `array.fill` instruction
+#[derive(Debug)]
+pub struct ArrayFill<'a> {
+    /// The index of the array type we're filling.
+    pub array: Index<'a>,
+}
+
+impl<'a> Parse<'a> for ArrayFill<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        Ok(ArrayFill {
+            array: parser.parse()?,
+        })
+    }
+}
+
+/// Extra data associated with the `array.copy` instruction
+#[derive(Debug)]
+pub struct ArrayCopy<'a> {
+    /// The index of the array type we're copying to.
+    pub dest_array: Index<'a>,
+    /// The index of the array type we're copying from.
+    pub src_array: Index<'a>,
+}
+
+impl<'a> Parse<'a> for ArrayCopy<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        Ok(ArrayCopy {
+            dest_array: parser.parse()?,
+            src_array: parser.parse()?,
+        })
+    }
+}
+
+/// Extra data associated with the `array.init_[data/elem]` instruction
+#[derive(Debug)]
+pub struct ArrayInit<'a> {
+    /// The index of the array type we're initializing.
+    pub array: Index<'a>,
+    /// The index of the data or elem segment we're reading from.
+    pub segment: Index<'a>,
+}
+
+impl<'a> Parse<'a> for ArrayInit<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        Ok(ArrayInit {
+            array: parser.parse()?,
+            segment: parser.parse()?,
+        })
+    }
+}
+
+/// Extra data associated with the `array.new_fixed` instruction
+#[derive(Debug)]
+pub struct ArrayNewFixed<'a> {
+    /// The index of the array type we're accessing.
+    pub array: Index<'a>,
+    /// The amount of values to initialize the array with.
+    pub length: u32,
+}
+
+impl<'a> Parse<'a> for ArrayNewFixed<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        Ok(ArrayNewFixed {
+            array: parser.parse()?,
+            length: parser.parse()?,
+        })
+    }
+}
+
+/// Extra data associated with the `array.new_data` instruction
+#[derive(Debug)]
+pub struct ArrayNewData<'a> {
+    /// The index of the array type we're accessing.
+    pub array: Index<'a>,
+    /// The data segment to initialize from.
+    pub data_idx: Index<'a>,
+}
+
+impl<'a> Parse<'a> for ArrayNewData<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        Ok(ArrayNewData {
+            array: parser.parse()?,
+            data_idx: parser.parse()?,
+        })
+    }
+}
+
+/// Extra data associated with the `array.new_elem` instruction
+#[derive(Debug)]
+pub struct ArrayNewElem<'a> {
+    /// The index of the array type we're accessing.
+    pub array: Index<'a>,
+    /// The elem segment to initialize from.
+    pub elem_idx: Index<'a>,
+}
+
+impl<'a> Parse<'a> for ArrayNewElem<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        Ok(ArrayNewElem {
+            array: parser.parse()?,
+            elem_idx: parser.parse()?,
+        })
+    }
+}
+
+/// Extra data associated with the `ref.cast` instruction
+#[derive(Debug)]
+pub struct RefCast<'a> {
+    /// The type to cast to.
+    pub r#type: RefType<'a>,
+}
+
+impl<'a> Parse<'a> for RefCast<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        Ok(RefCast {
+            r#type: parser.parse()?,
+        })
+    }
+}
+
+/// Extra data associated with the `ref.test` instruction
+#[derive(Debug)]
+pub struct RefTest<'a> {
+    /// The type to test for.
+    pub r#type: RefType<'a>,
+}
+
+impl<'a> Parse<'a> for RefTest<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        Ok(RefTest {
+            r#type: parser.parse()?,
+        })
+    }
+}
+
+/// Extra data associated with the `br_on_cast` instruction
+#[derive(Debug)]
+pub struct BrOnCast<'a> {
+    /// The label to branch to.
+    pub label: Index<'a>,
+    /// The type we're casting from.
+    pub from_type: RefType<'a>,
+    /// The type we're casting to.
+    pub to_type: RefType<'a>,
+}
+
+impl<'a> Parse<'a> for BrOnCast<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        Ok(BrOnCast {
+            label: parser.parse()?,
+            from_type: parser.parse()?,
+            to_type: parser.parse()?,
+        })
+    }
+}
+
+/// Extra data associated with the `br_on_cast_fail` instruction
+#[derive(Debug)]
+pub struct BrOnCastFail<'a> {
+    /// The label to branch to.
+    pub label: Index<'a>,
+    /// The type we're casting from.
+    pub from_type: RefType<'a>,
+    /// The type we're casting to.
+    pub to_type: RefType<'a>,
+}
+
+impl<'a> Parse<'a> for BrOnCastFail<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        Ok(BrOnCastFail {
+            label: parser.parse()?,
+            from_type: parser.parse()?,
+            to_type: parser.parse()?,
+        })
+    }
+}
+
+/// Different ways to specify a `v128.const` instruction
+#[derive(Debug)]
+#[allow(missing_docs)]
+pub enum V128Const {
+    I8x16([i8; 16]),
+    I16x8([i16; 8]),
+    I32x4([i32; 4]),
+    I64x2([i64; 2]),
+    F32x4([Float32; 4]),
+    F64x2([Float64; 2]),
+}
+
+impl V128Const {
+    /// Returns the raw little-ended byte sequence used to represent this
+    /// `v128` constant`
+    ///
+    /// This is typically suitable for encoding as the payload of the
+    /// `v128.const` instruction.
+    #[rustfmt::skip]
+    pub fn to_le_bytes(&self) -> [u8; 16] {
+        match self {
+            V128Const::I8x16(arr) => [
+                arr[0] as u8,
+                arr[1] as u8,
+                arr[2] as u8,
+                arr[3] as u8,
+                arr[4] as u8,
+                arr[5] as u8,
+                arr[6] as u8,
+                arr[7] as u8,
+                arr[8] as u8,
+                arr[9] as u8,
+                arr[10] as u8,
+                arr[11] as u8,
+                arr[12] as u8,
+                arr[13] as u8,
+                arr[14] as u8,
+                arr[15] as u8,
+            ],
+            V128Const::I16x8(arr) => {
+                let a1 = arr[0].to_le_bytes();
+                let a2 = arr[1].to_le_bytes();
+                let a3 = arr[2].to_le_bytes();
+                let a4 = arr[3].to_le_bytes();
+                let a5 = arr[4].to_le_bytes();
+                let a6 = arr[5].to_le_bytes();
+                let a7 = arr[6].to_le_bytes();
+                let a8 = arr[7].to_le_bytes();
+                [
+                    a1[0], a1[1],
+                    a2[0], a2[1],
+                    a3[0], a3[1],
+                    a4[0], a4[1],
+                    a5[0], a5[1],
+                    a6[0], a6[1],
+                    a7[0], a7[1],
+                    a8[0], a8[1],
+                ]
+            }
+            V128Const::I32x4(arr) => {
+                let a1 = arr[0].to_le_bytes();
+                let a2 = arr[1].to_le_bytes();
+                let a3 = arr[2].to_le_bytes();
+                let a4 = arr[3].to_le_bytes();
+                [
+                    a1[0], a1[1], a1[2], a1[3],
+                    a2[0], a2[1], a2[2], a2[3],
+                    a3[0], a3[1], a3[2], a3[3],
+                    a4[0], a4[1], a4[2], a4[3],
+                ]
+            }
+            V128Const::I64x2(arr) => {
+                let a1 = arr[0].to_le_bytes();
+                let a2 = arr[1].to_le_bytes();
+                [
+                    a1[0], a1[1], a1[2], a1[3], a1[4], a1[5], a1[6], a1[7],
+                    a2[0], a2[1], a2[2], a2[3], a2[4], a2[5], a2[6], a2[7],
+                ]
+            }
+            V128Const::F32x4(arr) => {
+                let a1 = arr[0].bits.to_le_bytes();
+                let a2 = arr[1].bits.to_le_bytes();
+                let a3 = arr[2].bits.to_le_bytes();
+                let a4 = arr[3].bits.to_le_bytes();
+                [
+                    a1[0], a1[1], a1[2], a1[3],
+                    a2[0], a2[1], a2[2], a2[3],
+                    a3[0], a3[1], a3[2], a3[3],
+                    a4[0], a4[1], a4[2], a4[3],
+                ]
+            }
+            V128Const::F64x2(arr) => {
+                let a1 = arr[0].bits.to_le_bytes();
+                let a2 = arr[1].bits.to_le_bytes();
+                [
+                    a1[0], a1[1], a1[2], a1[3], a1[4], a1[5], a1[6], a1[7],
+                    a2[0], a2[1], a2[2], a2[3], a2[4], a2[5], a2[6], a2[7],
+                ]
+            }
+        }
+    }
+}
+
+impl<'a> Parse<'a> for V128Const {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut l = parser.lookahead1();
+        if l.peek::<kw::i8x16>() {
+            parser.parse::<kw::i8x16>()?;
+            Ok(V128Const::I8x16([
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+            ]))
+        } else if l.peek::<kw::i16x8>() {
+            parser.parse::<kw::i16x8>()?;
+            Ok(V128Const::I16x8([
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+            ]))
+        } else if l.peek::<kw::i32x4>() {
+            parser.parse::<kw::i32x4>()?;
+            Ok(V128Const::I32x4([
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+            ]))
+        } else if l.peek::<kw::i64x2>() {
+            parser.parse::<kw::i64x2>()?;
+            Ok(V128Const::I64x2([parser.parse()?, parser.parse()?]))
+        } else if l.peek::<kw::f32x4>() {
+            parser.parse::<kw::f32x4>()?;
+            Ok(V128Const::F32x4([
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+            ]))
+        } else if l.peek::<kw::f64x2>() {
+            parser.parse::<kw::f64x2>()?;
+            Ok(V128Const::F64x2([parser.parse()?, parser.parse()?]))
+        } else {
+            Err(l.error())
+        }
+    }
+}
+
+/// Lanes being shuffled in the `i8x16.shuffle` instruction
+#[derive(Debug)]
+pub struct I8x16Shuffle {
+    #[allow(missing_docs)]
+    pub lanes: [u8; 16],
+}
+
+impl<'a> Parse<'a> for I8x16Shuffle {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        Ok(I8x16Shuffle {
+            lanes: [
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+            ],
+        })
+    }
+}
+
+/// Payload of the `select` instructions
+#[derive(Debug)]
+pub struct SelectTypes<'a> {
+    #[allow(missing_docs)]
+    pub tys: Option<Vec<ValType<'a>>>,
+}
+
+impl<'a> Parse<'a> for SelectTypes<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut found = false;
+        let mut list = Vec::new();
+        while parser.peek2::<kw::result>() {
+            found = true;
+            parser.parens(|p| {
+                p.parse::<kw::result>()?;
+                while !p.is_empty() {
+                    list.push(p.parse()?);
+                }
+                Ok(())
+            })?;
+        }
+        Ok(SelectTypes {
+            tys: if found { Some(list) } else { None },
+        })
+    }
+}
diff --git a/third_party/rust/wast/src/core/func.rs b/third_party/rust/wast/src/core/func.rs
new file mode 100644
index 0000000000..84abdf8578
--- /dev/null
+++ b/third_party/rust/wast/src/core/func.rs
@@ -0,0 +1,121 @@
+use crate::core::*;
+use crate::kw;
+use crate::parser::{Parse, Parser, Result};
+use crate::token::{Id, NameAnnotation, Span};
+
+/// A WebAssembly function to be inserted into a module.
+///
+/// This is a member of both the function and code sections.
+#[derive(Debug)]
+pub struct Func<'a> {
+    /// Where this `func` was defined.
+    pub span: Span,
+    /// An identifier that this function is resolved with (optionally) for name
+    /// resolution.
+    pub id: Option<Id<'a>>,
+    /// An optional name for this function stored in the custom `name` section.
+    pub name: Option<NameAnnotation<'a>>,
+    /// If present, inline export annotations which indicate names this
+    /// definition should be exported under.
+    pub exports: InlineExport<'a>,
+    /// What kind of function this is, be it an inline-defined or imported
+    /// function.
+    pub kind: FuncKind<'a>,
+    /// The type that this function will have.
+    pub ty: TypeUse<'a, FunctionType<'a>>,
+}
+
+/// Possible ways to define a function in the text format.
+#[derive(Debug)]
+pub enum FuncKind<'a> {
+    /// A function which is actually defined as an import, such as:
+    ///
+    /// ```text
+    /// (func (type 3) (import "foo" "bar"))
+    /// ```
+    Import(InlineImport<'a>),
+
+    /// Almost all functions, those defined inline in a wasm module.
+    Inline {
+        /// The list of locals, if any, for this function.
+        locals: Vec<Local<'a>>,
+
+        /// The instructions of the function.
+        expression: Expression<'a>,
+    },
+}
+
+impl<'a> Parse<'a> for Func<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let span = parser.parse::<kw::func>()?.0;
+        let id = parser.parse()?;
+        let name = parser.parse()?;
+        let exports = parser.parse()?;
+
+        let (ty, kind) = if let Some(import) = parser.parse()? {
+            (parser.parse()?, FuncKind::Import(import))
+        } else {
+            let ty = parser.parse()?;
+            let locals = Local::parse_remainder(parser)?;
+            (
+                ty,
+                FuncKind::Inline {
+                    locals,
+                    expression: parser.parse()?,
+                },
+            )
+        };
+
+        Ok(Func {
+            span,
+            id,
+            name,
+            exports,
+            ty,
+            kind,
+        })
+    }
+}
+
+/// A local for a `func` or `let` instruction.
+///
+/// Each local has an optional identifier for name resolution, an optional name
+/// for the custom `name` section, and a value type.
+#[derive(Debug)]
+pub struct Local<'a> {
+    /// An identifier that this local is resolved with (optionally) for name
+    /// resolution.
+    pub id: Option<Id<'a>>,
+    /// An optional name for this local stored in the custom `name` section.
+    pub name: Option<NameAnnotation<'a>>,
+    /// The value type of this local.
+    pub ty: ValType<'a>,
+}
+
+impl<'a> Local<'a> {
+    pub(crate) fn parse_remainder(parser: Parser<'a>) -> Result<Vec<Local<'a>>> {
+        let mut locals = Vec::new();
+        while parser.peek2::<kw::local>() {
+            parser.parens(|p| {
+                p.parse::<kw::local>()?;
+                if p.is_empty() {
+                    return Ok(());
+                }
+                let id: Option<_> = p.parse()?;
+                let name: Option<_> = p.parse()?;
+                let ty = p.parse()?;
+                let parse_more = id.is_none() && name.is_none();
+                locals.push(Local { id, name, ty });
+                while parse_more && !p.is_empty() {
+                    locals.push(Local {
+                        id: None,
+                        name: None,
+                        ty: p.parse()?,
+                    });
+                }
+                Ok(())
+            })?;
+        }
+        Ok(locals)
+    }
+}
diff --git a/third_party/rust/wast/src/core/global.rs b/third_party/rust/wast/src/core/global.rs
new file mode 100644
index 0000000000..b8ce287fd8
--- /dev/null
+++ b/third_party/rust/wast/src/core/global.rs
@@ -0,0 +1,59 @@
+use crate::core::*;
+use crate::kw;
+use crate::parser::{Parse, Parser, Result};
+use crate::token::{Id, NameAnnotation, Span};
+
+/// A WebAssembly global in a module
+#[derive(Debug)]
+pub struct Global<'a> {
+    /// Where this `global` was defined.
+    pub span: Span,
+    /// An optional name to reference this global by
+    pub id: Option<Id<'a>>,
+    /// An optional name for this function stored in the custom `name` section.
+    pub name: Option<NameAnnotation<'a>>,
+    /// If present, inline export annotations which indicate names this
+    /// definition should be exported under.
+    pub exports: InlineExport<'a>,
+    /// The type of this global, both its value type and whether it's mutable.
+    pub ty: GlobalType<'a>,
+    /// What kind of global this defined as.
+    pub kind: GlobalKind<'a>,
+}
+
+/// Different kinds of globals that can be defined in a module.
+#[derive(Debug)]
+pub enum GlobalKind<'a> {
+    /// A global which is actually defined as an import, such as:
+    ///
+    /// ```text
+    /// (global i32 (import "foo" "bar"))
+    /// ```
+    Import(InlineImport<'a>),
+
+    /// A global defined inline in the module itself
+    Inline(Expression<'a>),
+}
+
+impl<'a> Parse<'a> for Global<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let span = parser.parse::<kw::global>()?.0;
+        let id = parser.parse()?;
+        let name = parser.parse()?;
+        let exports = parser.parse()?;
+
+        let (ty, kind) = if let Some(import) = parser.parse()? {
+            (parser.parse()?, GlobalKind::Import(import))
+        } else {
+            (parser.parse()?, GlobalKind::Inline(parser.parse()?))
+        };
+        Ok(Global {
+            span,
+            id,
+            name,
+            exports,
+            ty,
+            kind,
+        })
+    }
+}
diff --git a/third_party/rust/wast/src/core/import.rs b/third_party/rust/wast/src/core/import.rs
new file mode 100644
index 0000000000..e44057f72f
--- /dev/null
+++ b/third_party/rust/wast/src/core/import.rs
@@ -0,0 +1,158 @@
+use crate::core::*;
+use crate::kw;
+use crate::parser::{Cursor, Parse, Parser, Peek, Result};
+use crate::token::{Id, NameAnnotation, Span};
+
+/// An `import` statement and entry in a WebAssembly module.
+#[derive(Debug, Clone)]
+pub struct Import<'a> {
+    /// Where this `import` was defined
+    pub span: Span,
+    /// The module that this statement is importing from
+    pub module: &'a str,
+    /// The name of the field in the module this statement imports from.
+    pub field: &'a str,
+    /// The item that's being imported.
+    pub item: ItemSig<'a>,
+}
+
+impl<'a> Parse<'a> for Import<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let span = parser.parse::<kw::import>()?.0;
+        let module = parser.parse()?;
+        let field = parser.parse()?;
+        let item = parser.parens(|p| p.parse())?;
+        Ok(Import {
+            span,
+            module,
+            field,
+            item,
+        })
+    }
+}
+
+#[derive(Debug, Clone)]
+#[allow(missing_docs)]
+pub struct ItemSig<'a> {
+    /// Where this item is defined in the source.
+    pub span: Span,
+    /// An optional identifier used during name resolution to refer to this item
+    /// from the rest of the module.
+    pub id: Option<Id<'a>>,
+    /// An optional name which, for functions, will be stored in the
+    /// custom `name` section.
+    pub name: Option<NameAnnotation<'a>>,
+    /// What kind of item this is.
+    pub kind: ItemKind<'a>,
+}
+
+#[derive(Debug, Clone)]
+#[allow(missing_docs)]
+pub enum ItemKind<'a> {
+    Func(TypeUse<'a, FunctionType<'a>>),
+    Table(TableType<'a>),
+    Memory(MemoryType),
+    Global(GlobalType<'a>),
+    Tag(TagType<'a>),
+}
+
+impl<'a> Parse<'a> for ItemSig<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut l = parser.lookahead1();
+        if l.peek::<kw::func>() {
+            let span = parser.parse::<kw::func>()?.0;
+            Ok(ItemSig {
+                span,
+                id: parser.parse()?,
+                name: parser.parse()?,
+                kind: ItemKind::Func(parser.parse()?),
+            })
+        } else if l.peek::<kw::table>() {
+            let span = parser.parse::<kw::table>()?.0;
+            Ok(ItemSig {
+                span,
+                id: parser.parse()?,
+                name: None,
+                kind: ItemKind::Table(parser.parse()?),
+            })
+        } else if l.peek::<kw::memory>() {
+            let span = parser.parse::<kw::memory>()?.0;
+            Ok(ItemSig {
+                span,
+                id: parser.parse()?,
+                name: None,
+                kind: ItemKind::Memory(parser.parse()?),
+            })
+        } else if l.peek::<kw::global>() {
+            let span = parser.parse::<kw::global>()?.0;
+            Ok(ItemSig {
+                span,
+                id: parser.parse()?,
+                name: None,
+                kind: ItemKind::Global(parser.parse()?),
+            })
+        } else if l.peek::<kw::tag>() {
+            let span = parser.parse::<kw::tag>()?.0;
+            Ok(ItemSig {
+                span,
+                id: parser.parse()?,
+                name: None,
+                kind: ItemKind::Tag(parser.parse()?),
+            })
+        } else {
+            Err(l.error())
+        }
+    }
+}
+
+/// A listing of a inline `(import "foo")` statement.
+///
+/// Note that when parsing this type it is somewhat unconventional that it
+/// parses its own surrounding parentheses. This is typically an optional type,
+/// so it's so far been a bit nicer to have the optionality handled through
+/// `Peek` rather than `Option<T>`.
+#[derive(Debug, Copy, Clone)]
+#[allow(missing_docs)]
+pub struct InlineImport<'a> {
+    pub module: &'a str,
+    pub field: &'a str,
+}
+
+impl<'a> Parse<'a> for InlineImport<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.parens(|p| {
+            p.parse::<kw::import>()?;
+            Ok(InlineImport {
+                module: p.parse()?,
+                field: p.parse()?,
+            })
+        })
+    }
+}
+
+impl Peek for InlineImport<'_> {
+    fn peek(cursor: Cursor<'_>) -> bool {
+        let cursor = match cursor.lparen() {
+            Some(cursor) => cursor,
+            None => return false,
+        };
+        let cursor = match cursor.keyword() {
+            Some(("import", cursor)) => cursor,
+            _ => return false,
+        };
+        let cursor = match cursor.string() {
+            Some((_, cursor)) => cursor,
+            None => return false,
+        };
+        let cursor = match cursor.string() {
+            Some((_, cursor)) => cursor,
+            None => return false,
+        };
+
+        cursor.rparen().is_some()
+    }
+
+    fn display() -> &'static str {
+        "inline import"
+    }
+}
diff --git a/third_party/rust/wast/src/core/memory.rs b/third_party/rust/wast/src/core/memory.rs
new file mode 100644
index 0000000000..ed845e055d
--- /dev/null
+++ b/third_party/rust/wast/src/core/memory.rs
@@ -0,0 +1,279 @@
+use crate::core::*;
+use crate::kw;
+use crate::parser::{Lookahead1, Parse, Parser, Peek, Result};
+use crate::token::*;
+
+/// A defined WebAssembly memory instance inside of a module.
+#[derive(Debug)]
+pub struct Memory<'a> {
+    /// Where this `memory` was defined
+    pub span: Span,
+    /// An optional name to refer to this memory by.
+    pub id: Option<Id<'a>>,
+    /// An optional name for this function stored in the custom `name` section.
+    pub name: Option<NameAnnotation<'a>>,
+    /// If present, inline export annotations which indicate names this
+    /// definition should be exported under.
+    pub exports: InlineExport<'a>,
+    /// How this memory is defined in the module.
+    pub kind: MemoryKind<'a>,
+}
+
+/// Different syntactical ways a memory can be defined in a module.
+#[derive(Debug)]
+pub enum MemoryKind<'a> {
+    /// This memory is actually an inlined import definition.
+    #[allow(missing_docs)]
+    Import {
+        import: InlineImport<'a>,
+        ty: MemoryType,
+    },
+
+    /// A typical memory definition which simply says the limits of the memory
+    Normal(MemoryType),
+
+    /// The data of this memory, starting from 0, explicitly listed
+    Inline {
+        /// Whether or not this will be creating a 32-bit memory
+        is_32: bool,
+        /// The inline data specified for this memory
+        data: Vec<DataVal<'a>>,
+    },
+}
+
+impl<'a> Parse<'a> for Memory<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let span = parser.parse::<kw::memory>()?.0;
+        let id = parser.parse()?;
+        let name = parser.parse()?;
+        let exports = parser.parse()?;
+
+        // Afterwards figure out which style this is, either:
+        //
+        //  *   `(import "a" "b") limits`
+        //  *   `(data ...)`
+        //  *   `limits`
+        let mut l = parser.lookahead1();
+        let kind = if let Some(import) = parser.parse()? {
+            MemoryKind::Import {
+                import,
+                ty: parser.parse()?,
+            }
+        } else if l.peek::<LParen>() || parser.peek2::<LParen>() {
+            let is_32 = if parser.parse::<Option<kw::i32>>()?.is_some() {
+                true
+            } else {
+                parser.parse::<Option<kw::i64>>()?.is_none()
+            };
+            let data = parser.parens(|parser| {
+                parser.parse::<kw::data>()?;
+                let mut data = Vec::new();
+                while !parser.is_empty() {
+                    data.push(parser.parse()?);
+                }
+                Ok(data)
+            })?;
+            MemoryKind::Inline { data, is_32 }
+        } else if l.peek::<u32>() || l.peek::<kw::i32>() || l.peek::<kw::i64>() {
+            MemoryKind::Normal(parser.parse()?)
+        } else {
+            return Err(l.error());
+        };
+        Ok(Memory {
+            span,
+            id,
+            name,
+            exports,
+            kind,
+        })
+    }
+}
+
+/// A `data` directive in a WebAssembly module.
+#[derive(Debug)]
+pub struct Data<'a> {
+    /// Where this `data` was defined
+    pub span: Span,
+
+    /// The optional name of this data segment
+    pub id: Option<Id<'a>>,
+
+    /// An optional name for this data stored in the custom `name` section.
+    pub name: Option<NameAnnotation<'a>>,
+
+    /// Whether this data segment is passive or active
+    pub kind: DataKind<'a>,
+
+    /// Bytes for this `Data` segment, viewed as the concatenation of all the
+    /// contained slices.
+    pub data: Vec<DataVal<'a>>,
+}
+
+/// Different kinds of data segments, either passive or active.
+#[derive(Debug)]
+pub enum DataKind<'a> {
+    /// A passive data segment which isn't associated with a memory and is
+    /// referenced from various instructions.
+    Passive,
+
+    /// An active data segment which is associated and loaded into a particular
+    /// memory on module instantiation.
+    Active {
+        /// The memory that this `Data` will be associated with.
+        memory: Index<'a>,
+
+        /// Initial offset to load this data segment at
+        offset: Expression<'a>,
+    },
+}
+
+impl<'a> Parse<'a> for Data<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let span = parser.parse::<kw::data>()?.0;
+        let id = parser.parse()?;
+        let name = parser.parse()?;
+
+        let kind = if parser.peek::<&[u8]>() {
+            DataKind::Passive
+
+        // ... and otherwise we must be attached to a particular memory as well
+        // as having an initialization offset.
+        } else {
+            let memory = if parser.peek::<u32>() {
+                // FIXME: this is only here to accomodate
+                // proposals/threads/imports.wast at this current moment in
+                // time, this probably should get removed when the threads
+                // proposal is rebased on the current spec.
+                Index::Num(parser.parse()?, span)
+            } else if parser.peek2::<kw::memory>() {
+                parser.parens(|p| {
+                    p.parse::<kw::memory>()?;
+                    p.parse()
+                })?
+            } else {
+                Index::Num(0, span)
+            };
+            let offset = parser.parens(|parser| {
+                if parser.peek::<kw::offset>() {
+                    parser.parse::<kw::offset>()?;
+                    parser.parse()
+                } else {
+                    // This is all that the spec allows, which is that if
+                    // `offset` isn't present then this is "sugar" for a
+                    // single-instruction expression.
+                    let insn = parser.parse()?;
+                    if parser.is_empty() {
+                        return Ok(Expression {
+                            instrs: [insn].into(),
+                        });
+                    }
+
+                    // This is support for what is currently invalid syntax
+                    // according to the strict specification but is otherwise
+                    // present in the spec test suite:
+                    //
+                    //    (data (i32.add (i32.const 0) (i32.const 0)))
+                    //
+                    // Technically the spec says this should be:
+                    //
+                    //    (data (offset ...))
+                    //
+                    // but alas
+                    let expr: Expression = parser.parse()?;
+                    let mut instrs = Vec::from(expr.instrs);
+                    instrs.push(insn);
+                    Ok(Expression {
+                        instrs: instrs.into(),
+                    })
+                }
+            })?;
+            DataKind::Active { memory, offset }
+        };
+
+        let mut data = Vec::new();
+        while !parser.is_empty() {
+            data.push(parser.parse()?);
+        }
+        Ok(Data {
+            span,
+            id,
+            name,
+            kind,
+            data,
+        })
+    }
+}
+
+/// Differnet ways the value of a data segment can be defined.
+#[derive(Debug)]
+#[allow(missing_docs)]
+pub enum DataVal<'a> {
+    String(&'a [u8]),
+    Integral(Vec<u8>),
+}
+
+impl DataVal<'_> {
+    /// Returns the length, in bytes, of the memory used to represent this data
+    /// value.
+    pub fn len(&self) -> usize {
+        match self {
+            DataVal::String(s) => s.len(),
+            DataVal::Integral(s) => s.len(),
+        }
+    }
+
+    /// Pushes the value of this data value onto the provided list of bytes.
+    pub fn push_onto(&self, dst: &mut Vec<u8>) {
+        match self {
+            DataVal::String(s) => dst.extend_from_slice(s),
+            DataVal::Integral(s) => dst.extend_from_slice(s),
+        }
+    }
+}
+
+impl<'a> Parse<'a> for DataVal<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        if !parser.peek::<LParen>() {
+            return Ok(DataVal::String(parser.parse()?));
+        }
+
+        return parser.parens(|p| {
+            let mut result = Vec::new();
+            let mut lookahead = p.lookahead1();
+            let l = &mut lookahead;
+            let r = &mut result;
+            if consume::<kw::i8, i8, _>(p, l, r, |u, v| v.push(u as u8))?
+                || consume::<kw::i16, i16, _>(p, l, r, |u, v| v.extend(&u.to_le_bytes()))?
+                || consume::<kw::i32, i32, _>(p, l, r, |u, v| v.extend(&u.to_le_bytes()))?
+                || consume::<kw::i64, i64, _>(p, l, r, |u, v| v.extend(&u.to_le_bytes()))?
+                || consume::<kw::f32, Float32, _>(p, l, r, |u, v| v.extend(&u.bits.to_le_bytes()))?
+                || consume::<kw::f64, Float64, _>(p, l, r, |u, v| v.extend(&u.bits.to_le_bytes()))?
+                || consume::<kw::v128, V128Const, _>(p, l, r, |u, v| v.extend(&u.to_le_bytes()))?
+            {
+                Ok(DataVal::Integral(result))
+            } else {
+                Err(lookahead.error())
+            }
+        });
+
+        fn consume<'a, T: Peek + Parse<'a>, U: Parse<'a>, F>(
+            parser: Parser<'a>,
+            lookahead: &mut Lookahead1<'a>,
+            dst: &mut Vec<u8>,
+            push: F,
+        ) -> Result<bool>
+        where
+            F: Fn(U, &mut Vec<u8>),
+        {
+            if !lookahead.peek::<T>() {
+                return Ok(false);
+            }
+            parser.parse::<T>()?;
+            while !parser.is_empty() {
+                let val = parser.parse::<U>()?;
+                push(val, dst);
+            }
+            Ok(true)
+        }
+    }
+}
diff --git a/third_party/rust/wast/src/core/module.rs b/third_party/rust/wast/src/core/module.rs
new file mode 100644
index 0000000000..b6e3ca0ad2
--- /dev/null
+++ b/third_party/rust/wast/src/core/module.rs
@@ -0,0 +1,210 @@
+use crate::core::*;
+use crate::parser::{Parse, Parser, Result};
+use crate::token::{Id, Index, NameAnnotation, Span};
+use crate::{annotation, kw};
+
+pub use crate::core::resolve::Names;
+
+/// A parsed WebAssembly core module.
+#[derive(Debug)]
+pub struct Module<'a> {
+    /// Where this `module` was defined
+    pub span: Span,
+    /// An optional identifier this module is known by
+    pub id: Option<Id<'a>>,
+    /// An optional `@name` annotation for this module
+    pub name: Option<NameAnnotation<'a>>,
+    /// What kind of module this was parsed as.
+    pub kind: ModuleKind<'a>,
+}
+
+/// The different kinds of ways to define a module.
+#[derive(Debug)]
+pub enum ModuleKind<'a> {
+    /// A module defined in the textual s-expression format.
+    Text(Vec<ModuleField<'a>>),
+    /// A module that had its raw binary bytes defined via the `binary`
+    /// directive.
+    Binary(Vec<&'a [u8]>),
+}
+
+impl<'a> Module<'a> {
+    /// Performs a name resolution pass on this [`Module`], resolving all
+    /// symbolic names to indices.
+    ///
+    /// The WAT format contains a number of shorthands to make it easier to
+    /// write, such as inline exports, inline imports, inline type definitions,
+    /// etc. Additionally it allows using symbolic names such as `$foo` instead
+    /// of using indices. This module will postprocess an AST to remove all of
+    /// this syntactic sugar, preparing the AST for binary emission.  This is
+    /// where expansion and name resolution happens.
+    ///
+    /// This function will mutate the AST of this [`Module`] and replace all
+    /// [`Index`](crate::token::Index) arguments with `Index::Num`. This will
+    /// also expand inline exports/imports listed on fields and handle various
+    /// other shorthands of the text format.
+    ///
+    /// If successful the AST was modified to be ready for binary encoding. A
+    /// [`Names`] structure is also returned so if you'd like to do your own
+    /// name lookups on the result you can do so as well.
+    ///
+    /// # Errors
+    ///
+    /// If an error happens during resolution, such a name resolution error or
+    /// items are found in the wrong order, then an error is returned.
+    pub fn resolve(&mut self) -> std::result::Result<Names<'a>, crate::Error> {
+        let names = match &mut self.kind {
+            ModuleKind::Text(fields) => crate::core::resolve::resolve(fields)?,
+            ModuleKind::Binary(_blobs) => Default::default(),
+        };
+        Ok(names)
+    }
+
+    /// Encodes this [`Module`] to its binary form.
+    ///
+    /// This function will take the textual representation in [`Module`] and
+    /// perform all steps necessary to convert it to a binary WebAssembly
+    /// module, suitable for writing to a `*.wasm` file. This function may
+    /// internally modify the [`Module`], for example:
+    ///
+    /// * Name resolution is performed to ensure that `Index::Id` isn't present
+    ///   anywhere in the AST.
+    ///
+    /// * Inline shorthands such as imports/exports/types are all expanded to be
+    ///   dedicated fields of the module.
+    ///
+    /// * Module fields may be shuffled around to preserve index ordering from
+    ///   expansions.
+    ///
+    /// After all of this expansion has happened the module will be converted to
+    /// its binary form and returned as a `Vec<u8>`. This is then suitable to
+    /// hand off to other wasm runtimes and such.
+    ///
+    /// # Errors
+    ///
+    /// This function can return an error for name resolution errors and other
+    /// expansion-related errors.
+    pub fn encode(&mut self) -> std::result::Result<Vec<u8>, crate::Error> {
+        self.resolve()?;
+        Ok(match &self.kind {
+            ModuleKind::Text(fields) => crate::core::binary::encode(&self.id, &self.name, fields),
+            ModuleKind::Binary(blobs) => blobs.iter().flat_map(|b| b.iter().cloned()).collect(),
+        })
+    }
+
+    pub(crate) fn validate(&self, parser: Parser<'_>) -> Result<()> {
+        let mut starts = 0;
+        if let ModuleKind::Text(fields) = &self.kind {
+            for item in fields.iter() {
+                if let ModuleField::Start(_) = item {
+                    starts += 1;
+                }
+            }
+        }
+        if starts > 1 {
+            return Err(parser.error("multiple start sections found"));
+        }
+        Ok(())
+    }
+}
+
+impl<'a> Parse<'a> for Module<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let _r = parser.register_annotation("custom");
+        let span = parser.parse::<kw::module>()?.0;
+        let id = parser.parse()?;
+        let name = parser.parse()?;
+
+        let kind = if parser.peek::<kw::binary>() {
+            parser.parse::<kw::binary>()?;
+            let mut data = Vec::new();
+            while !parser.is_empty() {
+                data.push(parser.parse()?);
+            }
+            ModuleKind::Binary(data)
+        } else {
+            ModuleKind::Text(ModuleField::parse_remaining(parser)?)
+        };
+        Ok(Module {
+            span,
+            id,
+            name,
+            kind,
+        })
+    }
+}
+
+/// A listing of all possible fields that can make up a WebAssembly module.
+#[allow(missing_docs)]
+#[derive(Debug)]
+pub enum ModuleField<'a> {
+    Type(Type<'a>),
+    Rec(Rec<'a>),
+    Import(Import<'a>),
+    Func(Func<'a>),
+    Table(Table<'a>),
+    Memory(Memory<'a>),
+    Global(Global<'a>),
+    Export(Export<'a>),
+    Start(Index<'a>),
+    Elem(Elem<'a>),
+    Data(Data<'a>),
+    Tag(Tag<'a>),
+    Custom(Custom<'a>),
+}
+
+impl<'a> ModuleField<'a> {
+    pub(crate) fn parse_remaining(parser: Parser<'a>) -> Result<Vec<ModuleField>> {
+        let mut fields = Vec::new();
+        while !parser.is_empty() {
+            fields.push(parser.parens(ModuleField::parse)?);
+        }
+        Ok(fields)
+    }
+}
+
+impl<'a> Parse<'a> for ModuleField<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        if parser.peek::<Type<'a>>() {
+            return Ok(ModuleField::Type(parser.parse()?));
+        }
+        if parser.peek::<kw::rec>() {
+            return Ok(ModuleField::Rec(parser.parse()?));
+        }
+        if parser.peek::<kw::import>() {
+            return Ok(ModuleField::Import(parser.parse()?));
+        }
+        if parser.peek::<kw::func>() {
+            return Ok(ModuleField::Func(parser.parse()?));
+        }
+        if parser.peek::<kw::table>() {
+            return Ok(ModuleField::Table(parser.parse()?));
+        }
+        if parser.peek::<kw::memory>() {
+            return Ok(ModuleField::Memory(parser.parse()?));
+        }
+        if parser.peek::<kw::global>() {
+            return Ok(ModuleField::Global(parser.parse()?));
+        }
+        if parser.peek::<kw::export>() {
+            return Ok(ModuleField::Export(parser.parse()?));
+        }
+        if parser.peek::<kw::start>() {
+            parser.parse::<kw::start>()?;
+            return Ok(ModuleField::Start(parser.parse()?));
+        }
+        if parser.peek::<kw::elem>() {
+            return Ok(ModuleField::Elem(parser.parse()?));
+        }
+        if parser.peek::<kw::data>() {
+            return Ok(ModuleField::Data(parser.parse()?));
+        }
+        if parser.peek::<kw::tag>() {
+            return Ok(ModuleField::Tag(parser.parse()?));
+        }
+        if parser.peek::<annotation::custom>() {
+            return Ok(ModuleField::Custom(parser.parse()?));
+        }
+        Err(parser.error("expected valid module field"))
+    }
+}
diff --git a/third_party/rust/wast/src/core/resolve/deinline_import_export.rs b/third_party/rust/wast/src/core/resolve/deinline_import_export.rs
new file mode 100644
index 0000000000..c338407182
--- /dev/null
+++ b/third_party/rust/wast/src/core/resolve/deinline_import_export.rs
@@ -0,0 +1,231 @@
+use crate::core::*;
+use crate::gensym;
+use crate::token::{Id, Index, Span};
+use std::mem;
+
+pub fn run(fields: &mut Vec<ModuleField>) {
+    for mut item in mem::take(fields) {
+        match &mut item {
+            ModuleField::Func(f) => {
+                for name in f.exports.names.drain(..) {
+                    fields.push(export(f.span, name, ExportKind::Func, &mut f.id));
+                }
+                match f.kind {
+                    FuncKind::Import(import) => {
+                        item = ModuleField::Import(Import {
+                            span: f.span,
+                            module: import.module,
+                            field: import.field,
+                            item: ItemSig {
+                                span: f.span,
+                                id: f.id,
+                                name: f.name,
+                                kind: ItemKind::Func(f.ty.clone()),
+                            },
+                        });
+                    }
+                    FuncKind::Inline { .. } => {}
+                }
+            }
+
+            ModuleField::Memory(m) => {
+                for name in m.exports.names.drain(..) {
+                    fields.push(export(m.span, name, ExportKind::Memory, &mut m.id));
+                }
+                match m.kind {
+                    MemoryKind::Import { import, ty } => {
+                        item = ModuleField::Import(Import {
+                            span: m.span,
+                            module: import.module,
+                            field: import.field,
+                            item: ItemSig {
+                                span: m.span,
+                                id: m.id,
+                                name: None,
+                                kind: ItemKind::Memory(ty),
+                            },
+                        });
+                    }
+                    // If data is defined inline insert an explicit `data` module
+                    // field here instead, switching this to a `Normal` memory.
+                    MemoryKind::Inline { is_32, ref data } => {
+                        let len = data.iter().map(|l| l.len()).sum::<usize>() as u32;
+                        let pages = (len + page_size() - 1) / page_size();
+                        let kind = MemoryKind::Normal(if is_32 {
+                            MemoryType::B32 {
+                                limits: Limits {
+                                    min: pages,
+                                    max: Some(pages),
+                                },
+                                shared: false,
+                            }
+                        } else {
+                            MemoryType::B64 {
+                                limits: Limits64 {
+                                    min: u64::from(pages),
+                                    max: Some(u64::from(pages)),
+                                },
+                                shared: false,
+                            }
+                        });
+                        let data = match mem::replace(&mut m.kind, kind) {
+                            MemoryKind::Inline { data, .. } => data,
+                            _ => unreachable!(),
+                        };
+                        let id = gensym::fill(m.span, &mut m.id);
+                        fields.push(ModuleField::Data(Data {
+                            span: m.span,
+                            id: None,
+                            name: None,
+                            kind: DataKind::Active {
+                                memory: Index::Id(id),
+                                offset: Expression {
+                                    instrs: Box::new([if is_32 {
+                                        Instruction::I32Const(0)
+                                    } else {
+                                        Instruction::I64Const(0)
+                                    }]),
+                                },
+                            },
+                            data,
+                        }));
+                    }
+
+                    MemoryKind::Normal(_) => {}
+                }
+            }
+
+            ModuleField::Table(t) => {
+                for name in t.exports.names.drain(..) {
+                    fields.push(export(t.span, name, ExportKind::Table, &mut t.id));
+                }
+                match &mut t.kind {
+                    TableKind::Import { import, ty } => {
+                        item = ModuleField::Import(Import {
+                            span: t.span,
+                            module: import.module,
+                            field: import.field,
+                            item: ItemSig {
+                                span: t.span,
+                                id: t.id,
+                                name: None,
+                                kind: ItemKind::Table(*ty),
+                            },
+                        });
+                    }
+                    // If data is defined inline insert an explicit `data` module
+                    // field here instead, switching this to a `Normal` memory.
+                    TableKind::Inline { payload, elem } => {
+                        let len = match payload {
+                            ElemPayload::Indices(v) => v.len(),
+                            ElemPayload::Exprs { exprs, .. } => exprs.len(),
+                        };
+                        let kind = TableKind::Normal {
+                            ty: TableType {
+                                limits: Limits {
+                                    min: len as u32,
+                                    max: Some(len as u32),
+                                },
+                                elem: *elem,
+                            },
+                            init_expr: None,
+                        };
+                        let payload = match mem::replace(&mut t.kind, kind) {
+                            TableKind::Inline { payload, .. } => payload,
+                            _ => unreachable!(),
+                        };
+                        let id = gensym::fill(t.span, &mut t.id);
+                        fields.push(ModuleField::Elem(Elem {
+                            span: t.span,
+                            id: None,
+                            name: None,
+                            kind: ElemKind::Active {
+                                table: Index::Id(id),
+                                offset: Expression {
+                                    instrs: Box::new([Instruction::I32Const(0)]),
+                                },
+                            },
+                            payload,
+                        }));
+                    }
+
+                    TableKind::Normal { .. } => {}
+                }
+            }
+
+            ModuleField::Global(g) => {
+                for name in g.exports.names.drain(..) {
+                    fields.push(export(g.span, name, ExportKind::Global, &mut g.id));
+                }
+                match g.kind {
+                    GlobalKind::Import(import) => {
+                        item = ModuleField::Import(Import {
+                            span: g.span,
+                            module: import.module,
+                            field: import.field,
+                            item: ItemSig {
+                                span: g.span,
+                                id: g.id,
+                                name: None,
+                                kind: ItemKind::Global(g.ty),
+                            },
+                        });
+                    }
+                    GlobalKind::Inline { .. } => {}
+                }
+            }
+
+            ModuleField::Tag(e) => {
+                for name in e.exports.names.drain(..) {
+                    fields.push(export(e.span, name, ExportKind::Tag, &mut e.id));
+                }
+                match e.kind {
+                    TagKind::Import(import) => {
+                        item = ModuleField::Import(Import {
+                            span: e.span,
+                            module: import.module,
+                            field: import.field,
+                            item: ItemSig {
+                                span: e.span,
+                                id: e.id,
+                                name: None,
+                                kind: ItemKind::Tag(e.ty.clone()),
+                            },
+                        });
+                    }
+                    TagKind::Inline { .. } => {}
+                }
+            }
+
+            ModuleField::Import(_)
+            | ModuleField::Type(_)
+            | ModuleField::Rec(_)
+            | ModuleField::Export(_)
+            | ModuleField::Start(_)
+            | ModuleField::Elem(_)
+            | ModuleField::Data(_)
+            | ModuleField::Custom(_) => {}
+        }
+
+        fields.push(item);
+    }
+
+    fn page_size() -> u32 {
+        1 << 16
+    }
+}
+
+fn export<'a>(
+    span: Span,
+    name: &'a str,
+    kind: ExportKind,
+    id: &mut Option<Id<'a>>,
+) -> ModuleField<'a> {
+    let id = gensym::fill(span, id);
+    ModuleField::Export(Export {
+        span,
+        name,
+        kind,
+        item: Index::Id(id),
+    })
+}
diff --git a/third_party/rust/wast/src/core/resolve/mod.rs b/third_party/rust/wast/src/core/resolve/mod.rs
new file mode 100644
index 0000000000..7b3ba2b1e3
--- /dev/null
+++ b/third_party/rust/wast/src/core/resolve/mod.rs
@@ -0,0 +1,109 @@
+use crate::core::*;
+use crate::token::Index;
+use crate::{gensym, Error};
+
+mod deinline_import_export;
+mod names;
+pub(crate) mod types;
+
+#[derive(PartialEq, Eq, Hash, Copy, Clone, Debug)]
+pub enum Ns {
+    Func,
+    Table,
+    Global,
+    Memory,
+    Tag,
+    Type,
+}
+
+pub fn resolve<'a>(fields: &mut Vec<ModuleField<'a>>) -> Result<Names<'a>, Error> {
+    // Ensure that each resolution of a module is deterministic in the names
+    // that it generates by resetting our thread-local symbol generator.
+    gensym::reset();
+
+    // First up, de-inline import/export annotations.
+    //
+    // This ensures we only have to deal with inline definitions and to
+    // calculate exports we only have to look for a particular kind of module
+    // field.
+    deinline_import_export::run(fields);
+
+    // With a canonical form of imports make sure that imports are all listed
+    // first.
+    let mut last = None;
+    for field in fields.iter() {
+        match field {
+            ModuleField::Import(i) => {
+                if let Some(name) = last {
+                    return Err(Error::new(i.span, format!("import after {}", name)));
+                }
+            }
+            ModuleField::Memory(_) => last = Some("memory"),
+            ModuleField::Func(_) => last = Some("function"),
+            ModuleField::Table(_) => last = Some("table"),
+            ModuleField::Global(_) => last = Some("global"),
+            _ => continue,
+        }
+    }
+
+    // Expand all `TypeUse` annotations so all necessary `type` nodes are
+    // present in the AST.
+    types::expand(fields);
+
+    // Perform name resolution over all `Index` items to resolve them all to
+    // indices instead of symbolic names.
+    let resolver = names::resolve(fields)?;
+    Ok(Names { resolver })
+}
+
+/// Representation of the results of name resolution for a module.
+///
+/// This structure is returned from the
+/// [`Module::resolve`](crate::core::Module::resolve) function and can be used
+/// to resolve your own name arguments if you have any.
+#[derive(Default)]
+pub struct Names<'a> {
+    resolver: names::Resolver<'a>,
+}
+
+impl<'a> Names<'a> {
+    /// Resolves `idx` within the function namespace.
+    ///
+    /// If `idx` is a `Num`, it is ignored, but if it's an `Id` then it will be
+    /// looked up in the function namespace and converted to a `Num`. If the
+    /// `Id` is not defined then an error will be returned.
+    pub fn resolve_func(&self, idx: &mut Index<'a>) -> Result<(), Error> {
+        self.resolver.resolve(idx, Ns::Func)?;
+        Ok(())
+    }
+
+    /// Resolves `idx` within the memory namespace.
+    ///
+    /// If `idx` is a `Num`, it is ignored, but if it's an `Id` then it will be
+    /// looked up in the memory namespace and converted to a `Num`. If the
+    /// `Id` is not defined then an error will be returned.
+    pub fn resolve_memory(&self, idx: &mut Index<'a>) -> Result<(), Error> {
+        self.resolver.resolve(idx, Ns::Memory)?;
+        Ok(())
+    }
+
+    /// Resolves `idx` within the table namespace.
+    ///
+    /// If `idx` is a `Num`, it is ignored, but if it's an `Id` then it will be
+    /// looked up in the table namespace and converted to a `Num`. If the
+    /// `Id` is not defined then an error will be returned.
+    pub fn resolve_table(&self, idx: &mut Index<'a>) -> Result<(), Error> {
+        self.resolver.resolve(idx, Ns::Table)?;
+        Ok(())
+    }
+
+    /// Resolves `idx` within the global namespace.
+    ///
+    /// If `idx` is a `Num`, it is ignored, but if it's an `Id` then it will be
+    /// looked up in the global namespace and converted to a `Num`. If the
+    /// `Id` is not defined then an error will be returned.
+    pub fn resolve_global(&self, idx: &mut Index<'a>) -> Result<(), Error> {
+        self.resolver.resolve(idx, Ns::Global)?;
+        Ok(())
+    }
+}
diff --git a/third_party/rust/wast/src/core/resolve/names.rs b/third_party/rust/wast/src/core/resolve/names.rs
new file mode 100644
index 0000000000..5ff2e8042a
--- /dev/null
+++ b/third_party/rust/wast/src/core/resolve/names.rs
@@ -0,0 +1,737 @@
+use crate::core::resolve::Ns;
+use crate::core::*;
+use crate::names::{resolve_error, Namespace};
+use crate::token::{Id, Index};
+use crate::Error;
+
+pub fn resolve<'a>(fields: &mut Vec<ModuleField<'a>>) -> Result<Resolver<'a>, Error> {
+    let mut resolver = Resolver::default();
+    resolver.process(fields)?;
+    Ok(resolver)
+}
+
+/// Context structure used to perform name resolution.
+#[derive(Default)]
+pub struct Resolver<'a> {
+    // Namespaces within each module. Note that each namespace carries with it
+    // information about the signature of the item in that namespace. The
+    // signature is later used to synthesize the type of a module and inject
+    // type annotations if necessary.
+    funcs: Namespace<'a>,
+    globals: Namespace<'a>,
+    tables: Namespace<'a>,
+    memories: Namespace<'a>,
+    types: Namespace<'a>,
+    tags: Namespace<'a>,
+    datas: Namespace<'a>,
+    elems: Namespace<'a>,
+    fields: Namespace<'a>,
+    type_info: Vec<TypeInfo<'a>>,
+}
+
+impl<'a> Resolver<'a> {
+    fn process(&mut self, fields: &mut Vec<ModuleField<'a>>) -> Result<(), Error> {
+        // Number everything in the module, recording what names correspond to
+        // what indices.
+        for field in fields.iter_mut() {
+            self.register(field)?;
+        }
+
+        // Then we can replace all our `Index::Id` instances with `Index::Num`
+        // in the AST. Note that this also recurses into nested modules.
+        for field in fields.iter_mut() {
+            self.resolve_field(field)?;
+        }
+        Ok(())
+    }
+
+    fn register_type(&mut self, ty: &Type<'a>) -> Result<(), Error> {
+        match &ty.def {
+            // For GC structure types we need to be sure to populate the
+            // field namespace here as well.
+            //
+            // The field namespace is global, but the resolved indices
+            // are relative to the struct they are defined in
+            TypeDef::Struct(r#struct) => {
+                for (i, field) in r#struct.fields.iter().enumerate() {
+                    if let Some(id) = field.id {
+                        self.fields.register_specific(id, i as u32, "field")?;
+                    }
+                }
+            }
+
+            TypeDef::Array(_) | TypeDef::Func(_) => {}
+        }
+
+        // Record function signatures as we see them to so we can
+        // generate errors for mismatches in references such as
+        // `call_indirect`.
+        match &ty.def {
+            TypeDef::Func(f) => {
+                let params = f.params.iter().map(|p| p.2).collect();
+                let results = f.results.clone();
+                self.type_info.push(TypeInfo::Func { params, results });
+            }
+            _ => self.type_info.push(TypeInfo::Other),
+        }
+
+        self.types.register(ty.id, "type")?;
+        Ok(())
+    }
+
+    fn register(&mut self, item: &ModuleField<'a>) -> Result<(), Error> {
+        match item {
+            ModuleField::Import(i) => match &i.item.kind {
+                ItemKind::Func(_) => self.funcs.register(i.item.id, "func")?,
+                ItemKind::Memory(_) => self.memories.register(i.item.id, "memory")?,
+                ItemKind::Table(_) => self.tables.register(i.item.id, "table")?,
+                ItemKind::Global(_) => self.globals.register(i.item.id, "global")?,
+                ItemKind::Tag(_) => self.tags.register(i.item.id, "tag")?,
+            },
+            ModuleField::Global(i) => self.globals.register(i.id, "global")?,
+            ModuleField::Memory(i) => self.memories.register(i.id, "memory")?,
+            ModuleField::Func(i) => self.funcs.register(i.id, "func")?,
+            ModuleField::Table(i) => self.tables.register(i.id, "table")?,
+
+            ModuleField::Type(i) => {
+                return self.register_type(i);
+            }
+            ModuleField::Rec(i) => {
+                for ty in &i.types {
+                    self.register_type(ty)?;
+                }
+                return Ok(());
+            }
+            ModuleField::Elem(e) => self.elems.register(e.id, "elem")?,
+            ModuleField::Data(d) => self.datas.register(d.id, "data")?,
+            ModuleField::Tag(t) => self.tags.register(t.id, "tag")?,
+
+            // These fields don't define any items in any index space.
+            ModuleField::Export(_) | ModuleField::Start(_) | ModuleField::Custom(_) => {
+                return Ok(())
+            }
+        };
+
+        Ok(())
+    }
+
+    fn resolve_type(&self, ty: &mut Type<'a>) -> Result<(), Error> {
+        match &mut ty.def {
+            TypeDef::Func(func) => func.resolve(self)?,
+            TypeDef::Struct(struct_) => {
+                for field in &mut struct_.fields {
+                    self.resolve_storagetype(&mut field.ty)?;
+                }
+            }
+            TypeDef::Array(array) => self.resolve_storagetype(&mut array.ty)?,
+        }
+        if let Some(parent) = &mut ty.parent {
+            self.resolve(parent, Ns::Type)?;
+        }
+        Ok(())
+    }
+
+    fn resolve_field(&self, field: &mut ModuleField<'a>) -> Result<(), Error> {
+        match field {
+            ModuleField::Import(i) => {
+                self.resolve_item_sig(&mut i.item)?;
+                Ok(())
+            }
+
+            ModuleField::Type(ty) => self.resolve_type(ty),
+            ModuleField::Rec(rec) => {
+                for ty in &mut rec.types {
+                    self.resolve_type(ty)?;
+                }
+                Ok(())
+            }
+
+            ModuleField::Func(f) => {
+                let (idx, inline) = self.resolve_type_use(&mut f.ty)?;
+                let n = match idx {
+                    Index::Num(n, _) => *n,
+                    Index::Id(_) => panic!("expected `Num`"),
+                };
+                if let FuncKind::Inline { locals, expression } = &mut f.kind {
+                    // Resolve (ref T) in locals
+                    for local in locals.iter_mut() {
+                        self.resolve_valtype(&mut local.ty)?;
+                    }
+
+                    // Build a scope with a local namespace for the function
+                    // body
+                    let mut scope = Namespace::default();
+
+                    // Parameters come first in the scope...
+                    if let Some(inline) = &inline {
+                        for (id, _, _) in inline.params.iter() {
+                            scope.register(*id, "local")?;
+                        }
+                    } else if let Some(TypeInfo::Func { params, .. }) =
+                        self.type_info.get(n as usize)
+                    {
+                        for _ in 0..params.len() {
+                            scope.register(None, "local")?;
+                        }
+                    }
+
+                    // .. followed by locals themselves
+                    for local in locals {
+                        scope.register(local.id, "local")?;
+                    }
+
+                    // Initialize the expression resolver with this scope
+                    let mut resolver = ExprResolver::new(self, scope);
+
+                    // and then we can resolve the expression!
+                    resolver.resolve(expression)?;
+
+                    // specifically save the original `sig`, if it was present,
+                    // because that's what we're using for local names.
+                    f.ty.inline = inline;
+                }
+                Ok(())
+            }
+
+            ModuleField::Elem(e) => {
+                match &mut e.kind {
+                    ElemKind::Active { table, offset } => {
+                        self.resolve(table, Ns::Table)?;
+                        self.resolve_expr(offset)?;
+                    }
+                    ElemKind::Passive { .. } | ElemKind::Declared { .. } => {}
+                }
+                match &mut e.payload {
+                    ElemPayload::Indices(elems) => {
+                        for idx in elems {
+                            self.resolve(idx, Ns::Func)?;
+                        }
+                    }
+                    ElemPayload::Exprs { exprs, ty } => {
+                        for expr in exprs {
+                            self.resolve_expr(expr)?;
+                        }
+                        self.resolve_heaptype(&mut ty.heap)?;
+                    }
+                }
+                Ok(())
+            }
+
+            ModuleField::Data(d) => {
+                if let DataKind::Active { memory, offset } = &mut d.kind {
+                    self.resolve(memory, Ns::Memory)?;
+                    self.resolve_expr(offset)?;
+                }
+                Ok(())
+            }
+
+            ModuleField::Start(i) => {
+                self.resolve(i, Ns::Func)?;
+                Ok(())
+            }
+
+            ModuleField::Export(e) => {
+                self.resolve(
+                    &mut e.item,
+                    match e.kind {
+                        ExportKind::Func => Ns::Func,
+                        ExportKind::Table => Ns::Table,
+                        ExportKind::Memory => Ns::Memory,
+                        ExportKind::Global => Ns::Global,
+                        ExportKind::Tag => Ns::Tag,
+                    },
+                )?;
+                Ok(())
+            }
+
+            ModuleField::Global(g) => {
+                self.resolve_valtype(&mut g.ty.ty)?;
+                if let GlobalKind::Inline(expr) = &mut g.kind {
+                    self.resolve_expr(expr)?;
+                }
+                Ok(())
+            }
+
+            ModuleField::Tag(t) => {
+                match &mut t.ty {
+                    TagType::Exception(ty) => {
+                        self.resolve_type_use(ty)?;
+                    }
+                }
+                Ok(())
+            }
+
+            ModuleField::Table(t) => {
+                if let TableKind::Normal { ty, init_expr } = &mut t.kind {
+                    self.resolve_heaptype(&mut ty.elem.heap)?;
+                    if let Some(init_expr) = init_expr {
+                        self.resolve_expr(init_expr)?;
+                    }
+                }
+                Ok(())
+            }
+
+            ModuleField::Memory(_) | ModuleField::Custom(_) => Ok(()),
+        }
+    }
+
+    fn resolve_valtype(&self, ty: &mut ValType<'a>) -> Result<(), Error> {
+        match ty {
+            ValType::Ref(ty) => self.resolve_heaptype(&mut ty.heap)?,
+            _ => {}
+        }
+        Ok(())
+    }
+
+    fn resolve_reftype(&self, ty: &mut RefType<'a>) -> Result<(), Error> {
+        self.resolve_heaptype(&mut ty.heap)
+    }
+
+    fn resolve_heaptype(&self, ty: &mut HeapType<'a>) -> Result<(), Error> {
+        match ty {
+            HeapType::Index(i) => {
+                self.resolve(i, Ns::Type)?;
+            }
+            _ => {}
+        }
+        Ok(())
+    }
+
+    fn resolve_storagetype(&self, ty: &mut StorageType<'a>) -> Result<(), Error> {
+        match ty {
+            StorageType::Val(ty) => self.resolve_valtype(ty)?,
+            _ => {}
+        }
+        Ok(())
+    }
+
+    fn resolve_item_sig(&self, item: &mut ItemSig<'a>) -> Result<(), Error> {
+        match &mut item.kind {
+            ItemKind::Func(t) | ItemKind::Tag(TagType::Exception(t)) => {
+                self.resolve_type_use(t)?;
+            }
+            ItemKind::Global(t) => self.resolve_valtype(&mut t.ty)?,
+            ItemKind::Table(t) => {
+                self.resolve_heaptype(&mut t.elem.heap)?;
+            }
+            ItemKind::Memory(_) => {}
+        }
+        Ok(())
+    }
+
+    fn resolve_type_use<'b, T>(
+        &self,
+        ty: &'b mut TypeUse<'a, T>,
+    ) -> Result<(&'b Index<'a>, Option<T>), Error>
+    where
+        T: TypeReference<'a>,
+    {
+        let idx = ty.index.as_mut().unwrap();
+        self.resolve(idx, Ns::Type)?;
+
+        // If the type was listed inline *and* it was specified via a type index
+        // we need to assert they're the same.
+        //
+        // Note that we resolve the type first to transform all names to
+        // indices to ensure that all the indices line up.
+        if let Some(inline) = &mut ty.inline {
+            inline.resolve(self)?;
+            inline.check_matches(idx, self)?;
+        }
+
+        Ok((idx, ty.inline.take()))
+    }
+
+    fn resolve_expr(&self, expr: &mut Expression<'a>) -> Result<(), Error> {
+        ExprResolver::new(self, Namespace::default()).resolve(expr)
+    }
+
+    pub fn resolve(&self, idx: &mut Index<'a>, ns: Ns) -> Result<u32, Error> {
+        match ns {
+            Ns::Func => self.funcs.resolve(idx, "func"),
+            Ns::Table => self.tables.resolve(idx, "table"),
+            Ns::Global => self.globals.resolve(idx, "global"),
+            Ns::Memory => self.memories.resolve(idx, "memory"),
+            Ns::Tag => self.tags.resolve(idx, "tag"),
+            Ns::Type => self.types.resolve(idx, "type"),
+        }
+    }
+}
+
+#[derive(Debug, Clone)]
+struct ExprBlock<'a> {
+    // The label of the block
+    label: Option<Id<'a>>,
+    // Whether this block pushed a new scope for resolving locals
+    pushed_scope: bool,
+}
+
+struct ExprResolver<'a, 'b> {
+    resolver: &'b Resolver<'a>,
+    // Scopes tracks the local namespace and dynamically grows as we enter/exit
+    // `let` blocks
+    scopes: Vec<Namespace<'a>>,
+    blocks: Vec<ExprBlock<'a>>,
+}
+
+impl<'a, 'b> ExprResolver<'a, 'b> {
+    fn new(resolver: &'b Resolver<'a>, initial_scope: Namespace<'a>) -> ExprResolver<'a, 'b> {
+        ExprResolver {
+            resolver,
+            scopes: vec![initial_scope],
+            blocks: Vec::new(),
+        }
+    }
+
+    fn resolve(&mut self, expr: &mut Expression<'a>) -> Result<(), Error> {
+        for instr in expr.instrs.iter_mut() {
+            self.resolve_instr(instr)?;
+        }
+        Ok(())
+    }
+
+    fn resolve_block_type(&mut self, bt: &mut BlockType<'a>) -> Result<(), Error> {
+        // If the index is specified on this block type then that's the source
+        // of resolution and the resolver step here will verify the inline type
+        // matches. Note that indexes may come from the source text itself but
+        // may also come from being injected as part of the type expansion phase
+        // of resolution.
+        //
+        // If no type is present then that means that the inline type is not
+        // present or has 0-1 results. In that case the nested value types are
+        // resolved, if they're there, to get encoded later on.
+        if bt.ty.index.is_some() {
+            self.resolver.resolve_type_use(&mut bt.ty)?;
+        } else if let Some(inline) = &mut bt.ty.inline {
+            inline.resolve(self.resolver)?;
+        }
+
+        Ok(())
+    }
+
+    fn resolve_instr(&mut self, instr: &mut Instruction<'a>) -> Result<(), Error> {
+        use Instruction::*;
+
+        if let Some(m) = instr.memarg_mut() {
+            self.resolver.resolve(&mut m.memory, Ns::Memory)?;
+        }
+
+        match instr {
+            MemorySize(i) | MemoryGrow(i) | MemoryFill(i) | MemoryDiscard(i) => {
+                self.resolver.resolve(&mut i.mem, Ns::Memory)?;
+            }
+            MemoryInit(i) => {
+                self.resolver.datas.resolve(&mut i.data, "data")?;
+                self.resolver.resolve(&mut i.mem, Ns::Memory)?;
+            }
+            MemoryCopy(i) => {
+                self.resolver.resolve(&mut i.src, Ns::Memory)?;
+                self.resolver.resolve(&mut i.dst, Ns::Memory)?;
+            }
+            DataDrop(i) => {
+                self.resolver.datas.resolve(i, "data")?;
+            }
+
+            TableInit(i) => {
+                self.resolver.elems.resolve(&mut i.elem, "elem")?;
+                self.resolver.resolve(&mut i.table, Ns::Table)?;
+            }
+            ElemDrop(i) => {
+                self.resolver.elems.resolve(i, "elem")?;
+            }
+
+            TableCopy(i) => {
+                self.resolver.resolve(&mut i.dst, Ns::Table)?;
+                self.resolver.resolve(&mut i.src, Ns::Table)?;
+            }
+
+            TableFill(i) | TableSet(i) | TableGet(i) | TableSize(i) | TableGrow(i) => {
+                self.resolver.resolve(&mut i.dst, Ns::Table)?;
+            }
+
+            GlobalSet(i) | GlobalGet(i) => {
+                self.resolver.resolve(i, Ns::Global)?;
+            }
+
+            LocalSet(i) | LocalGet(i) | LocalTee(i) => {
+                assert!(self.scopes.len() > 0);
+                // Resolve a local by iterating over scopes from most recent
+                // to less recent. This allows locals added by `let` blocks to
+                // shadow less recent locals.
+                for (depth, scope) in self.scopes.iter().enumerate().rev() {
+                    if let Err(e) = scope.resolve(i, "local") {
+                        if depth == 0 {
+                            // There are no more scopes left, report this as
+                            // the result
+                            return Err(e);
+                        }
+                    } else {
+                        break;
+                    }
+                }
+                // We must have taken the `break` and resolved the local
+                assert!(i.is_resolved());
+            }
+
+            Call(i) | RefFunc(i) | ReturnCall(i) => {
+                self.resolver.resolve(i, Ns::Func)?;
+            }
+
+            CallIndirect(c) | ReturnCallIndirect(c) => {
+                self.resolver.resolve(&mut c.table, Ns::Table)?;
+                self.resolver.resolve_type_use(&mut c.ty)?;
+            }
+
+            FuncBind(b) => {
+                self.resolver.resolve_type_use(&mut b.ty)?;
+            }
+
+            Let(t) => {
+                // Resolve (ref T) in locals
+                for local in &mut t.locals {
+                    self.resolver.resolve_valtype(&mut local.ty)?;
+                }
+
+                // Register all locals defined in this let
+                let mut scope = Namespace::default();
+                for local in &t.locals {
+                    scope.register(local.id, "local")?;
+                }
+                self.scopes.push(scope);
+                self.blocks.push(ExprBlock {
+                    label: t.block.label,
+                    pushed_scope: true,
+                });
+
+                self.resolve_block_type(&mut t.block)?;
+            }
+
+            Block(bt) | If(bt) | Loop(bt) | Try(bt) => {
+                self.blocks.push(ExprBlock {
+                    label: bt.label,
+                    pushed_scope: false,
+                });
+                self.resolve_block_type(bt)?;
+            }
+
+            // On `End` instructions we pop a label from the stack, and for both
+            // `End` and `Else` instructions if they have labels listed we
+            // verify that they match the label at the beginning of the block.
+            Else(_) | End(_) => {
+                let (matching_block, label) = match &instr {
+                    Else(label) => (self.blocks.last().cloned(), label),
+                    End(label) => (self.blocks.pop(), label),
+                    _ => unreachable!(),
+                };
+                let matching_block = match matching_block {
+                    Some(l) => l,
+                    None => return Ok(()),
+                };
+
+                // Reset the local scopes to before this block was entered
+                if matching_block.pushed_scope {
+                    if let End(_) = instr {
+                        self.scopes.pop();
+                    }
+                }
+
+                let label = match label {
+                    Some(l) => l,
+                    None => return Ok(()),
+                };
+                if Some(*label) == matching_block.label {
+                    return Ok(());
+                }
+                return Err(Error::new(
+                    label.span(),
+                    "mismatching labels between end and block".to_string(),
+                ));
+            }
+
+            Br(i) | BrIf(i) | BrOnNull(i) | BrOnNonNull(i) => {
+                self.resolve_label(i)?;
+            }
+
+            BrTable(i) => {
+                for label in i.labels.iter_mut() {
+                    self.resolve_label(label)?;
+                }
+                self.resolve_label(&mut i.default)?;
+            }
+
+            Throw(i) => {
+                self.resolver.resolve(i, Ns::Tag)?;
+            }
+            Rethrow(i) => {
+                self.resolve_label(i)?;
+            }
+            Catch(i) => {
+                self.resolver.resolve(i, Ns::Tag)?;
+            }
+            Delegate(i) => {
+                // Since a delegate starts counting one layer out from the
+                // current try-delegate block, we pop before we resolve labels.
+                self.blocks.pop();
+                self.resolve_label(i)?;
+            }
+
+            Select(s) => {
+                if let Some(list) = &mut s.tys {
+                    for ty in list {
+                        self.resolver.resolve_valtype(ty)?;
+                    }
+                }
+            }
+
+            RefTest(i) => {
+                self.resolver.resolve_reftype(&mut i.r#type)?;
+            }
+            RefCast(i) => {
+                self.resolver.resolve_reftype(&mut i.r#type)?;
+            }
+            BrOnCast(i) => {
+                self.resolve_label(&mut i.label)?;
+                self.resolver.resolve_reftype(&mut i.to_type)?;
+                self.resolver.resolve_reftype(&mut i.from_type)?;
+            }
+            BrOnCastFail(i) => {
+                self.resolve_label(&mut i.label)?;
+                self.resolver.resolve_reftype(&mut i.to_type)?;
+                self.resolver.resolve_reftype(&mut i.from_type)?;
+            }
+
+            StructNew(i) | StructNewDefault(i) | ArrayNew(i)
+            | ArrayNewDefault(i) | ArrayGet(i) | ArrayGetS(i) | ArrayGetU(i) | ArraySet(i) => {
+                self.resolver.resolve(i, Ns::Type)?;
+            }
+
+            StructSet(s) | StructGet(s) | StructGetS(s) | StructGetU(s) => {
+                self.resolver.resolve(&mut s.r#struct, Ns::Type)?;
+                self.resolver.fields.resolve(&mut s.field, "field")?;
+            }
+
+            ArrayNewFixed(a) => {
+                self.resolver.resolve(&mut a.array, Ns::Type)?;
+            }
+            ArrayNewData(a) => {
+                self.resolver.resolve(&mut a.array, Ns::Type)?;
+                self.resolver.datas.resolve(&mut a.data_idx, "data")?;
+            }
+            ArrayNewElem(a) => {
+                self.resolver.resolve(&mut a.array, Ns::Type)?;
+                self.resolver.elems.resolve(&mut a.elem_idx, "elem")?;
+            }
+            ArrayFill(a) => {
+                self.resolver.resolve(&mut a.array, Ns::Type)?;
+            }
+            ArrayCopy(a) => {
+                self.resolver.resolve(&mut a.dest_array, Ns::Type)?;
+                self.resolver.resolve(&mut a.src_array, Ns::Type)?;
+            }
+            ArrayInitData(a) => {
+                self.resolver.resolve(&mut a.array, Ns::Type)?;
+                self.resolver.datas.resolve(&mut a.segment, "data")?;
+            }
+            ArrayInitElem(a) => {
+                self.resolver.resolve(&mut a.array, Ns::Type)?;
+                self.resolver.elems.resolve(&mut a.segment, "elem")?;
+            }
+
+            RefNull(ty) | CallRef(ty) | ReturnCallRef(ty) => self.resolver.resolve_heaptype(ty)?,
+
+            _ => {}
+        }
+        Ok(())
+    }
+
+    fn resolve_label(&self, label: &mut Index<'a>) -> Result<(), Error> {
+        let id = match label {
+            Index::Num(..) => return Ok(()),
+            Index::Id(id) => *id,
+        };
+        let idx = self
+            .blocks
+            .iter()
+            .rev()
+            .enumerate()
+            .filter_map(|(i, b)| b.label.map(|l| (i, l)))
+            .find(|(_, l)| *l == id);
+        match idx {
+            Some((idx, _)) => {
+                *label = Index::Num(idx as u32, id.span());
+                Ok(())
+            }
+            None => Err(resolve_error(id, "label")),
+        }
+    }
+}
+
+enum TypeInfo<'a> {
+    Func {
+        params: Box<[ValType<'a>]>,
+        results: Box<[ValType<'a>]>,
+    },
+    Other,
+}
+
+trait TypeReference<'a> {
+    fn check_matches(&mut self, idx: &Index<'a>, cx: &Resolver<'a>) -> Result<(), Error>;
+    fn resolve(&mut self, cx: &Resolver<'a>) -> Result<(), Error>;
+}
+
+impl<'a> TypeReference<'a> for FunctionType<'a> {
+    fn check_matches(&mut self, idx: &Index<'a>, cx: &Resolver<'a>) -> Result<(), Error> {
+        let n = match idx {
+            Index::Num(n, _) => *n,
+            Index::Id(_) => panic!("expected `Num`"),
+        };
+        let (params, results) = match cx.type_info.get(n as usize) {
+            Some(TypeInfo::Func { params, results }) => (params, results),
+            _ => return Ok(()),
+        };
+
+        // Here we need to check that the inline type listed (ourselves) matches
+        // what was listed in the module itself (the `params` and `results`
+        // above). The listed values in `types` are not resolved yet, although
+        // we should be resolved. In any case we do name resolution
+        // opportunistically here to see if the values are equal.
+
+        let types_not_equal = |a: &ValType, b: &ValType| {
+            let mut a = a.clone();
+            let mut b = b.clone();
+            drop(cx.resolve_valtype(&mut a));
+            drop(cx.resolve_valtype(&mut b));
+            a != b
+        };
+
+        let not_equal = params.len() != self.params.len()
+            || results.len() != self.results.len()
+            || params
+                .iter()
+                .zip(self.params.iter())
+                .any(|(a, (_, _, b))| types_not_equal(a, b))
+            || results
+                .iter()
+                .zip(self.results.iter())
+                .any(|(a, b)| types_not_equal(a, b));
+        if not_equal {
+            return Err(Error::new(
+                idx.span(),
+                format!("inline function type doesn't match type reference"),
+            ));
+        }
+
+        Ok(())
+    }
+
+    fn resolve(&mut self, cx: &Resolver<'a>) -> Result<(), Error> {
+        // Resolve the (ref T) value types in the final function type
+        for param in self.params.iter_mut() {
+            cx.resolve_valtype(&mut param.2)?;
+        }
+        for result in self.results.iter_mut() {
+            cx.resolve_valtype(result)?;
+        }
+        Ok(())
+    }
+}
diff --git a/third_party/rust/wast/src/core/resolve/types.rs b/third_party/rust/wast/src/core/resolve/types.rs
new file mode 100644
index 0000000000..b3cc76d1f9
--- /dev/null
+++ b/third_party/rust/wast/src/core/resolve/types.rs
@@ -0,0 +1,269 @@
+use crate::core::*;
+use crate::gensym;
+use crate::token::{Index, Span};
+use std::collections::HashMap;
+
+pub fn expand<'a>(fields: &mut Vec<ModuleField<'a>>) {
+    let mut expander = Expander::default();
+    expander.process(fields);
+}
+
+#[derive(Default)]
+pub(crate) struct Expander<'a> {
+    // Maps used to "intern" types. These maps are populated as type annotations
+    // are seen and inline type annotations use previously defined ones if
+    // there's a match.
+    func_type_to_idx: HashMap<FuncKey<'a>, Index<'a>>,
+
+    /// Fields, during processing, which should be prepended to the
+    /// currently-being-processed field. This should always be empty after
+    /// processing is complete.
+    to_prepend: Vec<ModuleField<'a>>,
+}
+
+impl<'a> Expander<'a> {
+    fn process(&mut self, fields: &mut Vec<ModuleField<'a>>) {
+        // Next we expand "header" fields which are those like types and
+        // imports. In this context "header" is defined by the previous
+        // `process_imports_early` annotation.
+        let mut cur = 0;
+        while cur < fields.len() {
+            self.expand_header(&mut fields[cur]);
+            for item in self.to_prepend.drain(..) {
+                fields.insert(cur, item);
+                cur += 1;
+            }
+            cur += 1;
+        }
+
+        // Next after we've done that we expand remaining fields. Note that
+        // after this we actually append instead of prepend. This is because
+        // injected types are intended to come at the end of the type section
+        // and types will be sorted before all other items processed here in the
+        // final module anyway.
+        for field in fields.iter_mut() {
+            self.expand(field);
+        }
+        fields.append(&mut self.to_prepend);
+    }
+
+    fn expand_header(&mut self, item: &mut ModuleField<'a>) {
+        match item {
+            ModuleField::Type(ty) => {
+                let id = gensym::fill(ty.span, &mut ty.id);
+                match &mut ty.def {
+                    TypeDef::Func(f) => {
+                        f.key().insert(self, Index::Id(id));
+                    }
+                    TypeDef::Array(_) | TypeDef::Struct(_) => {}
+                }
+            }
+            _ => {}
+        }
+    }
+
+    fn expand(&mut self, item: &mut ModuleField<'a>) {
+        match item {
+            // This is pre-expanded above
+            ModuleField::Type(_) => {}
+            ModuleField::Rec(_) => {}
+
+            ModuleField::Import(i) => {
+                self.expand_item_sig(&mut i.item);
+            }
+            ModuleField::Func(f) => {
+                self.expand_type_use(&mut f.ty);
+                if let FuncKind::Inline { expression, .. } = &mut f.kind {
+                    self.expand_expression(expression);
+                }
+            }
+            ModuleField::Global(g) => {
+                if let GlobalKind::Inline(expr) = &mut g.kind {
+                    self.expand_expression(expr);
+                }
+            }
+            ModuleField::Data(d) => {
+                if let DataKind::Active { offset, .. } = &mut d.kind {
+                    self.expand_expression(offset);
+                }
+            }
+            ModuleField::Elem(e) => {
+                if let ElemKind::Active { offset, .. } = &mut e.kind {
+                    self.expand_expression(offset);
+                }
+                if let ElemPayload::Exprs { exprs, .. } = &mut e.payload {
+                    for expr in exprs {
+                        self.expand_expression(expr);
+                    }
+                }
+            }
+            ModuleField::Tag(t) => match &mut t.ty {
+                TagType::Exception(ty) => {
+                    self.expand_type_use(ty);
+                }
+            },
+
+            ModuleField::Table(t) => match &mut t.kind {
+                TableKind::Normal { init_expr, .. } => {
+                    if let Some(expr) = init_expr {
+                        self.expand_expression(expr);
+                    }
+                }
+                TableKind::Import { .. } | TableKind::Inline { .. } => {}
+            },
+
+            ModuleField::Memory(_)
+            | ModuleField::Start(_)
+            | ModuleField::Export(_)
+            | ModuleField::Custom(_) => {}
+        }
+    }
+
+    fn expand_item_sig(&mut self, item: &mut ItemSig<'a>) {
+        match &mut item.kind {
+            ItemKind::Func(t) | ItemKind::Tag(TagType::Exception(t)) => {
+                self.expand_type_use(t);
+            }
+            ItemKind::Global(_) | ItemKind::Table(_) | ItemKind::Memory(_) => {}
+        }
+    }
+
+    fn expand_expression(&mut self, expr: &mut Expression<'a>) {
+        for instr in expr.instrs.iter_mut() {
+            self.expand_instr(instr);
+        }
+    }
+
+    fn expand_instr(&mut self, instr: &mut Instruction<'a>) {
+        match instr {
+            Instruction::Block(bt)
+            | Instruction::If(bt)
+            | Instruction::Loop(bt)
+            | Instruction::Let(LetType { block: bt, .. })
+            | Instruction::Try(bt) => {
+                // No expansion necessary, a type reference is already here.
+                // We'll verify that it's the same as the inline type, if any,
+                // later.
+                if bt.ty.index.is_some() {
+                    return;
+                }
+
+                match &bt.ty.inline {
+                    // Only actually expand `TypeUse` with an index which appends a
+                    // type if it looks like we need one. This way if the
+                    // multi-value proposal isn't enabled and/or used we won't
+                    // encode it.
+                    Some(inline) => {
+                        if inline.params.len() == 0 && inline.results.len() <= 1 {
+                            return;
+                        }
+                    }
+
+                    // If we didn't have either an index or an inline type
+                    // listed then assume our block has no inputs/outputs, so
+                    // fill in the inline type here.
+                    //
+                    // Do not fall through to expanding the `TypeUse` because
+                    // this doesn't force an empty function type to go into the
+                    // type section.
+                    None => {
+                        bt.ty.inline = Some(FunctionType::default());
+                        return;
+                    }
+                }
+                self.expand_type_use(&mut bt.ty);
+            }
+            Instruction::FuncBind(b) => {
+                self.expand_type_use(&mut b.ty);
+            }
+            Instruction::CallIndirect(c) | Instruction::ReturnCallIndirect(c) => {
+                self.expand_type_use(&mut c.ty);
+            }
+            _ => {}
+        }
+    }
+
+    fn expand_type_use<T>(&mut self, item: &mut TypeUse<'a, T>) -> Index<'a>
+    where
+        T: TypeReference<'a>,
+    {
+        if let Some(idx) = &item.index {
+            return *idx;
+        }
+        let key = match item.inline.as_mut() {
+            Some(ty) => {
+                ty.expand(self);
+                ty.key()
+            }
+            None => T::default().key(),
+        };
+        let span = Span::from_offset(0); // FIXME(#613): don't manufacture
+        let idx = self.key_to_idx(span, key);
+        item.index = Some(idx);
+        idx
+    }
+
+    fn key_to_idx(&mut self, span: Span, key: impl TypeKey<'a>) -> Index<'a> {
+        // First see if this `key` already exists in the type definitions we've
+        // seen so far...
+        if let Some(idx) = key.lookup(self) {
+            return idx;
+        }
+
+        // ... and failing that we insert a new type definition.
+        let id = gensym::gen(span);
+        self.to_prepend.push(ModuleField::Type(Type {
+            span,
+            id: Some(id),
+            name: None,
+            def: key.to_def(span),
+            parent: None,
+        }));
+        let idx = Index::Id(id);
+        key.insert(self, idx);
+        idx
+    }
+}
+
+pub(crate) trait TypeReference<'a>: Default {
+    type Key: TypeKey<'a>;
+    fn key(&self) -> Self::Key;
+    fn expand(&mut self, cx: &mut Expander<'a>);
+}
+
+pub(crate) trait TypeKey<'a> {
+    fn lookup(&self, cx: &Expander<'a>) -> Option<Index<'a>>;
+    fn to_def(&self, span: Span) -> TypeDef<'a>;
+    fn insert(&self, cx: &mut Expander<'a>, id: Index<'a>);
+}
+
+pub(crate) type FuncKey<'a> = (Box<[ValType<'a>]>, Box<[ValType<'a>]>);
+
+impl<'a> TypeReference<'a> for FunctionType<'a> {
+    type Key = FuncKey<'a>;
+
+    fn key(&self) -> Self::Key {
+        let params = self.params.iter().map(|p| p.2).collect();
+        let results = self.results.clone();
+        (params, results)
+    }
+
+    fn expand(&mut self, _cx: &mut Expander<'a>) {}
+}
+
+impl<'a> TypeKey<'a> for FuncKey<'a> {
+    fn lookup(&self, cx: &Expander<'a>) -> Option<Index<'a>> {
+        cx.func_type_to_idx.get(self).cloned()
+    }
+
+    fn to_def(&self, _span: Span) -> TypeDef<'a> {
+        TypeDef::Func(FunctionType {
+            params: self.0.iter().map(|t| (None, None, *t)).collect(),
+            results: self.1.clone(),
+        })
+    }
+
+    fn insert(&self, cx: &mut Expander<'a>, idx: Index<'a>) {
+        cx.func_type_to_idx.entry(self.clone()).or_insert(idx);
+    }
+}
diff --git a/third_party/rust/wast/src/core/table.rs b/third_party/rust/wast/src/core/table.rs
new file mode 100644
index 0000000000..f279e174b9
--- /dev/null
+++ b/third_party/rust/wast/src/core/table.rs
@@ -0,0 +1,241 @@
+use crate::core::*;
+use crate::kw;
+use crate::parser::{Parse, Parser, Result};
+use crate::token::{Id, Index, LParen, NameAnnotation, Span};
+
+/// A WebAssembly `table` directive in a module.
+#[derive(Debug)]
+pub struct Table<'a> {
+    /// Where this table was defined.
+    pub span: Span,
+    /// An optional name to refer to this table by.
+    pub id: Option<Id<'a>>,
+    /// An optional name for this function stored in the custom `name` section.
+    pub name: Option<NameAnnotation<'a>>,
+    /// If present, inline export annotations which indicate names this
+    /// definition should be exported under.
+    pub exports: InlineExport<'a>,
+    /// How this table is textually defined in the module.
+    pub kind: TableKind<'a>,
+}
+
+/// Different ways to textually define a table.
+#[derive(Debug)]
+pub enum TableKind<'a> {
+    /// This table is actually an inlined import definition.
+    #[allow(missing_docs)]
+    Import {
+        import: InlineImport<'a>,
+        ty: TableType<'a>,
+    },
+
+    /// A typical memory definition which simply says the limits of the table
+    Normal {
+        /// Table type.
+        ty: TableType<'a>,
+        /// Optional items initializer expression.
+        init_expr: Option<Expression<'a>>,
+    },
+
+    /// The elem segments of this table, starting from 0, explicitly listed
+    Inline {
+        /// The element type of this table.
+        elem: RefType<'a>,
+        /// The element table entries to have, and the length of this list is
+        /// the limits of the table as well.
+        payload: ElemPayload<'a>,
+    },
+}
+
+impl<'a> Parse<'a> for Table<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let span = parser.parse::<kw::table>()?.0;
+        let id = parser.parse()?;
+        let name = parser.parse()?;
+        let exports = parser.parse()?;
+
+        // Afterwards figure out which style this is, either:
+        //
+        //  *   `elemtype (elem ...)`
+        //  *   `(import "a" "b") limits`
+        //  *   `limits`
+        let mut l = parser.lookahead1();
+        let kind = if l.peek::<RefType>() {
+            let elem = parser.parse()?;
+            let payload = parser.parens(|p| {
+                p.parse::<kw::elem>()?;
+                let ty = if parser.peek::<LParen>() {
+                    Some(elem)
+                } else {
+                    None
+                };
+                ElemPayload::parse_tail(parser, ty)
+            })?;
+            TableKind::Inline { elem, payload }
+        } else if l.peek::<u32>() {
+            TableKind::Normal {
+                ty: parser.parse()?,
+                init_expr: if !parser.is_empty() {
+                    Some(parser.parse::<Expression>()?)
+                } else {
+                    None
+                },
+            }
+        } else if let Some(import) = parser.parse()? {
+            TableKind::Import {
+                import,
+                ty: parser.parse()?,
+            }
+        } else {
+            return Err(l.error());
+        };
+        Ok(Table {
+            span,
+            id,
+            name,
+            exports,
+            kind,
+        })
+    }
+}
+
+/// An `elem` segment in a WebAssembly module.
+#[derive(Debug)]
+pub struct Elem<'a> {
+    /// Where this `elem` was defined.
+    pub span: Span,
+    /// An optional name by which to refer to this segment.
+    pub id: Option<Id<'a>>,
+    /// An optional name for this element stored in the custom `name` section.
+    pub name: Option<NameAnnotation<'a>>,
+    /// The way this segment was defined in the module.
+    pub kind: ElemKind<'a>,
+    /// The payload of this element segment, typically a list of functions.
+    pub payload: ElemPayload<'a>,
+}
+
+/// Different ways to define an element segment in an mdoule.
+#[derive(Debug)]
+pub enum ElemKind<'a> {
+    /// A passive segment that isn't associated with a table and can be used in
+    /// various bulk-memory instructions.
+    Passive,
+
+    /// A declared element segment that is purely used to declare function
+    /// references.
+    Declared,
+
+    /// An active segment associated with a table.
+    Active {
+        /// The table this `elem` is initializing.
+        table: Index<'a>,
+        /// The offset within `table` that we'll initialize at.
+        offset: Expression<'a>,
+    },
+}
+
+/// Different ways to define the element segment payload in a module.
+#[derive(Debug)]
+pub enum ElemPayload<'a> {
+    /// This element segment has a contiguous list of function indices
+    Indices(Vec<Index<'a>>),
+
+    /// This element segment has a list of optional function indices,
+    /// represented as expressions using `ref.func` and `ref.null`.
+    Exprs {
+        /// The desired type of each expression below.
+        ty: RefType<'a>,
+        /// The expressions in this segment.
+        exprs: Vec<Expression<'a>>,
+    },
+}
+
+impl<'a> Parse<'a> for Elem<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let span = parser.parse::<kw::elem>()?.0;
+        let id = parser.parse()?;
+        let name = parser.parse()?;
+
+        let kind = if parser.peek::<kw::declare>() {
+            parser.parse::<kw::declare>()?;
+            ElemKind::Declared
+        } else if parser.peek::<u32>() || (parser.peek::<LParen>() && !parser.peek::<RefType>()) {
+            let table = if parser.peek::<u32>() {
+                // FIXME: this is only here to accomodate
+                // proposals/threads/imports.wast at this current moment in
+                // time, this probably should get removed when the threads
+                // proposal is rebased on the current spec.
+                Index::Num(parser.parse()?, span)
+            } else if parser.peek2::<kw::table>() {
+                parser.parens(|p| {
+                    p.parse::<kw::table>()?;
+                    p.parse()
+                })?
+            } else {
+                Index::Num(0, span)
+            };
+            let offset = parser.parens(|parser| {
+                if parser.peek::<kw::offset>() {
+                    parser.parse::<kw::offset>()?;
+                }
+                parser.parse()
+            })?;
+            ElemKind::Active { table, offset }
+        } else {
+            ElemKind::Passive
+        };
+        let payload = parser.parse()?;
+        Ok(Elem {
+            span,
+            id,
+            name,
+            kind,
+            payload,
+        })
+    }
+}
+
+impl<'a> Parse<'a> for ElemPayload<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        ElemPayload::parse_tail(parser, parser.parse()?)
+    }
+}
+
+impl<'a> ElemPayload<'a> {
+    fn parse_tail(parser: Parser<'a>, ty: Option<RefType<'a>>) -> Result<Self> {
+        let (must_use_indices, ty) = match ty {
+            None => {
+                parser.parse::<Option<kw::func>>()?;
+                (true, RefType::func())
+            }
+            Some(ty) => (false, ty),
+        };
+        if let HeapType::Func = ty.heap {
+            if must_use_indices || parser.peek::<Index<'_>>() {
+                let mut elems = Vec::new();
+                while !parser.is_empty() {
+                    elems.push(parser.parse()?);
+                }
+                return Ok(ElemPayload::Indices(elems));
+            }
+        }
+        let mut exprs = Vec::new();
+        while !parser.is_empty() {
+            let expr = parser.parens(|parser| {
+                if parser.peek::<kw::item>() {
+                    parser.parse::<kw::item>()?;
+                    parser.parse()
+                } else {
+                    // Without `item` this is "sugar" for a single-instruction
+                    // expression.
+                    let insn = parser.parse()?;
+                    Ok(Expression {
+                        instrs: [insn].into(),
+                    })
+                }
+            })?;
+            exprs.push(expr);
+        }
+        Ok(ElemPayload::Exprs { exprs, ty })
+    }
+}
diff --git a/third_party/rust/wast/src/core/tag.rs b/third_party/rust/wast/src/core/tag.rs
new file mode 100644
index 0000000000..233b5e4cd0
--- /dev/null
+++ b/third_party/rust/wast/src/core/tag.rs
@@ -0,0 +1,71 @@
+use crate::core::*;
+use crate::kw;
+use crate::parser::{Parse, Parser, Result};
+use crate::token::{Id, NameAnnotation, Span};
+
+/// A WebAssembly tag directive, part of the exception handling proposal.
+#[derive(Debug)]
+pub struct Tag<'a> {
+    /// Where this tag was defined
+    pub span: Span,
+    /// An optional name by which to refer to this tag in name resolution.
+    pub id: Option<Id<'a>>,
+    /// An optional name for this function stored in the custom `name` section.
+    pub name: Option<NameAnnotation<'a>>,
+    /// Optional export directives for this tag.
+    pub exports: InlineExport<'a>,
+    /// The type of tag that is defined.
+    pub ty: TagType<'a>,
+    /// What kind of tag this is defined as.
+    pub kind: TagKind<'a>,
+}
+
+/// Listing of various types of tags that can be defined in a wasm module.
+#[derive(Clone, Debug)]
+pub enum TagType<'a> {
+    /// An exception tag, where the payload is the type signature of the tag
+    /// (constructor parameters, etc).
+    Exception(TypeUse<'a, FunctionType<'a>>),
+}
+
+/// Different kinds of tags that can be defined in a module.
+#[derive(Debug)]
+pub enum TagKind<'a> {
+    /// An tag which is actually defined as an import, such as:
+    ///
+    /// ```text
+    /// (tag (type 0) (import "foo" "bar"))
+    /// ```
+    Import(InlineImport<'a>),
+
+    /// A tag defined inline in the module itself
+    Inline(),
+}
+
+impl<'a> Parse<'a> for Tag<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let span = parser.parse::<kw::tag>()?.0;
+        let id = parser.parse()?;
+        let name = parser.parse()?;
+        let exports = parser.parse()?;
+        let (ty, kind) = if let Some(import) = parser.parse()? {
+            (parser.parse()?, TagKind::Import(import))
+        } else {
+            (parser.parse()?, TagKind::Inline())
+        };
+        Ok(Tag {
+            span,
+            id,
+            name,
+            exports,
+            ty,
+            kind,
+        })
+    }
+}
+
+impl<'a> Parse<'a> for TagType<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        Ok(TagType::Exception(parser.parse()?))
+    }
+}
diff --git a/third_party/rust/wast/src/core/types.rs b/third_party/rust/wast/src/core/types.rs
new file mode 100644
index 0000000000..9abb906806
--- /dev/null
+++ b/third_party/rust/wast/src/core/types.rs
@@ -0,0 +1,832 @@
+use crate::core::*;
+use crate::kw;
+use crate::parser::{Cursor, Parse, Parser, Peek, Result};
+use crate::token::{Id, Index, LParen, NameAnnotation, Span};
+use std::mem;
+
+/// The value types for a wasm module.
+#[allow(missing_docs)]
+#[derive(Debug, PartialEq, Eq, Hash, Copy, Clone)]
+pub enum ValType<'a> {
+    I32,
+    I64,
+    F32,
+    F64,
+    V128,
+    Ref(RefType<'a>),
+}
+
+impl<'a> Parse<'a> for ValType<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut l = parser.lookahead1();
+        if l.peek::<kw::i32>() {
+            parser.parse::<kw::i32>()?;
+            Ok(ValType::I32)
+        } else if l.peek::<kw::i64>() {
+            parser.parse::<kw::i64>()?;
+            Ok(ValType::I64)
+        } else if l.peek::<kw::f32>() {
+            parser.parse::<kw::f32>()?;
+            Ok(ValType::F32)
+        } else if l.peek::<kw::f64>() {
+            parser.parse::<kw::f64>()?;
+            Ok(ValType::F64)
+        } else if l.peek::<kw::v128>() {
+            parser.parse::<kw::v128>()?;
+            Ok(ValType::V128)
+        } else if l.peek::<RefType>() {
+            Ok(ValType::Ref(parser.parse()?))
+        } else {
+            Err(l.error())
+        }
+    }
+}
+
+impl<'a> Peek for ValType<'a> {
+    fn peek(cursor: Cursor<'_>) -> bool {
+        kw::i32::peek(cursor)
+            || kw::i64::peek(cursor)
+            || kw::f32::peek(cursor)
+            || kw::f64::peek(cursor)
+            || kw::v128::peek(cursor)
+            || RefType::peek(cursor)
+    }
+    fn display() -> &'static str {
+        "valtype"
+    }
+}
+
+/// A heap type for a reference type
+#[allow(missing_docs)]
+#[derive(Debug, PartialEq, Eq, Hash, Copy, Clone)]
+pub enum HeapType<'a> {
+    /// An untyped function reference: funcref. This is part of the reference
+    /// types proposal.
+    Func,
+    /// A reference to any host value: externref. This is part of the reference
+    /// types proposal.
+    Extern,
+    /// A reference to any reference value: anyref. This is part of the GC
+    /// proposal.
+    Any,
+    /// A reference that has an identity that can be compared: eqref. This is
+    /// part of the GC proposal.
+    Eq,
+    /// A reference to a GC struct. This is part of the GC proposal.
+    Struct,
+    /// A reference to a GC array. This is part of the GC proposal.
+    Array,
+    /// An unboxed 31-bit integer: i31ref. Part of the GC proposal.
+    I31,
+    /// The bottom type of the funcref hierarchy. Part of the GC proposal.
+    NoFunc,
+    /// The bottom type of the externref hierarchy. Part of the GC proposal.
+    NoExtern,
+    /// The bottom type of the anyref hierarchy. Part of the GC proposal.
+    None,
+    /// A reference to a function, struct, or array: ref T. This is part of the
+    /// GC proposal.
+    Index(Index<'a>),
+}
+
+impl<'a> Parse<'a> for HeapType<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut l = parser.lookahead1();
+        if l.peek::<kw::func>() {
+            parser.parse::<kw::func>()?;
+            Ok(HeapType::Func)
+        } else if l.peek::<kw::r#extern>() {
+            parser.parse::<kw::r#extern>()?;
+            Ok(HeapType::Extern)
+        } else if l.peek::<kw::r#any>() {
+            parser.parse::<kw::r#any>()?;
+            Ok(HeapType::Any)
+        } else if l.peek::<kw::eq>() {
+            parser.parse::<kw::eq>()?;
+            Ok(HeapType::Eq)
+        } else if l.peek::<kw::r#struct>() {
+            parser.parse::<kw::r#struct>()?;
+            Ok(HeapType::Struct)
+        } else if l.peek::<kw::array>() {
+            parser.parse::<kw::array>()?;
+            Ok(HeapType::Array)
+        } else if l.peek::<kw::i31>() {
+            parser.parse::<kw::i31>()?;
+            Ok(HeapType::I31)
+        } else if l.peek::<kw::nofunc>() {
+            parser.parse::<kw::nofunc>()?;
+            Ok(HeapType::NoFunc)
+        } else if l.peek::<kw::noextern>() {
+            parser.parse::<kw::noextern>()?;
+            Ok(HeapType::NoExtern)
+        } else if l.peek::<kw::none>() {
+            parser.parse::<kw::none>()?;
+            Ok(HeapType::None)
+        } else if l.peek::<Index>() {
+            Ok(HeapType::Index(parser.parse()?))
+        } else {
+            Err(l.error())
+        }
+    }
+}
+
+impl<'a> Peek for HeapType<'a> {
+    fn peek(cursor: Cursor<'_>) -> bool {
+        kw::func::peek(cursor)
+            || kw::r#extern::peek(cursor)
+            || kw::any::peek(cursor)
+            || kw::eq::peek(cursor)
+            || kw::r#struct::peek(cursor)
+            || kw::array::peek(cursor)
+            || kw::i31::peek(cursor)
+            || kw::nofunc::peek(cursor)
+            || kw::noextern::peek(cursor)
+            || kw::none::peek(cursor)
+            || (LParen::peek(cursor) && kw::r#type::peek2(cursor))
+    }
+    fn display() -> &'static str {
+        "heaptype"
+    }
+}
+
+/// A reference type in a wasm module.
+#[allow(missing_docs)]
+#[derive(Debug, PartialEq, Eq, Hash, Copy, Clone)]
+pub struct RefType<'a> {
+    pub nullable: bool,
+    pub heap: HeapType<'a>,
+}
+
+impl<'a> RefType<'a> {
+    /// A `funcref` as an abbreviation for `(ref null func)`.
+    pub fn func() -> Self {
+        RefType {
+            nullable: true,
+            heap: HeapType::Func,
+        }
+    }
+
+    /// An `externref` as an abbreviation for `(ref null extern)`.
+    pub fn r#extern() -> Self {
+        RefType {
+            nullable: true,
+            heap: HeapType::Extern,
+        }
+    }
+
+    /// An `anyref` as an abbreviation for `(ref null any)`.
+    pub fn any() -> Self {
+        RefType {
+            nullable: true,
+            heap: HeapType::Any,
+        }
+    }
+
+    /// An `eqref` as an abbreviation for `(ref null eq)`.
+    pub fn eq() -> Self {
+        RefType {
+            nullable: true,
+            heap: HeapType::Eq,
+        }
+    }
+
+    /// An `structref` as an abbreviation for `(ref null struct)`.
+    pub fn r#struct() -> Self {
+        RefType {
+            nullable: true,
+            heap: HeapType::Struct,
+        }
+    }
+
+    /// An `arrayref` as an abbreviation for `(ref null array)`.
+    pub fn array() -> Self {
+        RefType {
+            nullable: true,
+            heap: HeapType::Array,
+        }
+    }
+
+    /// An `i31ref` as an abbreviation for `(ref null i31)`.
+    pub fn i31() -> Self {
+        RefType {
+            nullable: true,
+            heap: HeapType::I31,
+        }
+    }
+
+    /// A `nullfuncref` as an abbreviation for `(ref null nofunc)`.
+    pub fn nullfuncref() -> Self {
+        RefType {
+            nullable: true,
+            heap: HeapType::NoFunc,
+        }
+    }
+
+    /// A `nullexternref` as an abbreviation for `(ref null noextern)`.
+    pub fn nullexternref() -> Self {
+        RefType {
+            nullable: true,
+            heap: HeapType::NoExtern,
+        }
+    }
+
+    /// A `nullref` as an abbreviation for `(ref null none)`.
+    pub fn nullref() -> Self {
+        RefType {
+            nullable: true,
+            heap: HeapType::None,
+        }
+    }
+}
+
+impl<'a> Parse<'a> for RefType<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut l = parser.lookahead1();
+        if l.peek::<kw::funcref>() {
+            parser.parse::<kw::funcref>()?;
+            Ok(RefType::func())
+        } else if l.peek::<kw::anyfunc>() {
+            parser.parse::<kw::anyfunc>()?;
+            Ok(RefType::func())
+        } else if l.peek::<kw::externref>() {
+            parser.parse::<kw::externref>()?;
+            Ok(RefType::r#extern())
+        } else if l.peek::<kw::anyref>() {
+            parser.parse::<kw::anyref>()?;
+            Ok(RefType::any())
+        } else if l.peek::<kw::eqref>() {
+            parser.parse::<kw::eqref>()?;
+            Ok(RefType::eq())
+        } else if l.peek::<kw::structref>() {
+            parser.parse::<kw::structref>()?;
+            Ok(RefType::r#struct())
+        } else if l.peek::<kw::arrayref>() {
+            parser.parse::<kw::arrayref>()?;
+            Ok(RefType::array())
+        } else if l.peek::<kw::i31ref>() {
+            parser.parse::<kw::i31ref>()?;
+            Ok(RefType::i31())
+        } else if l.peek::<kw::nullfuncref>() {
+            parser.parse::<kw::nullfuncref>()?;
+            Ok(RefType::nullfuncref())
+        } else if l.peek::<kw::nullexternref>() {
+            parser.parse::<kw::nullexternref>()?;
+            Ok(RefType::nullexternref())
+        } else if l.peek::<kw::nullref>() {
+            parser.parse::<kw::nullref>()?;
+            Ok(RefType::nullref())
+        } else if l.peek::<LParen>() {
+            parser.parens(|p| {
+                let mut l = parser.lookahead1();
+                if l.peek::<kw::r#ref>() {
+                    p.parse::<kw::r#ref>()?;
+
+                    let mut nullable = false;
+                    if parser.peek::<kw::null>() {
+                        parser.parse::<kw::null>()?;
+                        nullable = true;
+                    }
+
+                    Ok(RefType {
+                        nullable,
+                        heap: parser.parse()?,
+                    })
+                } else {
+                    Err(l.error())
+                }
+            })
+        } else {
+            Err(l.error())
+        }
+    }
+}
+
+impl<'a> Peek for RefType<'a> {
+    fn peek(cursor: Cursor<'_>) -> bool {
+        kw::funcref::peek(cursor)
+            || /* legacy */ kw::anyfunc::peek(cursor)
+            || kw::externref::peek(cursor)
+            || kw::anyref::peek(cursor)
+            || kw::eqref::peek(cursor)
+            || kw::structref::peek(cursor)
+            || kw::arrayref::peek(cursor)
+            || kw::i31ref::peek(cursor)
+            || kw::nullfuncref::peek(cursor)
+            || kw::nullexternref::peek(cursor)
+            || kw::nullref::peek(cursor)
+            || (LParen::peek(cursor) && kw::r#ref::peek2(cursor))
+    }
+    fn display() -> &'static str {
+        "reftype"
+    }
+}
+
+/// The types of values that may be used in a struct or array.
+#[allow(missing_docs)]
+#[derive(Debug, PartialEq, Eq, Hash, Copy, Clone)]
+pub enum StorageType<'a> {
+    I8,
+    I16,
+    Val(ValType<'a>),
+}
+
+impl<'a> Parse<'a> for StorageType<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut l = parser.lookahead1();
+        if l.peek::<kw::i8>() {
+            parser.parse::<kw::i8>()?;
+            Ok(StorageType::I8)
+        } else if l.peek::<kw::i16>() {
+            parser.parse::<kw::i16>()?;
+            Ok(StorageType::I16)
+        } else if l.peek::<ValType>() {
+            Ok(StorageType::Val(parser.parse()?))
+        } else {
+            Err(l.error())
+        }
+    }
+}
+
+/// Type for a `global` in a wasm module
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+pub struct GlobalType<'a> {
+    /// The element type of this `global`
+    pub ty: ValType<'a>,
+    /// Whether or not the global is mutable or not.
+    pub mutable: bool,
+}
+
+impl<'a> Parse<'a> for GlobalType<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        if parser.peek2::<kw::r#mut>() {
+            parser.parens(|p| {
+                p.parse::<kw::r#mut>()?;
+                Ok(GlobalType {
+                    ty: parser.parse()?,
+                    mutable: true,
+                })
+            })
+        } else {
+            Ok(GlobalType {
+                ty: parser.parse()?,
+                mutable: false,
+            })
+        }
+    }
+}
+
+/// Min/max limits used for tables/memories.
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+pub struct Limits {
+    /// The minimum number of units for this type.
+    pub min: u32,
+    /// An optional maximum number of units for this type.
+    pub max: Option<u32>,
+}
+
+impl<'a> Parse<'a> for Limits {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let min = parser.parse()?;
+        let max = if parser.peek::<u32>() {
+            Some(parser.parse()?)
+        } else {
+            None
+        };
+        Ok(Limits { min, max })
+    }
+}
+
+/// Min/max limits used for 64-bit memories
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+pub struct Limits64 {
+    /// The minimum number of units for this type.
+    pub min: u64,
+    /// An optional maximum number of units for this type.
+    pub max: Option<u64>,
+}
+
+impl<'a> Parse<'a> for Limits64 {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let min = parser.parse()?;
+        let max = if parser.peek::<u64>() {
+            Some(parser.parse()?)
+        } else {
+            None
+        };
+        Ok(Limits64 { min, max })
+    }
+}
+
+/// Configuration for a table of a wasm mdoule
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+pub struct TableType<'a> {
+    /// Limits on the element sizes of this table
+    pub limits: Limits,
+    /// The type of element stored in this table
+    pub elem: RefType<'a>,
+}
+
+impl<'a> Parse<'a> for TableType<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        Ok(TableType {
+            limits: parser.parse()?,
+            elem: parser.parse()?,
+        })
+    }
+}
+
+/// Configuration for a memory of a wasm module
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+pub enum MemoryType {
+    /// A 32-bit memory
+    B32 {
+        /// Limits on the page sizes of this memory
+        limits: Limits,
+        /// Whether or not this is a shared (atomic) memory type
+        shared: bool,
+    },
+    /// A 64-bit memory
+    B64 {
+        /// Limits on the page sizes of this memory
+        limits: Limits64,
+        /// Whether or not this is a shared (atomic) memory type
+        shared: bool,
+    },
+}
+
+impl<'a> Parse<'a> for MemoryType {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        if parser.peek::<kw::i64>() {
+            parser.parse::<kw::i64>()?;
+            let limits = parser.parse()?;
+            let shared = parser.parse::<Option<kw::shared>>()?.is_some();
+            Ok(MemoryType::B64 { limits, shared })
+        } else {
+            parser.parse::<Option<kw::i32>>()?;
+            let limits = parser.parse()?;
+            let shared = parser.parse::<Option<kw::shared>>()?.is_some();
+            Ok(MemoryType::B32 { limits, shared })
+        }
+    }
+}
+
+/// A function type with parameters and results.
+#[derive(Clone, Debug, Default)]
+pub struct FunctionType<'a> {
+    /// The parameters of a function, optionally each having an identifier for
+    /// name resolution and a name for the custom `name` section.
+    pub params: Box<[(Option<Id<'a>>, Option<NameAnnotation<'a>>, ValType<'a>)]>,
+    /// The results types of a function.
+    pub results: Box<[ValType<'a>]>,
+}
+
+impl<'a> FunctionType<'a> {
+    fn finish_parse(&mut self, allow_names: bool, parser: Parser<'a>) -> Result<()> {
+        let mut params = Vec::from(mem::take(&mut self.params));
+        let mut results = Vec::from(mem::take(&mut self.results));
+        while parser.peek2::<kw::param>() || parser.peek2::<kw::result>() {
+            parser.parens(|p| {
+                let mut l = p.lookahead1();
+                if l.peek::<kw::param>() {
+                    if results.len() > 0 {
+                        return Err(p.error(
+                            "result before parameter (or unexpected token): \
+                             cannot list params after results",
+                        ));
+                    }
+                    p.parse::<kw::param>()?;
+                    if p.is_empty() {
+                        return Ok(());
+                    }
+                    let (id, name) = if allow_names {
+                        (p.parse::<Option<_>>()?, p.parse::<Option<_>>()?)
+                    } else {
+                        (None, None)
+                    };
+                    let parse_more = id.is_none() && name.is_none();
+                    let ty = p.parse()?;
+                    params.push((id, name, ty));
+                    while parse_more && !p.is_empty() {
+                        params.push((None, None, p.parse()?));
+                    }
+                } else if l.peek::<kw::result>() {
+                    p.parse::<kw::result>()?;
+                    while !p.is_empty() {
+                        results.push(p.parse()?);
+                    }
+                } else {
+                    return Err(l.error());
+                }
+                Ok(())
+            })?;
+        }
+        self.params = params.into();
+        self.results = results.into();
+        Ok(())
+    }
+}
+
+impl<'a> Parse<'a> for FunctionType<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut ret = FunctionType {
+            params: Box::new([]),
+            results: Box::new([]),
+        };
+        ret.finish_parse(true, parser)?;
+        Ok(ret)
+    }
+}
+
+impl<'a> Peek for FunctionType<'a> {
+    fn peek(cursor: Cursor<'_>) -> bool {
+        if let Some(next) = cursor.lparen() {
+            match next.keyword() {
+                Some(("param", _)) | Some(("result", _)) => return true,
+                _ => {}
+            }
+        }
+
+        false
+    }
+
+    fn display() -> &'static str {
+        "function type"
+    }
+}
+
+/// A function type with parameters and results.
+#[derive(Clone, Debug, Default)]
+pub struct FunctionTypeNoNames<'a>(pub FunctionType<'a>);
+
+impl<'a> Parse<'a> for FunctionTypeNoNames<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut ret = FunctionType {
+            params: Box::new([]),
+            results: Box::new([]),
+        };
+        ret.finish_parse(false, parser)?;
+        Ok(FunctionTypeNoNames(ret))
+    }
+}
+
+impl<'a> Peek for FunctionTypeNoNames<'a> {
+    fn peek(cursor: Cursor<'_>) -> bool {
+        FunctionType::peek(cursor)
+    }
+
+    fn display() -> &'static str {
+        FunctionType::display()
+    }
+}
+
+impl<'a> From<FunctionTypeNoNames<'a>> for FunctionType<'a> {
+    fn from(ty: FunctionTypeNoNames<'a>) -> FunctionType<'a> {
+        ty.0
+    }
+}
+
+/// A struct type with fields.
+#[derive(Clone, Debug)]
+pub struct StructType<'a> {
+    /// The fields of the struct
+    pub fields: Vec<StructField<'a>>,
+}
+
+impl<'a> Parse<'a> for StructType<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut ret = StructType { fields: Vec::new() };
+        while !parser.is_empty() {
+            let field = if parser.peek2::<kw::field>() {
+                parser.parens(|parser| {
+                    parser.parse::<kw::field>()?;
+                    StructField::parse(parser, true)
+                })
+            } else {
+                StructField::parse(parser, false)
+            };
+            ret.fields.push(field?);
+        }
+        Ok(ret)
+    }
+}
+
+/// A field of a struct type.
+#[derive(Clone, Debug)]
+pub struct StructField<'a> {
+    /// An optional identifier for name resolution.
+    pub id: Option<Id<'a>>,
+    /// Whether this field may be mutated or not.
+    pub mutable: bool,
+    /// The storage type stored in this field.
+    pub ty: StorageType<'a>,
+}
+
+impl<'a> StructField<'a> {
+    fn parse(parser: Parser<'a>, with_id: bool) -> Result<Self> {
+        let id = if with_id { parser.parse()? } else { None };
+        let (ty, mutable) = if parser.peek2::<kw::r#mut>() {
+            let ty = parser.parens(|parser| {
+                parser.parse::<kw::r#mut>()?;
+                parser.parse()
+            })?;
+            (ty, true)
+        } else {
+            (parser.parse::<StorageType<'a>>()?, false)
+        };
+        Ok(StructField { id, mutable, ty })
+    }
+}
+
+/// An array type with fields.
+#[derive(Clone, Debug)]
+pub struct ArrayType<'a> {
+    /// Whether this field may be mutated or not.
+    pub mutable: bool,
+    /// The storage type stored in this field.
+    pub ty: StorageType<'a>,
+}
+
+impl<'a> Parse<'a> for ArrayType<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let (ty, mutable) = if parser.peek2::<kw::r#mut>() {
+            let ty = parser.parens(|parser| {
+                parser.parse::<kw::r#mut>()?;
+                parser.parse()
+            })?;
+            (ty, true)
+        } else {
+            (parser.parse::<StorageType<'a>>()?, false)
+        };
+        Ok(ArrayType { mutable, ty })
+    }
+}
+
+/// The type of an exported item from a module or instance.
+#[derive(Debug, Clone)]
+pub struct ExportType<'a> {
+    /// Where this export was defined.
+    pub span: Span,
+    /// The name of this export.
+    pub name: &'a str,
+    /// The signature of the item that's exported.
+    pub item: ItemSig<'a>,
+}
+
+impl<'a> Parse<'a> for ExportType<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let span = parser.parse::<kw::export>()?.0;
+        let name = parser.parse()?;
+        let item = parser.parens(|p| p.parse())?;
+        Ok(ExportType { span, name, item })
+    }
+}
+
+/// A definition of a type.
+#[derive(Debug)]
+pub enum TypeDef<'a> {
+    /// A function type definition.
+    Func(FunctionType<'a>),
+    /// A struct type definition.
+    Struct(StructType<'a>),
+    /// An array type definition.
+    Array(ArrayType<'a>),
+}
+
+impl<'a> Parse<'a> for TypeDef<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut l = parser.lookahead1();
+        if l.peek::<kw::func>() {
+            parser.parse::<kw::func>()?;
+            Ok(TypeDef::Func(parser.parse()?))
+        } else if l.peek::<kw::r#struct>() {
+            parser.parse::<kw::r#struct>()?;
+            Ok(TypeDef::Struct(parser.parse()?))
+        } else if l.peek::<kw::array>() {
+            parser.parse::<kw::array>()?;
+            Ok(TypeDef::Array(parser.parse()?))
+        } else {
+            Err(l.error())
+        }
+    }
+}
+
+/// A type declaration in a module
+#[derive(Debug)]
+pub struct Type<'a> {
+    /// Where this type was defined.
+    pub span: Span,
+    /// An optional identifier to refer to this `type` by as part of name
+    /// resolution.
+    pub id: Option<Id<'a>>,
+    /// An optional name for this function stored in the custom `name` section.
+    pub name: Option<NameAnnotation<'a>>,
+    /// The type that we're declaring.
+    pub def: TypeDef<'a>,
+    /// The declared parent type of this definition.
+    pub parent: Option<Index<'a>>,
+}
+
+impl<'a> Peek for Type<'a> {
+    fn peek(cursor: Cursor<'_>) -> bool {
+        kw::r#type::peek(cursor)
+    }
+    fn display() -> &'static str {
+        "type"
+    }
+}
+
+impl<'a> Parse<'a> for Type<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let span = parser.parse::<kw::r#type>()?.0;
+        let id = parser.parse()?;
+        let name = parser.parse()?;
+
+        let (parent, def) = if parser.peek2::<kw::sub>() {
+            parser.parens(|parser| {
+                parser.parse::<kw::sub>()?;
+                let parent = if parser.peek::<Index<'a>>() {
+                    parser.parse()?
+                } else {
+                    None
+                };
+                let def = parser.parens(|parser| parser.parse())?;
+                Ok((parent, def))
+            })?
+        } else {
+            (None, parser.parens(|parser| parser.parse())?)
+        };
+
+        Ok(Type {
+            span,
+            id,
+            name,
+            def,
+            parent,
+        })
+    }
+}
+
+/// A recursion group declaration in a module
+#[derive(Debug)]
+pub struct Rec<'a> {
+    /// Where this recursion group was defined.
+    pub span: Span,
+    /// The types that we're defining in this group.
+    pub types: Vec<Type<'a>>,
+}
+
+impl<'a> Parse<'a> for Rec<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let span = parser.parse::<kw::r#rec>()?.0;
+        let mut types = Vec::new();
+        while parser.peek2::<Type<'a>>() {
+            types.push(parser.parens(|p| p.parse())?);
+        }
+        Ok(Rec { span, types })
+    }
+}
+
+/// A reference to a type defined in this module.
+#[derive(Clone, Debug)]
+pub struct TypeUse<'a, T> {
+    /// The type that we're referencing, if it was present.
+    pub index: Option<Index<'a>>,
+    /// The inline type, if present.
+    pub inline: Option<T>,
+}
+
+impl<'a, T> TypeUse<'a, T> {
+    /// Constructs a new instance of `TypeUse` without an inline definition but
+    /// with an index specified.
+    pub fn new_with_index(idx: Index<'a>) -> TypeUse<'a, T> {
+        TypeUse {
+            index: Some(idx),
+            inline: None,
+        }
+    }
+}
+
+impl<'a, T: Peek + Parse<'a>> Parse<'a> for TypeUse<'a, T> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let index = if parser.peek2::<kw::r#type>() {
+            Some(parser.parens(|p| {
+                p.parse::<kw::r#type>()?;
+                p.parse()
+            })?)
+        } else {
+            None
+        };
+        let inline = parser.parse()?;
+
+        Ok(TypeUse { index, inline })
+    }
+}
+
+impl<'a> From<TypeUse<'a, FunctionTypeNoNames<'a>>> for TypeUse<'a, FunctionType<'a>> {
+    fn from(src: TypeUse<'a, FunctionTypeNoNames<'a>>) -> TypeUse<'a, FunctionType<'a>> {
+        TypeUse {
+            index: src.index,
+            inline: src.inline.map(|x| x.into()),
+        }
+    }
+}
diff --git a/third_party/rust/wast/src/core/wast.rs b/third_party/rust/wast/src/core/wast.rs
new file mode 100644
index 0000000000..41437e02d8
--- /dev/null
+++ b/third_party/rust/wast/src/core/wast.rs
@@ -0,0 +1,236 @@
+use crate::core::{HeapType, V128Const};
+use crate::kw;
+use crate::parser::{Cursor, Parse, Parser, Peek, Result};
+use crate::token::{Float32, Float64, Index};
+
+/// Expression that can be used inside of `invoke` expressions for core wasm
+/// functions.
+#[derive(Debug)]
+#[allow(missing_docs)]
+pub enum WastArgCore<'a> {
+    I32(i32),
+    I64(i64),
+    F32(Float32),
+    F64(Float64),
+    V128(V128Const),
+    RefNull(HeapType<'a>),
+    RefExtern(u32),
+}
+
+static ARGS: &[(&str, fn(Parser<'_>) -> Result<WastArgCore<'_>>)] = {
+    use WastArgCore::*;
+    &[
+        ("i32.const", |p| Ok(I32(p.parse()?))),
+        ("i64.const", |p| Ok(I64(p.parse()?))),
+        ("f32.const", |p| Ok(F32(p.parse()?))),
+        ("f64.const", |p| Ok(F64(p.parse()?))),
+        ("v128.const", |p| Ok(V128(p.parse()?))),
+        ("ref.null", |p| Ok(RefNull(p.parse()?))),
+        ("ref.extern", |p| Ok(RefExtern(p.parse()?))),
+    ]
+};
+
+impl<'a> Parse<'a> for WastArgCore<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let parse = parser.step(|c| {
+            if let Some((kw, rest)) = c.keyword() {
+                if let Some(i) = ARGS.iter().position(|(name, _)| *name == kw) {
+                    return Ok((ARGS[i].1, rest));
+                }
+            }
+            Err(c.error("expected a [type].const expression"))
+        })?;
+        parse(parser)
+    }
+}
+
+impl Peek for WastArgCore<'_> {
+    fn peek(cursor: Cursor<'_>) -> bool {
+        let kw = match cursor.keyword() {
+            Some((kw, _)) => kw,
+            None => return false,
+        };
+        ARGS.iter().find(|(name, _)| *name == kw).is_some()
+    }
+
+    fn display() -> &'static str {
+        "core wasm argument"
+    }
+}
+
+/// Expressions that can be used inside of `assert_return` to validate the
+/// return value of a core wasm function.
+#[derive(Debug)]
+#[allow(missing_docs)]
+pub enum WastRetCore<'a> {
+    I32(i32),
+    I64(i64),
+    F32(NanPattern<Float32>),
+    F64(NanPattern<Float64>),
+    V128(V128Pattern),
+
+    /// A null reference is expected, optionally with a specified type.
+    RefNull(Option<HeapType<'a>>),
+    /// A non-null externref is expected which should contain the specified
+    /// value.
+    RefExtern(u32),
+    /// A non-null funcref is expected.
+    RefFunc(Option<Index<'a>>),
+
+    Either(Vec<WastRetCore<'a>>),
+}
+
+static RETS: &[(&str, fn(Parser<'_>) -> Result<WastRetCore<'_>>)] = {
+    use WastRetCore::*;
+    &[
+        ("i32.const", |p| Ok(I32(p.parse()?))),
+        ("i64.const", |p| Ok(I64(p.parse()?))),
+        ("f32.const", |p| Ok(F32(p.parse()?))),
+        ("f64.const", |p| Ok(F64(p.parse()?))),
+        ("v128.const", |p| Ok(V128(p.parse()?))),
+        ("ref.null", |p| Ok(RefNull(p.parse()?))),
+        ("ref.extern", |p| Ok(RefExtern(p.parse()?))),
+        ("ref.func", |p| Ok(RefFunc(p.parse()?))),
+        ("either", |p| {
+            p.depth_check()?;
+            let mut cases = Vec::new();
+            while !p.is_empty() {
+                cases.push(p.parens(|p| p.parse())?);
+            }
+            Ok(Either(cases))
+        }),
+    ]
+};
+
+impl<'a> Parse<'a> for WastRetCore<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let parse = parser.step(|c| {
+            if let Some((kw, rest)) = c.keyword() {
+                if let Some(i) = RETS.iter().position(|(name, _)| *name == kw) {
+                    return Ok((RETS[i].1, rest));
+                }
+            }
+            Err(c.error("expected a [type].const expression"))
+        })?;
+        parse(parser)
+    }
+}
+
+impl Peek for WastRetCore<'_> {
+    fn peek(cursor: Cursor<'_>) -> bool {
+        let kw = match cursor.keyword() {
+            Some((kw, _)) => kw,
+            None => return false,
+        };
+        RETS.iter().find(|(name, _)| *name == kw).is_some()
+    }
+
+    fn display() -> &'static str {
+        "core wasm return value"
+    }
+}
+
+/// Either a NaN pattern (`nan:canonical`, `nan:arithmetic`) or a value of type `T`.
+#[derive(Debug, PartialEq)]
+#[allow(missing_docs)]
+pub enum NanPattern<T> {
+    CanonicalNan,
+    ArithmeticNan,
+    Value(T),
+}
+
+impl<'a, T> Parse<'a> for NanPattern<T>
+where
+    T: Parse<'a>,
+{
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        if parser.peek::<kw::nan_canonical>() {
+            parser.parse::<kw::nan_canonical>()?;
+            Ok(NanPattern::CanonicalNan)
+        } else if parser.peek::<kw::nan_arithmetic>() {
+            parser.parse::<kw::nan_arithmetic>()?;
+            Ok(NanPattern::ArithmeticNan)
+        } else {
+            let val = parser.parse()?;
+            Ok(NanPattern::Value(val))
+        }
+    }
+}
+
+/// A version of `V128Const` that allows `NanPattern`s.
+///
+/// This implementation is necessary because only float types can include NaN patterns; otherwise
+/// it is largely similar to the implementation of `V128Const`.
+#[derive(Debug)]
+#[allow(missing_docs)]
+pub enum V128Pattern {
+    I8x16([i8; 16]),
+    I16x8([i16; 8]),
+    I32x4([i32; 4]),
+    I64x2([i64; 2]),
+    F32x4([NanPattern<Float32>; 4]),
+    F64x2([NanPattern<Float64>; 2]),
+}
+
+impl<'a> Parse<'a> for V128Pattern {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut l = parser.lookahead1();
+        if l.peek::<kw::i8x16>() {
+            parser.parse::<kw::i8x16>()?;
+            Ok(V128Pattern::I8x16([
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+            ]))
+        } else if l.peek::<kw::i16x8>() {
+            parser.parse::<kw::i16x8>()?;
+            Ok(V128Pattern::I16x8([
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+            ]))
+        } else if l.peek::<kw::i32x4>() {
+            parser.parse::<kw::i32x4>()?;
+            Ok(V128Pattern::I32x4([
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+            ]))
+        } else if l.peek::<kw::i64x2>() {
+            parser.parse::<kw::i64x2>()?;
+            Ok(V128Pattern::I64x2([parser.parse()?, parser.parse()?]))
+        } else if l.peek::<kw::f32x4>() {
+            parser.parse::<kw::f32x4>()?;
+            Ok(V128Pattern::F32x4([
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+                parser.parse()?,
+            ]))
+        } else if l.peek::<kw::f64x2>() {
+            parser.parse::<kw::f64x2>()?;
+            Ok(V128Pattern::F64x2([parser.parse()?, parser.parse()?]))
+        } else {
+            Err(l.error())
+        }
+    }
+}
diff --git a/third_party/rust/wast/src/encode.rs b/third_party/rust/wast/src/encode.rs
new file mode 100644
index 0000000000..3fc932690e
--- /dev/null
+++ b/third_party/rust/wast/src/encode.rs
@@ -0,0 +1,75 @@
+pub(crate) trait Encode {
+    fn encode(&self, e: &mut Vec<u8>);
+}
+
+impl<T: Encode + ?Sized> Encode for &'_ T {
+    fn encode(&self, e: &mut Vec<u8>) {
+        T::encode(self, e)
+    }
+}
+
+impl<T: Encode> Encode for [T] {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.len().encode(e);
+        for item in self {
+            item.encode(e);
+        }
+    }
+}
+
+impl<T: Encode> Encode for Vec<T> {
+    fn encode(&self, e: &mut Vec<u8>) {
+        <[T]>::encode(self, e)
+    }
+}
+
+impl Encode for str {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.len().encode(e);
+        e.extend_from_slice(self.as_bytes());
+    }
+}
+
+impl Encode for usize {
+    fn encode(&self, e: &mut Vec<u8>) {
+        assert!(*self <= u32::max_value() as usize);
+        (*self as u32).encode(e)
+    }
+}
+
+impl Encode for u8 {
+    fn encode(&self, e: &mut Vec<u8>) {
+        e.push(*self);
+    }
+}
+
+impl Encode for u32 {
+    fn encode(&self, e: &mut Vec<u8>) {
+        leb128::write::unsigned(e, (*self).into()).unwrap();
+    }
+}
+
+impl Encode for i32 {
+    fn encode(&self, e: &mut Vec<u8>) {
+        leb128::write::signed(e, (*self).into()).unwrap();
+    }
+}
+
+impl Encode for u64 {
+    fn encode(&self, e: &mut Vec<u8>) {
+        leb128::write::unsigned(e, *self).unwrap();
+    }
+}
+
+impl Encode for i64 {
+    fn encode(&self, e: &mut Vec<u8>) {
+        leb128::write::signed(e, *self).unwrap();
+    }
+}
+
+impl<T: Encode, U: Encode> Encode for (T, U) {
+    fn encode(&self, e: &mut Vec<u8>) {
+        self.0.encode(e);
+        self.1.encode(e);
+    }
+}
diff --git a/third_party/rust/wast/src/error.rs b/third_party/rust/wast/src/error.rs
new file mode 100644
index 0000000000..214e678338
--- /dev/null
+++ b/third_party/rust/wast/src/error.rs
@@ -0,0 +1,196 @@
+use crate::lexer::LexError;
+use crate::token::Span;
+use std::fmt;
+use std::path::{Path, PathBuf};
+use unicode_width::UnicodeWidthStr;
+
+/// A convenience error type to tie together all the detailed errors produced by
+/// this crate.
+///
+/// This type can be created from a [`LexError`]. This also contains
+/// storage for file/text information so a nice error can be rendered along the
+/// same lines of rustc's own error messages (minus the color).
+///
+/// This type is typically suitable for use in public APIs for consumers of this
+/// crate.
+#[derive(Debug)]
+pub struct Error {
+    inner: Box<ErrorInner>,
+}
+
+#[derive(Debug)]
+struct ErrorInner {
+    text: Option<Text>,
+    file: Option<PathBuf>,
+    span: Span,
+    kind: ErrorKind,
+}
+
+#[derive(Debug)]
+struct Text {
+    line: usize,
+    col: usize,
+    snippet: String,
+}
+
+#[derive(Debug)]
+enum ErrorKind {
+    Lex(LexError),
+    Custom(String),
+}
+
+impl Error {
+    pub(crate) fn lex(span: Span, content: &str, kind: LexError) -> Error {
+        let mut ret = Error {
+            inner: Box::new(ErrorInner {
+                text: None,
+                file: None,
+                span,
+                kind: ErrorKind::Lex(kind),
+            }),
+        };
+        ret.set_text(content);
+        ret
+    }
+
+    pub(crate) fn parse(span: Span, content: &str, message: String) -> Error {
+        let mut ret = Error {
+            inner: Box::new(ErrorInner {
+                text: None,
+                file: None,
+                span,
+                kind: ErrorKind::Custom(message),
+            }),
+        };
+        ret.set_text(content);
+        ret
+    }
+
+    /// Creates a new error with the given `message` which is targeted at the
+    /// given `span`
+    ///
+    /// Note that you'll want to ensure that `set_text` or `set_path` is called
+    /// on the resulting error to improve the rendering of the error message.
+    pub fn new(span: Span, message: String) -> Error {
+        Error {
+            inner: Box::new(ErrorInner {
+                text: None,
+                file: None,
+                span,
+                kind: ErrorKind::Custom(message),
+            }),
+        }
+    }
+
+    /// Return the `Span` for this error.
+    pub fn span(&self) -> Span {
+        self.inner.span
+    }
+
+    /// To provide a more useful error this function can be used to extract
+    /// relevant textual information about this error into the error itself.
+    ///
+    /// The `contents` here should be the full text of the original file being
+    /// parsed, and this will extract a sub-slice as necessary to render in the
+    /// `Display` implementation later on.
+    pub fn set_text(&mut self, contents: &str) {
+        if self.inner.text.is_some() {
+            return;
+        }
+        self.inner.text = Some(Text::new(contents, self.inner.span));
+    }
+
+    /// To provide a more useful error this function can be used to set
+    /// the file name that this error is associated with.
+    ///
+    /// The `path` here will be stored in this error and later rendered in the
+    /// `Display` implementation.
+    pub fn set_path(&mut self, path: &Path) {
+        if self.inner.file.is_some() {
+            return;
+        }
+        self.inner.file = Some(path.to_path_buf());
+    }
+
+    /// Returns the underlying `LexError`, if any, that describes this error.
+    pub fn lex_error(&self) -> Option<&LexError> {
+        match &self.inner.kind {
+            ErrorKind::Lex(e) => Some(e),
+            _ => None,
+        }
+    }
+
+    /// Returns the underlying message, if any, that describes this error.
+    pub fn message(&self) -> String {
+        match &self.inner.kind {
+            ErrorKind::Lex(e) => e.to_string(),
+            ErrorKind::Custom(e) => e.clone(),
+        }
+    }
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let err = match &self.inner.kind {
+            ErrorKind::Lex(e) => e as &dyn fmt::Display,
+            ErrorKind::Custom(e) => e as &dyn fmt::Display,
+        };
+        let text = match &self.inner.text {
+            Some(text) => text,
+            None => {
+                return write!(f, "{} at byte offset {}", err, self.inner.span.offset);
+            }
+        };
+        let file = self
+            .inner
+            .file
+            .as_ref()
+            .and_then(|p| p.to_str())
+            .unwrap_or("<anon>");
+        write!(
+            f,
+            "\
+{err}
+     --> {file}:{line}:{col}
+      |
+ {line:4} | {text}
+      | {marker:>0$}",
+            text.col + 1,
+            file = file,
+            line = text.line + 1,
+            col = text.col + 1,
+            err = err,
+            text = text.snippet,
+            marker = "^",
+        )
+    }
+}
+
+impl std::error::Error for Error {}
+
+impl Text {
+    fn new(content: &str, span: Span) -> Text {
+        let (line, col) = span.linecol_in(content);
+        let contents = content.lines().nth(line).unwrap_or("");
+        let mut snippet = String::new();
+        for ch in contents.chars() {
+            match ch {
+                // Replace tabs with spaces to render consistently
+                '\t' => {
+                    snippet.push_str("    ");
+                }
+                // these codepoints change how text is rendered so for clarity
+                // in error messages they're dropped.
+                '\u{202a}' | '\u{202b}' | '\u{202d}' | '\u{202e}' | '\u{2066}' | '\u{2067}'
+                | '\u{2068}' | '\u{206c}' | '\u{2069}' => {}
+
+                c => snippet.push(c),
+            }
+        }
+        // Use the `unicode-width` crate to figure out how wide the snippet, up
+        // to our "column", actually is. That'll tell us how many spaces to
+        // place before the `^` character that points at the problem
+        let col = snippet.get(..col).map(|s| s.width()).unwrap_or(col);
+        Text { line, col, snippet }
+    }
+}
diff --git a/third_party/rust/wast/src/gensym.rs b/third_party/rust/wast/src/gensym.rs
new file mode 100644
index 0000000000..9f718f06d9
--- /dev/null
+++ b/third_party/rust/wast/src/gensym.rs
@@ -0,0 +1,20 @@
+use crate::token::{Id, Span};
+use std::cell::Cell;
+
+thread_local!(static NEXT: Cell<u32> = Cell::new(0));
+
+pub fn reset() {
+    NEXT.with(|c| c.set(0));
+}
+
+pub fn gen(span: Span) -> Id<'static> {
+    NEXT.with(|next| {
+        let gen = next.get() + 1;
+        next.set(gen);
+        Id::gensym(span, gen)
+    })
+}
+
+pub fn fill<'a>(span: Span, slot: &mut Option<Id<'a>>) -> Id<'a> {
+    *slot.get_or_insert_with(|| gen(span))
+}
diff --git a/third_party/rust/wast/src/lexer.rs b/third_party/rust/wast/src/lexer.rs
new file mode 100644
index 0000000000..a4f8f128c7
--- /dev/null
+++ b/third_party/rust/wast/src/lexer.rs
@@ -0,0 +1,1334 @@
+//! Definition of a lexer for the WebAssembly text format.
+//!
+//! This module provides a [`Lexer`][] type which is an iterate over the raw
+//! tokens of a WebAssembly text file. A [`Lexer`][] accounts for every single
+//! byte in a WebAssembly text field, returning tokens even for comments and
+//! whitespace. Typically you'll ignore comments and whitespace, however.
+//!
+//! If you'd like to iterate over the tokens in a file you can do so via:
+//!
+//! ```
+//! # fn foo() -> Result<(), wast::Error> {
+//! use wast::lexer::Lexer;
+//!
+//! let wat = "(module (func $foo))";
+//! for token in Lexer::new(wat) {
+//!     println!("{:?}", token?);
+//! }
+//! # Ok(())
+//! # }
+//! ```
+//!
+//! Note that you'll typically not use this module but will rather use
+//! [`ParseBuffer`](crate::parser::ParseBuffer) instead.
+//!
+//! [`Lexer`]: crate::lexer::Lexer
+
+use crate::token::Span;
+use crate::Error;
+use std::borrow::Cow;
+use std::char;
+use std::fmt;
+use std::str;
+
+/// A structure used to lex the s-expression syntax of WAT files.
+///
+/// This structure is used to generate [`Token`] items, which should account for
+/// every single byte of the input as we iterate over it. A [`LexError`] is
+/// returned for any non-lexable text.
+#[derive(Clone)]
+pub struct Lexer<'a> {
+    remaining: &'a str,
+    input: &'a str,
+    allow_confusing_unicode: bool,
+}
+
+/// A fragment of source lex'd from an input string.
+///
+/// This enumeration contains all kinds of fragments, including comments and
+/// whitespace. For most cases you'll probably ignore these and simply look at
+/// tokens.
+#[derive(Debug, PartialEq)]
+pub enum Token<'a> {
+    /// A line comment, preceded with `;;`
+    LineComment(&'a str),
+
+    /// A block comment, surrounded by `(;` and `;)`. Note that these can be
+    /// nested.
+    BlockComment(&'a str),
+
+    /// A fragment of source that represents whitespace.
+    Whitespace(&'a str),
+
+    /// A left-parenthesis, including the source text for where it comes from.
+    LParen(&'a str),
+    /// A right-parenthesis, including the source text for where it comes from.
+    RParen(&'a str),
+
+    /// A string literal, which is actually a list of bytes.
+    String(WasmString<'a>),
+
+    /// An identifier (like `$foo`).
+    ///
+    /// All identifiers start with `$` and the payload here is the original
+    /// source text.
+    Id(&'a str),
+
+    /// A keyword, or something that starts with an alphabetic character.
+    ///
+    /// The payload here is the original source text.
+    Keyword(&'a str),
+
+    /// A reserved series of `idchar` symbols. Unknown what this is meant to be
+    /// used for, you'll probably generate an error about an unexpected token.
+    Reserved(&'a str),
+
+    /// An integer.
+    Integer(Integer<'a>),
+
+    /// A float.
+    Float(Float<'a>),
+}
+
+enum ReservedKind<'a> {
+    String(Cow<'a, [u8]>),
+    Idchars,
+    Reserved,
+}
+
+/// Errors that can be generated while lexing.
+///
+/// All lexing errors have line/colum/position information as well as a
+/// `LexError` indicating what kind of error happened while lexing.
+#[derive(Debug, Clone, PartialEq, Eq)]
+#[non_exhaustive]
+pub enum LexError {
+    /// A dangling block comment was found with an unbalanced `(;` which was
+    /// never terminated in the file.
+    DanglingBlockComment,
+
+    /// An unexpected character was encountered when generally parsing and
+    /// looking for something else.
+    Unexpected(char),
+
+    /// An invalid `char` in a string literal was found.
+    InvalidStringElement(char),
+
+    /// An invalid string escape letter was found (the thing after the `\` in
+    /// string literals)
+    InvalidStringEscape(char),
+
+    /// An invalid hexadecimal digit was found.
+    InvalidHexDigit(char),
+
+    /// An invalid base-10 digit was found.
+    InvalidDigit(char),
+
+    /// Parsing expected `wanted` but ended up finding `found` instead where the
+    /// two characters aren't the same.
+    Expected {
+        /// The character that was expected to be found
+        wanted: char,
+        /// The character that was actually found
+        found: char,
+    },
+
+    /// We needed to parse more but EOF (or end of the string) was encountered.
+    UnexpectedEof,
+
+    /// A number failed to parse because it was too big to fit within the target
+    /// type.
+    NumberTooBig,
+
+    /// An invalid unicode value was found in a `\u{...}` escape in a string,
+    /// only valid unicode scalars can be escaped that way.
+    InvalidUnicodeValue(u32),
+
+    /// A lone underscore was found when parsing a number, since underscores
+    /// should always be preceded and succeeded with a digit of some form.
+    LoneUnderscore,
+
+    /// A "confusing" unicode character is present in a comment or a string
+    /// literal, such as a character that changes the direction text is
+    /// typically displayed in editors. This could cause the human-read
+    /// version to behave differently than the compiler-visible version, so
+    /// these are simply rejected for now.
+    ConfusingUnicode(char),
+}
+
+/// A sign token for an integer.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum SignToken {
+    /// Plus sign: "+",
+    Plus,
+    /// Minus sign: "-",
+    Minus,
+}
+
+/// A parsed integer, signed or unsigned.
+///
+/// Methods can be use to access the value of the integer.
+#[derive(Debug, PartialEq)]
+pub struct Integer<'a>(Box<IntegerInner<'a>>);
+
+#[derive(Debug, PartialEq)]
+struct IntegerInner<'a> {
+    sign: Option<SignToken>,
+    src: &'a str,
+    val: Cow<'a, str>,
+    hex: bool,
+}
+
+/// A parsed float.
+///
+/// Methods can be use to access the value of the float.
+#[derive(Debug, PartialEq)]
+pub struct Float<'a>(Box<FloatInner<'a>>);
+
+#[derive(Debug, PartialEq)]
+struct FloatInner<'a> {
+    src: &'a str,
+    val: FloatVal<'a>,
+}
+
+/// A parsed string.
+#[derive(Debug, PartialEq)]
+pub struct WasmString<'a>(Box<WasmStringInner<'a>>);
+
+#[derive(Debug, PartialEq)]
+struct WasmStringInner<'a> {
+    src: &'a str,
+    val: Cow<'a, [u8]>,
+}
+
+/// Possible parsed float values
+#[derive(Debug, PartialEq, Eq)]
+pub enum FloatVal<'a> {
+    /// A float `NaN` representation
+    Nan {
+        /// The specific bits to encode for this float, optionally
+        val: Option<u64>,
+        /// Whether or not this is a negative `NaN` or not.
+        negative: bool,
+    },
+    /// An float infinite representation,
+    Inf {
+        #[allow(missing_docs)]
+        negative: bool,
+    },
+    /// A parsed and separated floating point value
+    Val {
+        /// Whether or not the `integral` and `decimal` are specified in hex
+        hex: bool,
+        /// The float parts before the `.`
+        integral: Cow<'a, str>,
+        /// The float parts after the `.`
+        decimal: Option<Cow<'a, str>>,
+        /// The exponent to multiple this `integral.decimal` portion of the
+        /// float by. If `hex` is true this is `2^exponent` and otherwise it's
+        /// `10^exponent`
+        exponent: Option<Cow<'a, str>>,
+    },
+}
+
+// https://webassembly.github.io/spec/core/text/values.html#text-idchar
+macro_rules! idchars {
+    () => {
+        b'0'..=b'9'
+        | b'A'..=b'Z'
+        | b'a'..=b'z'
+        | b'!'
+        | b'#'
+        | b'$'
+        | b'%'
+        | b'&'
+        | b'\''
+        | b'*'
+        | b'+'
+        | b'-'
+        | b'.'
+        | b'/'
+        | b':'
+        | b'<'
+        | b'='
+        | b'>'
+        | b'?'
+        | b'@'
+        | b'\\'
+        | b'^'
+        | b'_'
+        | b'`'
+        | b'|'
+        | b'~'
+    }
+}
+
+impl<'a> Lexer<'a> {
+    /// Creates a new lexer which will lex the `input` source string.
+    pub fn new(input: &str) -> Lexer<'_> {
+        Lexer {
+            remaining: input,
+            input,
+            allow_confusing_unicode: false,
+        }
+    }
+
+    /// Returns the original source input that we're lexing.
+    pub fn input(&self) -> &'a str {
+        self.input
+    }
+
+    /// Configures whether "confusing" unicode characters are allowed while
+    /// lexing.
+    ///
+    /// If allowed then no error will happen if these characters are found, but
+    /// otherwise if disallowed a lex error will be produced when these
+    /// characters are found. Confusing characters are denied by default.
+    ///
+    /// For now "confusing characters" are primarily related to the "trojan
+    /// source" problem where it refers to characters which cause humans to read
+    /// text differently than this lexer, such as characters that alter the
+    /// left-to-right display of the source code.
+    pub fn allow_confusing_unicode(&mut self, allow: bool) -> &mut Self {
+        self.allow_confusing_unicode = allow;
+        self
+    }
+
+    /// Lexes the next token in the input.
+    ///
+    /// Returns `Some` if a token is found or `None` if we're at EOF.
+    ///
+    /// # Errors
+    ///
+    /// Returns an error if the input is malformed.
+    pub fn parse(&mut self) -> Result<Option<Token<'a>>, Error> {
+        let pos = self.cur();
+        // This `match` generally parses the grammar specified at
+        //
+        // https://webassembly.github.io/spec/core/text/lexical.html#text-token
+        let byte = match self.remaining.as_bytes().first() {
+            Some(b) => b,
+            None => return Ok(None),
+        };
+
+        match byte {
+            // Open-parens check the next character to see if this is the start
+            // of a block comment, otherwise it's just a bland left-paren
+            // token.
+            b'(' => match self.remaining.as_bytes().get(1) {
+                Some(b';') => {
+                    let mut level = 1;
+                    // Note that we're doing a byte-level search here for the
+                    // close-delimiter of `;)`. The actual source text is utf-8
+                    // encode in `self.remaining` but due to how utf-8 works we
+                    // can safely search for an ASCII byte since it'll never
+                    // otherwise appear in the middle of a codepoint and if we
+                    // find it then it's guaranteed to be the right byte.
+                    //
+                    // Mainly we're avoiding the overhead of decoding utf-8
+                    // characters into a Rust `char` since it's otherwise
+                    // unnecessary work.
+                    let mut iter = self.remaining.as_bytes()[2..].iter();
+                    while let Some(ch) = iter.next() {
+                        match ch {
+                            b'(' => {
+                                if let Some(b';') = iter.as_slice().first() {
+                                    level += 1;
+                                    iter.next();
+                                }
+                            }
+                            b';' => {
+                                if let Some(b')') = iter.as_slice().first() {
+                                    level -= 1;
+                                    iter.next();
+                                    if level == 0 {
+                                        let len = self.remaining.len() - iter.as_slice().len();
+                                        let (comment, remaining) = self.remaining.split_at(len);
+                                        self.remaining = remaining;
+                                        self.check_confusing_comment(comment)?;
+                                        return Ok(Some(Token::BlockComment(comment)));
+                                    }
+                                }
+                            }
+                            _ => {}
+                        }
+                    }
+                    Err(self.error(pos, LexError::DanglingBlockComment))
+                }
+                _ => Ok(Some(Token::LParen(self.split_first_byte()))),
+            },
+
+            b')' => Ok(Some(Token::RParen(self.split_first_byte()))),
+
+            // https://webassembly.github.io/spec/core/text/lexical.html#white-space
+            b' ' | b'\n' | b'\r' | b'\t' => Ok(Some(Token::Whitespace(self.split_ws()))),
+
+            c @ (idchars!() | b'"') => {
+                let (kind, src) = self.split_reserved()?;
+                match kind {
+                    // If the reserved token was simply a single string then
+                    // that is converted to a standalone string token
+                    ReservedKind::String(val) => {
+                        return Ok(Some(Token::String(WasmString(Box::new(WasmStringInner {
+                            val,
+                            src,
+                        })))));
+                    }
+
+                    // If only idchars were consumed then this could be a
+                    // specific kind of standalone token we're interested in.
+                    ReservedKind::Idchars => {
+                        // https://webassembly.github.io/spec/core/text/values.html#integers
+                        if let Some(number) = self.number(src) {
+                            return Ok(Some(number));
+                        // https://webassembly.github.io/spec/core/text/values.html#text-id
+                        } else if *c == b'$' && src.len() > 1 {
+                            return Ok(Some(Token::Id(src)));
+                        // https://webassembly.github.io/spec/core/text/lexical.html#text-keyword
+                        } else if b'a' <= *c && *c <= b'z' {
+                            return Ok(Some(Token::Keyword(src)));
+                        }
+                    }
+
+                    // ... otherwise this was a conglomeration of idchars,
+                    // strings, or just idchars that don't match a prior rule,
+                    // meaning this falls through to the fallback `Reserved`
+                    // token.
+                    ReservedKind::Reserved => {}
+                }
+
+                Ok(Some(Token::Reserved(src)))
+            }
+
+            // This could be a line comment, otherwise `;` is a reserved token.
+            // The second byte is checked to see if it's a `;;` line comment
+            //
+            // Note that this character being considered as part of a
+            // `reserved` token is part of the annotations proposal.
+            b';' => match self.remaining.as_bytes().get(1) {
+                Some(b';') => {
+                    let comment = self.split_until(b'\n');
+                    self.check_confusing_comment(comment)?;
+                    Ok(Some(Token::LineComment(comment)))
+                }
+                _ => Ok(Some(Token::Reserved(self.split_first_byte()))),
+            },
+
+            // Other known reserved tokens other than `;`
+            //
+            // Note that these characters being considered as part of a
+            // `reserved` token is part of the annotations proposal.
+            b',' | b'[' | b']' | b'{' | b'}' => Ok(Some(Token::Reserved(self.split_first_byte()))),
+
+            _ => {
+                let ch = self.remaining.chars().next().unwrap();
+                Err(self.error(pos, LexError::Unexpected(ch)))
+            }
+        }
+    }
+
+    fn split_first_byte(&mut self) -> &'a str {
+        let (token, remaining) = self.remaining.split_at(1);
+        self.remaining = remaining;
+        token
+    }
+
+    fn split_until(&mut self, byte: u8) -> &'a str {
+        let pos = memchr::memchr(byte, self.remaining.as_bytes()).unwrap_or(self.remaining.len());
+        let (ret, remaining) = self.remaining.split_at(pos);
+        self.remaining = remaining;
+        ret
+    }
+
+    fn split_ws(&mut self) -> &'a str {
+        // This table is a byte lookup table to determine whether a byte is a
+        // whitespace byte. There are only 4 whitespace bytes for the `*.wat`
+        // format right now which are ' ', '\t', '\r', and '\n'. These 4 bytes
+        // have a '1' in the table below.
+        //
+        // Due to how utf-8 works (our input is guaranteed to be utf-8) it is
+        // known that if these bytes are found they're guaranteed to be the
+        // whitespace byte, so they can be safely skipped and we don't have to
+        // do full utf-8 decoding. This means that the goal of this function is
+        // to find the first non-whitespace byte in `self.remaining`.
+        //
+        // For now this lookup table seems to be the fastest, but projects like
+        // https://github.com/lemire/despacer show other simd algorithms which
+        // can possibly accelerate this even more. Note that `*.wat` files often
+        // have a lot of whitespace so this function is typically quite hot when
+        // parsing inputs.
+        #[rustfmt::skip]
+        const WS: [u8; 256] = [
+            //                                   \t \n       \r
+            /* 0x00 */ 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 1, 0, 0,
+            /* 0x10 */ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+            //        ' '
+            /* 0x20 */ 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+            /* 0x30 */ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+            /* 0x40 */ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+            /* 0x50 */ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+            /* 0x60 */ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+            /* 0x70 */ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+            /* 0x80 */ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+            /* 0x90 */ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+            /* 0xa0 */ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+            /* 0xb0 */ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+            /* 0xc0 */ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+            /* 0xd0 */ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+            /* 0xe0 */ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+            /* 0xf0 */ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+        ];
+        let pos = self
+            .remaining
+            .as_bytes()
+            .iter()
+            .position(|b| WS[*b as usize] != 1)
+            .unwrap_or(self.remaining.len());
+        let (ret, remaining) = self.remaining.split_at(pos);
+        self.remaining = remaining;
+        ret
+    }
+
+    /// Splits off a "reserved" token which is then further processed later on
+    /// to figure out which kind of token it is `depending on `ReservedKind`.
+    ///
+    /// For more information on this method see the clarification at
+    /// https://github.com/WebAssembly/spec/pull/1499 but the general gist is
+    /// that this is parsing the grammar:
+    ///
+    /// ```text
+    /// reserved := (idchar | string)+
+    /// ```
+    ///
+    /// which means that it is eating any number of adjacent string/idchar
+    /// tokens (e.g. `a"b"c`) and returning the classification of what was
+    /// eaten. The classification assists in determining what the actual token
+    /// here eaten looks like.
+    fn split_reserved(&mut self) -> Result<(ReservedKind<'a>, &'a str), Error> {
+        let mut idchars = false;
+        let mut strings = 0u32;
+        let mut last_string_val = None;
+        let mut pos = 0;
+        while let Some(byte) = self.remaining.as_bytes().get(pos) {
+            match byte {
+                // Normal `idchars` production which appends to the reserved
+                // token that's being produced.
+                idchars!() => {
+                    idchars = true;
+                    pos += 1;
+                }
+
+                // https://webassembly.github.io/spec/core/text/values.html#text-string
+                b'"' => {
+                    strings += 1;
+                    pos += 1;
+                    let mut it = self.remaining[pos..].chars();
+                    let result = Lexer::parse_str(&mut it, self.allow_confusing_unicode);
+                    pos = self.remaining.len() - it.as_str().len();
+                    match result {
+                        Ok(s) => last_string_val = Some(s),
+                        Err(e) => {
+                            let start = self.input.len() - self.remaining.len();
+                            self.remaining = &self.remaining[pos..];
+                            let err_pos = match &e {
+                                LexError::UnexpectedEof => self.input.len(),
+                                _ => {
+                                    self.input[..start + pos]
+                                        .char_indices()
+                                        .next_back()
+                                        .unwrap()
+                                        .0
+                                }
+                            };
+                            return Err(self.error(err_pos, e));
+                        }
+                    }
+                }
+
+                // Nothing else is considered part of a reserved token
+                _ => break,
+            }
+        }
+        let (ret, remaining) = self.remaining.split_at(pos);
+        self.remaining = remaining;
+        Ok(match (idchars, strings) {
+            (false, 0) => unreachable!(),
+            (false, 1) => (ReservedKind::String(last_string_val.unwrap()), ret),
+            (true, 0) => (ReservedKind::Idchars, ret),
+            _ => (ReservedKind::Reserved, ret),
+        })
+    }
+
+    fn number(&self, src: &'a str) -> Option<Token<'a>> {
+        let (sign, num) = if let Some(stripped) = src.strip_prefix('+') {
+            (Some(SignToken::Plus), stripped)
+        } else if let Some(stripped) = src.strip_prefix('-') {
+            (Some(SignToken::Minus), stripped)
+        } else {
+            (None, src)
+        };
+
+        let negative = sign == Some(SignToken::Minus);
+
+        // Handle `inf` and `nan` which are special numbers here
+        if num == "inf" {
+            return Some(Token::Float(Float(Box::new(FloatInner {
+                src,
+                val: FloatVal::Inf { negative },
+            }))));
+        } else if num == "nan" {
+            return Some(Token::Float(Float(Box::new(FloatInner {
+                src,
+                val: FloatVal::Nan {
+                    val: None,
+                    negative,
+                },
+            }))));
+        } else if let Some(stripped) = num.strip_prefix("nan:0x") {
+            let mut it = stripped.chars();
+            let to_parse = skip_undescores(&mut it, false, char::is_ascii_hexdigit)?;
+            if it.next().is_some() {
+                return None;
+            }
+            let n = u64::from_str_radix(&to_parse, 16).ok()?;
+            return Some(Token::Float(Float(Box::new(FloatInner {
+                src,
+                val: FloatVal::Nan {
+                    val: Some(n),
+                    negative,
+                },
+            }))));
+        }
+
+        // Figure out if we're a hex number or not
+        let (mut it, hex, test_valid) = if let Some(stripped) = num.strip_prefix("0x") {
+            (
+                stripped.chars(),
+                true,
+                char::is_ascii_hexdigit as fn(&char) -> bool,
+            )
+        } else {
+            (
+                num.chars(),
+                false,
+                char::is_ascii_digit as fn(&char) -> bool,
+            )
+        };
+
+        // Evaluate the first part, moving out all underscores
+        let val = skip_undescores(&mut it, negative, test_valid)?;
+
+        match it.clone().next() {
+            // If we're followed by something this may be a float so keep going.
+            Some(_) => {}
+
+            // Otherwise this is a valid integer literal!
+            None => {
+                return Some(Token::Integer(Integer(Box::new(IntegerInner {
+                    sign,
+                    src,
+                    val,
+                    hex,
+                }))))
+            }
+        }
+
+        // A number can optionally be after the decimal so only actually try to
+        // parse one if it's there.
+        let decimal = if it.clone().next() == Some('.') {
+            it.next();
+            match it.clone().next() {
+                Some(c) if test_valid(&c) => Some(skip_undescores(&mut it, false, test_valid)?),
+                Some(_) | None => None,
+            }
+        } else {
+            None
+        };
+
+        // Figure out if there's an exponential part here to make a float, and
+        // if so parse it but defer its actual calculation until later.
+        let exponent = match (hex, it.next()) {
+            (true, Some('p')) | (true, Some('P')) | (false, Some('e')) | (false, Some('E')) => {
+                let negative = match it.clone().next() {
+                    Some('-') => {
+                        it.next();
+                        true
+                    }
+                    Some('+') => {
+                        it.next();
+                        false
+                    }
+                    _ => false,
+                };
+                Some(skip_undescores(&mut it, negative, char::is_ascii_digit)?)
+            }
+            (_, None) => None,
+            _ => return None,
+        };
+
+        // We should have eaten everything by now, if not then this is surely
+        // not a float or integer literal.
+        if it.next().is_some() {
+            return None;
+        }
+
+        return Some(Token::Float(Float(Box::new(FloatInner {
+            src,
+            val: FloatVal::Val {
+                hex,
+                integral: val,
+                exponent,
+                decimal,
+            },
+        }))));
+
+        fn skip_undescores<'a>(
+            it: &mut str::Chars<'a>,
+            negative: bool,
+            good: fn(&char) -> bool,
+        ) -> Option<Cow<'a, str>> {
+            enum State {
+                Raw,
+                Collecting(String),
+            }
+            let mut last_underscore = false;
+            let mut state = if negative {
+                State::Collecting("-".to_string())
+            } else {
+                State::Raw
+            };
+            let input = it.as_str();
+            let first = it.next()?;
+            if !good(&first) {
+                return None;
+            }
+            if let State::Collecting(s) = &mut state {
+                s.push(first);
+            }
+            let mut last = 1;
+            while let Some(c) = it.clone().next() {
+                if c == '_' && !last_underscore {
+                    if let State::Raw = state {
+                        state = State::Collecting(input[..last].to_string());
+                    }
+                    it.next();
+                    last_underscore = true;
+                    continue;
+                }
+                if !good(&c) {
+                    break;
+                }
+                if let State::Collecting(s) = &mut state {
+                    s.push(c);
+                }
+                last_underscore = false;
+                it.next();
+                last += 1;
+            }
+            if last_underscore {
+                return None;
+            }
+            Some(match state {
+                State::Raw => input[..last].into(),
+                State::Collecting(s) => s.into(),
+            })
+        }
+    }
+
+    /// Verifies that `comment`, which is about to be returned, has a "confusing
+    /// unicode character" in it and should instead be transformed into an
+    /// error.
+    fn check_confusing_comment(&self, comment: &str) -> Result<(), Error> {
+        if self.allow_confusing_unicode {
+            return Ok(());
+        }
+
+        // In an effort to avoid utf-8 decoding the entire `comment` the search
+        // here is a bit more optimized. This checks for the `0xe2` byte because
+        // in the utf-8 encoding that's the leading encoding byte for all
+        // "confusing characters". Each instance of 0xe2 is checked to see if it
+        // starts a confusing character, and if so that's returned.
+        //
+        // Also note that 0xe2 will never be found in the middle of a codepoint,
+        // it's always the start of a codepoint. This means that if our special
+        // characters show up they're guaranteed to start with 0xe2 bytes.
+        let bytes = comment.as_bytes();
+        for pos in memchr::Memchr::new(0xe2, bytes) {
+            if let Some(c) = comment[pos..].chars().next() {
+                if is_confusing_unicode(c) {
+                    // Note that `self.cur()` accounts for already having
+                    // parsed `comment`, so we move backwards to where
+                    // `comment` started and then add the index within
+                    // `comment`.
+                    let pos = self.cur() - comment.len() + pos;
+                    return Err(self.error(pos, LexError::ConfusingUnicode(c)));
+                }
+            }
+        }
+
+        Ok(())
+    }
+
+    fn parse_str(
+        it: &mut str::Chars<'a>,
+        allow_confusing_unicode: bool,
+    ) -> Result<Cow<'a, [u8]>, LexError> {
+        enum State {
+            Start,
+            String(Vec<u8>),
+        }
+        let orig = it.as_str();
+        let mut state = State::Start;
+        loop {
+            match it.next().ok_or(LexError::UnexpectedEof)? {
+                '"' => break,
+                '\\' => {
+                    match state {
+                        State::String(_) => {}
+                        State::Start => {
+                            let pos = orig.len() - it.as_str().len() - 1;
+                            state = State::String(orig[..pos].as_bytes().to_vec());
+                        }
+                    }
+                    let buf = match &mut state {
+                        State::String(b) => b,
+                        State::Start => unreachable!(),
+                    };
+                    match it.next().ok_or(LexError::UnexpectedEof)? {
+                        '"' => buf.push(b'"'),
+                        '\'' => buf.push(b'\''),
+                        't' => buf.push(b'\t'),
+                        'n' => buf.push(b'\n'),
+                        'r' => buf.push(b'\r'),
+                        '\\' => buf.push(b'\\'),
+                        'u' => {
+                            Lexer::must_eat_char(it, '{')?;
+                            let n = Lexer::hexnum(it)?;
+                            let c = char::from_u32(n).ok_or(LexError::InvalidUnicodeValue(n))?;
+                            buf.extend(c.encode_utf8(&mut [0; 4]).as_bytes());
+                            Lexer::must_eat_char(it, '}')?;
+                        }
+                        c1 if c1.is_ascii_hexdigit() => {
+                            let c2 = Lexer::hexdigit(it)?;
+                            buf.push(to_hex(c1) * 16 + c2);
+                        }
+                        c => return Err(LexError::InvalidStringEscape(c)),
+                    }
+                }
+                c if (c as u32) < 0x20 || c as u32 == 0x7f => {
+                    return Err(LexError::InvalidStringElement(c))
+                }
+                c if !allow_confusing_unicode && is_confusing_unicode(c) => {
+                    return Err(LexError::ConfusingUnicode(c))
+                }
+                c => match &mut state {
+                    State::Start => {}
+                    State::String(v) => {
+                        v.extend(c.encode_utf8(&mut [0; 4]).as_bytes());
+                    }
+                },
+            }
+        }
+        match state {
+            State::Start => Ok(orig[..orig.len() - it.as_str().len() - 1].as_bytes().into()),
+            State::String(s) => Ok(s.into()),
+        }
+    }
+
+    fn hexnum(it: &mut str::Chars<'_>) -> Result<u32, LexError> {
+        let n = Lexer::hexdigit(it)?;
+        let mut last_underscore = false;
+        let mut n = n as u32;
+        while let Some(c) = it.clone().next() {
+            if c == '_' {
+                it.next();
+                last_underscore = true;
+                continue;
+            }
+            if !c.is_ascii_hexdigit() {
+                break;
+            }
+            last_underscore = false;
+            it.next();
+            n = n
+                .checked_mul(16)
+                .and_then(|n| n.checked_add(to_hex(c) as u32))
+                .ok_or(LexError::NumberTooBig)?;
+        }
+        if last_underscore {
+            return Err(LexError::LoneUnderscore);
+        }
+        Ok(n)
+    }
+
+    /// Reads a hexidecimal digit from the input stream, returning where it's
+    /// defined and the hex value. Returns an error on EOF or an invalid hex
+    /// digit.
+    fn hexdigit(it: &mut str::Chars<'_>) -> Result<u8, LexError> {
+        let ch = Lexer::must_char(it)?;
+        if ch.is_ascii_hexdigit() {
+            Ok(to_hex(ch))
+        } else {
+            Err(LexError::InvalidHexDigit(ch))
+        }
+    }
+
+    /// Reads the next character from the input string and where it's located,
+    /// returning an error if the input stream is empty.
+    fn must_char(it: &mut str::Chars<'_>) -> Result<char, LexError> {
+        it.next().ok_or(LexError::UnexpectedEof)
+    }
+
+    /// Expects that a specific character must be read next
+    fn must_eat_char(it: &mut str::Chars<'_>, wanted: char) -> Result<(), LexError> {
+        let found = Lexer::must_char(it)?;
+        if wanted == found {
+            Ok(())
+        } else {
+            Err(LexError::Expected { wanted, found })
+        }
+    }
+
+    /// Returns the current position of our iterator through the input string
+    fn cur(&self) -> usize {
+        self.input.len() - self.remaining.len()
+    }
+
+    /// Creates an error at `pos` with the specified `kind`
+    fn error(&self, pos: usize, kind: LexError) -> Error {
+        Error::lex(Span { offset: pos }, self.input, kind)
+    }
+}
+
+impl<'a> Iterator for Lexer<'a> {
+    type Item = Result<Token<'a>, Error>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.parse().transpose()
+    }
+}
+
+impl<'a> Token<'a> {
+    /// Returns the original source text for this token.
+    pub fn src(&self) -> &'a str {
+        match self {
+            Token::Whitespace(s) => s,
+            Token::BlockComment(s) => s,
+            Token::LineComment(s) => s,
+            Token::LParen(s) => s,
+            Token::RParen(s) => s,
+            Token::String(s) => s.src(),
+            Token::Id(s) => s,
+            Token::Keyword(s) => s,
+            Token::Reserved(s) => s,
+            Token::Integer(i) => i.src(),
+            Token::Float(f) => f.src(),
+        }
+    }
+}
+
+impl<'a> Integer<'a> {
+    /// Returns the sign token for this integer.
+    pub fn sign(&self) -> Option<SignToken> {
+        self.0.sign
+    }
+
+    /// Returns the original source text for this integer.
+    pub fn src(&self) -> &'a str {
+        self.0.src
+    }
+
+    /// Returns the value string that can be parsed for this integer, as well as
+    /// the base that it should be parsed in
+    pub fn val(&self) -> (&str, u32) {
+        (&self.0.val, if self.0.hex { 16 } else { 10 })
+    }
+}
+
+impl<'a> Float<'a> {
+    /// Returns the original source text for this integer.
+    pub fn src(&self) -> &'a str {
+        self.0.src
+    }
+
+    /// Returns a parsed value of this float with all of the components still
+    /// listed as strings.
+    pub fn val(&self) -> &FloatVal<'a> {
+        &self.0.val
+    }
+}
+
+impl<'a> WasmString<'a> {
+    /// Returns the original source text for this string.
+    pub fn src(&self) -> &'a str {
+        self.0.src
+    }
+
+    /// Returns a parsed value, as a list of bytes, for this string.
+    pub fn val(&self) -> &[u8] {
+        &self.0.val
+    }
+}
+
+fn to_hex(c: char) -> u8 {
+    match c {
+        'a'..='f' => c as u8 - b'a' + 10,
+        'A'..='F' => c as u8 - b'A' + 10,
+        _ => c as u8 - b'0',
+    }
+}
+
+impl fmt::Display for LexError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        use LexError::*;
+        match self {
+            DanglingBlockComment => f.write_str("unterminated block comment")?,
+            Unexpected(c) => write!(f, "unexpected character '{}'", escape_char(*c))?,
+            InvalidStringElement(c) => {
+                write!(f, "invalid character in string '{}'", escape_char(*c))?
+            }
+            InvalidStringEscape(c) => write!(f, "invalid string escape '{}'", escape_char(*c))?,
+            InvalidHexDigit(c) => write!(f, "invalid hex digit '{}'", escape_char(*c))?,
+            InvalidDigit(c) => write!(f, "invalid decimal digit '{}'", escape_char(*c))?,
+            Expected { wanted, found } => write!(
+                f,
+                "expected '{}' but found '{}'",
+                escape_char(*wanted),
+                escape_char(*found)
+            )?,
+            UnexpectedEof => write!(f, "unexpected end-of-file")?,
+            NumberTooBig => f.write_str("number is too big to parse")?,
+            InvalidUnicodeValue(c) => write!(f, "invalid unicode scalar value 0x{:x}", c)?,
+            LoneUnderscore => write!(f, "bare underscore in numeric literal")?,
+            ConfusingUnicode(c) => write!(f, "likely-confusing unicode character found {:?}", c)?,
+        }
+        Ok(())
+    }
+}
+
+fn escape_char(c: char) -> String {
+    match c {
+        '\t' => String::from("\\t"),
+        '\r' => String::from("\\r"),
+        '\n' => String::from("\\n"),
+        '\\' => String::from("\\\\"),
+        '\'' => String::from("\\\'"),
+        '\"' => String::from("\""),
+        '\x20'..='\x7e' => String::from(c),
+        _ => c.escape_unicode().to_string(),
+    }
+}
+
+/// This is an attempt to protect agains the "trojan source" [1] problem where
+/// unicode characters can cause editors to render source code differently
+/// for humans than the compiler itself sees.
+///
+/// To mitigate this issue, and because it's relatively rare in practice,
+/// this simply rejects characters of that form.
+///
+/// [1]: https://www.trojansource.codes/
+fn is_confusing_unicode(ch: char) -> bool {
+    matches!(
+        ch,
+        '\u{202a}'
+            | '\u{202b}'
+            | '\u{202d}'
+            | '\u{202e}'
+            | '\u{2066}'
+            | '\u{2067}'
+            | '\u{2068}'
+            | '\u{206c}'
+            | '\u{2069}'
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn ws_smoke() {
+        fn get_whitespace(input: &str) -> &str {
+            match Lexer::new(input).parse().expect("no first token") {
+                Some(Token::Whitespace(s)) => s,
+                other => panic!("unexpected {:?}", other),
+            }
+        }
+        assert_eq!(get_whitespace(" "), " ");
+        assert_eq!(get_whitespace("  "), "  ");
+        assert_eq!(get_whitespace("  \n "), "  \n ");
+        assert_eq!(get_whitespace("  x"), "  ");
+        assert_eq!(get_whitespace("  ;"), "  ");
+    }
+
+    #[test]
+    fn line_comment_smoke() {
+        fn get_line_comment(input: &str) -> &str {
+            match Lexer::new(input).parse().expect("no first token") {
+                Some(Token::LineComment(s)) => s,
+                other => panic!("unexpected {:?}", other),
+            }
+        }
+        assert_eq!(get_line_comment(";;"), ";;");
+        assert_eq!(get_line_comment(";; xyz"), ";; xyz");
+        assert_eq!(get_line_comment(";; xyz\nabc"), ";; xyz");
+        assert_eq!(get_line_comment(";;\nabc"), ";;");
+        assert_eq!(get_line_comment(";;   \nabc"), ";;   ");
+    }
+
+    #[test]
+    fn block_comment_smoke() {
+        fn get_block_comment(input: &str) -> &str {
+            match Lexer::new(input).parse().expect("no first token") {
+                Some(Token::BlockComment(s)) => s,
+                other => panic!("unexpected {:?}", other),
+            }
+        }
+        assert_eq!(get_block_comment("(;;)"), "(;;)");
+        assert_eq!(get_block_comment("(; ;)"), "(; ;)");
+        assert_eq!(get_block_comment("(; (;;) ;)"), "(; (;;) ;)");
+    }
+
+    fn get_token(input: &str) -> Token<'_> {
+        Lexer::new(input)
+            .parse()
+            .expect("no first token")
+            .expect("no token")
+    }
+
+    #[test]
+    fn lparen() {
+        assert_eq!(get_token("(("), Token::LParen("("));
+    }
+
+    #[test]
+    fn rparen() {
+        assert_eq!(get_token(")("), Token::RParen(")"));
+    }
+
+    #[test]
+    fn strings() {
+        fn get_string(input: &str) -> Vec<u8> {
+            match get_token(input) {
+                Token::String(s) => {
+                    assert_eq!(input, s.src());
+                    s.val().to_vec()
+                }
+                other => panic!("not string {:?}", other),
+            }
+        }
+        assert_eq!(&*get_string("\"\""), b"");
+        assert_eq!(&*get_string("\"a\""), b"a");
+        assert_eq!(&*get_string("\"a b c d\""), b"a b c d");
+        assert_eq!(&*get_string("\"\\\"\""), b"\"");
+        assert_eq!(&*get_string("\"\\'\""), b"'");
+        assert_eq!(&*get_string("\"\\n\""), b"\n");
+        assert_eq!(&*get_string("\"\\t\""), b"\t");
+        assert_eq!(&*get_string("\"\\r\""), b"\r");
+        assert_eq!(&*get_string("\"\\\\\""), b"\\");
+        assert_eq!(&*get_string("\"\\01\""), &[1]);
+        assert_eq!(&*get_string("\"\\u{1}\""), &[1]);
+        assert_eq!(
+            &*get_string("\"\\u{0f3}\""),
+            '\u{0f3}'.encode_utf8(&mut [0; 4]).as_bytes()
+        );
+        assert_eq!(
+            &*get_string("\"\\u{0_f_3}\""),
+            '\u{0f3}'.encode_utf8(&mut [0; 4]).as_bytes()
+        );
+
+        for i in 0..=255i32 {
+            let s = format!("\"\\{:02x}\"", i);
+            assert_eq!(&*get_string(&s), &[i as u8]);
+        }
+    }
+
+    #[test]
+    fn id() {
+        fn get_id(input: &str) -> &str {
+            match get_token(input) {
+                Token::Id(s) => s,
+                other => panic!("not id {:?}", other),
+            }
+        }
+        assert_eq!(get_id("$x"), "$x");
+        assert_eq!(get_id("$xyz"), "$xyz");
+        assert_eq!(get_id("$x_z"), "$x_z");
+        assert_eq!(get_id("$0^"), "$0^");
+        assert_eq!(get_id("$0^;;"), "$0^");
+        assert_eq!(get_id("$0^ ;;"), "$0^");
+    }
+
+    #[test]
+    fn keyword() {
+        fn get_keyword(input: &str) -> &str {
+            match get_token(input) {
+                Token::Keyword(s) => s,
+                other => panic!("not id {:?}", other),
+            }
+        }
+        assert_eq!(get_keyword("x"), "x");
+        assert_eq!(get_keyword("xyz"), "xyz");
+        assert_eq!(get_keyword("x_z"), "x_z");
+        assert_eq!(get_keyword("x_z "), "x_z");
+        assert_eq!(get_keyword("x_z "), "x_z");
+    }
+
+    #[test]
+    fn reserved() {
+        fn get_reserved(input: &str) -> &str {
+            match get_token(input) {
+                Token::Reserved(s) => s,
+                other => panic!("not reserved {:?}", other),
+            }
+        }
+        assert_eq!(get_reserved("$ "), "$");
+        assert_eq!(get_reserved("^_x "), "^_x");
+    }
+
+    #[test]
+    fn integer() {
+        fn get_integer(input: &str) -> String {
+            match get_token(input) {
+                Token::Integer(i) => {
+                    assert_eq!(input, i.src());
+                    i.val().0.to_string()
+                }
+                other => panic!("not integer {:?}", other),
+            }
+        }
+        assert_eq!(get_integer("1"), "1");
+        assert_eq!(get_integer("0"), "0");
+        assert_eq!(get_integer("-1"), "-1");
+        assert_eq!(get_integer("+1"), "1");
+        assert_eq!(get_integer("+1_000"), "1000");
+        assert_eq!(get_integer("+1_0_0_0"), "1000");
+        assert_eq!(get_integer("+0x10"), "10");
+        assert_eq!(get_integer("-0x10"), "-10");
+        assert_eq!(get_integer("0x10"), "10");
+    }
+
+    #[test]
+    fn float() {
+        fn get_float(input: &str) -> FloatVal<'_> {
+            match get_token(input) {
+                Token::Float(i) => {
+                    assert_eq!(input, i.src());
+                    i.0.val
+                }
+                other => panic!("not reserved {:?}", other),
+            }
+        }
+        assert_eq!(
+            get_float("nan"),
+            FloatVal::Nan {
+                val: None,
+                negative: false
+            },
+        );
+        assert_eq!(
+            get_float("-nan"),
+            FloatVal::Nan {
+                val: None,
+                negative: true,
+            },
+        );
+        assert_eq!(
+            get_float("+nan"),
+            FloatVal::Nan {
+                val: None,
+                negative: false,
+            },
+        );
+        assert_eq!(
+            get_float("+nan:0x1"),
+            FloatVal::Nan {
+                val: Some(1),
+                negative: false,
+            },
+        );
+        assert_eq!(
+            get_float("nan:0x7f_ffff"),
+            FloatVal::Nan {
+                val: Some(0x7fffff),
+                negative: false,
+            },
+        );
+        assert_eq!(get_float("inf"), FloatVal::Inf { negative: false });
+        assert_eq!(get_float("-inf"), FloatVal::Inf { negative: true });
+        assert_eq!(get_float("+inf"), FloatVal::Inf { negative: false });
+
+        assert_eq!(
+            get_float("1.2"),
+            FloatVal::Val {
+                integral: "1".into(),
+                decimal: Some("2".into()),
+                exponent: None,
+                hex: false,
+            },
+        );
+        assert_eq!(
+            get_float("1.2e3"),
+            FloatVal::Val {
+                integral: "1".into(),
+                decimal: Some("2".into()),
+                exponent: Some("3".into()),
+                hex: false,
+            },
+        );
+        assert_eq!(
+            get_float("-1_2.1_1E+0_1"),
+            FloatVal::Val {
+                integral: "-12".into(),
+                decimal: Some("11".into()),
+                exponent: Some("01".into()),
+                hex: false,
+            },
+        );
+        assert_eq!(
+            get_float("+1_2.1_1E-0_1"),
+            FloatVal::Val {
+                integral: "12".into(),
+                decimal: Some("11".into()),
+                exponent: Some("-01".into()),
+                hex: false,
+            },
+        );
+        assert_eq!(
+            get_float("0x1_2.3_4p5_6"),
+            FloatVal::Val {
+                integral: "12".into(),
+                decimal: Some("34".into()),
+                exponent: Some("56".into()),
+                hex: true,
+            },
+        );
+        assert_eq!(
+            get_float("+0x1_2.3_4P-5_6"),
+            FloatVal::Val {
+                integral: "12".into(),
+                decimal: Some("34".into()),
+                exponent: Some("-56".into()),
+                hex: true,
+            },
+        );
+        assert_eq!(
+            get_float("1."),
+            FloatVal::Val {
+                integral: "1".into(),
+                decimal: None,
+                exponent: None,
+                hex: false,
+            },
+        );
+        assert_eq!(
+            get_float("0x1p-24"),
+            FloatVal::Val {
+                integral: "1".into(),
+                decimal: None,
+                exponent: Some("-24".into()),
+                hex: true,
+            },
+        );
+    }
+}
diff --git a/third_party/rust/wast/src/lib.rs b/third_party/rust/wast/src/lib.rs
new file mode 100644
index 0000000000..d5d04c07e4
--- /dev/null
+++ b/third_party/rust/wast/src/lib.rs
@@ -0,0 +1,518 @@
+//! A crate for low-level parsing of the WebAssembly text formats: WAT and WAST.
+//!
+//! This crate is intended to be a low-level detail of the `wat` crate,
+//! providing a low-level parsing API for parsing WebAssembly text format
+//! structures. The API provided by this crate is very similar to
+//! [`syn`](https://docs.rs/syn) and provides the ability to write customized
+//! parsers which may be an extension to the core WebAssembly text format. For
+//! more documentation see the [`parser`] module.
+//!
+//! # High-level Overview
+//!
+//! This crate provides a few major pieces of functionality
+//!
+//! * [`lexer`] - this is a raw lexer for the wasm text format. This is not
+//!   customizable, but if you'd like to iterate over raw tokens this is the
+//!   module for you. You likely won't use this much.
+//!
+//! * [`parser`] - this is the workhorse of this crate. The [`parser`] module
+//!   provides the [`Parse`][] trait primarily and utilities
+//!   around working with a [`Parser`](`parser::Parser`) to parse streams of
+//!   tokens.
+//!
+//! * [`Module`](crate::core::Module) - this contains an Abstract Syntax Tree
+//!   (AST) of the WebAssembly Text format (WAT) as well as the unofficial WAST
+//!   format. This also has a [`Module::encode`](crate::core::Module::encode)
+//!   method to emit a module in its binary form.
+//!
+//! # Stability and WebAssembly Features
+//!
+//! This crate provides support for many in-progress WebAssembly features such
+//! as reference types, multi-value, etc. Be sure to check out the documentation
+//! of the [`wast` crate](https://docs.rs/wast) for policy information on crate
+//! stability vs WebAssembly Features. The tl;dr; version is that this crate
+//! will issue semver-non-breaking releases which will break the parsing of the
+//! text format. This crate, unlike `wast`, is expected to have numerous Rust
+//! public API changes, all of which will be accompanied with a semver-breaking
+//! release.
+//!
+//! # Compile-time Cargo features
+//!
+//! This crate has a `wasm-module` feature which is turned on by default which
+//! includes all necessary support to parse full WebAssembly modules. If you
+//! don't need this (for example you're parsing your own s-expression format)
+//! then this feature can be disabled.
+//!
+//! [`Parse`]: parser::Parse
+//! [`LexError`]: lexer::LexError
+
+#![deny(missing_docs, rustdoc::broken_intra_doc_links)]
+
+/// A macro to create a custom keyword parser.
+///
+/// This macro is invoked in one of two forms:
+///
+/// ```
+/// // keyword derived from the Rust identifier:
+/// wast::custom_keyword!(foo);
+///
+/// // or an explicitly specified string representation of the keyword:
+/// wast::custom_keyword!(my_keyword = "the-wasm-keyword");
+/// ```
+///
+/// This can then be used to parse custom keyword for custom items, such as:
+///
+/// ```
+/// use wast::parser::{Parser, Result, Parse};
+///
+/// struct InlineModule<'a> {
+///     inline_text: &'a str,
+/// }
+///
+/// mod kw {
+///     wast::custom_keyword!(inline);
+/// }
+///
+/// // Parse an inline string module of the form:
+/// //
+/// //    (inline "(module (func))")
+/// impl<'a> Parse<'a> for InlineModule<'a> {
+///     fn parse(parser: Parser<'a>) -> Result<Self> {
+///         parser.parse::<kw::inline>()?;
+///         Ok(InlineModule {
+///             inline_text: parser.parse()?,
+///         })
+///     }
+/// }
+/// ```
+///
+/// Note that the keyword name can only start with a lower-case letter, i.e. 'a'..'z'.
+#[macro_export]
+macro_rules! custom_keyword {
+    ($name:ident) => {
+        $crate::custom_keyword!($name = stringify!($name));
+    };
+    ($name:ident = $kw:expr) => {
+        #[allow(non_camel_case_types)]
+        #[allow(missing_docs)]
+        #[derive(Debug, Copy, Clone)]
+        pub struct $name(pub $crate::token::Span);
+
+        impl<'a> $crate::parser::Parse<'a> for $name {
+            fn parse(parser: $crate::parser::Parser<'a>) -> $crate::parser::Result<Self> {
+                parser.step(|c| {
+                    if let Some((kw, rest)) = c.keyword() {
+                        if kw == $kw {
+                            return Ok(($name(c.cur_span()), rest));
+                        }
+                    }
+                    Err(c.error(concat!("expected keyword `", $kw, "`")))
+                })
+            }
+        }
+
+        impl $crate::parser::Peek for $name {
+            fn peek(cursor: $crate::parser::Cursor<'_>) -> bool {
+                if let Some((kw, _rest)) = cursor.keyword() {
+                    kw == $kw
+                } else {
+                    false
+                }
+            }
+
+            fn display() -> &'static str {
+                concat!("`", $kw, "`")
+            }
+        }
+    };
+}
+
+/// A macro for defining custom reserved symbols.
+///
+/// This is like `custom_keyword!` but for reserved symbols (`Token::Reserved`)
+/// instead of keywords (`Token::Keyword`).
+///
+/// ```
+/// use wast::parser::{Parser, Result, Parse};
+///
+/// // Define a custom reserved symbol, the "spaceship" operator: `<=>`.
+/// wast::custom_reserved!(spaceship = "<=>");
+///
+/// /// A "three-way comparison" like `(<=> a b)` that returns -1 if `a` is less
+/// /// than `b`, 0 if they're equal, and 1 if `a` is greater than `b`.
+/// struct ThreeWayComparison<'a> {
+///     lhs: wast::core::Expression<'a>,
+///     rhs: wast::core::Expression<'a>,
+/// }
+///
+/// impl<'a> Parse<'a> for ThreeWayComparison<'a> {
+///     fn parse(parser: Parser<'a>) -> Result<Self> {
+///         parser.parse::<spaceship>()?;
+///         let lhs = parser.parse()?;
+///         let rhs = parser.parse()?;
+///         Ok(ThreeWayComparison { lhs, rhs })
+///     }
+/// }
+/// ```
+#[macro_export]
+macro_rules! custom_reserved {
+    ($name:ident) => {
+        $crate::custom_reserved!($name = stringify!($name));
+    };
+    ($name:ident = $rsv:expr) => {
+        #[allow(non_camel_case_types)]
+        #[allow(missing_docs)]
+        #[derive(Debug)]
+        pub struct $name(pub $crate::token::Span);
+
+        impl<'a> $crate::parser::Parse<'a> for $name {
+            fn parse(parser: $crate::parser::Parser<'a>) -> $crate::parser::Result<Self> {
+                parser.step(|c| {
+                    if let Some((rsv, rest)) = c.reserved() {
+                        if rsv == $rsv {
+                            return Ok(($name(c.cur_span()), rest));
+                        }
+                    }
+                    Err(c.error(concat!("expected reserved symbol `", $rsv, "`")))
+                })
+            }
+        }
+
+        impl $crate::parser::Peek for $name {
+            fn peek(cursor: $crate::parser::Cursor<'_>) -> bool {
+                if let Some((rsv, _rest)) = cursor.reserved() {
+                    rsv == $rsv
+                } else {
+                    false
+                }
+            }
+
+            fn display() -> &'static str {
+                concat!("`", $rsv, "`")
+            }
+        }
+    };
+}
+
+/// A macro, like [`custom_keyword`], to create a type which can be used to
+/// parse/peek annotation directives.
+///
+/// Note that when you're parsing custom annotations it can be somewhat tricky
+/// due to the nature that most of them are skipped. You'll want to be sure to
+/// consult the documentation of [`Parser::register_annotation`][register] when
+/// using this macro.
+///
+/// # Examples
+///
+/// To see an example of how to use this macro, let's invent our own syntax for
+/// the [producers section][section] which looks like:
+///
+/// ```wat
+/// (@producer "wat" "1.0.2")
+/// ```
+///
+/// Here, for simplicity, we'll assume everything is a `processed-by` directive,
+/// but you could get much more fancy with this as well.
+///
+/// ```
+/// # use wast::*;
+/// # use wast::parser::*;
+///
+/// // First we define the custom annotation keyword we're using, and by
+/// // convention we define it in an `annotation` module.
+/// mod annotation {
+///     wast::annotation!(producer);
+/// }
+///
+/// struct Producer<'a> {
+///     name: &'a str,
+///     version: &'a str,
+/// }
+///
+/// impl<'a> Parse<'a> for Producer<'a> {
+///     fn parse(parser: Parser<'a>) -> Result<Self> {
+///         // Remember that parser conventionally parse the *interior* of an
+///         // s-expression, so we parse our `@producer` annotation and then we
+///         // parse the payload of our annotation.
+///         parser.parse::<annotation::producer>()?;
+///         Ok(Producer {
+///             name: parser.parse()?,
+///             version: parser.parse()?,
+///         })
+///     }
+/// }
+/// ```
+///
+/// Note though that this is only half of the parser for annotations. The other
+/// half is calling the [`register_annotation`][register] method at the right
+/// time to ensure the parser doesn't automatically skip our `@producer`
+/// directive. Note that we *can't* call it inside the `Parse for Producer`
+/// definition because that's too late and the annotation would already have
+/// been skipped.
+///
+/// Instead we'll need to call it from a higher level-parser before the
+/// parenthesis have been parsed, like so:
+///
+/// ```
+/// # use wast::*;
+/// # use wast::parser::*;
+/// struct Module<'a> {
+///     fields: Vec<ModuleField<'a>>,
+/// }
+///
+/// impl<'a> Parse<'a> for Module<'a> {
+///     fn parse(parser: Parser<'a>) -> Result<Self> {
+///         // .. parse module header here ...
+///
+///         // register our custom `@producer` annotation before we start
+///         // parsing the parentheses of each field
+///         let _r = parser.register_annotation("producer");
+///
+///         let mut fields = Vec::new();
+///         while !parser.is_empty() {
+///             fields.push(parser.parens(|p| p.parse())?);
+///         }
+///         Ok(Module { fields })
+///     }
+/// }
+///
+/// enum ModuleField<'a> {
+///     Producer(Producer<'a>),
+///     // ...
+/// }
+/// # struct Producer<'a>(&'a str);
+/// # impl<'a> Parse<'a> for Producer<'a> {
+/// #   fn parse(parser: Parser<'a>) -> Result<Self> { Ok(Producer(parser.parse()?)) }
+/// # }
+/// # mod annotation { wast::annotation!(producer); }
+///
+/// impl<'a> Parse<'a> for ModuleField<'a> {
+///     fn parse(parser: Parser<'a>) -> Result<Self> {
+///         // and here `peek` works and our delegated parsing works because the
+///         // annotation has been registered.
+///         if parser.peek::<annotation::producer>() {
+///             return Ok(ModuleField::Producer(parser.parse()?));
+///         }
+///
+///         // .. typically we'd parse other module fields here...
+///
+///         Err(parser.error("unknown module field"))
+///     }
+/// }
+/// ```
+///
+/// [register]: crate::parser::Parser::register_annotation
+/// [section]: https://github.com/WebAssembly/tool-conventions/blob/master/ProducersSection.md
+#[macro_export]
+macro_rules! annotation {
+    ($name:ident) => {
+        $crate::annotation!($name = stringify!($name));
+    };
+    ($name:ident = $annotation:expr) => {
+        #[allow(non_camel_case_types)]
+        #[allow(missing_docs)]
+        #[derive(Debug)]
+        pub struct $name(pub $crate::token::Span);
+
+        impl<'a> $crate::parser::Parse<'a> for $name {
+            fn parse(parser: $crate::parser::Parser<'a>) -> $crate::parser::Result<Self> {
+                parser.step(|c| {
+                    if let Some((a, rest)) = c.annotation() {
+                        if a == $annotation {
+                            return Ok(($name(c.cur_span()), rest));
+                        }
+                    }
+                    Err(c.error(concat!("expected annotation `@", $annotation, "`")))
+                })
+            }
+        }
+
+        impl $crate::parser::Peek for $name {
+            fn peek(cursor: $crate::parser::Cursor<'_>) -> bool {
+                if let Some((a, _rest)) = cursor.annotation() {
+                    a == $annotation
+                } else {
+                    false
+                }
+            }
+
+            fn display() -> &'static str {
+                concat!("`@", $annotation, "`")
+            }
+        }
+    };
+}
+
+pub mod lexer;
+pub mod parser;
+pub mod token;
+
+mod encode;
+mod error;
+mod gensym;
+mod names;
+pub use self::error::*;
+
+macro_rules! id {
+    ($($t:tt)*) => ($($t)*)
+}
+
+#[cfg(feature = "wasm-module")]
+id! {
+    mod wast;
+    mod wat;
+    pub use self::wast::*;
+    pub use self::wat::*;
+
+    // Support for core wasm parsing
+    pub mod core;
+
+    // Support for component model parsing
+    pub mod component;
+}
+
+/// Common keyword used to parse WebAssembly text files.
+pub mod kw {
+    custom_keyword!(after);
+    custom_keyword!(alias);
+    custom_keyword!(any);
+    custom_keyword!(anyfunc);
+    custom_keyword!(anyref);
+    custom_keyword!(arg);
+    custom_keyword!(array);
+    custom_keyword!(arrayref);
+    custom_keyword!(assert_exception);
+    custom_keyword!(assert_exhaustion);
+    custom_keyword!(assert_invalid);
+    custom_keyword!(assert_malformed);
+    custom_keyword!(assert_return);
+    custom_keyword!(assert_trap);
+    custom_keyword!(assert_unlinkable);
+    custom_keyword!(before);
+    custom_keyword!(binary);
+    custom_keyword!(block);
+    custom_keyword!(catch);
+    custom_keyword!(catch_all);
+    custom_keyword!(code);
+    custom_keyword!(component);
+    custom_keyword!(data);
+    custom_keyword!(declare);
+    custom_keyword!(delegate);
+    custom_keyword!(r#do = "do");
+    custom_keyword!(elem);
+    custom_keyword!(end);
+    custom_keyword!(tag);
+    custom_keyword!(export);
+    custom_keyword!(r#extern = "extern");
+    custom_keyword!(externref);
+    custom_keyword!(eq);
+    custom_keyword!(eqref);
+    custom_keyword!(f32);
+    custom_keyword!(f32x4);
+    custom_keyword!(f64);
+    custom_keyword!(f64x2);
+    custom_keyword!(field);
+    custom_keyword!(first);
+    custom_keyword!(func);
+    custom_keyword!(funcref);
+    custom_keyword!(get);
+    custom_keyword!(global);
+    custom_keyword!(i16);
+    custom_keyword!(i16x8);
+    custom_keyword!(i31);
+    custom_keyword!(i31ref);
+    custom_keyword!(i32);
+    custom_keyword!(i32x4);
+    custom_keyword!(i64);
+    custom_keyword!(i64x2);
+    custom_keyword!(i8);
+    custom_keyword!(i8x16);
+    custom_keyword!(import);
+    custom_keyword!(instance);
+    custom_keyword!(instantiate);
+    custom_keyword!(invoke);
+    custom_keyword!(item);
+    custom_keyword!(last);
+    custom_keyword!(local);
+    custom_keyword!(memory);
+    custom_keyword!(module);
+    custom_keyword!(modulecode);
+    custom_keyword!(nan_arithmetic = "nan:arithmetic");
+    custom_keyword!(nan_canonical = "nan:canonical");
+    custom_keyword!(nofunc);
+    custom_keyword!(noextern);
+    custom_keyword!(none);
+    custom_keyword!(null);
+    custom_keyword!(nullfuncref);
+    custom_keyword!(nullexternref);
+    custom_keyword!(nullref);
+    custom_keyword!(offset);
+    custom_keyword!(outer);
+    custom_keyword!(param);
+    custom_keyword!(parent);
+    custom_keyword!(passive);
+    custom_keyword!(quote);
+    custom_keyword!(r#else = "else");
+    custom_keyword!(r#if = "if");
+    custom_keyword!(r#loop = "loop");
+    custom_keyword!(r#mut = "mut");
+    custom_keyword!(r#type = "type");
+    custom_keyword!(r#ref = "ref");
+    custom_keyword!(ref_func = "ref.func");
+    custom_keyword!(ref_null = "ref.null");
+    custom_keyword!(register);
+    custom_keyword!(rec);
+    custom_keyword!(result);
+    custom_keyword!(shared);
+    custom_keyword!(start);
+    custom_keyword!(sub);
+    custom_keyword!(table);
+    custom_keyword!(then);
+    custom_keyword!(r#try = "try");
+    custom_keyword!(v128);
+    custom_keyword!(value);
+    custom_keyword!(s8);
+    custom_keyword!(s16);
+    custom_keyword!(s32);
+    custom_keyword!(s64);
+    custom_keyword!(u8);
+    custom_keyword!(u16);
+    custom_keyword!(u32);
+    custom_keyword!(u64);
+    custom_keyword!(char);
+    custom_keyword!(case);
+    custom_keyword!(refines);
+    custom_keyword!(record);
+    custom_keyword!(string);
+    custom_keyword!(bool_ = "bool");
+    custom_keyword!(float32);
+    custom_keyword!(float64);
+    custom_keyword!(variant);
+    custom_keyword!(flags);
+    custom_keyword!(option);
+    custom_keyword!(tuple);
+    custom_keyword!(list);
+    custom_keyword!(error);
+    custom_keyword!(union);
+    custom_keyword!(canon);
+    custom_keyword!(lift);
+    custom_keyword!(lower);
+    custom_keyword!(enum_ = "enum");
+    custom_keyword!(string_utf8 = "string-encoding=utf8");
+    custom_keyword!(string_utf16 = "string-encoding=utf16");
+    custom_keyword!(string_latin1_utf16 = "string-encoding=latin1+utf16");
+    custom_keyword!(r#struct = "struct");
+    custom_keyword!(structref);
+    custom_keyword!(realloc);
+    custom_keyword!(post_return = "post-return");
+    custom_keyword!(with);
+    custom_keyword!(core);
+    custom_keyword!(true_ = "true");
+    custom_keyword!(false_ = "false");
+}
+
+/// Common annotations used to parse WebAssembly text files.
+pub mod annotation {
+    annotation!(custom);
+    annotation!(name);
+}
diff --git a/third_party/rust/wast/src/names.rs b/third_party/rust/wast/src/names.rs
new file mode 100644
index 0000000000..7cbfc5d9ca
--- /dev/null
+++ b/third_party/rust/wast/src/names.rs
@@ -0,0 +1,86 @@
+use crate::token::{Id, Index};
+use crate::Error;
+use std::collections::HashMap;
+
+#[derive(Default)]
+pub struct Namespace<'a> {
+    names: HashMap<Id<'a>, u32>,
+    count: u32,
+}
+
+impl<'a> Namespace<'a> {
+    pub fn register(&mut self, name: Option<Id<'a>>, desc: &str) -> Result<u32, Error> {
+        let index = self.alloc();
+        if let Some(name) = name {
+            if let Some(_prev) = self.names.insert(name, index) {
+                // FIXME: temporarily allow duplicately-named data and element
+                // segments. This is a sort of dumb hack to get the spec test
+                // suite working (ironically).
+                //
+                // So as background, the text format disallows duplicate
+                // identifiers, causing a parse error if they're found. There
+                // are two tests currently upstream, however, data.wast and
+                // elem.wast, which *look* like they have duplicately named
+                // element and data segments. These tests, however, are using
+                // pre-bulk-memory syntax where a bare identifier was the
+                // table/memory being initialized. In post-bulk-memory this
+                // identifier is the name of the segment. Since we implement
+                // post-bulk-memory features that means that we're parsing the
+                // memory/table-to-initialize as the name of the segment.
+                //
+                // This is technically incorrect behavior but no one is
+                // hopefully relying on this too much. To get the spec tests
+                // passing we ignore errors for elem/data segments. Once the
+                // spec tests get updated enough we can remove this condition
+                // and return errors for them.
+                if desc != "elem" && desc != "data" {
+                    return Err(Error::new(
+                        name.span(),
+                        format!("duplicate {} identifier", desc),
+                    ));
+                }
+            }
+        }
+        Ok(index)
+    }
+
+    pub fn alloc(&mut self) -> u32 {
+        let index = self.count;
+        self.count += 1;
+        index
+    }
+
+    pub fn register_specific(&mut self, name: Id<'a>, index: u32, desc: &str) -> Result<(), Error> {
+        if let Some(_prev) = self.names.insert(name, index) {
+            return Err(Error::new(
+                name.span(),
+                format!("duplicate identifier for {}", desc),
+            ));
+        }
+        Ok(())
+    }
+
+    pub fn resolve(&self, idx: &mut Index<'a>, desc: &str) -> Result<u32, Error> {
+        let id = match idx {
+            Index::Num(n, _) => return Ok(*n),
+            Index::Id(id) => id,
+        };
+        if let Some(&n) = self.names.get(id) {
+            *idx = Index::Num(n, id.span());
+            return Ok(n);
+        }
+        Err(resolve_error(*id, desc))
+    }
+}
+
+pub fn resolve_error(id: Id<'_>, ns: &str) -> Error {
+    assert!(
+        !id.is_gensym(),
+        "symbol generated by `wast` itself cannot be resolved {:?}",
+        id
+    );
+    Error::new(
+        id.span(),
+        format!("unknown {ns}: failed to find name `${}`", id.name()),
+    )
+}
diff --git a/third_party/rust/wast/src/parser.rs b/third_party/rust/wast/src/parser.rs
new file mode 100644
index 0000000000..6b1a9debf6
--- /dev/null
+++ b/third_party/rust/wast/src/parser.rs
@@ -0,0 +1,1315 @@
+//! Traits for parsing the WebAssembly Text format
+//!
+//! This module contains the traits, abstractions, and utilities needed to
+//! define custom parsers for WebAssembly text format items. This module exposes
+//! a recursive descent parsing strategy and centers around the
+//! [`Parse`](crate::parser::Parse) trait for defining new fragments of
+//! WebAssembly text syntax.
+//!
+//! The top-level [`parse`](crate::parser::parse) function can be used to fully parse AST fragments:
+//!
+//! ```
+//! use wast::Wat;
+//! use wast::parser::{self, ParseBuffer};
+//!
+//! # fn foo() -> Result<(), wast::Error> {
+//! let wat = "(module (func))";
+//! let buf = ParseBuffer::new(wat)?;
+//! let module = parser::parse::<Wat>(&buf)?;
+//! # Ok(())
+//! # }
+//! ```
+//!
+//! and you can also define your own new syntax with the
+//! [`Parse`](crate::parser::Parse) trait:
+//!
+//! ```
+//! use wast::kw;
+//! use wast::core::{Import, Func};
+//! use wast::parser::{Parser, Parse, Result};
+//!
+//! // Fields of a WebAssembly which only allow imports and functions, and all
+//! // imports must come before all the functions
+//! struct OnlyImportsAndFunctions<'a> {
+//!     imports: Vec<Import<'a>>,
+//!     functions: Vec<Func<'a>>,
+//! }
+//!
+//! impl<'a> Parse<'a> for OnlyImportsAndFunctions<'a> {
+//!     fn parse(parser: Parser<'a>) -> Result<Self> {
+//!         // While the second token is `import` (the first is `(`, so we care
+//!         // about the second) we parse an `ast::ModuleImport` inside of
+//!         // parentheses. The `parens` function here ensures that what we
+//!         // parse inside of it is surrounded by `(` and `)`.
+//!         let mut imports = Vec::new();
+//!         while parser.peek2::<kw::import>() {
+//!             let import = parser.parens(|p| p.parse())?;
+//!             imports.push(import);
+//!         }
+//!
+//!         // Afterwards we assume everything else is a function. Note that
+//!         // `parse` here is a generic function and type inference figures out
+//!         // that we're parsing functions here and imports above.
+//!         let mut functions = Vec::new();
+//!         while !parser.is_empty() {
+//!             let func = parser.parens(|p| p.parse())?;
+//!             functions.push(func);
+//!         }
+//!
+//!         Ok(OnlyImportsAndFunctions { imports, functions })
+//!     }
+//! }
+//! ```
+//!
+//! This module is heavily inspired by [`syn`](https://docs.rs/syn) so you can
+//! likely also draw inspiration from the excellent examples in the `syn` crate.
+
+use crate::lexer::{Float, Integer, Lexer, Token};
+use crate::token::Span;
+use crate::Error;
+use std::cell::{Cell, RefCell};
+use std::collections::HashMap;
+use std::fmt;
+use std::usize;
+
+/// The maximum recursive depth of parens to parse.
+///
+/// This is sort of a fundamental limitation of the way this crate is
+/// designed. Everything is done through recursive descent parsing which
+/// means, well, that we're recursively going down the stack as we parse
+/// nested data structures. While we can handle this for wasm expressions
+/// since that's a pretty local decision, handling this for nested
+/// modules/components which be far trickier. For now we just say that when
+/// the parser goes too deep we return an error saying there's too many
+/// nested items. It would be great to not return an error here, though!
+pub(crate) const MAX_PARENS_DEPTH: usize = 100;
+
+/// A top-level convenience parsing function that parses a `T` from `buf` and
+/// requires that all tokens in `buf` are consume.
+///
+/// This generic parsing function can be used to parse any `T` implementing the
+/// [`Parse`] trait. It is not used from [`Parse`] trait implementations.
+///
+/// # Examples
+///
+/// ```
+/// use wast::Wat;
+/// use wast::parser::{self, ParseBuffer};
+///
+/// # fn foo() -> Result<(), wast::Error> {
+/// let wat = "(module (func))";
+/// let buf = ParseBuffer::new(wat)?;
+/// let module = parser::parse::<Wat>(&buf)?;
+/// # Ok(())
+/// # }
+/// ```
+///
+/// or parsing simply a fragment
+///
+/// ```
+/// use wast::parser::{self, ParseBuffer};
+///
+/// # fn foo() -> Result<(), wast::Error> {
+/// let wat = "12";
+/// let buf = ParseBuffer::new(wat)?;
+/// let val = parser::parse::<u32>(&buf)?;
+/// assert_eq!(val, 12);
+/// # Ok(())
+/// # }
+/// ```
+pub fn parse<'a, T: Parse<'a>>(buf: &'a ParseBuffer<'a>) -> Result<T> {
+    let parser = buf.parser();
+    let result = parser.parse()?;
+    if parser.cursor().advance_token().is_none() {
+        Ok(result)
+    } else {
+        Err(parser.error("extra tokens remaining after parse"))
+    }
+}
+
+/// A trait for parsing a fragment of syntax in a recursive descent fashion.
+///
+/// The [`Parse`] trait is main abstraction you'll be working with when defining
+/// custom parser or custom syntax for your WebAssembly text format (or when
+/// using the official format items). Almost all items in the
+/// [`core`](crate::core) module implement the [`Parse`] trait, and you'll
+/// commonly use this with:
+///
+/// * The top-level [`parse`] function to parse an entire input.
+/// * The intermediate [`Parser::parse`] function to parse an item out of an
+///   input stream and then parse remaining items.
+///
+/// Implementation of [`Parse`] take a [`Parser`] as input and will mutate the
+/// parser as they parse syntax. Once a token is consume it cannot be
+/// "un-consumed". Utilities such as [`Parser::peek`] and [`Parser::lookahead1`]
+/// can be used to determine what to parse next.
+///
+/// ## When to parse `(` and `)`?
+///
+/// Conventionally types are not responsible for parsing their own `(` and `)`
+/// tokens which surround the type. For example WebAssembly imports look like:
+///
+/// ```text
+/// (import "foo" "bar" (func (type 0)))
+/// ```
+///
+/// but the [`Import`](crate::core::Import) type parser looks like:
+///
+/// ```
+/// # use wast::kw;
+/// # use wast::parser::{Parser, Parse, Result};
+/// # struct Import<'a>(&'a str);
+/// impl<'a> Parse<'a> for Import<'a> {
+///     fn parse(parser: Parser<'a>) -> Result<Self> {
+///         parser.parse::<kw::import>()?;
+///         // ...
+/// # panic!()
+///     }
+/// }
+/// ```
+///
+/// It is assumed here that the `(` and `)` tokens which surround an `import`
+/// statement in the WebAssembly text format are parsed by the parent item
+/// parsing `Import`.
+///
+/// Note that this is just a convention, so it's not necessarily required for
+/// all types. It's recommended that your types stick to this convention where
+/// possible to avoid nested calls to [`Parser::parens`] or accidentally trying
+/// to parse too many parenthesis.
+///
+/// # Examples
+///
+/// Let's say you want to define your own WebAssembly text format which only
+/// contains imports and functions. You also require all imports to be listed
+/// before all functions. An example [`Parse`] implementation might look like:
+///
+/// ```
+/// use wast::core::{Import, Func};
+/// use wast::kw;
+/// use wast::parser::{Parser, Parse, Result};
+///
+/// // Fields of a WebAssembly which only allow imports and functions, and all
+/// // imports must come before all the functions
+/// struct OnlyImportsAndFunctions<'a> {
+///     imports: Vec<Import<'a>>,
+///     functions: Vec<Func<'a>>,
+/// }
+///
+/// impl<'a> Parse<'a> for OnlyImportsAndFunctions<'a> {
+///     fn parse(parser: Parser<'a>) -> Result<Self> {
+///         // While the second token is `import` (the first is `(`, so we care
+///         // about the second) we parse an `ast::ModuleImport` inside of
+///         // parentheses. The `parens` function here ensures that what we
+///         // parse inside of it is surrounded by `(` and `)`.
+///         let mut imports = Vec::new();
+///         while parser.peek2::<kw::import>() {
+///             let import = parser.parens(|p| p.parse())?;
+///             imports.push(import);
+///         }
+///
+///         // Afterwards we assume everything else is a function. Note that
+///         // `parse` here is a generic function and type inference figures out
+///         // that we're parsing functions here and imports above.
+///         let mut functions = Vec::new();
+///         while !parser.is_empty() {
+///             let func = parser.parens(|p| p.parse())?;
+///             functions.push(func);
+///         }
+///
+///         Ok(OnlyImportsAndFunctions { imports, functions })
+///     }
+/// }
+/// ```
+pub trait Parse<'a>: Sized {
+    /// Attempts to parse `Self` from `parser`, returning an error if it could
+    /// not be parsed.
+    ///
+    /// This method will mutate the state of `parser` after attempting to parse
+    /// an instance of `Self`. If an error happens then it is likely fatal and
+    /// there is no guarantee of how many tokens have been consumed from
+    /// `parser`.
+    ///
+    /// As recommended in the documentation of [`Parse`], implementations of
+    /// this function should not start out by parsing `(` and `)` tokens, but
+    /// rather parents calling recursive parsers should parse the `(` and `)`
+    /// tokens for their child item that's being parsed.
+    ///
+    /// # Errors
+    ///
+    /// This function will return an error if `Self` could not be parsed. Note
+    /// that creating an [`Error`] is not exactly a cheap operation, so
+    /// [`Error`] is typically fatal and propagated all the way back to the top
+    /// parse call site.
+    fn parse(parser: Parser<'a>) -> Result<Self>;
+}
+
+/// A trait for types which be used to "peek" to see if they're the next token
+/// in an input stream of [`Parser`].
+///
+/// Often when implementing [`Parse`] you'll need to query what the next token
+/// in the stream is to figure out what to parse next. This [`Peek`] trait
+/// defines the set of types that can be tested whether they're the next token
+/// in the input stream.
+///
+/// Implementations of [`Peek`] should only be present on types that consume
+/// exactly one token (not zero, not more, exactly one). Types implementing
+/// [`Peek`] should also typically implement [`Parse`] should also typically
+/// implement [`Parse`].
+///
+/// See the documentation of [`Parser::peek`] for example usage.
+pub trait Peek {
+    /// Tests to see whether this token is the first token within the [`Cursor`]
+    /// specified.
+    ///
+    /// Returns `true` if [`Parse`] for this type is highly likely to succeed
+    /// failing no other error conditions happening (like an integer literal
+    /// being too big).
+    fn peek(cursor: Cursor<'_>) -> bool;
+
+    /// The same as `peek`, except it checks the token immediately following
+    /// the current token.
+    fn peek2(mut cursor: Cursor<'_>) -> bool {
+        if cursor.advance_token().is_some() {
+            Self::peek(cursor)
+        } else {
+            false
+        }
+    }
+
+    /// Returns a human-readable name of this token to display when generating
+    /// errors about this token missing.
+    fn display() -> &'static str;
+}
+
+/// A convenience type definition for `Result` where the error is hardwired to
+/// [`Error`].
+pub type Result<T, E = Error> = std::result::Result<T, E>;
+
+/// A low-level buffer of tokens which represents a completely lexed file.
+///
+/// A `ParseBuffer` will immediately lex an entire file and then store all
+/// tokens internally. A `ParseBuffer` only used to pass to the top-level
+/// [`parse`] function.
+pub struct ParseBuffer<'a> {
+    // list of tokens from the tokenized source (including whitespace and
+    // comments), and the second element is how to skip this token, if it can be
+    // skipped.
+    tokens: Box<[(Token<'a>, Cell<NextTokenAt>)]>,
+    input: &'a str,
+    cur: Cell<usize>,
+    known_annotations: RefCell<HashMap<String, usize>>,
+    depth: Cell<usize>,
+}
+
+#[derive(Copy, Clone, Debug)]
+enum NextTokenAt {
+    /// Haven't computed where the next token is yet.
+    Unknown,
+    /// Previously computed the index of the next token.
+    Index(usize),
+    /// There is no next token, this is the last token.
+    Eof,
+}
+
+/// An in-progress parser for the tokens of a WebAssembly text file.
+///
+/// A `Parser` is argument to the [`Parse`] trait and is now the input stream is
+/// interacted with to parse new items. Cloning [`Parser`] or copying a parser
+/// refers to the same stream of tokens to parse, you cannot clone a [`Parser`]
+/// and clone two items.
+///
+/// For more information about a [`Parser`] see its methods.
+#[derive(Copy, Clone)]
+pub struct Parser<'a> {
+    buf: &'a ParseBuffer<'a>,
+}
+
+/// A helpful structure to perform a lookahead of one token to determine what to
+/// parse.
+///
+/// For more information see the [`Parser::lookahead1`] method.
+pub struct Lookahead1<'a> {
+    parser: Parser<'a>,
+    attempts: Vec<&'static str>,
+}
+
+/// An immutable cursor into a list of tokens.
+///
+/// This cursor cannot be mutated but can be used to parse more tokens in a list
+/// of tokens. Cursors are created from the [`Parser::step`] method. This is a
+/// very low-level parsing structure and you likely won't use it much.
+#[derive(Copy, Clone)]
+pub struct Cursor<'a> {
+    parser: Parser<'a>,
+    cur: usize,
+}
+
+impl ParseBuffer<'_> {
+    /// Creates a new [`ParseBuffer`] by lexing the given `input` completely.
+    ///
+    /// # Errors
+    ///
+    /// Returns an error if `input` fails to lex.
+    pub fn new(input: &str) -> Result<ParseBuffer<'_>> {
+        ParseBuffer::new_with_lexer(Lexer::new(input))
+    }
+
+    /// Creates a new [`ParseBuffer`] by lexing the given `input` completely.
+    ///
+    /// # Errors
+    ///
+    /// Returns an error if `input` fails to lex.
+    pub fn new_with_lexer(lexer: Lexer<'_>) -> Result<ParseBuffer<'_>> {
+        let mut tokens = Vec::new();
+        let input = lexer.input();
+        for token in lexer {
+            tokens.push((token?, Cell::new(NextTokenAt::Unknown)));
+        }
+        let ret = ParseBuffer {
+            tokens: tokens.into_boxed_slice(),
+            cur: Cell::new(0),
+            depth: Cell::new(0),
+            input,
+            known_annotations: Default::default(),
+        };
+        ret.validate_annotations()?;
+        Ok(ret)
+    }
+
+    fn parser(&self) -> Parser<'_> {
+        Parser { buf: self }
+    }
+
+    // Validates that all annotations properly parse in that they have balanced
+    // delimiters. This is required since while parsing we generally skip
+    // annotations and there's no real opportunity to return a parse error.
+    fn validate_annotations(&self) -> Result<()> {
+        use crate::lexer::Token::*;
+        enum State {
+            None,
+            LParen,
+            Annotation { depth: usize, span: Span },
+        }
+        let mut state = State::None;
+        for token in self.tokens.iter() {
+            state = match (&token.0, state) {
+                // From nothing, a `(` starts the search for an annotation
+                (LParen(_), State::None) => State::LParen,
+                // ... otherwise in nothing we always preserve that state.
+                (_, State::None) => State::None,
+
+                // If the previous state was an `LParen`, we may have an
+                // annotation if the next keyword is reserved
+                (Reserved(s), State::LParen) if s.starts_with('@') && !s.is_empty() => {
+                    let offset = self.input_pos(s);
+                    State::Annotation {
+                        span: Span { offset },
+                        depth: 1,
+                    }
+                }
+                // ... otherwise anything after an `LParen` kills the lparen
+                // state.
+                (_, State::LParen) => State::None,
+
+                // Once we're in an annotation we need to balance parentheses,
+                // so handle the depth changes.
+                (LParen(_), State::Annotation { span, depth }) => State::Annotation {
+                    span,
+                    depth: depth + 1,
+                },
+                (RParen(_), State::Annotation { depth: 1, .. }) => State::None,
+                (RParen(_), State::Annotation { span, depth }) => State::Annotation {
+                    span,
+                    depth: depth - 1,
+                },
+                // ... and otherwise all tokens are allowed in annotations.
+                (_, s @ State::Annotation { .. }) => s,
+            };
+        }
+        if let State::Annotation { span, .. } = state {
+            return Err(Error::new(span, "unclosed annotation".to_string()));
+        }
+        Ok(())
+    }
+
+    fn input_pos(&self, src: &str) -> usize {
+        src.as_ptr() as usize - self.input.as_ptr() as usize
+    }
+}
+
+impl<'a> Parser<'a> {
+    /// Returns whether there are no more `Token` tokens to parse from this
+    /// [`Parser`].
+    ///
+    /// This indicates that either we've reached the end of the input, or we're
+    /// a sub-[`Parser`] inside of a parenthesized expression and we've hit the
+    /// `)` token.
+    ///
+    /// Note that if `false` is returned there *may* be more comments. Comments
+    /// and whitespace are not considered for whether this parser is empty.
+    pub fn is_empty(self) -> bool {
+        match self.cursor().advance_token() {
+            Some(Token::RParen(_)) | None => true,
+            Some(_) => false, // more tokens to parse!
+        }
+    }
+
+    pub(crate) fn has_meaningful_tokens(self) -> bool {
+        self.buf.tokens[self.cursor().cur..].iter().any(|(t, _)| {
+            !matches!(
+                t,
+                Token::Whitespace(_) | Token::LineComment(_) | Token::BlockComment(_)
+            )
+        })
+    }
+
+    /// Parses a `T` from this [`Parser`].
+    ///
+    /// This method has a trivial definition (it simply calls
+    /// [`T::parse`](Parse::parse)) but is here for syntactic purposes. This is
+    /// what you'll call 99% of the time in a [`Parse`] implementation in order
+    /// to parse sub-items.
+    ///
+    /// Typically you always want to use `?` with the result of this method, you
+    /// should not handle errors and decide what else to parse. To handle
+    /// branches in parsing, use [`Parser::peek`].
+    ///
+    /// # Examples
+    ///
+    /// A good example of using `parse` is to see how the [`TableType`] type is
+    /// parsed in this crate. A [`TableType`] is defined in the official
+    /// specification as [`tabletype`][spec] and is defined as:
+    ///
+    /// [spec]: https://webassembly.github.io/spec/core/text/types.html#table-types
+    ///
+    /// ```text
+    /// tabletype ::= lim:limits et:reftype
+    /// ```
+    ///
+    /// so to parse a [`TableType`] we recursively need to parse a [`Limits`]
+    /// and a [`RefType`]
+    ///
+    /// ```
+    /// # use wast::core::*;
+    /// # use wast::parser::*;
+    /// struct TableType<'a> {
+    ///     limits: Limits,
+    ///     elem: RefType<'a>,
+    /// }
+    ///
+    /// impl<'a> Parse<'a> for TableType<'a> {
+    ///     fn parse(parser: Parser<'a>) -> Result<Self> {
+    ///         // parse the `lim` then `et` in sequence
+    ///         Ok(TableType {
+    ///             limits: parser.parse()?,
+    ///             elem: parser.parse()?,
+    ///         })
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// [`Limits`]: crate::core::Limits
+    /// [`TableType`]: crate::core::TableType
+    /// [`RefType`]: crate::core::RefType
+    pub fn parse<T: Parse<'a>>(self) -> Result<T> {
+        T::parse(self)
+    }
+
+    /// Performs a cheap test to see whether the current token in this stream is
+    /// `T`.
+    ///
+    /// This method can be used to efficiently determine what next to parse. The
+    /// [`Peek`] trait is defined for types which can be used to test if they're
+    /// the next item in the input stream.
+    ///
+    /// Nothing is actually parsed in this method, nor does this mutate the
+    /// state of this [`Parser`]. Instead, this simply performs a check.
+    ///
+    /// This method is frequently combined with the [`Parser::lookahead1`]
+    /// method to automatically produce nice error messages if some tokens
+    /// aren't found.
+    ///
+    /// # Examples
+    ///
+    /// For an example of using the `peek` method let's take a look at parsing
+    /// the [`Limits`] type. This is [defined in the official spec][spec] as:
+    ///
+    /// ```text
+    /// limits ::= n:u32
+    ///          | n:u32 m:u32
+    /// ```
+    ///
+    /// which means that it's either one `u32` token or two, so we need to know
+    /// whether to consume two tokens or one:
+    ///
+    /// ```
+    /// # use wast::parser::*;
+    /// struct Limits {
+    ///     min: u32,
+    ///     max: Option<u32>,
+    /// }
+    ///
+    /// impl<'a> Parse<'a> for Limits {
+    ///     fn parse(parser: Parser<'a>) -> Result<Self> {
+    ///         // Always parse the first number...
+    ///         let min = parser.parse()?;
+    ///
+    ///         // ... and then test if there's a second number before parsing
+    ///         let max = if parser.peek::<u32>() {
+    ///             Some(parser.parse()?)
+    ///         } else {
+    ///             None
+    ///         };
+    ///
+    ///         Ok(Limits { min, max })
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// [spec]: https://webassembly.github.io/spec/core/text/types.html#limits
+    /// [`Limits`]: crate::core::Limits
+    pub fn peek<T: Peek>(self) -> bool {
+        T::peek(self.cursor())
+    }
+
+    /// Same as the [`Parser::peek`] method, except checks the next token, not
+    /// the current token.
+    pub fn peek2<T: Peek>(self) -> bool {
+        let mut cursor = self.cursor();
+        if cursor.advance_token().is_some() {
+            T::peek(cursor)
+        } else {
+            false
+        }
+    }
+
+    /// Same as the [`Parser::peek2`] method, except checks the next next token,
+    /// not the next token.
+    pub fn peek3<T: Peek>(self) -> bool {
+        let mut cursor = self.cursor();
+        if cursor.advance_token().is_some() && cursor.advance_token().is_some() {
+            T::peek(cursor)
+        } else {
+            false
+        }
+    }
+
+    /// A helper structure to perform a sequence of `peek` operations and if
+    /// they all fail produce a nice error message.
+    ///
+    /// This method purely exists for conveniently producing error messages and
+    /// provides no functionality that [`Parser::peek`] doesn't already give.
+    /// The [`Lookahead1`] structure has one main method [`Lookahead1::peek`],
+    /// which is the same method as [`Parser::peek`]. The difference is that the
+    /// [`Lookahead1::error`] method needs no arguments.
+    ///
+    /// # Examples
+    ///
+    /// Let's look at the parsing of [`Index`]. This type is either a `u32` or
+    /// an [`Id`] and is used in name resolution primarily. The [official
+    /// grammar for an index][spec] is:
+    ///
+    /// ```text
+    /// idx ::= x:u32
+    ///       | v:id
+    /// ```
+    ///
+    /// Which is to say that an index is either a `u32` or an [`Id`]. When
+    /// parsing an [`Index`] we can do:
+    ///
+    /// ```
+    /// # use wast::token::*;
+    /// # use wast::parser::*;
+    /// enum Index<'a> {
+    ///     Num(u32),
+    ///     Id(Id<'a>),
+    /// }
+    ///
+    /// impl<'a> Parse<'a> for Index<'a> {
+    ///     fn parse(parser: Parser<'a>) -> Result<Self> {
+    ///         let mut l = parser.lookahead1();
+    ///         if l.peek::<Id>() {
+    ///             Ok(Index::Id(parser.parse()?))
+    ///         } else if l.peek::<u32>() {
+    ///             Ok(Index::Num(parser.parse()?))
+    ///         } else {
+    ///             // produces error message of `expected identifier or u32`
+    ///             Err(l.error())
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// [spec]: https://webassembly.github.io/spec/core/text/modules.html#indices
+    /// [`Index`]: crate::token::Index
+    /// [`Id`]: crate::token::Id
+    pub fn lookahead1(self) -> Lookahead1<'a> {
+        Lookahead1 {
+            attempts: Vec::new(),
+            parser: self,
+        }
+    }
+
+    /// Parse an item surrounded by parentheses.
+    ///
+    /// WebAssembly's text format is all based on s-expressions, so naturally
+    /// you're going to want to parse a lot of parenthesized things! As noted in
+    /// the documentation of [`Parse`] you typically don't parse your own
+    /// surrounding `(` and `)` tokens, but the parser above you parsed them for
+    /// you. This is method method the parser above you uses.
+    ///
+    /// This method will parse a `(` token, and then call `f` on a sub-parser
+    /// which when finished asserts that a `)` token is the next token. This
+    /// requires that `f` consumes all tokens leading up to the paired `)`.
+    ///
+    /// Usage will often simply be `parser.parens(|p| p.parse())?` to
+    /// automatically parse a type within parentheses, but you can, as always,
+    /// go crazy and do whatever you'd like too.
+    ///
+    /// # Examples
+    ///
+    /// A good example of this is to see how a `Module` is parsed. This isn't
+    /// the exact definition, but it's close enough!
+    ///
+    /// ```
+    /// # use wast::kw;
+    /// # use wast::core::*;
+    /// # use wast::parser::*;
+    /// struct Module<'a> {
+    ///     fields: Vec<ModuleField<'a>>,
+    /// }
+    ///
+    /// impl<'a> Parse<'a> for Module<'a> {
+    ///     fn parse(parser: Parser<'a>) -> Result<Self> {
+    ///         // Modules start out with a `module` keyword
+    ///         parser.parse::<kw::module>()?;
+    ///
+    ///         // And then everything else is `(field ...)`, so while we've got
+    ///         // items left we continuously parse parenthesized items.
+    ///         let mut fields = Vec::new();
+    ///         while !parser.is_empty() {
+    ///             fields.push(parser.parens(|p| p.parse())?);
+    ///         }
+    ///         Ok(Module { fields })
+    ///     }
+    /// }
+    /// ```
+    pub fn parens<T>(self, f: impl FnOnce(Parser<'a>) -> Result<T>) -> Result<T> {
+        self.buf.depth.set(self.buf.depth.get() + 1);
+        let before = self.buf.cur.get();
+        let res = self.step(|cursor| {
+            let mut cursor = match cursor.lparen() {
+                Some(rest) => rest,
+                None => return Err(cursor.error("expected `(`")),
+            };
+            cursor.parser.buf.cur.set(cursor.cur);
+            let result = f(cursor.parser)?;
+            cursor.cur = cursor.parser.buf.cur.get();
+            match cursor.rparen() {
+                Some(rest) => Ok((result, rest)),
+                None => Err(cursor.error("expected `)`")),
+            }
+        });
+        self.buf.depth.set(self.buf.depth.get() - 1);
+        if res.is_err() {
+            self.buf.cur.set(before);
+        }
+        res
+    }
+
+    /// Return the depth of nested parens we've parsed so far.
+    ///
+    /// This is a low-level method that is only useful for implementing
+    /// recursion limits in custom parsers.
+    pub fn parens_depth(&self) -> usize {
+        self.buf.depth.get()
+    }
+
+    /// Checks that the parser parens depth hasn't exceeded the maximum depth.
+    pub(crate) fn depth_check(&self) -> Result<()> {
+        if self.parens_depth() > MAX_PARENS_DEPTH {
+            Err(self.error("item nesting too deep"))
+        } else {
+            Ok(())
+        }
+    }
+
+    fn cursor(self) -> Cursor<'a> {
+        Cursor {
+            parser: self,
+            cur: self.buf.cur.get(),
+        }
+    }
+
+    /// A low-level parsing method you probably won't use.
+    ///
+    /// This is used to implement parsing of the most primitive types in the
+    /// [`core`](crate::core) module. You probably don't want to use this, but
+    /// probably want to use something like [`Parser::parse`] or
+    /// [`Parser::parens`].
+    pub fn step<F, T>(self, f: F) -> Result<T>
+    where
+        F: FnOnce(Cursor<'a>) -> Result<(T, Cursor<'a>)>,
+    {
+        let (result, cursor) = f(self.cursor())?;
+        self.buf.cur.set(cursor.cur);
+        Ok(result)
+    }
+
+    /// Creates an error whose line/column information is pointing at the
+    /// current token.
+    ///
+    /// This is used to produce human-readable error messages which point to the
+    /// right location in the input stream, and the `msg` here is arbitrary text
+    /// used to associate with the error and indicate why it was generated.
+    pub fn error(self, msg: impl fmt::Display) -> Error {
+        self.error_at(self.cursor().cur_span(), msg)
+    }
+
+    /// Creates an error whose line/column information is pointing at the
+    /// given span.
+    pub fn error_at(self, span: Span, msg: impl fmt::Display) -> Error {
+        Error::parse(span, self.buf.input, msg.to_string())
+    }
+
+    /// Returns the span of the current token
+    pub fn cur_span(&self) -> Span {
+        self.cursor().cur_span()
+    }
+
+    /// Returns the span of the previous token
+    pub fn prev_span(&self) -> Span {
+        self.cursor()
+            .prev_span()
+            .unwrap_or_else(|| Span::from_offset(0))
+    }
+
+    /// Registers a new known annotation with this parser to allow parsing
+    /// annotations with this name.
+    ///
+    /// [WebAssembly annotations][annotation] are a proposal for the text format
+    /// which allows decorating the text format with custom structured
+    /// information. By default all annotations are ignored when parsing, but
+    /// the whole purpose of them is to sometimes parse them!
+    ///
+    /// To support parsing text annotations this method is used to allow
+    /// annotations and their tokens to *not* be skipped. Once an annotation is
+    /// registered with this method, then while the return value has not been
+    /// dropped (e.g. the scope of where this function is called) annotations
+    /// with the name `annotation` will be parse of the token stream and not
+    /// implicitly skipped.
+    ///
+    /// # Skipping annotations
+    ///
+    /// The behavior of skipping unknown/unregistered annotations can be
+    /// somewhat subtle and surprising, so if you're interested in parsing
+    /// annotations it's important to point out the importance of this method
+    /// and where to call it.
+    ///
+    /// Generally when parsing tokens you'll be bottoming out in various
+    /// `Cursor` methods. These are all documented as advancing the stream as
+    /// much as possible to the next token, skipping "irrelevant stuff" like
+    /// comments, whitespace, etc. The `Cursor` methods will also skip unknown
+    /// annotations. This means that if you parse *any* token, it will skip over
+    /// any number of annotations that are unknown at all times.
+    ///
+    /// To parse an annotation you must, before parsing any token of the
+    /// annotation, register the annotation via this method. This includes the
+    /// beginning `(` token, which is otherwise skipped if the annotation isn't
+    /// marked as registered. Typically parser parse the *contents* of an
+    /// s-expression, so this means that the outer parser of an s-expression
+    /// must register the custom annotation name, rather than the inner parser.
+    ///
+    /// # Return
+    ///
+    /// This function returns an RAII guard which, when dropped, will unregister
+    /// the `annotation` given. Parsing `annotation` is only supported while the
+    /// returned value is still alive, and once dropped the parser will go back
+    /// to skipping annotations with the name `annotation`.
+    ///
+    /// # Example
+    ///
+    /// Let's see an example of how the `@name` annotation is parsed for modules
+    /// to get an idea of how this works:
+    ///
+    /// ```
+    /// # use wast::kw;
+    /// # use wast::token::NameAnnotation;
+    /// # use wast::parser::*;
+    /// struct Module<'a> {
+    ///     name: Option<NameAnnotation<'a>>,
+    /// }
+    ///
+    /// impl<'a> Parse<'a> for Module<'a> {
+    ///     fn parse(parser: Parser<'a>) -> Result<Self> {
+    ///         // Modules start out with a `module` keyword
+    ///         parser.parse::<kw::module>()?;
+    ///
+    ///         // Next may be `(@name "foo")`. Typically this annotation would
+    ///         // skipped, but we don't want it skipped, so we register it.
+    ///         // Note that the parse implementation of
+    ///         // `Option<NameAnnotation>` is the one that consumes the
+    ///         // parentheses here.
+    ///         let _r = parser.register_annotation("name");
+    ///         let name = parser.parse()?;
+    ///
+    ///         // ... and normally you'd otherwise parse module fields here ...
+    ///
+    ///         Ok(Module { name })
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// Another example is how we parse the `@custom` annotation. Note that this
+    /// is parsed as part of `ModuleField`, so note how the annotation is
+    /// registered *before* we parse the parentheses of the annotation.
+    ///
+    /// ```
+    /// # use wast::{kw, annotation};
+    /// # use wast::core::Custom;
+    /// # use wast::parser::*;
+    /// struct Module<'a> {
+    ///     fields: Vec<ModuleField<'a>>,
+    /// }
+    ///
+    /// impl<'a> Parse<'a> for Module<'a> {
+    ///     fn parse(parser: Parser<'a>) -> Result<Self> {
+    ///         // Modules start out with a `module` keyword
+    ///         parser.parse::<kw::module>()?;
+    ///
+    ///         // register the `@custom` annotation *first* before we start
+    ///         // parsing fields, because each field is contained in
+    ///         // parentheses and to parse the parentheses of an annotation we
+    ///         // have to known to not skip it.
+    ///         let _r = parser.register_annotation("custom");
+    ///
+    ///         let mut fields = Vec::new();
+    ///         while !parser.is_empty() {
+    ///             fields.push(parser.parens(|p| p.parse())?);
+    ///         }
+    ///         Ok(Module { fields })
+    ///     }
+    /// }
+    ///
+    /// enum ModuleField<'a> {
+    ///     Custom(Custom<'a>),
+    ///     // ...
+    /// }
+    ///
+    /// impl<'a> Parse<'a> for ModuleField<'a> {
+    ///     fn parse(parser: Parser<'a>) -> Result<Self> {
+    ///         // Note that because we have previously registered the `@custom`
+    ///         // annotation with the parser we known that `peek` methods like
+    ///         // this, working on the annotation token, are enabled to ever
+    ///         // return `true`.
+    ///         if parser.peek::<annotation::custom>() {
+    ///             return Ok(ModuleField::Custom(parser.parse()?));
+    ///         }
+    ///
+    ///         // .. typically we'd parse other module fields here...
+    ///
+    ///         Err(parser.error("unknown module field"))
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// [annotation]: https://github.com/WebAssembly/annotations
+    pub fn register_annotation<'b>(self, annotation: &'b str) -> impl Drop + 'b
+    where
+        'a: 'b,
+    {
+        let mut annotations = self.buf.known_annotations.borrow_mut();
+        if !annotations.contains_key(annotation) {
+            annotations.insert(annotation.to_string(), 0);
+        }
+        *annotations.get_mut(annotation).unwrap() += 1;
+
+        return RemoveOnDrop(self, annotation);
+
+        struct RemoveOnDrop<'a>(Parser<'a>, &'a str);
+
+        impl Drop for RemoveOnDrop<'_> {
+            fn drop(&mut self) {
+                let mut annotations = self.0.buf.known_annotations.borrow_mut();
+                let slot = annotations.get_mut(self.1).unwrap();
+                *slot -= 1;
+            }
+        }
+    }
+}
+
+impl<'a> Cursor<'a> {
+    /// Returns the span of the next `Token` token.
+    ///
+    /// Does not take into account whitespace or comments.
+    pub fn cur_span(&self) -> Span {
+        let offset = match self.clone().advance_token() {
+            Some(t) => self.parser.buf.input_pos(t.src()),
+            None => self.parser.buf.input.len(),
+        };
+        Span { offset }
+    }
+
+    /// Returns the span of the previous `Token` token.
+    ///
+    /// Does not take into account whitespace or comments.
+    pub(crate) fn prev_span(&self) -> Option<Span> {
+        let (token, _) = self.parser.buf.tokens.get(self.cur.checked_sub(1)?)?;
+        Some(Span {
+            offset: self.parser.buf.input_pos(token.src()),
+        })
+    }
+
+    /// Same as [`Parser::error`], but works with the current token in this
+    /// [`Cursor`] instead.
+    pub fn error(&self, msg: impl fmt::Display) -> Error {
+        self.parser.error_at(self.cur_span(), msg)
+    }
+
+    /// Attempts to advance this cursor if the current token is a `(`.
+    ///
+    /// If the current token is `(`, returns a new [`Cursor`] pointing at the
+    /// rest of the tokens in the stream. Otherwise returns `None`.
+    ///
+    /// This function will automatically skip over any comments, whitespace, or
+    /// unknown annotations.
+    pub fn lparen(mut self) -> Option<Self> {
+        match self.advance_token()? {
+            Token::LParen(_) => Some(self),
+            _ => None,
+        }
+    }
+
+    /// Attempts to advance this cursor if the current token is a `)`.
+    ///
+    /// If the current token is `)`, returns a new [`Cursor`] pointing at the
+    /// rest of the tokens in the stream. Otherwise returns `None`.
+    ///
+    /// This function will automatically skip over any comments, whitespace, or
+    /// unknown annotations.
+    pub fn rparen(mut self) -> Option<Self> {
+        match self.advance_token()? {
+            Token::RParen(_) => Some(self),
+            _ => None,
+        }
+    }
+
+    /// Attempts to advance this cursor if the current token is a
+    /// [`Token::Id`](crate::lexer::Token)
+    ///
+    /// If the current token is `Id`, returns the identifier minus the leading
+    /// `$` character as well as a new [`Cursor`] pointing at the rest of the
+    /// tokens in the stream. Otherwise returns `None`.
+    ///
+    /// This function will automatically skip over any comments, whitespace, or
+    /// unknown annotations.
+    pub fn id(mut self) -> Option<(&'a str, Self)> {
+        match self.advance_token()? {
+            Token::Id(id) => Some((&id[1..], self)),
+            _ => None,
+        }
+    }
+
+    /// Attempts to advance this cursor if the current token is a
+    /// [`Token::Keyword`](crate::lexer::Token)
+    ///
+    /// If the current token is `Keyword`, returns the keyword as well as a new
+    /// [`Cursor`] pointing at the rest of the tokens in the stream. Otherwise
+    /// returns `None`.
+    ///
+    /// This function will automatically skip over any comments, whitespace, or
+    /// unknown annotations.
+    pub fn keyword(mut self) -> Option<(&'a str, Self)> {
+        match self.advance_token()? {
+            Token::Keyword(id) => Some((id, self)),
+            _ => None,
+        }
+    }
+
+    /// Attempts to advance this cursor if the current token is a
+    /// [`Token::Reserved`](crate::lexer::Token)
+    ///
+    /// If the current token is `Reserved`, returns the reserved token as well
+    /// as a new [`Cursor`] pointing at the rest of the tokens in the stream.
+    /// Otherwise returns `None`.
+    ///
+    /// This function will automatically skip over any comments, whitespace, or
+    /// unknown annotations.
+    pub fn reserved(mut self) -> Option<(&'a str, Self)> {
+        match self.advance_token()? {
+            Token::Reserved(id) => Some((id, self)),
+            _ => None,
+        }
+    }
+
+    /// Attempts to advance this cursor if the current token is a
+    /// [`Token::Integer`](crate::lexer::Token)
+    ///
+    /// If the current token is `Integer`, returns the integer as well as a new
+    /// [`Cursor`] pointing at the rest of the tokens in the stream. Otherwise
+    /// returns `None`.
+    ///
+    /// This function will automatically skip over any comments, whitespace, or
+    /// unknown annotations.
+    pub fn integer(mut self) -> Option<(&'a Integer<'a>, Self)> {
+        match self.advance_token()? {
+            Token::Integer(i) => Some((i, self)),
+            _ => None,
+        }
+    }
+
+    /// Attempts to advance this cursor if the current token is a
+    /// [`Token::Float`](crate::lexer::Token)
+    ///
+    /// If the current token is `Float`, returns the float as well as a new
+    /// [`Cursor`] pointing at the rest of the tokens in the stream. Otherwise
+    /// returns `None`.
+    ///
+    /// This function will automatically skip over any comments, whitespace, or
+    /// unknown annotations.
+    pub fn float(mut self) -> Option<(&'a Float<'a>, Self)> {
+        match self.advance_token()? {
+            Token::Float(f) => Some((f, self)),
+            _ => None,
+        }
+    }
+
+    /// Attempts to advance this cursor if the current token is a
+    /// [`Token::String`](crate::lexer::Token)
+    ///
+    /// If the current token is `String`, returns the byte value of the string
+    /// as well as a new [`Cursor`] pointing at the rest of the tokens in the
+    /// stream. Otherwise returns `None`.
+    ///
+    /// This function will automatically skip over any comments, whitespace, or
+    /// unknown annotations.
+    pub fn string(mut self) -> Option<(&'a [u8], Self)> {
+        match self.advance_token()? {
+            Token::String(s) => Some((s.val(), self)),
+            _ => None,
+        }
+    }
+
+    /// Attempts to advance this cursor if the current token is a
+    /// [`Token::Reserved`](crate::lexer::Token) and looks like the start of an
+    /// annotation.
+    ///
+    /// [Annotations][annotation] are a WebAssembly proposal for the text format
+    /// which allows placing structured text inside of a text file, for example
+    /// to specify the name section or other custom sections.
+    ///
+    /// This function will attempt to see if the current token is the `@foo`
+    /// part of the annotation. This requires the previous token to be `(` and
+    /// the current token is `Reserved` which starts with `@` and has a nonzero
+    /// length for the following name.
+    ///
+    /// Note that this will skip *unknown* annotations. Only pre-registered
+    /// annotations will be returned here.
+    ///
+    /// This function will automatically skip over any comments, whitespace, or
+    /// unknown annotations.
+    ///
+    /// [annotation]: https://github.com/WebAssembly/annotations
+    pub fn annotation(self) -> Option<(&'a str, Self)> {
+        let (token, cursor) = self.reserved()?;
+        if !token.starts_with('@') || token.len() <= 1 {
+            return None;
+        }
+        match &self.parser.buf.tokens.get(self.cur.wrapping_sub(1))?.0 {
+            Token::LParen(_) => Some((&token[1..], cursor)),
+            _ => None,
+        }
+    }
+
+    /// Attempts to advance this cursor if the current token is a
+    /// [`Token::LineComment`](crate::lexer::Token) or a
+    /// [`Token::BlockComment`](crate::lexer::Token)
+    ///
+    /// This function will only skip whitespace, no other tokens.
+    pub fn comment(mut self) -> Option<(&'a str, Self)> {
+        let comment = loop {
+            match &self.parser.buf.tokens.get(self.cur)?.0 {
+                Token::LineComment(c) | Token::BlockComment(c) => {
+                    self.cur += 1;
+                    break c;
+                }
+                Token::Whitespace(_) => {
+                    self.cur += 1;
+                }
+                _ => return None,
+            }
+        };
+        Some((comment, self))
+    }
+
+    fn advance_token(&mut self) -> Option<&'a Token<'a>> {
+        let known_annotations = self.parser.buf.known_annotations.borrow();
+        let is_known_annotation = |name: &str| match known_annotations.get(name) {
+            Some(0) | None => false,
+            Some(_) => true,
+        };
+
+        loop {
+            let (token, next) = self.parser.buf.tokens.get(self.cur)?;
+
+            // If we're currently pointing at a token, and it's not the start
+            // of an annotation, then we return that token and advance
+            // ourselves to just after that token.
+            match token {
+                Token::Whitespace(_) | Token::LineComment(_) | Token::BlockComment(_) => {}
+                _ => match self.annotation_start() {
+                    Some(n) if !is_known_annotation(n) => {}
+                    _ => {
+                        self.cur += 1;
+                        return Some(token);
+                    }
+                },
+            }
+
+            // ... otherwise we need to skip the current token, and possibly
+            // more. Here we're skipping whitespace, comments, annotations, etc.
+            // Basically stuff that's intended to not be that relevant to the
+            // text format. This is a pretty common operation, though, and we
+            // may do it multiple times through peeks and such. As a result
+            // this is somewhat cached.
+            //
+            // The `next` field, if "unknown", means we haven't calculated the
+            // next token. Otherwise it's an index of where to resume searching
+            // for the next token.
+            //
+            // Note that this entire operation happens in a loop (hence the
+            // "somewhat cached") because the set of known annotations is
+            // dynamic and we can't cache which annotations are skipped. What we
+            // can do though is cache the number of tokens in the annotation so
+            // we know how to skip ahead of it.
+            match next.get() {
+                NextTokenAt::Unknown => match self.find_next() {
+                    Some(i) => {
+                        next.set(NextTokenAt::Index(i));
+                        self.cur = i;
+                    }
+                    None => {
+                        next.set(NextTokenAt::Eof);
+                        return None;
+                    }
+                },
+                NextTokenAt::Eof => return None,
+                NextTokenAt::Index(i) => self.cur = i,
+            }
+        }
+    }
+
+    fn annotation_start(&self) -> Option<&'a str> {
+        match self.parser.buf.tokens.get(self.cur).map(|p| &p.0) {
+            Some(Token::LParen(_)) => {}
+            _ => return None,
+        }
+        let reserved = match self.parser.buf.tokens.get(self.cur + 1).map(|p| &p.0) {
+            Some(Token::Reserved(n)) => n,
+            _ => return None,
+        };
+        if reserved.starts_with('@') && reserved.len() > 1 {
+            Some(&reserved[1..])
+        } else {
+            None
+        }
+    }
+
+    /// Finds the next "real" token from the current position onwards.
+    ///
+    /// This is a somewhat expensive operation to call quite a lot, so it's
+    /// cached in the token list. See the comment above in `advance_token` for
+    /// how this works.
+    ///
+    /// Returns the index of the next relevant token to parse
+    fn find_next(mut self) -> Option<usize> {
+        // If we're pointing to the start of annotation we need to skip it
+        // in its entirety, so match the parentheses and figure out where
+        // the annotation ends.
+        if self.annotation_start().is_some() {
+            let mut depth = 1;
+            self.cur += 1;
+            while depth > 0 {
+                match &self.parser.buf.tokens.get(self.cur)?.0 {
+                    Token::LParen(_) => depth += 1,
+                    Token::RParen(_) => depth -= 1,
+                    _ => {}
+                }
+                self.cur += 1;
+            }
+            return Some(self.cur);
+        }
+
+        // ... otherwise we're pointing at whitespace/comments, so we need to
+        // figure out how many of them we can skip.
+        loop {
+            let (token, _) = self.parser.buf.tokens.get(self.cur)?;
+            // and otherwise we skip all comments/whitespace and only
+            // get interested once a normal `Token` pops up.
+            match token {
+                Token::Whitespace(_) | Token::LineComment(_) | Token::BlockComment(_) => {
+                    self.cur += 1
+                }
+                _ => return Some(self.cur),
+            }
+        }
+    }
+}
+
+impl Lookahead1<'_> {
+    /// Attempts to see if `T` is the next token in the [`Parser`] this
+    /// [`Lookahead1`] references.
+    ///
+    /// For more information see [`Parser::lookahead1`] and [`Parser::peek`]
+    pub fn peek<T: Peek>(&mut self) -> bool {
+        if self.parser.peek::<T>() {
+            true
+        } else {
+            self.attempts.push(T::display());
+            false
+        }
+    }
+
+    /// Generates an error message saying that one of the tokens passed to
+    /// [`Lookahead1::peek`] method was expected.
+    ///
+    /// Before calling this method you should call [`Lookahead1::peek`] for all
+    /// possible tokens you'd like to parse.
+    pub fn error(self) -> Error {
+        match self.attempts.len() {
+            0 => {
+                if self.parser.is_empty() {
+                    self.parser.error("unexpected end of input")
+                } else {
+                    self.parser.error("unexpected token")
+                }
+            }
+            1 => {
+                let message = format!("unexpected token, expected {}", self.attempts[0]);
+                self.parser.error(&message)
+            }
+            2 => {
+                let message = format!(
+                    "unexpected token, expected {} or {}",
+                    self.attempts[0], self.attempts[1]
+                );
+                self.parser.error(&message)
+            }
+            _ => {
+                let join = self.attempts.join(", ");
+                let message = format!("unexpected token, expected one of: {}", join);
+                self.parser.error(&message)
+            }
+        }
+    }
+}
+
+impl<'a, T: Peek + Parse<'a>> Parse<'a> for Option<T> {
+    fn parse(parser: Parser<'a>) -> Result<Option<T>> {
+        if parser.peek::<T>() {
+            Ok(Some(parser.parse()?))
+        } else {
+            Ok(None)
+        }
+    }
+}
diff --git a/third_party/rust/wast/src/token.rs b/third_party/rust/wast/src/token.rs
new file mode 100644
index 0000000000..a2bcfed5bd
--- /dev/null
+++ b/third_party/rust/wast/src/token.rs
@@ -0,0 +1,695 @@
+//! Common tokens that implement the [`Parse`] trait which are otherwise not
+//! associated specifically with the wasm text format per se (useful in other
+//! contexts too perhaps).
+
+use crate::annotation;
+use crate::lexer::FloatVal;
+use crate::parser::{Cursor, Parse, Parser, Peek, Result};
+use std::fmt;
+use std::hash::{Hash, Hasher};
+use std::str;
+
+/// A position in the original source stream, used to render errors.
+#[derive(Copy, Clone, Debug, PartialOrd, Ord, PartialEq, Eq, Hash)]
+pub struct Span {
+    pub(crate) offset: usize,
+}
+
+impl Span {
+    /// Construct a `Span` from a byte offset in the source file.
+    pub fn from_offset(offset: usize) -> Self {
+        Span { offset }
+    }
+
+    /// Returns the line/column information of this span within `text`.
+    /// Line and column numbers are 0-indexed. User presentation is typically
+    /// 1-indexed, but 0-indexing is appropriate for internal use with
+    /// iterators and slices.
+    pub fn linecol_in(&self, text: &str) -> (usize, usize) {
+        let mut cur = 0;
+        // Use split_terminator instead of lines so that if there is a `\r`,
+        // it is included in the offset calculation. The `+1` values below
+        // account for the `\n`.
+        for (i, line) in text.split_terminator('\n').enumerate() {
+            if cur + line.len() + 1 > self.offset {
+                return (i, self.offset - cur);
+            }
+            cur += line.len() + 1;
+        }
+        (text.lines().count(), 0)
+    }
+
+    /// Returns the byte offset of this span.
+    pub fn offset(&self) -> usize {
+        self.offset
+    }
+}
+
+/// An identifier in a WebAssembly module, prefixed by `$` in the textual
+/// format.
+///
+/// An identifier is used to symbolically refer to items in a a wasm module,
+/// typically via the [`Index`] type.
+#[derive(Copy, Clone)]
+pub struct Id<'a> {
+    name: &'a str,
+    gen: u32,
+    span: Span,
+}
+
+impl<'a> Id<'a> {
+    fn new(name: &'a str, span: Span) -> Id<'a> {
+        Id { name, gen: 0, span }
+    }
+
+    pub(crate) fn gensym(span: Span, gen: u32) -> Id<'a> {
+        Id {
+            name: "gensym",
+            gen,
+            span,
+        }
+    }
+
+    /// Returns the underlying name of this identifier.
+    ///
+    /// The name returned does not contain the leading `$`.
+    pub fn name(&self) -> &'a str {
+        self.name
+    }
+
+    /// Returns span of this identifier in the original source
+    pub fn span(&self) -> Span {
+        self.span
+    }
+
+    pub(crate) fn is_gensym(&self) -> bool {
+        self.gen != 0
+    }
+}
+
+impl<'a> Hash for Id<'a> {
+    fn hash<H: Hasher>(&self, hasher: &mut H) {
+        self.name.hash(hasher);
+        self.gen.hash(hasher);
+    }
+}
+
+impl<'a> PartialEq for Id<'a> {
+    fn eq(&self, other: &Id<'a>) -> bool {
+        self.name == other.name && self.gen == other.gen
+    }
+}
+
+impl<'a> Eq for Id<'a> {}
+
+impl<'a> Parse<'a> for Id<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.step(|c| {
+            if let Some((name, rest)) = c.id() {
+                return Ok((Id::new(name, c.cur_span()), rest));
+            }
+            Err(c.error("expected an identifier"))
+        })
+    }
+}
+
+impl fmt::Debug for Id<'_> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if self.gen != 0 {
+            f.debug_struct("Id").field("gen", &self.gen).finish()
+        } else {
+            self.name.fmt(f)
+        }
+    }
+}
+
+impl Peek for Id<'_> {
+    fn peek(cursor: Cursor<'_>) -> bool {
+        cursor.id().is_some()
+    }
+
+    fn display() -> &'static str {
+        "an identifier"
+    }
+}
+
+/// A reference to another item in a wasm module.
+///
+/// This type is used for items referring to other items (such as `call $foo`
+/// referencing function `$foo`). References can be either an index (u32) or an
+/// [`Id`] in the textual format.
+///
+/// The emission phase of a module will ensure that `Index::Id` is never used
+/// and switch them all to `Index::Num`.
+#[derive(Copy, Clone, Debug)]
+pub enum Index<'a> {
+    /// A numerical index that this references. The index space this is
+    /// referencing is implicit based on where this [`Index`] is stored.
+    Num(u32, Span),
+    /// A human-readable identifier this references. Like `Num`, the namespace
+    /// this references is based on where this is stored.
+    Id(Id<'a>),
+}
+
+impl Index<'_> {
+    /// Returns the source location where this `Index` was defined.
+    pub fn span(&self) -> Span {
+        match self {
+            Index::Num(_, span) => *span,
+            Index::Id(id) => id.span(),
+        }
+    }
+
+    pub(crate) fn is_resolved(&self) -> bool {
+        matches!(self, Index::Num(..))
+    }
+}
+
+impl<'a> Parse<'a> for Index<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut l = parser.lookahead1();
+        if l.peek::<Id>() {
+            Ok(Index::Id(parser.parse()?))
+        } else if l.peek::<u32>() {
+            let (val, span) = parser.parse()?;
+            Ok(Index::Num(val, span))
+        } else {
+            Err(l.error())
+        }
+    }
+}
+
+impl Peek for Index<'_> {
+    fn peek(cursor: Cursor<'_>) -> bool {
+        u32::peek(cursor) || Id::peek(cursor)
+    }
+
+    fn display() -> &'static str {
+        "an index"
+    }
+}
+
+impl<'a> From<Id<'a>> for Index<'a> {
+    fn from(id: Id<'a>) -> Index<'a> {
+        Index::Id(id)
+    }
+}
+
+impl PartialEq for Index<'_> {
+    fn eq(&self, other: &Index<'_>) -> bool {
+        match (self, other) {
+            (Index::Num(a, _), Index::Num(b, _)) => a == b,
+            (Index::Id(a), Index::Id(b)) => a == b,
+            _ => false,
+        }
+    }
+}
+
+impl Eq for Index<'_> {}
+
+impl Hash for Index<'_> {
+    fn hash<H: Hasher>(&self, hasher: &mut H) {
+        match self {
+            Index::Num(a, _) => {
+                0u8.hash(hasher);
+                a.hash(hasher);
+            }
+            Index::Id(a) => {
+                1u8.hash(hasher);
+                a.hash(hasher);
+            }
+        }
+    }
+}
+
+/// Parses `(func $foo)`
+#[derive(Clone, Debug)]
+#[allow(missing_docs)]
+pub struct ItemRef<'a, K> {
+    pub kind: K,
+    pub idx: Index<'a>,
+}
+
+impl<'a, K: Parse<'a>> Parse<'a> for ItemRef<'a, K> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.parens(|parser| {
+            let kind = parser.parse::<K>()?;
+            let idx = parser.parse()?;
+            Ok(ItemRef { kind, idx })
+        })
+    }
+}
+
+impl<'a, K: Peek> Peek for ItemRef<'a, K> {
+    fn peek(cursor: Cursor<'_>) -> bool {
+        match cursor.lparen() {
+            Some(remaining) => K::peek(remaining),
+            None => false,
+        }
+    }
+
+    fn display() -> &'static str {
+        "an item reference"
+    }
+}
+
+/// An `@name` annotation in source, currently of the form `@name "foo"`
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub struct NameAnnotation<'a> {
+    /// The name specified for the item
+    pub name: &'a str,
+}
+
+impl<'a> Parse<'a> for NameAnnotation<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.parse::<annotation::name>()?;
+        let name = parser.parse()?;
+        Ok(NameAnnotation { name })
+    }
+}
+
+impl<'a> Parse<'a> for Option<NameAnnotation<'a>> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let _r = parser.register_annotation("name");
+        Ok(if parser.peek2::<annotation::name>() {
+            Some(parser.parens(|p| p.parse())?)
+        } else {
+            None
+        })
+    }
+}
+
+macro_rules! integers {
+    ($($i:ident($u:ident))*) => ($(
+        impl<'a> Parse<'a> for $i {
+            fn parse(parser: Parser<'a>) -> Result<Self> {
+                Ok(parser.parse::<($i, Span)>()?.0)
+            }
+        }
+
+        impl<'a> Parse<'a> for ($i, Span) {
+            fn parse(parser: Parser<'a>) -> Result<Self> {
+                parser.step(|c| {
+                    if let Some((i, rest)) = c.integer() {
+                        let (s, base) = i.val();
+                        let val = $i::from_str_radix(s, base)
+                            .or_else(|_| {
+                                $u::from_str_radix(s, base).map(|i| i as $i)
+                            });
+                        return match val {
+                            Ok(n) => Ok(((n, c.cur_span()), rest)),
+                            Err(_) => Err(c.error(concat!(
+                                "invalid ",
+                                stringify!($i),
+                                " number: constant out of range",
+                            ))),
+                        };
+                    }
+                    Err(c.error(concat!("expected a ", stringify!($i))))
+                })
+            }
+        }
+
+        impl Peek for $i {
+            fn peek(cursor: Cursor<'_>) -> bool {
+                cursor.integer().is_some()
+            }
+
+            fn display() -> &'static str {
+                stringify!($i)
+            }
+        }
+    )*)
+}
+
+integers! {
+    u8(u8) u16(u16) u32(u32) u64(u64)
+    i8(u8) i16(u16) i32(u32) i64(u64)
+}
+
+impl<'a> Parse<'a> for &'a [u8] {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        parser.step(|c| {
+            if let Some((i, rest)) = c.string() {
+                return Ok((i, rest));
+            }
+            Err(c.error("expected a string"))
+        })
+    }
+}
+
+impl Peek for &'_ [u8] {
+    fn peek(cursor: Cursor<'_>) -> bool {
+        cursor.string().is_some()
+    }
+
+    fn display() -> &'static str {
+        "string"
+    }
+}
+
+impl<'a> Parse<'a> for &'a str {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        str::from_utf8(parser.parse()?)
+            .map_err(|_| parser.error_at(parser.prev_span(), "malformed UTF-8 encoding"))
+    }
+}
+
+impl Parse<'_> for String {
+    fn parse(parser: Parser<'_>) -> Result<Self> {
+        Ok(<&str>::parse(parser)?.to_string())
+    }
+}
+
+impl Peek for &'_ str {
+    fn peek(cursor: Cursor<'_>) -> bool {
+        <&[u8]>::peek(cursor)
+    }
+
+    fn display() -> &'static str {
+        <&[u8]>::display()
+    }
+}
+
+macro_rules! float {
+    ($($name:ident => {
+        bits: $int:ident,
+        float: $float:ident,
+        exponent_bits: $exp_bits:tt,
+        name: $parse:ident,
+    })*) => ($(
+        /// A parsed floating-point type
+        #[derive(Debug, Copy, Clone)]
+        pub struct $name {
+            /// The raw bits that this floating point number represents.
+            pub bits: $int,
+        }
+
+        impl<'a> Parse<'a> for $name {
+            fn parse(parser: Parser<'a>) -> Result<Self> {
+                parser.step(|c| {
+                    let (val, rest) = if let Some((f, rest)) = c.float() {
+                        ($parse(f.val()), rest)
+                    } else if let Some((i, rest)) = c.integer() {
+                        let (s, base) = i.val();
+                        (
+                            $parse(&FloatVal::Val {
+                                hex: base == 16,
+                                integral: s.into(),
+                                decimal: None,
+                                exponent: None,
+                            }),
+                            rest,
+                        )
+                    } else {
+                        return Err(c.error("expected a float"));
+                    };
+                    match val {
+                        Some(bits) => Ok(($name { bits }, rest)),
+                        None => Err(c.error("invalid float value: constant out of range")),
+                    }
+                })
+            }
+        }
+
+        fn $parse(val: &FloatVal<'_>) -> Option<$int> {
+            // Compute a few well-known constants about the float representation
+            // given the parameters to the macro here.
+            let width = std::mem::size_of::<$int>() * 8;
+            let neg_offset = width - 1;
+            let exp_offset = neg_offset - $exp_bits;
+            let signif_bits = width - 1 - $exp_bits;
+            let signif_mask = (1 << exp_offset) - 1;
+            let bias = (1 << ($exp_bits - 1)) - 1;
+
+            let (hex, integral, decimal, exponent_str) = match val {
+                // Infinity is when the exponent bits are all set and
+                // the significand is zero.
+                FloatVal::Inf { negative } => {
+                    let exp_bits = (1 << $exp_bits) - 1;
+                    let neg_bit = *negative as $int;
+                    return Some(
+                        (neg_bit << neg_offset) |
+                        (exp_bits << exp_offset)
+                    );
+                }
+
+                // NaN is when the exponent bits are all set and
+                // the significand is nonzero. The default of NaN is
+                // when only the highest bit of the significand is set.
+                FloatVal::Nan { negative, val } => {
+                    let exp_bits = (1 << $exp_bits) - 1;
+                    let neg_bit = *negative as $int;
+                    let signif = val.unwrap_or(1 << (signif_bits - 1)) as $int;
+                    // If the significand is zero then this is actually infinity
+                    // so we fail to parse it.
+                    if signif & signif_mask == 0 {
+                        return None;
+                    }
+                    return Some(
+                        (neg_bit << neg_offset) |
+                        (exp_bits << exp_offset) |
+                        (signif & signif_mask)
+                    );
+                }
+
+                // This is trickier, handle this below
+                FloatVal::Val { hex, integral, decimal, exponent } => {
+                    (hex, integral, decimal, exponent)
+                }
+            };
+
+            // Rely on Rust's standard library to parse base 10 floats
+            // correctly.
+            if !*hex {
+                let mut s = integral.to_string();
+                if let Some(decimal) = decimal {
+                    s.push_str(".");
+                    s.push_str(&decimal);
+                }
+                if let Some(exponent) = exponent_str {
+                    s.push_str("e");
+                    s.push_str(&exponent);
+                }
+                let float = s.parse::<$float>().ok()?;
+                // looks like the `*.wat` format considers infinite overflow to
+                // be invalid.
+                if float.is_infinite() {
+                    return None;
+                }
+                return Some(float.to_bits());
+            }
+
+            // Parsing hex floats is... hard! I don't really know what most of
+            // this below does. It was copied from Gecko's implementation in
+            // `WasmTextToBinary.cpp`. Would love comments on this if you have
+            // them!
+            let decimal = decimal.as_ref().map(|s| &**s).unwrap_or("");
+            let negative = integral.starts_with('-');
+            let integral = integral.trim_start_matches('-').trim_start_matches('0');
+
+            // Do a bunch of work up front to locate the first non-zero digit
+            // to determine the initial exponent. There's a number of
+            // adjustments depending on where the digit was found, but the
+            // general idea here is that I'm not really sure why things are
+            // calculated the way they are but it should match Gecko.
+            let decimal_no_leading = decimal.trim_start_matches('0');
+            let decimal_iter = if integral.is_empty() {
+                decimal_no_leading.chars()
+            } else {
+                decimal.chars()
+            };
+            let mut digits = integral.chars()
+                .map(|c| (to_hex(c) as $int, false))
+                .chain(decimal_iter.map(|c| (to_hex(c) as $int, true)));
+            let lead_nonzero_digit = match digits.next() {
+                Some((c, _)) => c,
+                // No digits? Must be `+0` or `-0`, being careful to handle the
+                // sign encoding here.
+                None if negative => return Some(1 << (width - 1)),
+                None => return Some(0),
+            };
+            let mut significand = 0 as $int;
+            let mut exponent = if !integral.is_empty() {
+                1
+            } else {
+                -((decimal.len() - decimal_no_leading.len() + 1) as i32) + 1
+            };
+            let lz = (lead_nonzero_digit as u8).leading_zeros() as i32 - 4;
+            exponent = exponent.checked_mul(4)?.checked_sub(lz + 1)?;
+            let mut significand_pos = (width - (4 - (lz as usize))) as isize;
+            assert!(significand_pos >= 0);
+            significand |= lead_nonzero_digit << significand_pos;
+
+            // Now that we've got an anchor in the string we parse the remaining
+            // digits. Again, not entirely sure why everything is the way it is
+            // here! This is copied frmo gecko.
+            let mut discarded_extra_nonzero = false;
+            for (digit, decimal) in digits {
+                if !decimal {
+                    exponent += 4;
+                }
+                if significand_pos > -4 {
+                    significand_pos -= 4;
+                }
+
+                if significand_pos >= 0 {
+                    significand |= digit << significand_pos;
+                } else if significand_pos > -4 {
+                    significand |= digit >> (4 - significand_pos);
+                    discarded_extra_nonzero = (digit & !((!0) >> (4 - significand_pos))) != 0;
+                } else if digit != 0 {
+                    discarded_extra_nonzero = true;
+                }
+            }
+
+            exponent = exponent.checked_add(match exponent_str {
+                Some(s) => s.parse::<i32>().ok()?,
+                None => 0,
+            })?;
+            debug_assert!(significand != 0);
+
+            let (encoded_exponent, encoded_significand, discarded_significand) =
+                if exponent <= -bias {
+                    // Underflow to subnormal or zero.
+                    let shift = exp_offset as i32 + exponent + bias;
+                    if shift == 0 {
+                        (0, 0, significand)
+                    } else if shift < 0 || shift >= width as i32 {
+                        (0, 0, 0)
+                    } else {
+                        (
+                            0,
+                            significand >> (width as i32 - shift),
+                            significand << shift,
+                        )
+                    }
+                } else if exponent <= bias {
+                    // Normal (non-zero). The significand's leading 1 is encoded
+                    // implicitly.
+                    (
+                        ((exponent + bias) as $int) << exp_offset,
+                        (significand >> (width - exp_offset - 1)) & signif_mask,
+                        significand << (exp_offset + 1),
+                    )
+                } else {
+                    // Overflow to infinity.
+                    (
+                        ((1 << $exp_bits) - 1) << exp_offset,
+                        0,
+                        0,
+                    )
+                };
+
+            let bits = encoded_exponent | encoded_significand;
+
+            // Apply rounding. If this overflows the significand, it carries
+            // into the exponent bit according to the magic of the IEEE 754
+            // encoding.
+            //
+            // Or rather, the comment above is what Gecko says so it's copied
+            // here too.
+            let msb = 1 << (width - 1);
+            let bits = bits
+                + (((discarded_significand & msb != 0)
+                    && ((discarded_significand & !msb != 0) ||
+                         discarded_extra_nonzero ||
+                         // ties to even
+                         (encoded_significand & 1 != 0))) as $int);
+
+            // Just before we return the bits be sure to handle the sign bit we
+            // found at the beginning.
+            let bits = if negative {
+                bits | (1 << (width - 1))
+            } else {
+                bits
+            };
+            // looks like the `*.wat` format considers infinite overflow to
+            // be invalid.
+            if $float::from_bits(bits).is_infinite() {
+                return None;
+            }
+            Some(bits)
+        }
+
+    )*)
+}
+
+float! {
+    Float32 => {
+        bits: u32,
+        float: f32,
+        exponent_bits: 8,
+        name: strtof,
+    }
+    Float64 => {
+        bits: u64,
+        float: f64,
+        exponent_bits: 11,
+        name: strtod,
+    }
+}
+
+fn to_hex(c: char) -> u8 {
+    match c {
+        'a'..='f' => c as u8 - b'a' + 10,
+        'A'..='F' => c as u8 - b'A' + 10,
+        _ => c as u8 - b'0',
+    }
+}
+
+/// A convenience type to use with [`Parser::peek`](crate::parser::Parser::peek)
+/// to see if the next token is an s-expression.
+pub struct LParen {
+    _priv: (),
+}
+
+impl Peek for LParen {
+    fn peek(cursor: Cursor<'_>) -> bool {
+        cursor.lparen().is_some()
+    }
+
+    fn display() -> &'static str {
+        "left paren"
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn hex_strtof() {
+        macro_rules! f {
+            ($a:tt) => (f!(@mk $a, None, None));
+            ($a:tt p $e:tt) => (f!(@mk $a, None, Some($e.into())));
+            ($a:tt . $b:tt) => (f!(@mk $a, Some($b.into()), None));
+            ($a:tt . $b:tt p $e:tt) => (f!(@mk $a, Some($b.into()), Some($e.into())));
+            (@mk $a:tt, $b:expr, $e:expr) => (crate::lexer::FloatVal::Val {
+                hex: true,
+                integral: $a.into(),
+                decimal: $b,
+                exponent: $e
+            });
+        }
+        assert_eq!(super::strtof(&f!("0")), Some(0));
+        assert_eq!(super::strtof(&f!("0" . "0")), Some(0));
+        assert_eq!(super::strtof(&f!("0" . "0" p "2354")), Some(0));
+        assert_eq!(super::strtof(&f!("-0")), Some(1 << 31));
+        assert_eq!(super::strtof(&f!("f32")), Some(0x45732000));
+        assert_eq!(super::strtof(&f!("0" . "f32")), Some(0x3f732000));
+        assert_eq!(super::strtof(&f!("1" . "2")), Some(0x3f900000));
+        assert_eq!(
+            super::strtof(&f!("0" . "00000100000000000" p "-126")),
+            Some(0)
+        );
+        assert_eq!(
+            super::strtof(&f!("1" . "fffff4" p "-106")),
+            Some(0x0afffffa)
+        );
+        assert_eq!(super::strtof(&f!("fffff98" p "-133")), Some(0x0afffffa));
+        assert_eq!(super::strtof(&f!("0" . "081" p "023")), Some(0x48810000));
+        assert_eq!(
+            super::strtof(&f!("1" . "00000100000000000" p "-50")),
+            Some(0x26800000)
+        );
+    }
+}
diff --git a/third_party/rust/wast/src/wast.rs b/third_party/rust/wast/src/wast.rs
new file mode 100644
index 0000000000..ec589e59d6
--- /dev/null
+++ b/third_party/rust/wast/src/wast.rs
@@ -0,0 +1,365 @@
+use crate::component::WastVal;
+use crate::core::{WastArgCore, WastRetCore};
+use crate::kw;
+use crate::parser::{self, Cursor, Parse, ParseBuffer, Parser, Peek, Result};
+use crate::token::{Id, Span};
+use crate::{Error, Wat};
+
+/// A parsed representation of a `*.wast` file.
+///
+/// WAST files are not officially specified but are used in the official test
+/// suite to write official spec tests for wasm. This type represents a parsed
+/// `*.wast` file which parses a list of directives in a file.
+#[derive(Debug)]
+pub struct Wast<'a> {
+    #[allow(missing_docs)]
+    pub directives: Vec<WastDirective<'a>>,
+}
+
+impl<'a> Parse<'a> for Wast<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut directives = Vec::new();
+
+        // If it looks like a directive token is in the stream then we parse a
+        // bunch of directives, otherwise assume this is an inline module.
+        if parser.peek2::<WastDirectiveToken>() {
+            while !parser.is_empty() {
+                directives.push(parser.parens(|p| p.parse())?);
+            }
+        } else {
+            let module = parser.parse::<Wat>()?;
+            directives.push(WastDirective::Wat(QuoteWat::Wat(module)));
+        }
+        Ok(Wast { directives })
+    }
+}
+
+struct WastDirectiveToken;
+
+impl Peek for WastDirectiveToken {
+    fn peek(cursor: Cursor<'_>) -> bool {
+        let kw = match cursor.keyword() {
+            Some((kw, _)) => kw,
+            None => return false,
+        };
+        kw.starts_with("assert_")
+            || kw == "module"
+            || kw == "component"
+            || kw == "register"
+            || kw == "invoke"
+    }
+
+    fn display() -> &'static str {
+        unimplemented!()
+    }
+}
+
+/// The different kinds of directives found in a `*.wast` file.
+///
+/// It's not entirely clear to me what all of these are per se, but they're only
+/// really interesting to test harnesses mostly.
+#[allow(missing_docs)]
+#[derive(Debug)]
+pub enum WastDirective<'a> {
+    Wat(QuoteWat<'a>),
+    AssertMalformed {
+        span: Span,
+        module: QuoteWat<'a>,
+        message: &'a str,
+    },
+    AssertInvalid {
+        span: Span,
+        module: QuoteWat<'a>,
+        message: &'a str,
+    },
+    Register {
+        span: Span,
+        name: &'a str,
+        module: Option<Id<'a>>,
+    },
+    Invoke(WastInvoke<'a>),
+    AssertTrap {
+        span: Span,
+        exec: WastExecute<'a>,
+        message: &'a str,
+    },
+    AssertReturn {
+        span: Span,
+        exec: WastExecute<'a>,
+        results: Vec<WastRet<'a>>,
+    },
+    AssertExhaustion {
+        span: Span,
+        call: WastInvoke<'a>,
+        message: &'a str,
+    },
+    AssertUnlinkable {
+        span: Span,
+        module: Wat<'a>,
+        message: &'a str,
+    },
+    AssertException {
+        span: Span,
+        exec: WastExecute<'a>,
+    },
+}
+
+impl WastDirective<'_> {
+    /// Returns the location in the source that this directive was defined at
+    pub fn span(&self) -> Span {
+        match self {
+            WastDirective::Wat(QuoteWat::Wat(Wat::Module(m))) => m.span,
+            WastDirective::Wat(QuoteWat::Wat(Wat::Component(c))) => c.span,
+            WastDirective::Wat(QuoteWat::QuoteModule(span, _)) => *span,
+            WastDirective::Wat(QuoteWat::QuoteComponent(span, _)) => *span,
+            WastDirective::AssertMalformed { span, .. }
+            | WastDirective::Register { span, .. }
+            | WastDirective::AssertTrap { span, .. }
+            | WastDirective::AssertReturn { span, .. }
+            | WastDirective::AssertExhaustion { span, .. }
+            | WastDirective::AssertUnlinkable { span, .. }
+            | WastDirective::AssertInvalid { span, .. }
+            | WastDirective::AssertException { span, .. } => *span,
+            WastDirective::Invoke(i) => i.span,
+        }
+    }
+}
+
+impl<'a> Parse<'a> for WastDirective<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut l = parser.lookahead1();
+        if l.peek::<kw::module>() || l.peek::<kw::component>() {
+            Ok(WastDirective::Wat(parser.parse()?))
+        } else if l.peek::<kw::assert_malformed>() {
+            let span = parser.parse::<kw::assert_malformed>()?.0;
+            Ok(WastDirective::AssertMalformed {
+                span,
+                module: parser.parens(|p| p.parse())?,
+                message: parser.parse()?,
+            })
+        } else if l.peek::<kw::assert_invalid>() {
+            let span = parser.parse::<kw::assert_invalid>()?.0;
+            Ok(WastDirective::AssertInvalid {
+                span,
+                module: parser.parens(|p| p.parse())?,
+                message: parser.parse()?,
+            })
+        } else if l.peek::<kw::register>() {
+            let span = parser.parse::<kw::register>()?.0;
+            Ok(WastDirective::Register {
+                span,
+                name: parser.parse()?,
+                module: parser.parse()?,
+            })
+        } else if l.peek::<kw::invoke>() {
+            Ok(WastDirective::Invoke(parser.parse()?))
+        } else if l.peek::<kw::assert_trap>() {
+            let span = parser.parse::<kw::assert_trap>()?.0;
+            Ok(WastDirective::AssertTrap {
+                span,
+                exec: parser.parens(|p| p.parse())?,
+                message: parser.parse()?,
+            })
+        } else if l.peek::<kw::assert_return>() {
+            let span = parser.parse::<kw::assert_return>()?.0;
+            let exec = parser.parens(|p| p.parse())?;
+            let mut results = Vec::new();
+            while !parser.is_empty() {
+                results.push(parser.parens(|p| p.parse())?);
+            }
+            Ok(WastDirective::AssertReturn {
+                span,
+                exec,
+                results,
+            })
+        } else if l.peek::<kw::assert_exhaustion>() {
+            let span = parser.parse::<kw::assert_exhaustion>()?.0;
+            Ok(WastDirective::AssertExhaustion {
+                span,
+                call: parser.parens(|p| p.parse())?,
+                message: parser.parse()?,
+            })
+        } else if l.peek::<kw::assert_unlinkable>() {
+            let span = parser.parse::<kw::assert_unlinkable>()?.0;
+            Ok(WastDirective::AssertUnlinkable {
+                span,
+                module: parser.parens(parse_wat)?,
+                message: parser.parse()?,
+            })
+        } else if l.peek::<kw::assert_exception>() {
+            let span = parser.parse::<kw::assert_exception>()?.0;
+            Ok(WastDirective::AssertException {
+                span,
+                exec: parser.parens(|p| p.parse())?,
+            })
+        } else {
+            Err(l.error())
+        }
+    }
+}
+
+#[allow(missing_docs)]
+#[derive(Debug)]
+pub enum WastExecute<'a> {
+    Invoke(WastInvoke<'a>),
+    Wat(Wat<'a>),
+    Get {
+        module: Option<Id<'a>>,
+        global: &'a str,
+    },
+}
+
+impl<'a> Parse<'a> for WastExecute<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let mut l = parser.lookahead1();
+        if l.peek::<kw::invoke>() {
+            Ok(WastExecute::Invoke(parser.parse()?))
+        } else if l.peek::<kw::module>() || l.peek::<kw::component>() {
+            Ok(WastExecute::Wat(parse_wat(parser)?))
+        } else if l.peek::<kw::get>() {
+            parser.parse::<kw::get>()?;
+            Ok(WastExecute::Get {
+                module: parser.parse()?,
+                global: parser.parse()?,
+            })
+        } else {
+            Err(l.error())
+        }
+    }
+}
+
+fn parse_wat(parser: Parser) -> Result<Wat> {
+    // Note that this doesn't use `Parse for Wat` since the `parser` provided
+    // has already peeled back the first layer of parentheses while `Parse for
+    // Wat` expects to be the top layer which means it also tries to peel off
+    // the parens. Instead we can skip the sugar that `Wat` has for simply a
+    // list of fields (no `(module ...)` container) and just parse the `Module`
+    // itself.
+    if parser.peek::<kw::component>() {
+        Ok(Wat::Component(parser.parse()?))
+    } else {
+        Ok(Wat::Module(parser.parse()?))
+    }
+}
+
+#[allow(missing_docs)]
+#[derive(Debug)]
+pub struct WastInvoke<'a> {
+    pub span: Span,
+    pub module: Option<Id<'a>>,
+    pub name: &'a str,
+    pub args: Vec<WastArg<'a>>,
+}
+
+impl<'a> Parse<'a> for WastInvoke<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        let span = parser.parse::<kw::invoke>()?.0;
+        let module = parser.parse()?;
+        let name = parser.parse()?;
+        let mut args = Vec::new();
+        while !parser.is_empty() {
+            args.push(parser.parens(|p| p.parse())?);
+        }
+        Ok(WastInvoke {
+            span,
+            module,
+            name,
+            args,
+        })
+    }
+}
+
+#[allow(missing_docs)]
+#[derive(Debug)]
+pub enum QuoteWat<'a> {
+    Wat(Wat<'a>),
+    QuoteModule(Span, Vec<(Span, &'a [u8])>),
+    QuoteComponent(Span, Vec<(Span, &'a [u8])>),
+}
+
+impl QuoteWat<'_> {
+    /// Encodes this module to bytes, either by encoding the module directly or
+    /// parsing the contents and then encoding it.
+    pub fn encode(&mut self) -> Result<Vec<u8>, Error> {
+        let (source, prefix) = match self {
+            QuoteWat::Wat(m) => return m.encode(),
+            QuoteWat::QuoteModule(_, source) => (source, None),
+            QuoteWat::QuoteComponent(_, source) => (source, Some("(component")),
+        };
+        let mut ret = String::new();
+        for (span, src) in source {
+            match std::str::from_utf8(src) {
+                Ok(s) => ret.push_str(s),
+                Err(_) => {
+                    return Err(Error::new(*span, "malformed UTF-8 encoding".to_string()));
+                }
+            }
+            ret.push(' ');
+        }
+        if let Some(prefix) = prefix {
+            ret.insert_str(0, prefix);
+            ret.push(')');
+        }
+        let buf = ParseBuffer::new(&ret)?;
+        let mut wat = parser::parse::<Wat<'_>>(&buf)?;
+        wat.encode()
+    }
+}
+
+impl<'a> Parse<'a> for QuoteWat<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        if parser.peek2::<kw::quote>() {
+            let ctor = if parser.peek::<kw::component>() {
+                parser.parse::<kw::component>()?;
+                QuoteWat::QuoteComponent
+            } else {
+                parser.parse::<kw::module>()?;
+                QuoteWat::QuoteModule
+            };
+            let span = parser.parse::<kw::quote>()?.0;
+            let mut src = Vec::new();
+            while !parser.is_empty() {
+                let span = parser.cur_span();
+                let string = parser.parse()?;
+                src.push((span, string));
+            }
+            Ok(ctor(span, src))
+        } else {
+            Ok(QuoteWat::Wat(parse_wat(parser)?))
+        }
+    }
+}
+
+#[derive(Debug)]
+#[allow(missing_docs)]
+pub enum WastArg<'a> {
+    Core(WastArgCore<'a>),
+    Component(WastVal<'a>),
+}
+
+impl<'a> Parse<'a> for WastArg<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        if parser.peek::<WastArgCore<'_>>() {
+            Ok(WastArg::Core(parser.parse()?))
+        } else {
+            Ok(WastArg::Component(parser.parse()?))
+        }
+    }
+}
+
+#[derive(Debug)]
+#[allow(missing_docs)]
+pub enum WastRet<'a> {
+    Core(WastRetCore<'a>),
+    Component(WastVal<'a>),
+}
+
+impl<'a> Parse<'a> for WastRet<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        if parser.peek::<WastRetCore<'_>>() {
+            Ok(WastRet::Core(parser.parse()?))
+        } else {
+            Ok(WastRet::Component(parser.parse()?))
+        }
+    }
+}
diff --git a/third_party/rust/wast/src/wat.rs b/third_party/rust/wast/src/wat.rs
new file mode 100644
index 0000000000..631bc3d0ed
--- /dev/null
+++ b/third_party/rust/wast/src/wat.rs
@@ -0,0 +1,60 @@
+use crate::component::Component;
+use crate::core::{Module, ModuleField, ModuleKind};
+use crate::kw;
+use crate::parser::{Parse, Parser, Result};
+use crate::token::Span;
+
+/// A `*.wat` file parser, or a parser for one parenthesized module.
+///
+/// This is the top-level type which you'll frequently parse when working with
+/// this crate. A `*.wat` file is either one `module` s-expression or a sequence
+/// of s-expressions that are module fields.
+#[derive(Debug)]
+#[allow(missing_docs)]
+pub enum Wat<'a> {
+    Module(Module<'a>),
+    Component(Component<'a>),
+}
+
+impl Wat<'_> {
+    fn validate(&self, parser: Parser<'_>) -> Result<()> {
+        match self {
+            Wat::Module(m) => m.validate(parser),
+            Wat::Component(c) => c.validate(parser),
+        }
+    }
+
+    /// Encodes this `Wat` to binary form. This calls either [`Module::encode`]
+    /// or [`Component::encode`].
+    pub fn encode(&mut self) -> std::result::Result<Vec<u8>, crate::Error> {
+        match self {
+            Wat::Module(m) => m.encode(),
+            Wat::Component(c) => c.encode(),
+        }
+    }
+}
+
+impl<'a> Parse<'a> for Wat<'a> {
+    fn parse(parser: Parser<'a>) -> Result<Self> {
+        if !parser.has_meaningful_tokens() {
+            return Err(parser.error("expected at least one module field"));
+        }
+
+        let _r = parser.register_annotation("custom");
+        let wat = if parser.peek2::<kw::module>() {
+            Wat::Module(parser.parens(|parser| parser.parse())?)
+        } else if parser.peek2::<kw::component>() {
+            Wat::Component(parser.parens(|parser| parser.parse())?)
+        } else {
+            let fields = ModuleField::parse_remaining(parser)?;
+            Wat::Module(Module {
+                span: Span { offset: 0 },
+                id: None,
+                name: None,
+                kind: ModuleKind::Text(fields),
+            })
+        };
+        wat.validate(parser)?;
+        Ok(wat)
+    }
+}