1 files changed, 129 insertions, 0 deletions
diff --git a/third_party/rust/wasm-encoder/src/component/aliases.rs b/third_party/rust/wasm-encoder/src/component/aliases.rs
new file mode 100644
index 0000000000..a78d52643a
--- /dev/null
+++ b/third_party/rust/wasm-encoder/src/component/aliases.rs
@@ -0,0 +1,129 @@
+use super::{COMPONENT_SORT, CORE_MODULE_SORT, CORE_SORT, CORE_TYPE_SORT, TYPE_SORT};
+use crate::{
+    encode_section, ComponentExportKind, ComponentSection, ComponentSectionId, Encode, ExportKind,
+};
+
+/// Represents the kinds of outer aliasable items in a component.
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum ComponentOuterAliasKind {
+    /// The alias is to a core module.
+    CoreModule,
+    /// The alias is to a core type.
+    CoreType,
+    /// The alias is to a type.
+    Type,
+    /// The alias is to a component.
+    Component,
+}
+
+impl Encode for ComponentOuterAliasKind {
+    fn encode(&self, sink: &mut Vec<u8>) {
+        match self {
+            Self::CoreModule => {
+                sink.push(CORE_SORT);
+                sink.push(CORE_MODULE_SORT);
+            }
+            Self::CoreType => {
+                sink.push(CORE_SORT);
+                sink.push(CORE_TYPE_SORT);
+            }
+            Self::Type => sink.push(TYPE_SORT),
+            Self::Component => sink.push(COMPONENT_SORT),
+        }
+    }
+}
+
+/// An encoder for the alias section of WebAssembly component.
+///
+/// # Example
+///
+/// ```rust
+/// use wasm_encoder::{Component, ComponentAliasSection, ComponentExportKind, ComponentOuterAliasKind};
+///
+/// let mut aliases = ComponentAliasSection::new();
+/// aliases.instance_export(0, ComponentExportKind::Func, "f");
+/// aliases.outer(0, ComponentOuterAliasKind::Type, 1);
+///
+/// let mut component = Component::new();
+/// component.section(&aliases);
+///
+/// let bytes = component.finish();
+/// ```
+#[derive(Clone, Debug, Default)]
+pub struct ComponentAliasSection {
+    bytes: Vec<u8>,
+    num_added: u32,
+}
+
+impl ComponentAliasSection {
+    /// Create a new alias section encoder.
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// The number of aliases in the section.
+    pub fn len(&self) -> u32 {
+        self.num_added
+    }
+
+    /// Determines if the section is empty.
+    pub fn is_empty(&self) -> bool {
+        self.num_added == 0
+    }
+
+    /// Define an alias to a component instance's export.
+    pub fn instance_export(
+        &mut self,
+        instance_index: u32,
+        kind: ComponentExportKind,
+        name: &str,
+    ) -> &mut Self {
+        kind.encode(&mut self.bytes);
+        self.bytes.push(0x00);
+        instance_index.encode(&mut self.bytes);
+        name.encode(&mut self.bytes);
+        self.num_added += 1;
+        self
+    }
+
+    /// Define an alias to a core instance's export.
+    pub fn core_instance_export(
+        &mut self,
+        instance_index: u32,
+        kind: ExportKind,
+        name: &str,
+    ) -> &mut Self {
+        self.bytes.push(CORE_SORT);
+        kind.encode(&mut self.bytes);
+        self.bytes.push(0x01);
+        instance_index.encode(&mut self.bytes);
+        name.encode(&mut self.bytes);
+        self.num_added += 1;
+        self
+    }
+
+    /// Define an alias to an outer component item.
+    ///
+    /// The count starts at 0 to indicate the current component, 1 indicates the direct
+    /// parent, 2 the grandparent, etc.
+    pub fn outer(&mut self, count: u32, kind: ComponentOuterAliasKind, index: u32) -> &mut Self {
+        kind.encode(&mut self.bytes);
+        self.bytes.push(0x02);
+        count.encode(&mut self.bytes);
+        index.encode(&mut self.bytes);
+        self.num_added += 1;
+        self
+    }
+}
+
+impl Encode for ComponentAliasSection {
+    fn encode(&self, sink: &mut Vec<u8>) {
+        encode_section(sink, self.num_added, &self.bytes);
+    }
+}
+
+impl ComponentSection for ComponentAliasSection {
+    fn id(&self) -> u8 {
+        ComponentSectionId::Alias.into()
+    }
+}