Adding upstream version 124.0.1.upstream/124.0.1

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

7 files changed, 4115 insertions, 0 deletions

diff --git a/third_party/rust/jsparagus-scope/.cargo-checksum.json b/third_party/rust/jsparagus-scope/.cargo-checksum.json
new file mode 100644
index 0000000000..b73043f980
--- /dev/null
+++ b/third_party/rust/jsparagus-scope/.cargo-checksum.json
@@ -0,0 +1 @@
+{"files":{"Cargo.toml":"d66c27f46f6da2bd7a84f762b938be6f4d0f3e20bdcd22862aba780c1039b5ee","src/builder.rs":"3aa261f329a6f4ee45683f4a69f85408d63e6bd5531b74dbbb4b4abbe8093b2f","src/data.rs":"a3cf1e7b1a96a619bcb8bd87f39bbd44dda0fc554c70a5d4d45b70eb03e69401","src/free_name_tracker.rs":"322228be4262d79d148f954a656b4f09fe953b324393fcc5925675c0e7777828","src/lib.rs":"529f7598a3034b347a20307a752b467091d820df6be67ebc4a3bd8e02568511b","src/pass.rs":"e13b2677ddf03b504efd287963caaa28b8a16c5fc0896f97bea2584f8280063d"},"package":null}
\ No newline at end of file
diff --git a/third_party/rust/jsparagus-scope/Cargo.toml b/third_party/rust/jsparagus-scope/Cargo.toml
new file mode 100644
index 0000000000..32b17df1c0
--- /dev/null
+++ b/third_party/rust/jsparagus-scope/Cargo.toml
@@ -0,0 +1,26 @@
+# THIS FILE IS AUTOMATICALLY GENERATED BY CARGO
+#
+# When uploading crates to the registry Cargo will automatically
+# "normalize" Cargo.toml files for maximal compatibility
+# with all versions of Cargo and also rewrite `path` dependencies
+# to registry (e.g., crates.io) dependencies.
+#
+# If you are reading this file be aware that the original Cargo.toml
+# will likely look very different (and much more reasonable).
+# See Cargo.toml.orig for the original contents.
+
+[package]
+edition = "2018"
+name = "jsparagus-scope"
+version = "0.1.0"
+authors = ["The jsparagus Project Developers"]
+license = "MIT/Apache-2.0"
+
+[dependencies]
+indexmap = "2.0"
+
+[dependencies.jsparagus-ast]
+path = "../ast"
+
+[dependencies.jsparagus-stencil]
+path = "../stencil"
diff --git a/third_party/rust/jsparagus-scope/src/builder.rs b/third_party/rust/jsparagus-scope/src/builder.rs
new file mode 100644
index 0000000000..e170194166
--- /dev/null
+++ b/third_party/rust/jsparagus-scope/src/builder.rs
@@ -0,0 +1,3485 @@
+//! Data collection.
+//!
+//! `ScopeBuilder` is the entry point of this module.
+//!
+//! Each AST node that will hold bindings (global, block, function, etc.) has a
+//! corresponding scope builder type defined in this module:
+//!   * `GlobalScopeBuilder`
+//!   * `BlockScopeBuilder`
+//!   * `FunctionExpressionScopeBuilder`
+//!   * `FunctionParametersScopeBuilder`
+//!   * `FunctionBodyScopeBuilder`
+//!
+//! They follow the pattern:
+//!   * They are created and pushed to the `ScopeBuilderStack` when the
+//!     algorithm enters a scope.
+//!   * They collect the information necessary to build a `ScopeData` object
+//!     (which will eventually become a `js::ScopeCreationData` on the
+//!      C++ side).
+//!   * They stay on the scope builder stack until the algorithm leaves that
+//!     scope.
+//!   * Then they are converted by `into_scope_data()`.
+//!
+//! Fields in the builder types mostly correspond to local variables in spec
+//! algorithms.  For example, `GlobalScopeBuilder` has fields named
+//! `functions_to_initialize`, `declared_function_names`, and
+//! `declared_var_names` which correspond to the
+//! [GlobalDeclarationInstantiation][1] algorithm's local variables
+//! *functionsToInitialize*, *declaredFunctionNames*, and *declaredVarNames*.
+//!
+//! This module performs some steps of those algorithms -- the parts that can
+//! be done at compile time. The results are passed along to the emitter and
+//! ultimately the JS runtime.
+//!
+//! # Syntax-only mode
+//!
+//! When doing syntax-only parsing, we collect minimal information, that does
+//! not include `ScopeData`, but `ScriptStencil` for functions.
+//!
+//! [1]: https://tc39.es/ecma262/#sec-globaldeclarationinstantiation
+
+use crate::data::FunctionDeclarationPropertyMap;
+use crate::free_name_tracker::FreeNameTracker;
+use ast::associated_data::AssociatedData;
+use ast::source_atom_set::{CommonSourceAtomSetIndices, SourceAtomSetIndex};
+use ast::source_location_accessor::SourceLocationAccessor;
+use ast::type_id::NodeTypeIdAccessor;
+use indexmap::set::IndexSet;
+use std::collections::hash_map::Keys;
+use std::collections::{HashMap, HashSet};
+use stencil::function::{FunctionFlags, FunctionSyntaxKind};
+use stencil::scope::{
+    BindingName, FunctionScopeData, GlobalScopeData, LexicalScopeData, ScopeData, ScopeDataList,
+    ScopeDataMap, ScopeIndex, VarScopeData,
+};
+use stencil::script::{ScriptStencil, ScriptStencilIndex, ScriptStencilList, SourceExtent};
+
+/// The kind of items inside the result of VarScopedDeclarations.
+///
+/// This enum isn't actually used, but just for simplifying comment in
+/// ScopeKind.
+#[derive(Debug, Clone, PartialEq)]
+enum VarScopedDeclarationsItemKind {
+    /// Static Semantics: VarScopedDeclarations
+    /// https://tc39.es/ecma262/#sec-variable-statement-static-semantics-varscopeddeclarations
+    ///
+    /// VariableDeclarationList : VariableDeclaration
+    ///
+    /// 1. Return a new List containing VariableDeclaration.
+    ///
+    /// VariableDeclarationList : VariableDeclarationList, VariableDeclaration
+    ///
+    /// 1. Let declarations be VarScopedDeclarations of VariableDeclarationList.
+    /// 2. Append VariableDeclaration to declarations.
+    /// 3. Return declarations.
+    #[allow(dead_code)]
+    VariableDeclaration,
+
+    /// Static Semantics: VarScopedDeclarations
+    /// https://tc39.es/ecma262/#sec-for-in-and-for-of-statements-static-semantics-varscopeddeclarations
+    ///
+    /// IterationStatement :
+    ///   for ( var ForBinding in Expression ) Statement
+    ///   for ( var ForBinding of AssignmentExpression ) Statement
+    ///   for await ( var ForBinding of AssignmentExpression ) Statement
+    ///
+    /// 1. Let declarations be a List containing ForBinding.
+    /// 2. Append to declarations the elements of the VarScopedDeclarations of
+    ///    Statement.
+    /// 3. Return declarations.
+    #[allow(dead_code)]
+    ForBinding,
+
+    /// Static Semantics: VarScopedDeclarations
+    /// https://tc39.es/ecma262/#sec-function-definitions-static-semantics-varscopeddeclarations
+    ///
+    /// FunctionStatementList : StatementList
+    ///
+    /// 1. Return the TopLevelVarScopedDeclarations of StatementList.
+
+    /// Static Semantics: VarScopedDeclarations
+    /// https://tc39.es/ecma262/#sec-scripts-static-semantics-varscopeddeclarations
+    ///
+    /// ScriptBody : StatementList
+    ///
+    /// 1. Return TopLevelVarScopedDeclarations of StatementList.
+
+    /// Static Semantics: TopLevelVarScopedDeclarations
+    /// https://tc39.es/ecma262/#sec-block-static-semantics-toplevelvarscopeddeclarations
+    ///
+    /// StatementListItem : Declaration
+    ///
+    /// 1. If Declaration is Declaration : HoistableDeclaration, then
+    ///   a. Let declaration be DeclarationPart of HoistableDeclaration.
+    ///   b. Return « declaration ».
+    /// 2. Return a new empty List.
+
+    /// Static Semantics: DeclarationPart
+    /// https://tc39.es/ecma262/#sec-static-semantics-declarationpart
+    ///
+    /// HoistableDeclaration : FunctionDeclaration
+    ///
+    /// 1. Return FunctionDeclaration.
+    #[allow(dead_code)]
+    FunctionDeclaration,
+
+    /// HoistableDeclaration : GeneratorDeclaration
+    ///
+    /// 1. Return GeneratorDeclaration.
+    #[allow(dead_code)]
+    GeneratorDeclaration,
+
+    /// HoistableDeclaration : AsyncFunctionDeclaration
+    ///
+    /// 1. Return AsyncFunctionDeclaration.
+    #[allow(dead_code)]
+    AsyncFunctionDeclaration,
+
+    /// HoistableDeclaration : AsyncGeneratorDeclaration
+    ///
+    /// 1. Return AsyncGeneratorDeclaration.
+    #[allow(dead_code)]
+    AsyncGeneratorDeclaration,
+
+    /// Static Semantics: TopLevelVarScopedDeclarations
+    /// https://tc39.es/ecma262/#sec-labelled-statements-static-semantics-toplevelvarscopeddeclarations
+    ///
+    /// LabelledItem : FunctionDeclaration
+    ///
+    /// 1. Return a new List containing FunctionDeclaration.
+    /* FunctionDeclaration */
+
+    /// Annex B Initializers in ForIn Statement Heads
+    /// https://tc39.es/ecma262/#sec-initializers-in-forin-statement-heads
+    ///
+    /// IterationStatement :
+    ///   for ( var BindingIdentifier Initializer in Expression ) Statement
+    ///
+    /// 1. Let declarations be a List containing BindingIdentifier.
+    /// 2. Append to declarations the elements of the VarScopedDeclarations of
+    ///    Statement.
+    /// 3. Return declarations.
+    #[allow(dead_code)]
+    BindingIdentifier,
+}
+
+/// The kind of items inside the result of LexicallyScopedDeclarations.
+///
+/// This enum isn't actually used, but just for simplifying comment in
+/// ScopeKind.
+#[derive(Debug, Clone, PartialEq)]
+enum LexicallyScopedDeclarations {
+    /// Static Semantics: LexicallyScopedDeclarations
+    /// https://tc39.es/ecma262/#sec-block-static-semantics-lexicallyscopeddeclarations
+    ///
+    /// StatementListItem : Declaration
+    ///
+    /// 1. Return a new List containing DeclarationPart of Declaration.
+
+    /// Static Semantics: DeclarationPart
+    /// https://tc39.es/ecma262/#sec-static-semantics-declarationpart
+    ///
+    /// HoistableDeclaration : FunctionDeclaration
+    ///
+    /// 1. Return FunctionDeclaration.
+    #[allow(dead_code)]
+    FunctionDeclaration,
+
+    /// HoistableDeclaration : GeneratorDeclaration
+    ///
+    /// 1. Return GeneratorDeclaration.
+    #[allow(dead_code)]
+    GeneratorDeclaration,
+
+    /// HoistableDeclaration : AsyncFunctionDeclaration
+    ///
+    /// 1. Return AsyncFunctionDeclaration.
+    #[allow(dead_code)]
+    AsyncFunctionDeclaration,
+
+    /// HoistableDeclaration : AsyncGeneratorDeclaration
+    ///
+    /// 1. Return AsyncGeneratorDeclaration.
+    #[allow(dead_code)]
+    AsyncGeneratorDeclaration,
+
+    /// Declaration : ClassDeclaration
+    ///
+    /// 1. Return ClassDeclaration.
+    #[allow(dead_code)]
+    ClassDeclaration,
+
+    /// Declaration : LexicalDeclaration
+    ///
+    /// 1. Return LexicalDeclaration.
+    #[allow(dead_code)]
+    LexicalDeclarationWithLet,
+    #[allow(dead_code)]
+    LexicalDeclarationWithConst,
+
+    /// Static Semantics: LexicallyScopedDeclarations
+    /// https://tc39.es/ecma262/#sec-labelled-statements-static-semantics-lexicallyscopeddeclarations
+    ///
+    /// LabelledItem : FunctionDeclaration
+    ///
+    /// 1. Return a new List containing FunctionDeclaration.
+    /* FunctionDeclaration */
+
+    /// Static Semantics: LexicallyScopedDeclarations
+    /// https://tc39.es/ecma262/#sec-function-definitions-static-semantics-lexicallyscopeddeclarations
+    ///
+    /// FunctionStatementList : StatementList
+    ///
+    /// 1. Return the TopLevelLexicallyScopedDeclarations of StatementList.
+
+    /// Static Semantics: LexicallyScopedDeclarations
+    /// https://tc39.es/ecma262/#sec-scripts-static-semantics-lexicallyscopeddeclarations
+    ///
+    /// ScriptBody : StatementList
+    ///
+    /// 1. Return TopLevelLexicallyScopedDeclarations of StatementList.
+
+    /// Static Semantics: TopLevelLexicallyScopedDeclarations
+    /// https://tc39.es/ecma262/#sec-block-static-semantics-toplevellexicallyscopeddeclarations
+    ///
+    /// StatementListItem : Declaration
+    ///
+    /// 1. If Declaration is Declaration : HoistableDeclaration, then
+    ///   a. Return « ».
+    /// 2. Return a new List containing Declaration.
+
+    /// Static Semantics: LexicallyScopedDeclarations
+    /// https://tc39.es/ecma262/#sec-exports-static-semantics-lexicallyscopeddeclarations
+    ///
+    /// ExportDeclaration : export Declaration
+    ///
+    /// 1. Return a new List containing DeclarationPart of Declaration.
+
+    /// ExportDeclaration : export default HoistableDeclaration
+    ///
+    /// 1. Return a new List containing DeclarationPart of HoistableDeclaration.
+
+    /// ExportDeclaration : export default ClassDeclaration
+    ///
+    /// 1. Return a new List containing ClassDeclaration.
+    /* ClassDeclaration */
+
+    /// ExportDeclaration : export default AssignmentExpression ;
+    ///
+    /// 1. Return a new List containing this ExportDeclaration.
+    #[allow(dead_code)]
+    ExportDeclarationWithAssignmentExpression,
+}
+
+/// Items on the ScopeBuilder.scope_stack.
+/// Specifies the kind of BindingIdentifier.
+///
+/// This includes only BindingIdentifier that appears inside list or recursive
+/// structure.
+///
+/// BindingIdentifier that appears only once for a structure
+/// (e.g. Function.name) should be handled immediately, without using
+/// ScopeBuilder.scope_stack.
+#[derive(Debug, Clone, PartialEq)]
+enum ScopeKind {
+    /// VarScopedDeclarationsItemKind::VariableDeclaration
+    /// VarScopedDeclarationsItemKind::ForBinding
+    /// VarScopedDeclarationsItemKind::BindingIdentifier
+    Var,
+
+    /// LexicallyScopedDeclarations::LexicalDeclarationWithLet
+    Let,
+
+    /// LexicallyScopedDeclarations::LexicalDeclarationWithConst
+    Const,
+
+    /// Pushed when entering function, to catch function name.
+    FunctionName,
+
+    /// Pushed when entering function parameter, to disable FunctionName's
+    /// effect.
+    /// Equivalent to the case there's no kind on the stack.
+    FunctionParametersAndBody,
+
+    FormalParameter,
+
+    #[allow(dead_code)]
+    CatchParameter,
+
+    /// LexicallyScopedDeclarations::ExportDeclarationWithAssignmentExpression
+    #[allow(dead_code)]
+    Export,
+
+    /// VarScopedDeclarationsItemKind::FunctionDeclaration
+    /// VarScopedDeclarationsItemKind::GeneratorDeclaration
+    /// VarScopedDeclarationsItemKind::AsyncFunctionDeclaration
+    /// VarScopedDeclarationsItemKind::AsyncGeneratorDeclaration
+    #[allow(dead_code)]
+    ScriptBodyStatementList,
+    #[allow(dead_code)]
+    FunctionStatementList,
+
+    /// LexicallyScopedDeclarations::FunctionDeclaration
+    /// LexicallyScopedDeclarations::GeneratorDeclaration
+    /// LexicallyScopedDeclarations::AsyncFunctionDeclaration
+    /// LexicallyScopedDeclarations::AsyncGeneratorDeclaration
+    /// LexicallyScopedDeclarations::ClassDeclaration
+    #[allow(dead_code)]
+    BlockStatementList,
+}
+
+/// Index into BaseScopeData.bindings.
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub struct BindingIndex {
+    index: usize,
+}
+impl BindingIndex {
+    fn new(index: usize) -> Self {
+        Self { index }
+    }
+
+    pub fn next(&self) -> Self {
+        Self {
+            index: self.index + 1,
+        }
+    }
+}
+
+impl From<BindingIndex> for usize {
+    fn from(index: BindingIndex) -> usize {
+        index.index
+    }
+}
+
+#[derive(Debug)]
+struct PossiblyAnnexBFunction {
+    #[allow(dead_code)]
+    name: SourceAtomSetIndex,
+    #[allow(dead_code)]
+    owner_scope_index: ScopeIndex,
+    #[allow(dead_code)]
+    binding_index: BindingIndex,
+
+    /// Index of the script in the list of `functions` in the
+    /// `FunctionScriptStencilBuilder`.
+    script_index: ScriptStencilIndex,
+}
+
+#[derive(Debug)]
+struct PossiblyAnnexBFunctionList {
+    functions: HashMap<SourceAtomSetIndex, Vec<PossiblyAnnexBFunction>>,
+}
+
+impl PossiblyAnnexBFunctionList {
+    fn new() -> Self {
+        Self {
+            functions: HashMap::new(),
+        }
+    }
+
+    fn push(
+        &mut self,
+        name: SourceAtomSetIndex,
+        owner_scope_index: ScopeIndex,
+        binding_index: BindingIndex,
+        script_index: ScriptStencilIndex,
+    ) {
+        if let Some(functions) = self.functions.get_mut(&name) {
+            functions.push(PossiblyAnnexBFunction {
+                name,
+                owner_scope_index,
+                binding_index,
+                script_index,
+            });
+            return;
+        }
+
+        let mut functions = Vec::with_capacity(1);
+        functions.push(PossiblyAnnexBFunction {
+            name,
+            owner_scope_index,
+            binding_index,
+            script_index,
+        });
+        self.functions.insert(name, functions);
+    }
+
+    fn remove_if_exists(&mut self, name: SourceAtomSetIndex) {
+        self.functions.remove(&name);
+    }
+
+    fn mark_annex_b(&self, function_declaration_properties: &mut FunctionDeclarationPropertyMap) {
+        for functions in &mut self.functions.values() {
+            for fun in functions {
+                function_declaration_properties.mark_annex_b(fun.script_index);
+            }
+        }
+    }
+
+    fn names(&self) -> Keys<SourceAtomSetIndex, Vec<PossiblyAnnexBFunction>> {
+        self.functions.keys()
+    }
+
+    fn clear(&mut self) {
+        self.functions.clear();
+    }
+}
+
+/// Common fields across all *ScopeBuilder.
+#[derive(Debug)]
+struct BaseScopeBuilder {
+    name_tracker: FreeNameTracker,
+
+    /// Bindings in this scope can be accessed dynamically by:
+    ///   * direct `eval`
+    ///   * `with` statement
+    ///   * `delete name` statement
+    bindings_accessed_dynamically: bool,
+}
+
+impl BaseScopeBuilder {
+    fn new() -> Self {
+        Self {
+            name_tracker: FreeNameTracker::new(),
+            bindings_accessed_dynamically: false,
+        }
+    }
+
+    fn propagate_common(&mut self, inner: &BaseScopeBuilder) {
+        // When construct such as `eval`, `with` and `delete` access
+        // name dynamically in inner scopes, we have to propagate this
+        // flag to the outer scope such that we prevent optimizations.
+        self.bindings_accessed_dynamically |= inner.bindings_accessed_dynamically;
+    }
+
+    fn propagate_from_inner_non_script(&mut self, inner: &BaseScopeBuilder) {
+        self.propagate_common(inner);
+        self.name_tracker
+            .propagate_from_inner_non_script(&inner.name_tracker);
+    }
+
+    fn propagate_from_inner_script(&mut self, inner: &BaseScopeBuilder) {
+        self.propagate_common(inner);
+        self.name_tracker
+            .propagate_from_inner_script(&inner.name_tracker);
+    }
+
+    fn declare_var(&mut self, name: SourceAtomSetIndex) {
+        self.name_tracker.note_def(name);
+    }
+
+    fn declare_let(&mut self, name: SourceAtomSetIndex) {
+        self.name_tracker.note_def(name);
+    }
+
+    fn declare_const(&mut self, name: SourceAtomSetIndex) {
+        self.name_tracker.note_def(name);
+    }
+
+    fn declare_function(&mut self, name: SourceAtomSetIndex) {
+        self.name_tracker.note_def(name);
+    }
+
+    fn set_function_name(&mut self, name: SourceAtomSetIndex) {
+        self.name_tracker.note_def(name);
+    }
+
+    fn declare_param(&mut self, name: SourceAtomSetIndex) {
+        self.name_tracker.note_def(name);
+    }
+}
+
+/// Variables declared/used in GlobalDeclarationInstantiation.
+#[derive(Debug)]
+struct GlobalScopeBuilder {
+    base: BaseScopeBuilder,
+
+    /// Runtime Semantics: GlobalDeclarationInstantiation ( script, env )
+    /// https://tc39.es/ecma262/#sec-globaldeclarationinstantiation
+    ///
+    /// Step 8. Let functionsToInitialize be a new empty List.
+    functions_to_initialize: Vec<ScriptStencilIndex>,
+
+    /// Step 9. Let declaredFunctionNames be a new empty List.
+    declared_function_names: IndexSet<SourceAtomSetIndex>,
+
+    /// Step 11. Let declaredVarNames be a new empty List.
+    /// NOTE: This is slightly different than the spec that this can contain
+    ///       names in declaredFunctionNames.
+    ///       The duplication should be filtered before the use.
+    declared_var_names: IndexSet<SourceAtomSetIndex>,
+
+    /// Step 15. Let lexDeclarations be the LexicallyScopedDeclarations of
+    ///          script.
+    let_names: Vec<SourceAtomSetIndex>,
+    const_names: Vec<SourceAtomSetIndex>,
+
+    scope_index: ScopeIndex,
+}
+
+impl GlobalScopeBuilder {
+    fn new(scope_index: ScopeIndex) -> Self {
+        Self {
+            base: BaseScopeBuilder::new(),
+            functions_to_initialize: Vec::new(),
+            declared_function_names: IndexSet::new(),
+            declared_var_names: IndexSet::new(),
+            let_names: Vec::new(),
+            const_names: Vec::new(),
+            scope_index,
+        }
+    }
+
+    fn declare_var(&mut self, name: SourceAtomSetIndex) {
+        // Runtime Semantics: GlobalDeclarationInstantiation ( script, env )
+        // https://tc39.es/ecma262/#sec-globaldeclarationinstantiation
+        //
+        // Step 7. Let varDeclarations be the VarScopedDeclarations of script.
+        //
+        // Step 12. For each d in varDeclarations, do
+        // Step 12.a. If d is a VariableDeclaration, a ForBinding, or a
+        //            BindingIdentifier, then
+        // Step 12.a.i. For each String vn in the BoundNames of d, do
+        // (implicit)
+
+        // Step 12.a.i.i If vn is not an element of declaredFunctionNames, then
+        // (done in remove_function_names_from_var_names)
+
+        // Step 12.a.i.1.a. Let vnDefinable be ? envRec.CanDeclareGlobalVar(vn).
+        // Step 12.a.i.1.b. If vnDefinable is false, throw a TypeError
+        //                  exception.
+        // (done in runtime)
+
+        // Step 12.a.i.1.c. If vn is not an element of declaredVarNames, then
+        // Step 12.a.i.1.a.i. Append vn to declaredVarNames.
+        self.declared_var_names.insert(name);
+        self.base.declare_var(name);
+    }
+
+    fn declare_let(&mut self, name: SourceAtomSetIndex) {
+        // Runtime Semantics: GlobalDeclarationInstantiation ( script, env )
+        // https://tc39.es/ecma262/#sec-globaldeclarationinstantiation
+        //
+        // Step 15. Let lexDeclarations be the LexicallyScopedDeclarations of
+        //          script.
+        self.let_names.push(name);
+        self.base.declare_let(name);
+    }
+
+    fn declare_const(&mut self, name: SourceAtomSetIndex) {
+        // Runtime Semantics: GlobalDeclarationInstantiation ( script, env )
+        // https://tc39.es/ecma262/#sec-globaldeclarationinstantiation
+        //
+        // Step 15. Let lexDeclarations be the LexicallyScopedDeclarations of
+        //          script.
+        self.const_names.push(name);
+        self.base.declare_const(name);
+    }
+
+    fn declare_function(&mut self, name: SourceAtomSetIndex, fun_index: ScriptStencilIndex) {
+        // Runtime Semantics: GlobalDeclarationInstantiation ( script, env )
+        // https://tc39.es/ecma262/#sec-globaldeclarationinstantiation
+        //
+        // Step 10. For each d in varDeclarations, in reverse list order, do
+        // Step 10.a. If d is neither a VariableDeclaration nor a ForBinding
+        //            nor a BindingIdentifier, then
+        // (implicit)
+
+        // Step 10.a.i. Assert: d is either a FunctionDeclaration,
+        //              a GeneratorDeclaration, an AsyncFunctionDeclaration,
+        //              or an AsyncGeneratorDeclaration.
+
+        // Step 10.a.ii. NOTE: If there are multiple function declarations for
+        //               the same name, the last declaration is used.
+
+        // Step 10.a.iii. Let fn be the sole element of the BoundNames of d.
+
+        // Step 10.a.iv. If fn is not an element of declaredFunctionNames, then
+        //
+        // NOTE: Instead of iterating in reverse list oder, we iterate in
+        // normal order and overwrite existing item.
+
+        // Steps 10.a.iv.1. Let fnDefinable be
+        //                  ? envRec.CanDeclareGlobalFunction(fn).
+        // Steps 10.a.iv.2. If fnDefinable is false, throw a TypeError
+        //                  exception.
+        // (done in runtime)
+
+        // Step 10.a.iv.3. Append fn to declaredFunctionNames.
+        self.declared_function_names.insert(name.clone());
+
+        // Step 10.a.iv.4. Insert d as the first element of
+        //                 functionsToInitialize.
+        self.functions_to_initialize.push(fun_index);
+
+        self.base.declare_function(name);
+    }
+
+    fn remove_function_names_from_var_names(&mut self) {
+        // Runtime Semantics: GlobalDeclarationInstantiation ( script, env )
+        // https://tc39.es/ecma262/#sec-globaldeclarationinstantiation
+        //
+        // Step 12.a.i.i If vn is not an element of declaredFunctionNames, then
+        //
+        // To avoid doing 2-pass, we note all var names, and filter function
+        // names out after visiting all of them.
+        for n in &self.declared_function_names {
+            self.declared_var_names.remove(n);
+        }
+    }
+
+    fn perform_annex_b(
+        &mut self,
+        function_declaration_properties: &mut FunctionDeclarationPropertyMap,
+        possibly_annex_b_functions: &mut PossiblyAnnexBFunctionList,
+    ) {
+        // Annex B
+        // Changes to GlobalDeclarationInstantiation
+        // https://tc39.es/ecma262/#sec-web-compat-globaldeclarationinstantiation
+        //
+        // Step 1. Let strict be IsStrict of script.
+        //
+        // FIXME: Once directives are supported, reflect it here.
+        let strict = false;
+
+        // Step 2. If strict is false, then
+        if strict {
+            return;
+        }
+
+        // Step 2.a. Let declaredFunctionOrVarNames be a new empty List.
+        // Step 2.b. Append to declaredFunctionOrVarNames the elements of
+        //           declaredFunctionNames.
+        // Step 2.c. Append to declaredFunctionOrVarNames the elements of
+        //           declaredVarNames.
+        //
+        // NOTE: Use `self.declared_var_names` to avoid duplication against
+        //       `declaredVarNames`.
+        //       And duplication against `declaredFunctionNames` will be
+        //       removed in `remove_function_names_from_var_names`.
+
+        // Step 2.d. For each FunctionDeclaration f that is directly contained
+        //           in the StatementList of a Block, CaseClause, or
+        //           DefaultClause Contained within script, do
+        //
+        // NOTE: `possibly_annex_b_functions` contains all of them.
+
+        // Step 2.d.i. Let F be StringValue of the BindingIdentifier of f.
+        // Step 2.d.ii. If replacing the FunctionDeclaration f with a
+        //              VariableStatement that has F as a BindingIdentifier
+        //              would not produce any Early Errors for script, then
+        //
+        // NOTE: Early Errors happen if any of top-level lexical has
+        //       the same name.  Filter out those functions here.
+        for n in &self.let_names {
+            possibly_annex_b_functions.remove_if_exists(*n);
+        }
+        for n in &self.const_names {
+            possibly_annex_b_functions.remove_if_exists(*n);
+        }
+
+        // Step 2.d.ii.1. If env.HasLexicalDeclaration(F) is false, then
+        // Step 2.d.ii.1.a. Let fnDefinable be ? env.CanDeclareGlobalVar(F).
+        // Step 2.d.ii.1.b. If fnDefinable is true, then
+        //
+        // FIXME: Are these steps performed by any implementation?
+        //        https://github.com/tc39/ecma262/issues/2019
+
+        // Step 2.d.ii.1.b.i. NOTE: A var binding for F is only instantiated
+        //                    here if it is neither a VarDeclaredName nor
+        //                    the name of another FunctionDeclaration.
+        // Step 2.d.ii.1.b.ii. If declaredFunctionOrVarNames does not
+        //                     contain F, then
+        // Step 2.d.ii.1.b.ii.1. Perform
+        //                       ?env.CreateGlobalVarBinding(F, false).
+        // Step 2.d.ii.1.b.ii.2. Append F to declaredFunctionOrVarNames.
+        for n in possibly_annex_b_functions.names() {
+            self.declare_var(*n);
+        }
+
+        // Step 2.d.ii.1.b.iii. When the FunctionDeclaration f is evaluated,
+        //                      perform the following steps in place of the
+        //                      FunctionDeclaration Evaluation algorithm
+        //                      provided in
+        //                      https://tc39.es/ecma262/#sec-function-definitions-runtime-semantics-evaluation :
+        // Step 2.d.ii.1.b.iii.1. Let genv be the running execution
+        //                        context's VariableEnvironment.
+        // Step 2.d.ii.1.b.iii.2. Let benv be the running execution
+        //                        context's LexicalEnvironment.
+        // Step 2.d.ii.1.b.iii.3. Let fobj be
+        //                        ! benv.GetBindingValue(F, false).
+        // Step 2.d.ii.1.b.iii.4. Perform
+        //                        ? genv.SetMutableBinding(F, fobj, false).
+        // Step 2.d.ii.1.b.iii.5. Return NormalCompletion(empty).
+        possibly_annex_b_functions.mark_annex_b(function_declaration_properties);
+    }
+
+    fn into_scope_data(
+        mut self,
+        function_declaration_properties: &mut FunctionDeclarationPropertyMap,
+        possibly_annex_b_functions: &mut PossiblyAnnexBFunctionList,
+    ) -> ScopeData {
+        // Runtime Semantics: GlobalDeclarationInstantiation ( script, env )
+        // https://tc39.es/ecma262/#sec-globaldeclarationinstantiation
+        //
+        // NOTE: Steps are reordered to match the order of binding in runtime.
+
+        // Step 13. NOTE: Annex B adds additional steps at this point.
+        //
+        // NOTE: Reordered here to reflect the change to
+        //       self.declared_var_names.
+        self.perform_annex_b(function_declaration_properties, possibly_annex_b_functions);
+
+        // Step 12.a.i.i If vn is not an element of declaredFunctionNames, then
+        self.remove_function_names_from_var_names();
+
+        let mut data = GlobalScopeData::new(
+            self.declared_var_names.len() + self.declared_function_names.len(),
+            self.let_names.len(),
+            self.const_names.len(),
+            self.functions_to_initialize,
+        );
+
+        // Step 18. For each String vn in declaredVarNames, in list order, do
+        for n in &self.declared_var_names {
+            // 18.a. Perform ? envRec.CreateGlobalVarBinding(vn, false).
+            let is_closed_over = self.base.name_tracker.is_closed_over_def(n);
+            data.base
+                .bindings
+                .push(BindingName::new(*n, is_closed_over))
+        }
+
+        // Step 17. For each Parse Node f in functionsToInitialize, do
+        for n in &self.declared_function_names {
+            // Step 17.a. Let fn be the sole element of the BoundNames of f.
+            // Step 17.b. Let fo be InstantiateFunctionObject of f with
+            //            argument env.
+            // Step 17.c. Perform
+            //            ? envRec.CreateGlobalFunctionBinding(fn, fo, false).
+            let is_closed_over = self.base.name_tracker.is_closed_over_def(n);
+            data.base
+                .bindings
+                .push(BindingName::new_top_level_function(*n, is_closed_over));
+        }
+
+        // Step 15. Let lexDeclarations be the LexicallyScopedDeclarations of
+        //          script.
+        // Step 16. For each element d in lexDeclarations, do
+        // Step 16.b. For each element dn of the BoundNames of d, do
+        for n in &self.let_names {
+            // Step 16.b.ii. Else,
+            // Step 16.b.ii.1. Perform ? envRec.CreateMutableBinding(dn, false).
+            let is_closed_over = self.base.name_tracker.is_closed_over_def(n);
+            data.base
+                .bindings
+                .push(BindingName::new(*n, is_closed_over))
+        }
+        for n in &self.const_names {
+            // Step 16.b.i. If IsConstantDeclaration of d is true, then
+            // Step 16.b.i.1. Perform ? envRec.CreateImmutableBinding(dn, true).
+            let is_closed_over = self.base.name_tracker.is_closed_over_def(n);
+            data.base
+                .bindings
+                .push(BindingName::new(*n, is_closed_over))
+        }
+
+        ScopeData::Global(data)
+    }
+}
+
+#[derive(Debug)]
+struct FunctionNameAndStencilIndex {
+    name: SourceAtomSetIndex,
+    stencil: ScriptStencilIndex,
+}
+
+/// Variables declared/used in BlockDeclarationInstantiation
+#[derive(Debug)]
+struct BlockScopeBuilder {
+    base: BaseScopeBuilder,
+
+    /// Runtime Semantics: BlockDeclarationInstantiation ( code, env )
+    /// https://tc39.es/ecma262/#sec-blockdeclarationinstantiation
+    ///
+    /// Step 3. Let declarations be the LexicallyScopedDeclarations of code.
+    let_names: Vec<SourceAtomSetIndex>,
+    const_names: Vec<SourceAtomSetIndex>,
+
+    /// Runtime Semantics: BlockDeclarationInstantiation ( code, env )
+    /// https://tc39.es/ecma262/#sec-blockdeclarationinstantiation
+    ///
+    /// Step 4.b. If d is a FunctionDeclaration, a GeneratorDeclaration, an
+    ///           AsyncFunctionDeclaration, or an AsyncGeneratorDeclaration,
+    ///           then
+    functions: Vec<FunctionNameAndStencilIndex>,
+
+    /// Scope associated to this builder.
+    scope_index: ScopeIndex,
+}
+
+impl BlockScopeBuilder {
+    fn new(scope_index: ScopeIndex) -> Self {
+        Self {
+            base: BaseScopeBuilder::new(),
+            let_names: Vec::new(),
+            const_names: Vec::new(),
+            functions: Vec::new(),
+            scope_index,
+        }
+    }
+
+    fn declare_let(&mut self, name: SourceAtomSetIndex) {
+        // Runtime Semantics: BlockDeclarationInstantiation ( code, env )
+        // https://tc39.es/ecma262/#sec-blockdeclarationinstantiation
+        //
+        // Step 3. Let declarations be the LexicallyScopedDeclarations of code.
+        self.let_names.push(name);
+        self.base.declare_let(name);
+    }
+
+    fn declare_const(&mut self, name: SourceAtomSetIndex) {
+        // Runtime Semantics: BlockDeclarationInstantiation ( code, env )
+        // https://tc39.es/ecma262/#sec-blockdeclarationinstantiation
+        //
+        // Step 3. Let declarations be the LexicallyScopedDeclarations of code.
+        self.const_names.push(name);
+        self.base.declare_const(name);
+    }
+
+    fn declare_function(&mut self, name: SourceAtomSetIndex, fun_index: ScriptStencilIndex) {
+        // Runtime Semantics: BlockDeclarationInstantiation ( code, env )
+        // https://tc39.es/ecma262/#sec-blockdeclarationinstantiation
+        //
+        // Step 3. Let declarations be the LexicallyScopedDeclarations of code.
+        //
+        // Step 4.b. If d is a FunctionDeclaration, a GeneratorDeclaration, an
+        //           AsyncFunctionDeclaration, or an AsyncGeneratorDeclaration,
+        //           then
+        self.functions.push(FunctionNameAndStencilIndex {
+            name,
+            stencil: fun_index,
+        });
+
+        self.base.declare_function(name);
+    }
+
+    fn into_scope_data(
+        self,
+        enclosing: ScopeIndex,
+        possibly_annex_b_functions: &mut PossiblyAnnexBFunctionList,
+    ) -> ScopeData {
+        let mut data = LexicalScopeData::new_block(
+            self.let_names.len() + self.functions.len(),
+            self.const_names.len(),
+            enclosing,
+            self.functions.iter().map(|n| n.stencil).collect(),
+        );
+
+        // Runtime Semantics: BlockDeclarationInstantiation ( code, env )
+        // https://tc39.es/ecma262/#sec-blockdeclarationinstantiation
+        //
+        // Step 1. Let envRec be env's EnvironmentRecord.
+        // Step 2. Assert: envRec is a declarative Environment Record.
+        // (implicit)
+
+        // Step 4. For each element d in declarations, do
+        // Step 4.a. For each element dn of the BoundNames of d, do
+        for n in &self.let_names {
+            // Step 4.a.ii. Else,
+            // Step 4.a.ii.1. Perform ! envRec.CreateMutableBinding(dn, false).
+            let is_closed_over = self.base.name_tracker.is_closed_over_def(n);
+            data.base
+                .bindings
+                .push(BindingName::new(*n, is_closed_over));
+        }
+        for n in &self.functions {
+            // Step 4.b. If d is a FunctionDeclaration, a GeneratorDeclaration,
+            //           an AsyncFunctionDeclaration,
+            //           or an AsyncGeneratorDeclaration, then
+            // Step 4.b.i. Let fn be the sole element of the BoundNames of d.
+            // Step 4.b.ii. Let fo be InstantiateFunctionObject of d with
+            //              argument env.
+            // Step 4.b.iii. Perform envRec.InitializeBinding(fn, fo).
+            let is_closed_over = self.base.name_tracker.is_closed_over_def(&n.name);
+            let binding_index = BindingIndex::new(data.base.bindings.len());
+            data.base
+                .bindings
+                .push(BindingName::new(n.name, is_closed_over));
+
+            possibly_annex_b_functions.push(n.name, self.scope_index, binding_index, n.stencil);
+        }
+        for n in &self.const_names {
+            // Step 4.a.i. If IsConstantDeclaration of d is true, then
+            // Step 4.a.i.1. Perform ! envRec.CreateImmutableBinding(dn, true).
+            let is_closed_over = self.base.name_tracker.is_closed_over_def(n);
+            data.base
+                .bindings
+                .push(BindingName::new(*n, is_closed_over));
+        }
+
+        ScopeData::Lexical(data)
+    }
+}
+
+/// Scope for a FunctionExpression.
+///
+/// The FunctionExpression `(function f() { return f; })` introduces a lexical
+/// scope with a single binding `f`, set to the function itself. We create this
+/// scope builder whether the FunctionExpression has a name or not, for
+/// consistency.
+#[derive(Debug)]
+struct FunctionExpressionScopeBuilder {
+    base: BaseScopeBuilder,
+
+    function_expression_name: Option<SourceAtomSetIndex>,
+
+    scope_index: ScopeIndex,
+}
+
+impl FunctionExpressionScopeBuilder {
+    fn new(scope_index: ScopeIndex) -> Self {
+        Self {
+            base: BaseScopeBuilder::new(),
+            function_expression_name: None,
+            scope_index,
+        }
+    }
+
+    fn set_function_name(&mut self, name: SourceAtomSetIndex) {
+        self.function_expression_name = Some(name);
+        self.base.set_function_name(name);
+    }
+
+    fn into_scope_data(self, enclosing: ScopeIndex) -> ScopeData {
+        match &self.function_expression_name {
+            Some(name) => {
+                // Runtime Semantics: Evaluation
+                // https://tc39.es/ecma262/#sec-function-definitions-runtime-semantics-evaluation
+                //
+                // FunctionExpression :
+                //   function BindingIdentifier ( FormalParameters )
+                //   { FunctionBody }
+                //
+                // Step 1. Let scope be the running execution context's
+                //         LexicalEnvironment.
+                // Step 2. Let funcEnv be NewDeclarativeEnvironment(scope).
+                // Step 3. Let envRec be funcEnv's EnvironmentRecord.
+                let mut data = LexicalScopeData::new_named_lambda(enclosing);
+
+                // Step 4. Let name be StringValue of BindingIdentifier .
+                // Step 5. Perform envRec.CreateImmutableBinding(name, false).
+                let is_closed_over = self.base.name_tracker.is_closed_over_def(name);
+                data.base
+                    .bindings
+                    .push(BindingName::new(*name, is_closed_over));
+
+                ScopeData::Lexical(data)
+            }
+            None => ScopeData::Alias(enclosing),
+        }
+    }
+}
+
+/// The value of [[ThisMode]] internal slot of function object.
+/// https://tc39.es/ecma262/#sec-ecmascript-function-objects
+///
+/// Defines how this references are interpreted within the formal parameters
+/// and code body of the function.
+#[derive(Debug, Clone, PartialEq)]
+enum ThisMode {
+    /// `this` refers to the `this` value of a lexically enclosing function.
+    Lexical,
+
+    /// `this` value is used exactly as provided by an invocation of the
+    /// function.
+    #[allow(dead_code)]
+    Strict,
+
+    /// `this` value of `undefined` is interpreted as a reference to the global
+    /// object.
+    Global,
+}
+
+/// The result of converting the builder of function parameters and body
+/// into scope data.
+struct FunctionScopeDataSet {
+    /// ScopeData::Function.
+    function: ScopeData,
+
+    /// Either ScopeData::Var or ScopeData::Alias.
+    extra_body_var: ScopeData,
+
+    /// Either ScopeData::Lexical or ScopeData::Alias.
+    lexical: ScopeData,
+}
+
+/// See FunctionParametersScopeBuilder.state.
+#[derive(Debug)]
+enum FunctionParametersState {
+    /// Entered FormalParameters.
+    Init,
+
+    /// Entered Parameter.
+    /// At this point, this parameter can be either non-destructuring or
+    /// destructuring.
+    /// If BindingIdentifier is found in this state, this parameter is
+    /// non-destructuring.
+    Parameter,
+
+    /// Entered BindingPattern inside Parameter.
+    /// This parameter is destructuring.
+    DestructuringParameter,
+
+    /// Entered rest parameter.
+    /// At this point, the rest parameter can be either non-destructuring or
+    /// destructuring.
+    /// If BindingIdentifier is found in this state, the rest parameter is
+    /// non-destructuring.
+    RestParameter,
+
+    /// Entered BindingPattern inside rest parameter.
+    /// The rest parameter is destructuring.
+    DestructuringRestParameter,
+}
+
+/// Function parameters in FormalParameters, and variables used in
+/// FormalParameters
+/// Shared part between full-parse and syntax-only parse.
+#[derive(Debug)]
+struct SharedFunctionParametersScopeBuilder {
+    base: BaseScopeBuilder,
+
+    /// FunctionDeclarationInstantiation ( func, argumentsList )
+    /// https://tc39.es/ecma262/#sec-functiondeclarationinstantiation
+    ///
+    /// Step 3. Let strict be func.[[Strict]].
+    strict: bool,
+
+    /// Step 5. Let parameterNames be the BoundNames of formals.
+    parameter_names: HashSet<SourceAtomSetIndex>,
+
+    /// Step 7. Let simpleParameterList be IsSimpleParameterList of formals.
+    simple_parameter_list: bool,
+
+    /// Step 8. Let hasParameterExpressions be ContainsExpression of formals.
+    has_parameter_expressions: bool,
+
+    /// Step 17. Else if "arguments" is an element of parameterNames, then
+    parameter_has_arguments: bool,
+}
+
+impl SharedFunctionParametersScopeBuilder {
+    fn new(is_arrow: bool) -> Self {
+        let mut base = BaseScopeBuilder::new();
+
+        if !is_arrow {
+            // Arrow function closes over this/arguments from enclosing
+            // function.
+            base.name_tracker
+                .note_def(CommonSourceAtomSetIndices::this());
+            base.name_tracker
+                .note_def(CommonSourceAtomSetIndices::arguments());
+        }
+
+        Self {
+            base,
+
+            // FIMXE: Receive the enclosing strictness,
+            //        and update on directive in body.
+            strict: false,
+
+            parameter_names: HashSet::new(),
+            simple_parameter_list: true,
+            has_parameter_expressions: false,
+            parameter_has_arguments: false,
+        }
+    }
+
+    fn perform_annex_b(
+        &self,
+        function_declaration_properties: &mut FunctionDeclarationPropertyMap,
+        possibly_annex_b_functions: &mut PossiblyAnnexBFunctionList,
+        body_scope_builder: &mut SharedFunctionBodyScopeBuilder,
+    ) {
+        // Annex B
+        // Changes to FunctionDeclarationInstantiation
+        // https://tc39.es/ecma262/#sec-web-compat-functiondeclarationinstantiation
+        //
+        // Step 1. If strict is false, then
+        //
+        // FIXME: Once directives are supported, reflect it here.
+        let strict = false;
+        if strict {
+            return;
+        }
+
+        // Step 1.a. For each FunctionDeclaration f that is directly contained
+        //           in the StatementList of a Block, CaseClause, or
+        //           DefaultClause, do
+        //
+        // NOTE: `possibly_annex_b_functions` contains all of them.
+
+        // Step 1.a.i. Let F be StringValue of the BindingIdentifier of f.
+        // Step 1.a.ii. If replacing the FunctionDeclaration f with a
+        //              VariableStatement that has F as a BindingIdentifier
+        //              would not produce any Early Errors for func and F is
+        //              not an element of parameterNames, then
+        //
+        // NOTE: Early Errors happen if any of top-level lexical has
+        //       the same name.  Filter out those functions here.
+        for n in &body_scope_builder.let_names {
+            possibly_annex_b_functions.remove_if_exists(*n);
+        }
+        for n in &body_scope_builder.const_names {
+            possibly_annex_b_functions.remove_if_exists(*n);
+        }
+        for n in &self.parameter_names {
+            possibly_annex_b_functions.remove_if_exists(*n);
+        }
+
+        // Step 1.a.ii.1. NOTE: A var binding for F is only instantiated here
+        //                if it is neither a VarDeclaredName, the name of a
+        //                formal parameter, or another FunctionDeclaration.
+        //
+        // NOTE: The binding is merged into the list of other var names.
+
+        // Step 1.a.ii.2. If initializedBindings does not contain F and F is
+        //                not "arguments", then
+        possibly_annex_b_functions.remove_if_exists(CommonSourceAtomSetIndices::arguments());
+
+        // Step 1.a.ii.2.a. Perform ! varEnv.CreateMutableBinding(F, false).
+        // Step 1.a.ii.2.b. Perform varEnv.InitializeBinding(F, undefined).
+        // Step 1.a.ii.2.c. Append F to instantiatedVarNames.
+        for n in possibly_annex_b_functions.names() {
+            body_scope_builder.declare_var(*n);
+        }
+
+        // Step 1.a.ii.3. When the FunctionDeclaration f is evaluated, perform
+        //                the following steps in place of the
+        //                FunctionDeclaration Evaluation algorithm provided in
+        //                https://tc39.es/ecma262/#sec-function-definitions-runtime-semantics-evaluation
+        // Step 1.a.ii.3.a. Let fenv be the running execution context's
+        //                  VariableEnvironment.
+        // Step 1.a.ii.3.b. Let benv be the running execution context's
+        //                  LexicalEnvironment.
+        // Step 1.a.ii.3.c. Let fobj be ! benv.GetBindingValue(F, false).
+        // Step 1.a.ii.3.d. Perform ! fenv.SetMutableBinding(F, fobj, false).
+        // Step 1.a.ii.3.e. Return NormalCompletion(empty).
+        possibly_annex_b_functions.mark_annex_b(function_declaration_properties);
+    }
+
+    fn before_binding_pattern(&mut self) {
+        // Static Semantics: IsSimpleParameterList
+        // https://tc39.es/ecma262/#sec-destructuring-binding-patterns-static-semantics-issimpleparameterlist
+        //
+        // BindingElement : BindingPattern
+        //
+        //   1. Return false.
+        //
+        // BindingElement : BindingPattern Initializer
+        //
+        //   1. Return false.
+        self.simple_parameter_list = false;
+    }
+
+    fn before_rest_parameter(&mut self) {
+        // Static Semantics: IsSimpleParameterList
+        // https://tc39.es/ecma262/#sec-function-definitions-static-semantics-issimpleparameterlist
+        //
+        // FormalParameters : FunctionRestParameter
+        //
+        //   1. Return false.
+        //
+        // FormalParameters : FormalParameterList , FunctionRestParameter
+        //
+        //   1. Return false.
+        self.simple_parameter_list = false;
+    }
+
+    fn after_initializer(&mut self) {
+        // Static Semantics: IsSimpleParameterList
+        // https://tc39.es/ecma262/#sec-destructuring-binding-patterns-static-semantics-issimpleparameterlist
+        //
+        // BindingElement : BindingPattern Initializer
+        //
+        //   1. Return false.
+        //
+        // SingleNameBinding : BindingIdentifier Initializer
+        //
+        //   1. Return false.
+        self.simple_parameter_list = false;
+
+        // FunctionDeclarationInstantiation ( func, argumentsList )
+        // https://tc39.es/ecma262/#sec-functiondeclarationinstantiation
+        //
+        // Step 8. Let hasParameterExpressions be ContainsExpression of formals.
+
+        // Static Semantics: ContainsExpression
+        // https://tc39.es/ecma262/#sec-destructuring-binding-patterns-static-semantics-containsexpression
+        //
+        // BindingElement : BindingPattern Initializer
+        //
+        //   1. Return true.
+        //
+        // SingleNameBinding : BindingIdentifier Initializer
+        //
+        //   1. Return true.
+        self.has_parameter_expressions = true;
+    }
+
+    fn before_computed_property_name(&mut self) {
+        // FunctionDeclarationInstantiation ( func, argumentsList )
+        // https://tc39.es/ecma262/#sec-functiondeclarationinstantiation
+        //
+        // Step 8. Let hasParameterExpressions be ContainsExpression of formals.
+
+        // Static Semantics: ContainsExpression
+        // https://tc39.es/ecma262/#sec-destructuring-binding-patterns-static-semantics-containsexpression
+        //
+        // BindingProperty : PropertyName : BindingElement
+        //
+        //   1. Let has be IsComputedPropertyKey of PropertyName .
+        //   2. If has is true, return true.
+        //   3. Return ContainsExpression of BindingElement .
+        self.has_parameter_expressions = true;
+    }
+
+    fn declare_param(&mut self, name: SourceAtomSetIndex) {
+        // Step 17. Else if "arguments" is an element of parameterNames,
+        //          then
+        if name == CommonSourceAtomSetIndices::arguments() {
+            self.parameter_has_arguments = true;
+        }
+
+        self.parameter_names.insert(name.clone());
+        self.base.declare_param(name);
+    }
+
+    fn is_parameter_closed_over(&self) -> bool {
+        for name in &self.parameter_names {
+            if self.base.name_tracker.is_closed_over_def(name) {
+                return true;
+            }
+        }
+
+        false
+    }
+}
+
+/// Function parameters in FormalParameters, and variables used in
+/// FormalParameters
+/// For full-parse.
+#[derive(Debug)]
+struct FunctionParametersScopeBuilder {
+    shared: SharedFunctionParametersScopeBuilder,
+
+    /// State of the analysis.
+    /// This is used to determine what kind of binding the parameter is.
+    state: FunctionParametersState,
+
+    /// List of positional parameter or None if destructuring.
+    /// This includes rest parameter.
+    positional_parameter_names: Vec<Option<SourceAtomSetIndex>>,
+
+    /// List of non-positional parameters (destructuring parameters).
+    non_positional_parameter_names: Vec<SourceAtomSetIndex>,
+
+    /// FunctionDeclarationInstantiation ( func, argumentsList )
+    /// https://tc39.es/ecma262/#sec-functiondeclarationinstantiation
+    ///
+    /// Step 16. If func.[[ThisMode]] is lexical, then
+    this_mode: ThisMode,
+
+    /// Step 6. If parameterNames has any duplicate entries, let hasDuplicates
+    ///         be true. Otherwise, let hasDuplicates be false.
+    has_duplicates: bool,
+
+    scope_index: ScopeIndex,
+
+    /// Index of the script in the list of `functions` in the
+    /// `FunctionScriptStencilBuilder`.
+    script_index: ScriptStencilIndex,
+
+    has_direct_eval: bool,
+
+    is_arrow: bool,
+}
+
+impl FunctionParametersScopeBuilder {
+    fn new(scope_index: ScopeIndex, is_arrow: bool, script_index: ScriptStencilIndex) -> Self {
+        Self {
+            shared: SharedFunctionParametersScopeBuilder::new(is_arrow),
+
+            state: FunctionParametersState::Init,
+
+            positional_parameter_names: Vec::new(),
+            non_positional_parameter_names: Vec::new(),
+
+            // FIXME: Receive correct value.
+            this_mode: ThisMode::Global,
+
+            has_duplicates: false,
+            scope_index,
+            script_index,
+            has_direct_eval: false,
+            is_arrow,
+        }
+    }
+
+    fn before_parameter(&mut self) {
+        match self.state {
+            FunctionParametersState::Init => {
+                self.state = FunctionParametersState::Parameter;
+            }
+            FunctionParametersState::Parameter => {
+                self.state = FunctionParametersState::Parameter;
+            }
+            FunctionParametersState::DestructuringParameter => {
+                self.state = FunctionParametersState::Parameter;
+            }
+            FunctionParametersState::RestParameter
+            | FunctionParametersState::DestructuringRestParameter => panic!("Invalid transition"),
+        }
+    }
+
+    fn before_binding_pattern(&mut self) {
+        self.shared.before_binding_pattern();
+
+        match self.state {
+            FunctionParametersState::Parameter => {
+                self.positional_parameter_names.push(None);
+                self.state = FunctionParametersState::DestructuringParameter;
+            }
+            FunctionParametersState::DestructuringParameter => {}
+            FunctionParametersState::RestParameter => {
+                self.positional_parameter_names.push(None);
+                self.state = FunctionParametersState::DestructuringRestParameter;
+            }
+            FunctionParametersState::DestructuringRestParameter => {}
+            FunctionParametersState::Init => panic!("Invalid transition"),
+        }
+    }
+
+    fn before_rest_parameter(&mut self) {
+        self.shared.before_rest_parameter();
+
+        match self.state {
+            FunctionParametersState::Init
+            | FunctionParametersState::Parameter
+            | FunctionParametersState::DestructuringParameter => {
+                self.state = FunctionParametersState::RestParameter;
+            }
+            FunctionParametersState::RestParameter
+            | FunctionParametersState::DestructuringRestParameter => panic!("Invalid transition"),
+        }
+    }
+
+    fn after_initializer(&mut self) {
+        self.shared.after_initializer();
+    }
+
+    fn before_computed_property_name(&mut self) {
+        self.shared.before_computed_property_name();
+    }
+
+    fn declare_param(&mut self, name: SourceAtomSetIndex) {
+        // FunctionDeclarationInstantiation ( func, argumentsList )
+        // https://tc39.es/ecma262/#sec-functiondeclarationinstantiation
+        //
+        // Step 5. Let parameterNames be the BoundNames of formals.
+        match self.state {
+            FunctionParametersState::Init => panic!("Invalid state"),
+            FunctionParametersState::Parameter => {
+                self.positional_parameter_names.push(Some(name.clone()));
+            }
+            FunctionParametersState::DestructuringParameter => {
+                self.non_positional_parameter_names.push(name.clone());
+            }
+            FunctionParametersState::RestParameter => {
+                self.positional_parameter_names.push(Some(name.clone()));
+            }
+            FunctionParametersState::DestructuringRestParameter => {
+                self.non_positional_parameter_names.push(name.clone());
+            }
+        }
+
+        // Step 6. If parameterNames has any duplicate entries, let
+        //         hasDuplicates be true. Otherwise, let hasDuplicates be
+        //         false.
+        if self.shared.parameter_names.contains(&name) {
+            self.has_duplicates = true;
+        }
+
+        self.shared.declare_param(name);
+    }
+
+    fn into_scope_data_set(
+        self,
+        enclosing: ScopeIndex,
+        body_scope_builder: FunctionBodyScopeBuilder,
+    ) -> FunctionScopeDataSet {
+        // FunctionDeclarationInstantiation ( func, argumentsList )
+        // https://tc39.es/ecma262/#sec-functiondeclarationinstantiation
+        //
+        // Step 15. Let argumentsObjectNeeded be true.
+        let mut arguments_object_needed = true;
+
+        // Step 16. If func.[[ThisMode]] is lexical, then
+        if self.this_mode == ThisMode::Lexical {
+            // Step 16.a. NOTE: Arrow functions never have an arguments objects.
+            // Step 16.b. Set argumentsObjectNeeded to false.
+            arguments_object_needed = false;
+        }
+        // Step 17. Else if "arguments" is an element of parameterNames,
+        //          then
+        else if self.shared.parameter_has_arguments {
+            // Step 17.a. Set argumentsObjectNeeded to false.
+            arguments_object_needed = false;
+        }
+        // Step 18. Else if hasParameterExpressions is false, then
+        else if !self.shared.parameter_has_arguments {
+            // Step 18.a. If "arguments" is an element of functionNames or if
+            //            "arguments" is
+            //            an element of lexicalNames, then
+            if body_scope_builder.shared.function_or_lexical_has_arguments {
+                // Step 18.a.i. Set argumentsObjectNeeded to false.
+                arguments_object_needed = false;
+            }
+        }
+
+        // NOTE: In SpiderMonkey, single environment can have multiple
+        //       binding kind.
+        //       It's not necessary to create yet another environment here.
+        //
+        // Step 19. If strict is true or if hasParameterExpressions is false,
+        //          then
+        if self.shared.strict || !self.shared.has_parameter_expressions {
+            // Step 19.a. NOTE: Only a single lexical environment is needed for
+            //            the parameters and top-level vars.
+            // Step 19.b. Let env be the LexicalEnvironment of calleeContext.
+            // Step 19.c. Let envRec be env's EnvironmentRecord.
+        }
+        // Step 20. Else,
+        else {
+            // Step 20.a. NOTE: A separate Environment Record is needed to
+            //            ensure that bindings created by direct eval calls in
+            //            the formal parameter list are outside the environment
+            //            where parameters are declared.
+            // Step 20.b. Let calleeEnv be the LexicalEnvironment of
+            //            calleeContext.
+            // Step 20.c. Let env be NewDeclarativeEnvironment(calleeEnv).
+            // Step 20.d. Let envRec be env's EnvironmentRecord.
+            // Step 20.e. Assert: The VariableEnvironment of calleeContext is
+            //            calleeEnv.
+            // Step 20.f. Set the LexicalEnvironment of calleeContext to env.
+        }
+
+        let has_extra_body_var_scope = self.shared.has_parameter_expressions;
+
+        // NOTE: Names in `body_scope_builder.var_names` is skipped if
+        //       it's `arguments`, at step 27.c.i.
+        //       The count here isn't the exact number of var bindings, but
+        //       it's fine given FunctionScopeData::new doesn't require the
+        //       exact number, but just maximum number.
+        let function_max_var_names_count = if has_extra_body_var_scope {
+            0
+        } else {
+            body_scope_builder.shared.var_names.len()
+        };
+
+        let mut function_scope_data = FunctionScopeData::new(
+            self.shared.has_parameter_expressions,
+            self.positional_parameter_names.len(),
+            self.non_positional_parameter_names.len(),
+            function_max_var_names_count,
+            enclosing,
+            self.script_index,
+            self.is_arrow,
+        );
+
+        // FunctionDeclarationInstantiation ( func, argumentsList )
+        // https://tc39.es/ecma262/#sec-functiondeclarationinstantiation
+        //
+        // Step 21. For each String paramName in parameterNames, do
+        // Step 21.a. Let alreadyDeclared be envRec.HasBinding(paramName).
+        // Step 21.b. NOTE: Early errors ensure that duplicate parameter names
+        //            can only occur in non-strict functions that do not have
+        //            parameter default values or rest parameters.
+        // Step 21.c. If alreadyDeclared is false, then
+        // Step 21.c.i. Perform ! envRec.CreateMutableBinding(paramName, false).
+        // Step 21.c.ii. If hasDuplicates is true, then
+        // Step 21.c.ii.1. Perform
+        //                 ! envRec.InitializeBinding(paramName, undefined).
+        //
+        // NOTE: The existence of duplication isn't encoded in scope data.
+        for maybe_name in &self.positional_parameter_names {
+            match maybe_name {
+                Some(n) => {
+                    let is_closed_over = self.shared.base.name_tracker.is_closed_over_def(n)
+                        || (!has_extra_body_var_scope
+                            && body_scope_builder
+                                .shared
+                                .base
+                                .name_tracker
+                                .is_closed_over_def(n));
+                    function_scope_data
+                        .base
+                        .bindings
+                        .push(Some(BindingName::new(*n, is_closed_over)))
+                }
+                None => function_scope_data.base.bindings.push(None),
+            }
+        }
+        for n in &self.non_positional_parameter_names {
+            let is_closed_over = self.shared.base.name_tracker.is_closed_over_def(n)
+                || (!has_extra_body_var_scope
+                    && body_scope_builder
+                        .shared
+                        .base
+                        .name_tracker
+                        .is_closed_over_def(n));
+            function_scope_data
+                .base
+                .bindings
+                .push(Some(BindingName::new(*n, is_closed_over)))
+        }
+
+        // Step 22. If argumentsObjectNeeded is true, then
+        // Steps 22.a-b. Create{Unm,M}appedArgumentsObject
+        // (done in emitter)
+
+        // Step 22.c. If strict is true, then
+        // Step 22.c.i. Perform
+        //              ! envRec.CreateImmutableBinding("arguments", false).
+        // Step 22.d. Else,
+        // Step 22.d.i. Perform
+        //              ! envRec.CreateMutableBinding("arguments", false).
+        // Step 22.e. Call envRec.InitializeBinding("arguments", ao).
+        //
+        // NOTE: In SpiderMonkey, whether immutable or not is not stored
+        //       in scope data, but checked while parsing, including
+        //       when parsing eval inside function.
+
+        // Step 22.f. Let parameterBindings be a new List of parameterNames
+        //            with "arguments" appended.
+        //
+        // NOTE: Done in each consumer of parameterNames.
+
+        // Step 23. Else,
+        // Step 23.a. Let parameterBindings be parameterNames.
+        //
+        // NOTE: Done in each consumer of parameterNames.
+
+        // Steps 24-26. IteratorBindingInitialization
+        // (done in emitter)
+
+        // Step 27. If hasParameterExpressions is false, then
+        let extra_body_var_scope_data = if !self.shared.has_parameter_expressions {
+            debug_assert!(!has_extra_body_var_scope);
+
+            // Step 27.a. NOTE: Only a single lexical environment is needed for
+            //            the parameters and top-level vars.
+
+            // Step 27.b. Let instantiatedVarNames be a copy of the List
+            //            parameterBindings.
+
+            // Step 27.c. For each n in varNames, do
+            for n in &body_scope_builder.shared.var_names {
+                // Step 27.c.i. If n is not an element of instantiatedVarNames,
+                //              then
+                // Step 27.c.i.1. Append n to instantiatedVarNames.
+                //
+                // NOTE: var_names is already unique.
+                //       Check against parameters and `arguments` here.
+                if self.shared.parameter_names.contains(n)
+                    || (arguments_object_needed && *n == CommonSourceAtomSetIndices::arguments())
+                {
+                    continue;
+                }
+
+                // Step 27.c.i.2. Perform
+                //                ! envRec.CreateMutableBinding(n, false).
+                let is_closed_over = body_scope_builder
+                    .shared
+                    .base
+                    .name_tracker
+                    .is_closed_over_def(n);
+                function_scope_data
+                    .base
+                    .bindings
+                    .push(Some(BindingName::new(*n, is_closed_over)));
+
+                // Step 27.c.i.3. Call envRec.InitializeBinding(n, undefined).
+                // (done in runtime)
+            }
+
+            // Step 27.d. Let varEnv be env.
+            // Step 27.e. Let varEnvRec be envRec.
+            ScopeData::Alias(self.scope_index)
+        }
+        // Step 28. Else,
+        else {
+            debug_assert!(has_extra_body_var_scope);
+
+            // In non-strict mode code, direct `eval` can extend function's
+            // scope.
+            let function_has_extensible_scope = !self.shared.strict && self.has_direct_eval;
+
+            // Step 28.a. NOTE: A separate Environment Record is needed to
+            //            ensure that closures created by expressions in the
+            //            formal parameter list do not have visibility of
+            //            declarations in the function body.
+
+            // Step 28.b. Let varEnv be NewDeclarativeEnvironment(env).
+            // Step 28.c. Set the VariableEnvironment of calleeContext to
+            //            varEnv.
+            let mut data = VarScopeData::new(
+                body_scope_builder.shared.var_names.len(),
+                function_has_extensible_scope,
+                /* encloding= */ self.scope_index,
+            );
+
+            // Step 28.d. Let instantiatedVarNames be a new empty List.
+
+            // Step 28.e. For each n in varNames, do
+            for n in &body_scope_builder.shared.var_names {
+                // Step 28.e.i. If n is not an element of instantiatedVarNames, then
+                // Step 28.e.i.1. Append n to instantiatedVarNames.
+                //
+                // NOTE: var_names is already unique.
+
+                // Step 28.e.i.2. Perform
+                //                ! varEnv.CreateMutableBinding(n, false).
+                let is_closed_over = body_scope_builder
+                    .shared
+                    .base
+                    .name_tracker
+                    .is_closed_over_def(n);
+                data.base
+                    .bindings
+                    .push(BindingName::new(*n, is_closed_over));
+
+                // Step 28.e.i.3. If n is not an element of parameterBindings or if
+                //                n is an element of functionNames, let
+                //                initialValue be undefined.
+                // Step 28.e.i.4. Else,
+                // Step 28.e.i.4.a. Let initialValue be
+                //                  ! env.GetBindingValue(n, false).
+                // Step 28.e.i.5. Call varEnv.InitializeBinding(n, initialValue).
+                // (done in emitter)
+
+                // Step 28.e.i.6. NOTE: A var with the same name as a formal
+                //                parameter initially has the same value as the
+                //                corresponding initialized parameter.
+            }
+
+            ScopeData::Var(data)
+        };
+
+        // Step 30. If strict is false, then
+        // Step 30.a. Let lexEnv be NewDeclarativeEnvironment(varEnv).
+        // Step 30.b. NOTE: Non-strict functions use a separate lexical
+        //            Environment Record for top-level lexical declarations so
+        //            that a direct eval can determine whether any var scoped
+        //            declarations introduced by the eval code conflict with
+        //            pre-existing top-level lexically scoped declarations.
+        //            This is not needed for strict functions because a strict
+        //            direct eval always places all declarations into a new
+        //            Environment Record.
+        // Step 31. Else, let lexEnv be varEnv.
+        // Step 32. Let lexEnvRec be lexEnv's EnvironmentRecord.
+        //
+        // NOTE: SpiderMonkey creates lexical env whenever lexical binding
+        //       exists.
+
+        let lexical_scope_data = if body_scope_builder.shared.let_names.len() > 0
+            || body_scope_builder.shared.const_names.len() > 0
+        {
+            let mut data = LexicalScopeData::new_function_lexical(
+                body_scope_builder.shared.let_names.len(),
+                body_scope_builder.shared.const_names.len(),
+                /* encloding= */ body_scope_builder.var_scope_index,
+            );
+
+            // Step 33. Set the LexicalEnvironment of calleeContext to lexEnv.
+            // Step 34. Let lexDeclarations be the LexicallyScopedDeclarations
+            //          of code.
+            // Step 35. For each element d in lexDeclarations, do
+            // Step 35.a. NOTE: A lexically declared name cannot be the same as
+            //            a function/generator declaration, formal parameter,
+            //            or a var name. Lexically declared names are only
+            //            instantiated here but not initialized.
+            // Step 35.b. For each element dn of the BoundNames of d, do
+
+            for n in &body_scope_builder.shared.let_names {
+                // Step 35.b.ii. Else,
+                // Step 35.b.ii.1. Perform
+                //                 ! lexEnvRec.CreateMutableBinding(dn, false).
+                let is_closed_over = body_scope_builder
+                    .shared
+                    .base
+                    .name_tracker
+                    .is_closed_over_def(n);
+                data.base
+                    .bindings
+                    .push(BindingName::new(*n, is_closed_over))
+            }
+            for n in &body_scope_builder.shared.const_names {
+                // Step 35.b.i. If IsConstantDeclaration of d is true, then
+                // Step 35.b.i.1. Perform
+                //                ! lexEnvRec.CreateImmutableBinding(dn, true).
+                let is_closed_over = body_scope_builder
+                    .shared
+                    .base
+                    .name_tracker
+                    .is_closed_over_def(n);
+                data.base
+                    .bindings
+                    .push(BindingName::new(*n, is_closed_over))
+            }
+
+            ScopeData::Lexical(data)
+        } else {
+            ScopeData::Alias(body_scope_builder.var_scope_index)
+        };
+
+        // Step 36. For each Parse Node f in functionsToInitialize, do
+        // (done in emitter)
+
+        FunctionScopeDataSet {
+            function: ScopeData::Function(function_scope_data),
+            extra_body_var: extra_body_var_scope_data,
+            lexical: lexical_scope_data,
+        }
+    }
+}
+
+/// Variables declared/used in FunctionBody.
+/// Shared part between full-parse and syntax-only parse.
+#[derive(Debug)]
+struct SharedFunctionBodyScopeBuilder {
+    base: BaseScopeBuilder,
+
+    /// FunctionDeclarationInstantiation ( func, argumentsList )
+    /// https://tc39.es/ecma262/#sec-functiondeclarationinstantiation
+    ///
+    /// Step 9. Let varNames be the VarDeclaredNames of code.
+    var_names: IndexSet<SourceAtomSetIndex>,
+
+    /// Step 11. Let lexicalNames be the LexicallyDeclaredNames of code.
+    let_names: Vec<SourceAtomSetIndex>,
+    const_names: Vec<SourceAtomSetIndex>,
+
+    /// Step 18. Else if hasParameterExpressions is false, then
+    /// Step 18.a. If "arguments" is an element of functionNames or
+    ///            if "arguments" is an element of lexicalNames, then
+    function_or_lexical_has_arguments: bool,
+}
+
+impl SharedFunctionBodyScopeBuilder {
+    fn new() -> Self {
+        Self {
+            base: BaseScopeBuilder::new(),
+            var_names: IndexSet::new(),
+            let_names: Vec::new(),
+            const_names: Vec::new(),
+            function_or_lexical_has_arguments: false,
+        }
+    }
+
+    fn declare_var(&mut self, name: SourceAtomSetIndex) {
+        // FunctionDeclarationInstantiation ( func, argumentsList )
+        // https://tc39.es/ecma262/#sec-functiondeclarationinstantiation
+        //
+        // Step 9. Let varNames be the VarDeclaredNames of code.
+        self.var_names.insert(name);
+        self.base.declare_var(name);
+    }
+
+    fn check_lexical_or_function_name(&mut self, name: SourceAtomSetIndex) {
+        // FunctionDeclarationInstantiation ( func, argumentsList )
+        // https://tc39.es/ecma262/#sec-functiondeclarationinstantiation
+        //
+        // Step 18.a. If "arguments" is an element of functionNames or if
+        //            "arguments" is an element of lexicalNames, then
+        if name == CommonSourceAtomSetIndices::arguments() {
+            self.function_or_lexical_has_arguments = true;
+        }
+    }
+
+    fn declare_let(&mut self, name: SourceAtomSetIndex) {
+        // FunctionDeclarationInstantiation ( func, argumentsList )
+        // https://tc39.es/ecma262/#sec-functiondeclarationinstantiation
+        //
+        // Step 11. Let lexicalNames be the LexicallyDeclaredNames of code.
+        self.let_names.push(name.clone());
+        self.check_lexical_or_function_name(name.clone());
+        self.base.declare_let(name);
+    }
+
+    fn declare_const(&mut self, name: SourceAtomSetIndex) {
+        // FunctionDeclarationInstantiation ( func, argumentsList )
+        // https://tc39.es/ecma262/#sec-functiondeclarationinstantiation
+        //
+        // Step 11. Let lexicalNames be the LexicallyDeclaredNames of code.
+        self.let_names.push(name.clone());
+        self.check_lexical_or_function_name(name.clone());
+        self.base.declare_const(name);
+    }
+
+    fn declare_function(&mut self, name: SourceAtomSetIndex) {
+        // FunctionDeclarationInstantiation ( func, argumentsList )
+        // https://tc39.es/ecma262/#sec-functiondeclarationinstantiation
+        //
+        // Step 9. Let varNames be the VarDeclaredNames of code.
+        self.var_names.insert(name.clone());
+
+        // Step 14. For each d in varDeclarations, in reverse list order, do
+        // Step 14.a. If d is neither a VariableDeclaration nor a ForBinding
+        //            nor a BindingIdentifier , then
+        // (implicit)
+
+        // Step 14.a.i. Assert: d is either a FunctionDeclaration, a
+        //              GeneratorDeclaration, an AsyncFunctionDeclaration,
+        //              or an AsyncGeneratorDeclaration.
+
+        // Step 14.a.ii. Let fn be the sole element of the BoundNames of d.
+
+        // Step 14.a.iii. If fn is not an element of functionNames, then
+        //
+        // NOTE: Instead of iterating in reverse list oder, we iterate in
+        // normal order and overwrite existing item.
+
+        // Step 14.a.iii.1. Insert fn as the first element of functionNames.
+        // Step 14.a.iii.2. NOTE: If there are multiple function declarations
+        //                  for the same name, the last declaration is used.
+        self.check_lexical_or_function_name(name);
+
+        self.base.declare_function(name)
+    }
+
+    fn is_var_closed_over(&self) -> bool {
+        for name in &self.var_names {
+            if self.base.name_tracker.is_closed_over_def(name) {
+                return true;
+            }
+        }
+
+        false
+    }
+}
+
+/// Variables declared/used in FunctionBody.
+/// For full-parse.
+#[derive(Debug)]
+struct FunctionBodyScopeBuilder {
+    shared: SharedFunctionBodyScopeBuilder,
+
+    /// FunctionDeclarationInstantiation ( func, argumentsList )
+    /// https://tc39.es/ecma262/#sec-functiondeclarationinstantiation
+    ///
+    /// Step 13. Let functionsToInitialize be a new empty List.
+    functions_to_initialize: Vec<ScriptStencilIndex>,
+
+    var_scope_index: ScopeIndex,
+    lexical_scope_index: ScopeIndex,
+}
+
+impl FunctionBodyScopeBuilder {
+    fn new(var_scope_index: ScopeIndex, lexical_scope_index: ScopeIndex) -> Self {
+        Self {
+            shared: SharedFunctionBodyScopeBuilder::new(),
+            functions_to_initialize: Vec::new(),
+            var_scope_index,
+            lexical_scope_index,
+        }
+    }
+
+    fn declare_var(&mut self, name: SourceAtomSetIndex) {
+        self.shared.declare_var(name);
+    }
+
+    fn declare_let(&mut self, name: SourceAtomSetIndex) {
+        self.shared.declare_let(name);
+    }
+
+    fn declare_const(&mut self, name: SourceAtomSetIndex) {
+        self.shared.declare_const(name);
+    }
+
+    fn declare_function(&mut self, name: SourceAtomSetIndex, fun_index: ScriptStencilIndex) {
+        self.shared.declare_function(name);
+
+        // FunctionDeclarationInstantiation ( func, argumentsList )
+        // https://tc39.es/ecma262/#sec-functiondeclarationinstantiation
+        //
+        // Step 14.a.iii.3. Insert d as the first element of
+        //                  functionsToInitialize.
+        self.functions_to_initialize.push(fun_index);
+    }
+}
+
+#[derive(Debug)]
+enum ScopeBuilder {
+    Global(GlobalScopeBuilder),
+    SyntaxOnlyGlobal(BaseScopeBuilder),
+
+    Block(BlockScopeBuilder),
+    SyntaxOnlyBlock(BaseScopeBuilder),
+
+    FunctionExpression(FunctionExpressionScopeBuilder),
+    SyntaxOnlyFunctionExpression(BaseScopeBuilder),
+
+    FunctionParameters(FunctionParametersScopeBuilder),
+    SyntaxOnlyFunctionParameters(SharedFunctionParametersScopeBuilder),
+
+    FunctionBody(FunctionBodyScopeBuilder),
+    SyntaxOnlyFunctionBody(SharedFunctionBodyScopeBuilder),
+}
+
+impl ScopeBuilder {
+    fn get_scope_index(&self) -> Option<ScopeIndex> {
+        match self {
+            ScopeBuilder::Global(builder) => Some(builder.scope_index),
+            ScopeBuilder::SyntaxOnlyGlobal(_) => None,
+            ScopeBuilder::Block(builder) => Some(builder.scope_index),
+            ScopeBuilder::SyntaxOnlyBlock(_) => None,
+            ScopeBuilder::FunctionExpression(builder) => Some(builder.scope_index),
+            ScopeBuilder::SyntaxOnlyFunctionExpression(_) => None,
+            ScopeBuilder::FunctionParameters(builder) => Some(builder.scope_index),
+            ScopeBuilder::SyntaxOnlyFunctionParameters(_) => None,
+            ScopeBuilder::FunctionBody(builder) => Some(builder.lexical_scope_index),
+            ScopeBuilder::SyntaxOnlyFunctionBody(_) => None,
+        }
+    }
+
+    fn declare_var(&mut self, name: SourceAtomSetIndex) {
+        match self {
+            ScopeBuilder::Global(ref mut builder) => builder.declare_var(name),
+            ScopeBuilder::SyntaxOnlyGlobal(ref mut builder) => builder.declare_var(name),
+            ScopeBuilder::FunctionBody(ref mut builder) => builder.declare_var(name),
+            ScopeBuilder::SyntaxOnlyFunctionBody(ref mut builder) => builder.declare_var(name),
+            _ => panic!("unexpected var scope builder"),
+        }
+    }
+
+    fn declare_let(&mut self, name: SourceAtomSetIndex) {
+        match self {
+            ScopeBuilder::Global(ref mut builder) => builder.declare_let(name),
+            ScopeBuilder::SyntaxOnlyGlobal(ref mut builder) => builder.declare_let(name),
+            ScopeBuilder::Block(ref mut builder) => builder.declare_let(name),
+            ScopeBuilder::SyntaxOnlyBlock(ref mut builder) => builder.declare_let(name),
+            ScopeBuilder::FunctionBody(ref mut builder) => builder.declare_let(name),
+            ScopeBuilder::SyntaxOnlyFunctionBody(ref mut builder) => builder.declare_let(name),
+            _ => panic!("unexpected lexical scope builder"),
+        }
+    }
+
+    fn declare_const(&mut self, name: SourceAtomSetIndex) {
+        match self {
+            ScopeBuilder::Global(ref mut builder) => builder.declare_const(name),
+            ScopeBuilder::SyntaxOnlyGlobal(ref mut builder) => builder.declare_const(name),
+            ScopeBuilder::Block(ref mut builder) => builder.declare_const(name),
+            ScopeBuilder::SyntaxOnlyBlock(ref mut builder) => builder.declare_const(name),
+            ScopeBuilder::FunctionBody(ref mut builder) => builder.declare_const(name),
+            ScopeBuilder::SyntaxOnlyFunctionBody(ref mut builder) => builder.declare_const(name),
+            _ => panic!("unexpected lexical scope builder"),
+        }
+    }
+
+    fn set_function_name(&mut self, name: SourceAtomSetIndex) {
+        match self {
+            ScopeBuilder::FunctionExpression(ref mut builder) => builder.set_function_name(name),
+            ScopeBuilder::SyntaxOnlyFunctionExpression(ref mut builder) => {
+                builder.set_function_name(name)
+            }
+            // FunctionDeclaration etc doesn't push any scope builder.
+            // Just ignore.
+            _ => {}
+        }
+    }
+
+    fn declare_param(&mut self, name: SourceAtomSetIndex) {
+        match self {
+            ScopeBuilder::FunctionParameters(ref mut builder) => builder.declare_param(name),
+            ScopeBuilder::SyntaxOnlyFunctionParameters(ref mut builder) => {
+                builder.declare_param(name)
+            }
+            _ => panic!("unexpected function scope builder"),
+        }
+    }
+
+    fn base_mut(&mut self) -> &mut BaseScopeBuilder {
+        match self {
+            ScopeBuilder::Global(builder) => &mut builder.base,
+            ScopeBuilder::SyntaxOnlyGlobal(builder) => builder,
+            ScopeBuilder::Block(builder) => &mut builder.base,
+            ScopeBuilder::SyntaxOnlyBlock(builder) => builder,
+            ScopeBuilder::FunctionExpression(builder) => &mut builder.base,
+            ScopeBuilder::SyntaxOnlyFunctionExpression(builder) => builder,
+            ScopeBuilder::FunctionParameters(builder) => &mut builder.shared.base,
+            ScopeBuilder::SyntaxOnlyFunctionParameters(builder) => &mut builder.base,
+            ScopeBuilder::FunctionBody(builder) => &mut builder.shared.base,
+            ScopeBuilder::SyntaxOnlyFunctionBody(builder) => &mut builder.base,
+        }
+    }
+}
+
+/// Tracks what kind of binding the BindingIdentifier node corresponds to.
+#[derive(Debug)]
+struct ScopeKindStack {
+    stack: Vec<ScopeKind>,
+}
+
+impl ScopeKindStack {
+    fn new() -> Self {
+        Self { stack: Vec::new() }
+    }
+
+    fn innermost<'a>(&'a self) -> &'a ScopeKind {
+        self.stack
+            .last()
+            .expect("There should be at least one scope on the stack")
+    }
+
+    fn push(&mut self, kind: ScopeKind) {
+        self.stack.push(kind)
+    }
+
+    fn pop(&mut self, kind: ScopeKind) {
+        match self.stack.pop() {
+            Some(k) if k == kind => {}
+            _ => panic!("unmatching scope kind"),
+        }
+    }
+
+    fn is_empty(&self) -> bool {
+        self.stack.len() == 0
+    }
+}
+
+/// The stack of scope builder for creating binding into.
+#[derive(Debug)]
+struct ScopeBuilderStack {
+    stack: Vec<ScopeBuilder>,
+
+    /// Stack of lists of names that is
+    ///   1. defined in the scope
+    ///   2. closed over by inner script
+    ///
+    /// Each list is delimited by `None`, for each scope.
+    ///
+    /// The order of scopes is depth-first post-order, and the order of names
+    /// inside each scope is in not defined.
+    ///
+    /// When entering a function, empty list is pushed to this stack, and
+    /// when leaving each function, top-most list is popped, and
+    /// added to gcthings of the function, and this list is reset to empty.
+    closed_over_bindings_for_lazy: Vec<Vec<Option<SourceAtomSetIndex>>>,
+}
+
+impl ScopeBuilderStack {
+    fn new() -> Self {
+        Self {
+            stack: Vec::new(),
+            closed_over_bindings_for_lazy: Vec::new(),
+        }
+    }
+
+    fn innermost_var<'a>(&'a mut self) -> &'a mut ScopeBuilder {
+        for builder in self.stack.iter_mut().rev() {
+            match builder {
+                ScopeBuilder::Global(_) => return builder,
+                ScopeBuilder::SyntaxOnlyGlobal(_) => return builder,
+                // NOTE: Function's body-level variable goes to
+                // `FunctionBodyScopeBuilder`, regardless of the existence of
+                // extra body var scope.
+                // See `FunctionParametersScopeBuilder::into_scope_data_set`
+                // for how those vars are stored into either function scope or
+                // extra body var scope.
+                ScopeBuilder::FunctionBody(_) => return builder,
+                ScopeBuilder::SyntaxOnlyFunctionBody(_) => return builder,
+                _ => {}
+            }
+        }
+
+        panic!("There should be at least one scope on the stack");
+    }
+
+    fn maybe_innermost_function_parameters<'a>(
+        &'a mut self,
+    ) -> Option<&'a mut FunctionParametersScopeBuilder> {
+        for builder in self.stack.iter_mut().rev() {
+            match builder {
+                ScopeBuilder::FunctionParameters(builder) => return Some(builder),
+                _ => {}
+            }
+        }
+
+        None
+    }
+
+    fn innermost_lexical<'a>(&'a mut self) -> &'a mut ScopeBuilder {
+        // FIXME: If there's no other case, merge with innermost.
+        self.innermost()
+    }
+
+    fn innermost<'a>(&'a mut self) -> &'a mut ScopeBuilder {
+        self.stack
+            .last_mut()
+            .expect("There should be at least one scope on the stack")
+    }
+
+    fn maybe_innermost<'a>(&'a mut self) -> Option<&'a mut ScopeBuilder> {
+        self.stack.last_mut()
+    }
+
+    fn current_scope_index(&self) -> ScopeIndex {
+        self.maybe_current_scope_index()
+            .expect("Shouldn't be in syntax-only mode")
+    }
+
+    fn maybe_current_scope_index(&self) -> Option<ScopeIndex> {
+        self.stack
+            .last()
+            .expect("There should be at least one scope on the stack")
+            .get_scope_index()
+    }
+
+    fn push_global(&mut self, builder: GlobalScopeBuilder) {
+        self.stack.push(ScopeBuilder::Global(builder))
+    }
+    fn push_syntax_only_global(&mut self, builder: BaseScopeBuilder) {
+        self.stack.push(ScopeBuilder::SyntaxOnlyGlobal(builder))
+    }
+
+    fn pop_global(&mut self) -> GlobalScopeBuilder {
+        match self.pop() {
+            ScopeBuilder::Global(builder) => {
+                debug_assert!(self.stack.is_empty());
+                builder
+            }
+            _ => panic!("unmatching scope builder"),
+        }
+    }
+    fn pop_syntax_only_global(&mut self) {
+        match self.pop() {
+            ScopeBuilder::SyntaxOnlyGlobal(_) => {
+                debug_assert!(self.stack.is_empty());
+            }
+            _ => panic!("unmatching scope builder"),
+        }
+    }
+
+    fn push_block(&mut self, builder: BlockScopeBuilder) {
+        self.stack.push(ScopeBuilder::Block(builder))
+    }
+    fn push_syntax_only_block(&mut self, builder: BaseScopeBuilder) {
+        self.stack.push(ScopeBuilder::SyntaxOnlyBlock(builder))
+    }
+
+    fn handle_popped_block(&mut self, builder: &BaseScopeBuilder) {
+        self.innermost()
+            .base_mut()
+            .propagate_from_inner_non_script(builder);
+
+        self.update_closed_over_bindings_for_lazy(builder);
+    }
+
+    fn pop_block(&mut self) -> BlockScopeBuilder {
+        match self.pop() {
+            ScopeBuilder::Block(builder) => {
+                self.handle_popped_block(&builder.base);
+                builder
+            }
+            _ => panic!("unmatching scope builder"),
+        }
+    }
+    fn pop_syntax_only_block(&mut self) {
+        match self.pop() {
+            ScopeBuilder::SyntaxOnlyBlock(builder) => self.handle_popped_block(&builder),
+            _ => panic!("unmatching scope builder"),
+        }
+    }
+
+    fn push_function_expression(&mut self, builder: FunctionExpressionScopeBuilder) {
+        self.stack.push(ScopeBuilder::FunctionExpression(builder))
+    }
+    fn push_syntax_only_function_expression(&mut self, builder: BaseScopeBuilder) {
+        self.stack
+            .push(ScopeBuilder::SyntaxOnlyFunctionExpression(builder))
+    }
+
+    fn handle_popped_function_expression(&mut self, builder: &BaseScopeBuilder) {
+        if let Some(outer) = self.maybe_innermost() {
+            // NOTE: Function expression's name cannot have any
+            //       used free variables.
+            //       We can treat it as non-script here, so that
+            //       any closed-over free variables inside this
+            //       function is propagated from FunctionParameters
+            //       to enclosing scope builder.
+            outer.base_mut().propagate_from_inner_non_script(builder);
+        }
+
+        self.update_closed_over_bindings_for_lazy(builder);
+    }
+
+    fn pop_function_expression(&mut self) -> FunctionExpressionScopeBuilder {
+        match self.pop() {
+            ScopeBuilder::FunctionExpression(builder) => {
+                self.handle_popped_function_expression(&builder.base);
+                builder
+            }
+            _ => panic!("unmatching scope builder"),
+        }
+    }
+    fn pop_syntax_only_function_expression(&mut self) {
+        match self.pop() {
+            ScopeBuilder::SyntaxOnlyFunctionExpression(builder) => {
+                self.handle_popped_function_expression(&builder);
+            }
+            _ => panic!("unmatching scope builder"),
+        }
+    }
+
+    fn push_function_parameters(&mut self, builder: FunctionParametersScopeBuilder) {
+        self.stack.push(ScopeBuilder::FunctionParameters(builder))
+    }
+    fn push_syntax_only_function_parameters(
+        &mut self,
+        builder: SharedFunctionParametersScopeBuilder,
+    ) {
+        self.stack
+            .push(ScopeBuilder::SyntaxOnlyFunctionParameters(builder))
+    }
+
+    fn handle_popped_function_parameters_and_body(
+        &mut self,
+        function_declaration_properties: &mut FunctionDeclarationPropertyMap,
+        possibly_annex_b_functions: &mut PossiblyAnnexBFunctionList,
+        parameter_scope_builder: &mut SharedFunctionParametersScopeBuilder,
+        body_scope_builder: &mut SharedFunctionBodyScopeBuilder,
+    ) {
+        // FunctionDeclarationInstantiation ( func, argumentsList )
+        // https://tc39.es/ecma262/#sec-functiondeclarationinstantiation
+        //
+        // Step 29. NOTE: Annex B adds additional steps at this point.
+        //
+        // NOTE: Reordered here in order to reflect Annex B functions
+        //       to FreeNameTracker.
+        parameter_scope_builder.perform_annex_b(
+            function_declaration_properties,
+            possibly_annex_b_functions,
+            body_scope_builder,
+        );
+
+        parameter_scope_builder
+            .base
+            .propagate_from_inner_non_script(&body_scope_builder.base);
+        if let Some(outer) = self.maybe_innermost() {
+            outer
+                .base_mut()
+                .propagate_from_inner_script(&parameter_scope_builder.base);
+        }
+
+        let has_extra_body_var_scope = parameter_scope_builder.has_parameter_expressions;
+        if has_extra_body_var_scope {
+            self.update_closed_over_bindings_for_lazy(&body_scope_builder.base);
+            self.update_closed_over_bindings_for_lazy(&parameter_scope_builder.base);
+        } else {
+            self.update_closed_over_bindings_for_lazy_with_parameters_and_body(
+                &parameter_scope_builder.base,
+                &body_scope_builder.base,
+            );
+        }
+    }
+
+    fn pop_function_parameters_and_body(
+        &mut self,
+        function_declaration_properties: &mut FunctionDeclarationPropertyMap,
+        possibly_annex_b_functions: &mut PossiblyAnnexBFunctionList,
+    ) -> (FunctionParametersScopeBuilder, FunctionBodyScopeBuilder) {
+        let mut body_scope_builder = match self.pop() {
+            ScopeBuilder::FunctionBody(builder) => builder,
+            _ => panic!("unmatching scope builder"),
+        };
+
+        let mut parameter_scope_builder = match self.pop() {
+            ScopeBuilder::FunctionParameters(builder) => builder,
+            _ => panic!("unmatching scope builder"),
+        };
+
+        self.handle_popped_function_parameters_and_body(
+            function_declaration_properties,
+            possibly_annex_b_functions,
+            &mut parameter_scope_builder.shared,
+            &mut body_scope_builder.shared,
+        );
+
+        (parameter_scope_builder, body_scope_builder)
+    }
+    fn pop_syntax_only_function_parameters_and_body(
+        &mut self,
+        function_declaration_properties: &mut FunctionDeclarationPropertyMap,
+        possibly_annex_b_functions: &mut PossiblyAnnexBFunctionList,
+    ) -> (
+        SharedFunctionParametersScopeBuilder,
+        SharedFunctionBodyScopeBuilder,
+    ) {
+        let mut body_scope_builder = match self.pop() {
+            ScopeBuilder::SyntaxOnlyFunctionBody(builder) => builder,
+            _ => panic!("unmatching scope builder"),
+        };
+
+        let mut parameter_scope_builder = match self.pop() {
+            ScopeBuilder::SyntaxOnlyFunctionParameters(builder) => builder,
+            _ => panic!("unmatching scope builder"),
+        };
+
+        self.handle_popped_function_parameters_and_body(
+            function_declaration_properties,
+            possibly_annex_b_functions,
+            &mut parameter_scope_builder,
+            &mut body_scope_builder,
+        );
+
+        (parameter_scope_builder, body_scope_builder)
+    }
+
+    fn get_function_parameters<'a>(&'a mut self) -> &'a mut FunctionParametersScopeBuilder {
+        match self.innermost() {
+            ScopeBuilder::FunctionParameters(builder) => builder,
+            _ => panic!("unmatching scope builder"),
+        }
+    }
+
+    fn get_syntax_only_function_parameters<'a>(
+        &'a mut self,
+    ) -> &'a mut SharedFunctionParametersScopeBuilder {
+        match self.innermost() {
+            ScopeBuilder::SyntaxOnlyFunctionParameters(builder) => builder,
+            _ => panic!("unmatching scope builder"),
+        }
+    }
+
+    fn push_function_body(&mut self, builder: FunctionBodyScopeBuilder) {
+        self.stack.push(ScopeBuilder::FunctionBody(builder))
+    }
+    fn push_syntax_only_function_body(&mut self, builder: SharedFunctionBodyScopeBuilder) {
+        self.stack
+            .push(ScopeBuilder::SyntaxOnlyFunctionBody(builder))
+    }
+
+    fn update_closed_over_bindings_for_lazy(&mut self, builder: &BaseScopeBuilder) {
+        match self.closed_over_bindings_for_lazy.last_mut() {
+            Some(bindings) => {
+                for name in builder.name_tracker.defined_and_closed_over_vars() {
+                    bindings.push(Some(*name));
+                }
+                bindings.push(None);
+            }
+            None => {
+                // We're leaving lexical scope in top-level script.
+            }
+        }
+    }
+
+    // Just like update_closed_over_bindings_for_lazy, but merge
+    // 2 builders for parameters and body, in case the function doesn't have
+    // extra body scope.
+    fn update_closed_over_bindings_for_lazy_with_parameters_and_body(
+        &mut self,
+        builder1: &BaseScopeBuilder,
+        builder2: &BaseScopeBuilder,
+    ) {
+        match self.closed_over_bindings_for_lazy.last_mut() {
+            Some(bindings) => {
+                for name in builder1.name_tracker.defined_and_closed_over_vars() {
+                    bindings.push(Some(*name));
+                }
+                for name in builder2.name_tracker.defined_and_closed_over_vars() {
+                    bindings.push(Some(*name));
+                }
+                bindings.push(None);
+            }
+            None => {
+                // We're leaving lexical scope in top-level script.
+            }
+        }
+    }
+
+    /// Pop the current scope.
+    fn pop(&mut self) -> ScopeBuilder {
+        self.stack.pop().expect("unmatching scope builder")
+    }
+
+    fn depth(&self) -> usize {
+        self.stack.len()
+    }
+}
+
+/// Builds `ScriptStencil` for all functions (both non-lazy and lazy).
+/// The script is set to lazy function, with inner functions and
+/// closed over bindings populated in gcthings list.
+///
+/// TODO: For non-lazy function, gcthings list should be populated in the
+///       emitter pass, not here.
+#[derive(Debug)]
+pub struct FunctionScriptStencilBuilder {
+    /// The map from function node to ScriptStencil.
+    ///
+    /// The map is separated into `function_stencil_indicies` and `functions`,
+    /// because it can be referred to in different ways from multiple places:
+    ///   * map from Function AST node (`function_stencil_indices`)
+    ///   * enclosing script/function, to list inner functions
+    function_stencil_indices: AssociatedData<ScriptStencilIndex>,
+    scripts: ScriptStencilList,
+
+    /// The stack of functions that the current context is in.
+    ///
+    /// The last element in this stack represents the current function, where
+    /// the inner function will be stored
+    function_stack: Vec<ScriptStencilIndex>,
+}
+
+impl FunctionScriptStencilBuilder {
+    fn new() -> Self {
+        let scripts = ScriptStencilList::new_with_empty_top_level();
+
+        Self {
+            function_stencil_indices: AssociatedData::new(),
+            scripts,
+            function_stack: Vec::new(),
+        }
+    }
+
+    /// Enter a function.
+    ///
+    /// This creates `ScriptStencil` for the function, and adds it to
+    /// enclosing function if exists.
+    fn enter<T>(
+        &mut self,
+        fun: &T,
+        syntax_kind: FunctionSyntaxKind,
+        enclosing_scope_index: Option<ScopeIndex>,
+    ) -> ScriptStencilIndex
+    where
+        T: SourceLocationAccessor + NodeTypeIdAccessor,
+    {
+        let loc = fun.get_loc();
+        let source_start = loc.start as u32;
+
+        // FIXME: Map from offset to line/column.
+        let lineno = 1;
+        let column = 0;
+
+        let function_stencil = ScriptStencil::lazy_function(
+            SourceExtent {
+                source_start,
+                source_end: 0,
+                to_string_start: source_start,
+                to_string_end: 0,
+                lineno,
+                column,
+            },
+            None,
+            syntax_kind.is_generator(),
+            syntax_kind.is_async(),
+            FunctionFlags::interpreted(syntax_kind),
+            enclosing_scope_index,
+        );
+        let index = self.scripts.push(function_stencil);
+        self.function_stencil_indices.insert(fun, index);
+
+        match self.maybe_current_mut() {
+            Some(enclosing) => {
+                enclosing.push_inner_function(index);
+            }
+            None => {}
+        }
+
+        self.function_stack.push(index);
+
+        index
+    }
+
+    /// Leave a function, setting its source location.
+    fn leave<T>(&mut self, fun: &T)
+    where
+        T: SourceLocationAccessor + NodeTypeIdAccessor,
+    {
+        let loc = fun.get_loc();
+        let source_end = loc.end;
+
+        self.current_mut().set_source_end(source_end);
+        self.current_mut().set_to_string_end(source_end);
+
+        self.function_stack.pop();
+    }
+
+    /// Returns the current function's index.
+    /// Panics if no current function is found.
+    fn current_index(&self) -> ScriptStencilIndex {
+        *self
+            .function_stack
+            .last()
+            .expect("should be inside function")
+    }
+
+    /// Returns a immutable reference to the innermost function. None otherwise.
+    fn maybe_current<'a>(&'a self) -> Option<&'a ScriptStencil> {
+        let maybe_index = self.function_stack.last();
+        maybe_index.map(move |index| self.scripts.get(*index))
+    }
+
+    /// Returns a immutable reference to the current function.
+    /// Panics if no current function is found.
+    fn current<'a>(&'a self) -> &'a ScriptStencil {
+        self.maybe_current().expect("should be inside function")
+    }
+
+    /// Returns a mutable reference to the innermost function. None otherwise.
+    fn maybe_current_mut<'a>(&'a mut self) -> Option<&'a mut ScriptStencil> {
+        let maybe_index = self.function_stack.last().cloned();
+        maybe_index.map(move |index| self.scripts.get_mut(index))
+    }
+
+    /// Returns a mutable reference to the current function.
+    /// Panics if no current function is found.
+    fn current_mut<'a>(&'a mut self) -> &'a mut ScriptStencil {
+        self.maybe_current_mut().expect("should be inside function")
+    }
+
+    /// Sets the name of the current function.
+    fn set_function_name(&mut self, name: SourceAtomSetIndex) {
+        self.current_mut().set_fun_name(name);
+    }
+
+    /// Sets the position of the function parameters.
+    /// `params` should point to the `(` of the function parameters.
+    /// If it's an arrow function without parenthesis, `params` should point
+    /// the parameter binding.
+    fn on_function_parameters<T>(&mut self, params: &T)
+    where
+        T: SourceLocationAccessor + NodeTypeIdAccessor,
+    {
+        let loc = params.get_loc();
+        let params_start = loc.start;
+        self.current_mut().set_source_starts(params_start);
+    }
+
+    fn on_non_rest_parameter(&mut self) {
+        let fun = self.current_mut();
+        fun.add_fun_nargs();
+    }
+
+    /// Flags that the current function has rest parameter.
+    fn on_rest_parameter(&mut self) {
+        let fun = self.current_mut();
+        fun.add_fun_nargs();
+        fun.set_has_rest();
+    }
+
+    fn add_closed_over_bindings(
+        &mut self,
+        mut closed_over_bindings_for_lazy: Vec<Option<SourceAtomSetIndex>>,
+    ) {
+        // Remove trailing `None`s.
+        loop {
+            match closed_over_bindings_for_lazy.last() {
+                Some(Some(_)) => {
+                    // The last item isn't None.
+                    break;
+                }
+
+                Some(None) => {
+                    // The last item is None, remove it
+                    closed_over_bindings_for_lazy.pop();
+                }
+
+                None => {
+                    // List is empty.
+                    break;
+                }
+            }
+        }
+
+        let current = self.current_mut();
+        for name in closed_over_bindings_for_lazy {
+            match name {
+                Some(name) => current.push_closed_over_bindings(name),
+                None => current.push_closed_over_bindings_delimiter(),
+            }
+        }
+    }
+}
+
+/// Scope builder shouldn't raise any error except not-implemented.
+/// This struct should eventually be removed.
+#[derive(Clone, Debug)]
+pub enum ScopeBuildError {
+    NotImplemented(&'static str),
+}
+
+/// Receives method calls telling about a JS script and builds a
+/// `ScopeDataMap`.
+///
+/// Usage: This struct's public methods must be called for each scope,
+/// declaration, and identifier in a JS script, in source order. Then use
+/// `ScopeDataMap::from()` to extract the results. Currently this object is
+/// driven by method calls from a `pass::ScopePass`.
+#[derive(Debug)]
+pub struct ScopeDataMapBuilder {
+    scope_kind_stack: ScopeKindStack,
+    builder_stack: ScopeBuilderStack,
+    scopes: ScopeDataList,
+
+    /// The global scope information.
+    /// Using `Option` to make this field populated later.
+    global: Option<ScopeIndex>,
+
+    /// The map from non-global AST node to scope information.
+    non_global: AssociatedData<ScopeIndex>,
+
+    function_stencil_builder: FunctionScriptStencilBuilder,
+
+    function_declaration_properties: FunctionDeclarationPropertyMap,
+
+    possibly_annex_b_functions: PossiblyAnnexBFunctionList,
+
+    error: Option<ScopeBuildError>,
+
+    // The depth of `builder_stack` where syntax-only mode started.
+    // The pointed `builder_stack` item should be enclosing scope of
+    // function.
+    //
+    // None if not in syntax-only mode.
+    syntax_only_depth: Option<usize>,
+}
+
+impl ScopeDataMapBuilder {
+    pub fn new() -> Self {
+        Self {
+            scope_kind_stack: ScopeKindStack::new(),
+            builder_stack: ScopeBuilderStack::new(),
+            scopes: ScopeDataList::new(),
+            global: None,
+            non_global: AssociatedData::new(),
+            function_stencil_builder: FunctionScriptStencilBuilder::new(),
+            function_declaration_properties: FunctionDeclarationPropertyMap::new(),
+            possibly_annex_b_functions: PossiblyAnnexBFunctionList::new(),
+            error: None,
+            syntax_only_depth: None,
+        }
+    }
+
+    fn set_error(&mut self, e: ScopeBuildError) {
+        if self.error.is_none() {
+            self.error = Some(e);
+        }
+    }
+
+    pub fn enter_syntax_only_mode(&mut self) {
+        assert!(self.syntax_only_depth.is_none());
+        self.syntax_only_depth = Some(self.builder_stack.depth());
+    }
+
+    fn maybe_exit_syntax_only_mode(&mut self) {
+        if self.syntax_only_depth.is_none() {
+            return;
+        }
+
+        let depth = self.syntax_only_depth.unwrap();
+        if self.builder_stack.depth() == depth {
+            self.syntax_only_depth = None;
+            return;
+        }
+
+        debug_assert!(self.builder_stack.depth() > depth);
+    }
+
+    pub fn is_syntax_only_mode(&self) -> bool {
+        self.syntax_only_depth.is_some()
+    }
+
+    pub fn before_script(&mut self) {
+        if self.is_syntax_only_mode() {
+            let builder = BaseScopeBuilder::new();
+            self.builder_stack.push_syntax_only_global(builder);
+            return;
+        }
+
+        // SetRealmGlobalObject ( realmRec, globalObj, thisValue )
+        // https://tc39.es/ecma262/#sec-setrealmglobalobject
+        //
+        // Steps 1-4, 7.
+        // (done in runtime)
+
+        // Step 5. Let newGlobalEnv be
+        //         NewGlobalEnvironment(globalObj, thisValue).
+        let index = self.scopes.allocate();
+        let builder = GlobalScopeBuilder::new(index);
+        self.global = Some(index);
+
+        // Step 6. Set realmRec.[[GlobalEnv]] to newGlobalEnv.
+        // (implicit)
+
+        // ScriptEvaluation ( scriptRecord )
+        // https://tc39.es/ecma262/#sec-runtime-semantics-scriptevaluation
+        //
+        // Step 1. Let globalEnv be scriptRecord.[[Realm]].[[GlobalEnv]].
+        // (implicit)
+
+        // Step 2. Let scriptContext be a new ECMAScript code execution context.
+        // (implicit)
+
+        // Steps 3-5.
+        // (done in runtime)
+
+        // Step 6. Set the VariableEnvironment of scriptContext to globalEnv.
+        // Step 7. Set the LexicalEnvironment of scriptContext to globalEnv.
+        self.builder_stack.push_global(builder);
+
+        // Steps 8-17.
+        // (done in runtime)
+    }
+
+    pub fn after_script(&mut self) {
+        if self.is_syntax_only_mode() {
+            self.builder_stack.pop_syntax_only_global();
+            self.maybe_exit_syntax_only_mode();
+            return;
+        }
+
+        let builder = self.builder_stack.pop_global();
+
+        // Runtime Semantics: GlobalDeclarationInstantiation ( script, env )
+        // https://tc39.es/ecma262/#sec-globaldeclarationinstantiation
+        //
+        // Steps 3-6.
+        // (done in runtime)
+
+        // Steps 12-18.
+        let scope_index = builder.scope_index;
+        let scope = builder.into_scope_data(
+            &mut self.function_declaration_properties,
+            &mut self.possibly_annex_b_functions,
+        );
+        self.scopes.populate(scope_index, scope);
+    }
+
+    pub fn before_block_statement<T>(&mut self, block: &T)
+    where
+        T: SourceLocationAccessor + NodeTypeIdAccessor,
+    {
+        if self.is_syntax_only_mode() {
+            let builder = BaseScopeBuilder::new();
+            self.builder_stack.push_syntax_only_block(builder);
+            return;
+        }
+
+        // Runtime Semantics: Evaluation
+        // https://tc39.es/ecma262/#sec-block-runtime-semantics-evaluation
+        //
+        // Block : { StatementList }
+        //
+        // Step 1. Let oldEnv be the running execution context's
+        //         LexicalEnvironment.
+        // (implicit)
+
+        // Step 2. Let blockEnv be NewDeclarativeEnvironment(oldEnv).
+        let index = self.scopes.allocate();
+        let builder = BlockScopeBuilder::new(index);
+        self.non_global.insert(block, index);
+
+        // Step 3. Perform
+        //         BlockDeclarationInstantiation(StatementList, blockEnv).
+        // (done in leave_enum_statement_variant_block_statement)
+
+        // Step 4. Set the running execution context's LexicalEnvironment to
+        //         blockEnv.
+        self.builder_stack.push_block(builder);
+
+        // Step 5. Let blockValue be the result of evaluating StatementList.
+        // (done in runtime)
+    }
+
+    pub fn after_block_statement(&mut self) {
+        if self.is_syntax_only_mode() {
+            self.builder_stack.pop_syntax_only_block();
+            return;
+        }
+
+        let builder = self.builder_stack.pop_block();
+        let enclosing = self.builder_stack.current_scope_index();
+
+        // Runtime Semantics: Evaluation
+        // https://tc39.es/ecma262/#sec-block-runtime-semantics-evaluation
+        //
+        // Block : { StatementList }
+        //
+        // Step 3. Perform
+        //         BlockDeclarationInstantiation(StatementList, blockEnv).
+        self.scopes.populate(
+            builder.scope_index,
+            builder.into_scope_data(enclosing, &mut self.possibly_annex_b_functions),
+        );
+
+        // Step 6. Set the running execution context's LexicalEnvironment to
+        //         oldEnv.
+
+        // Step 7. Return blockValue.
+        // (implicit)
+    }
+
+    pub fn before_var_declaration(&mut self) {
+        self.scope_kind_stack.push(ScopeKind::Var);
+    }
+
+    pub fn after_var_declaration(&mut self) {
+        self.scope_kind_stack.pop(ScopeKind::Var);
+    }
+
+    pub fn before_let_declaration(&mut self) {
+        self.scope_kind_stack.push(ScopeKind::Let);
+    }
+
+    pub fn after_let_declaration(&mut self) {
+        self.scope_kind_stack.pop(ScopeKind::Let);
+    }
+
+    pub fn before_const_declaration(&mut self) {
+        self.scope_kind_stack.push(ScopeKind::Const);
+    }
+
+    pub fn after_const_declaration(&mut self) {
+        self.scope_kind_stack.pop(ScopeKind::Const);
+    }
+
+    pub fn on_binding_identifier(&mut self, name: SourceAtomSetIndex) {
+        if self.scope_kind_stack.is_empty() {
+            // FIXME
+            // Do nothing for unsupported case.
+            self.set_error(ScopeBuildError::NotImplemented(
+                "Unsupported binding identifier",
+            ));
+            return;
+        }
+
+        match self.scope_kind_stack.innermost() {
+            ScopeKind::Var => self.builder_stack.innermost_var().declare_var(name),
+            ScopeKind::Let => self.builder_stack.innermost_lexical().declare_let(name),
+            ScopeKind::Const => self.builder_stack.innermost_lexical().declare_const(name),
+            ScopeKind::FunctionName => {
+                self.builder_stack.innermost().set_function_name(name);
+                self.function_stencil_builder.set_function_name(name);
+            }
+            ScopeKind::FunctionParametersAndBody => {
+                // FIXME
+                // Do nothing for unsupported case.
+                self.set_error(ScopeBuildError::NotImplemented(
+                    "Unsupported binding identifier",
+                ));
+                return;
+            }
+            ScopeKind::FormalParameter => self.builder_stack.innermost().declare_param(name),
+            _ => panic!("Not implemeneted"),
+        }
+    }
+
+    pub fn on_non_binding_identifier(&mut self, name: SourceAtomSetIndex) {
+        self.builder_stack
+            .innermost()
+            .base_mut()
+            .name_tracker
+            .note_use(name);
+    }
+
+    pub fn before_function_declaration<T>(
+        &mut self,
+        name: SourceAtomSetIndex,
+        fun: &T,
+        is_generator: bool,
+        is_async: bool,
+    ) -> ScriptStencilIndex
+    where
+        T: SourceLocationAccessor + NodeTypeIdAccessor,
+    {
+        if is_generator || is_async {
+            // FIXME: Generator and async should mark all bindings closed over.
+            self.set_error(ScopeBuildError::NotImplemented(
+                "Generator or async function",
+            ));
+        }
+
+        let fun_index = self.function_stencil_builder.enter(
+            fun,
+            FunctionSyntaxKind::function_declaration(is_generator, is_async),
+            self.builder_stack.maybe_current_scope_index(),
+        );
+
+        match self.builder_stack.innermost_lexical() {
+            ScopeBuilder::Global(ref mut builder) => builder.declare_function(name, fun_index),
+            ScopeBuilder::SyntaxOnlyGlobal(ref mut builder) => builder.declare_function(name),
+            ScopeBuilder::Block(ref mut builder) => builder.declare_function(name, fun_index),
+            ScopeBuilder::SyntaxOnlyBlock(ref mut builder) => builder.declare_function(name),
+            ScopeBuilder::FunctionBody(ref mut builder) => {
+                builder.declare_function(name, fun_index)
+            }
+            ScopeBuilder::SyntaxOnlyFunctionBody(ref mut builder) => builder.declare_function(name),
+            _ => panic!("unexpected lexical for FunctionDeclaration"),
+        }
+
+        self.scope_kind_stack.push(ScopeKind::FunctionName);
+
+        fun_index
+    }
+
+    pub fn after_function_declaration<T>(&mut self, fun: &T)
+    where
+        T: SourceLocationAccessor + NodeTypeIdAccessor,
+    {
+        self.function_stencil_builder.leave(fun);
+
+        self.scope_kind_stack.pop(ScopeKind::FunctionName);
+    }
+
+    pub fn before_function_expression<T>(&mut self, fun: &T, is_generator: bool, is_async: bool)
+    where
+        T: SourceLocationAccessor + NodeTypeIdAccessor,
+    {
+        // FIXME: Anonymous function expression needs inferred name.
+        self.set_error(ScopeBuildError::NotImplemented(
+            "Function expression (name analysis)",
+        ));
+
+        self.scope_kind_stack.push(ScopeKind::FunctionName);
+
+        self.function_stencil_builder.enter(
+            fun,
+            FunctionSyntaxKind::function_expression(is_generator, is_async),
+            self.builder_stack.maybe_current_scope_index(),
+        );
+
+        if self.is_syntax_only_mode() {
+            let builder = BaseScopeBuilder::new();
+            self.builder_stack
+                .push_syntax_only_function_expression(builder);
+            return;
+        }
+
+        let index = self.scopes.allocate();
+        let builder = FunctionExpressionScopeBuilder::new(index);
+        self.non_global.insert(fun, index);
+
+        self.builder_stack.push_function_expression(builder);
+    }
+
+    pub fn after_function_expression<T>(&mut self, fun: &T)
+    where
+        T: SourceLocationAccessor + NodeTypeIdAccessor,
+    {
+        self.function_stencil_builder.leave(fun);
+
+        self.scope_kind_stack.pop(ScopeKind::FunctionName);
+
+        if self.is_syntax_only_mode() {
+            self.builder_stack.pop_syntax_only_function_expression();
+            self.maybe_exit_syntax_only_mode();
+            return;
+        }
+
+        let builder = self.builder_stack.pop_function_expression();
+        let enclosing = self.builder_stack.current_scope_index();
+
+        self.scopes
+            .populate(builder.scope_index, builder.into_scope_data(enclosing));
+    }
+
+    pub fn before_method<T>(&mut self, fun: &T, is_generator: bool, is_async: bool)
+    where
+        T: SourceLocationAccessor + NodeTypeIdAccessor,
+    {
+        // FIXME: Support PropertyName as function name.
+        self.set_error(ScopeBuildError::NotImplemented("Method (name calculation)"));
+
+        self.function_stencil_builder.enter(
+            fun,
+            FunctionSyntaxKind::method(is_generator, is_async),
+            self.builder_stack.maybe_current_scope_index(),
+        );
+    }
+
+    pub fn after_method<T>(&mut self, fun: &T)
+    where
+        T: SourceLocationAccessor + NodeTypeIdAccessor,
+    {
+        self.function_stencil_builder.leave(fun);
+    }
+
+    pub fn before_getter<T>(&mut self, fun: &T)
+    where
+        T: SourceLocationAccessor + NodeTypeIdAccessor,
+    {
+        // FIXME: Support PropertyName as function name.
+        self.set_error(ScopeBuildError::NotImplemented("Getter (name calculation)"));
+
+        self.function_stencil_builder.enter(
+            fun,
+            FunctionSyntaxKind::getter(),
+            self.builder_stack.maybe_current_scope_index(),
+        );
+    }
+
+    pub fn on_getter_parameter<T>(&mut self, param: &T)
+    where
+        T: SourceLocationAccessor + NodeTypeIdAccessor,
+    {
+        self.before_function_parameters(param);
+        self.after_function_parameters();
+    }
+
+    pub fn after_getter<T>(&mut self, fun: &T)
+    where
+        T: SourceLocationAccessor + NodeTypeIdAccessor,
+    {
+        self.function_stencil_builder.leave(fun);
+    }
+
+    pub fn before_setter<T>(&mut self, fun: &T)
+    where
+        T: SourceLocationAccessor + NodeTypeIdAccessor,
+    {
+        // FIXME: Support PropertyName as function name.
+        self.set_error(ScopeBuildError::NotImplemented("Setter (name calculation)"));
+
+        self.function_stencil_builder.enter(
+            fun,
+            FunctionSyntaxKind::setter(),
+            self.builder_stack.maybe_current_scope_index(),
+        );
+    }
+
+    pub fn before_setter_parameter<T>(&mut self, param: &T)
+    where
+        T: SourceLocationAccessor + NodeTypeIdAccessor,
+    {
+        self.before_function_parameters(param);
+        self.before_parameter();
+    }
+
+    pub fn after_setter_parameter(&mut self) {
+        self.after_function_parameters();
+    }
+
+    pub fn after_setter<T>(&mut self, fun: &T)
+    where
+        T: SourceLocationAccessor + NodeTypeIdAccessor,
+    {
+        self.function_stencil_builder.leave(fun);
+    }
+
+    pub fn before_arrow_function<T>(&mut self, is_async: bool, params: &T)
+    where
+        T: SourceLocationAccessor + NodeTypeIdAccessor,
+    {
+        // FIXME: Arrow function needs to access enclosing scope's
+        //        `this` and `arguments`.
+        self.set_error(ScopeBuildError::NotImplemented(
+            "Arrow function (special name handling)",
+        ));
+
+        self.function_stencil_builder.enter(
+            params,
+            FunctionSyntaxKind::arrow(is_async),
+            self.builder_stack.maybe_current_scope_index(),
+        );
+    }
+
+    pub fn after_arrow_function<T>(&mut self, body: &T)
+    where
+        T: SourceLocationAccessor + NodeTypeIdAccessor,
+    {
+        self.function_stencil_builder.leave(body);
+    }
+
+    pub fn before_function_parameters<T>(&mut self, params: &T)
+    where
+        T: SourceLocationAccessor + NodeTypeIdAccessor,
+    {
+        self.scope_kind_stack
+            .push(ScopeKind::FunctionParametersAndBody);
+
+        self.builder_stack
+            .closed_over_bindings_for_lazy
+            .push(Vec::new());
+
+        self.function_stencil_builder.on_function_parameters(params);
+
+        self.scope_kind_stack.push(ScopeKind::FormalParameter);
+
+        let is_arrow = self.function_stencil_builder.current().is_arrow_function();
+
+        if self.is_syntax_only_mode() {
+            let builder = SharedFunctionParametersScopeBuilder::new(is_arrow);
+            self.builder_stack
+                .push_syntax_only_function_parameters(builder);
+            return;
+        }
+
+        let index = self.scopes.allocate();
+
+        let builder = FunctionParametersScopeBuilder::new(
+            index,
+            is_arrow,
+            self.function_stencil_builder.current_index(),
+        );
+        self.non_global.insert(params, index);
+
+        self.builder_stack.push_function_parameters(builder);
+    }
+
+    pub fn after_function_parameters(&mut self) {
+        self.scope_kind_stack.pop(ScopeKind::FormalParameter);
+    }
+
+    pub fn before_parameter(&mut self) {
+        self.function_stencil_builder.on_non_rest_parameter();
+
+        if self.is_syntax_only_mode() {
+            return;
+        }
+
+        let builder = self.builder_stack.get_function_parameters();
+        builder.before_parameter();
+    }
+
+    pub fn before_binding_pattern(&mut self) {
+        match self.builder_stack.innermost() {
+            ScopeBuilder::FunctionParameters(builder) => {
+                builder.before_binding_pattern();
+            }
+            ScopeBuilder::SyntaxOnlyFunctionParameters(builder) => {
+                builder.before_binding_pattern();
+            }
+            _ => {}
+        }
+    }
+
+    pub fn after_initializer(&mut self) {
+        match self.builder_stack.innermost() {
+            ScopeBuilder::FunctionParameters(builder) => {
+                builder.after_initializer();
+            }
+            ScopeBuilder::SyntaxOnlyFunctionParameters(builder) => {
+                builder.after_initializer();
+            }
+            _ => {}
+        }
+    }
+
+    pub fn before_computed_property_name(&mut self) {
+        match self.builder_stack.innermost() {
+            ScopeBuilder::FunctionParameters(builder) => {
+                builder.before_computed_property_name();
+            }
+            ScopeBuilder::SyntaxOnlyFunctionParameters(builder) => {
+                builder.before_computed_property_name();
+            }
+            _ => {}
+        }
+    }
+
+    pub fn before_rest_parameter(&mut self) {
+        self.function_stencil_builder.on_rest_parameter();
+
+        if self.is_syntax_only_mode() {
+            let builder = self.builder_stack.get_syntax_only_function_parameters();
+            builder.before_rest_parameter();
+            return;
+        }
+
+        let builder = self.builder_stack.get_function_parameters();
+        builder.before_rest_parameter();
+    }
+
+    pub fn before_function_body<T>(&mut self, body: &T)
+    where
+        T: SourceLocationAccessor + NodeTypeIdAccessor,
+    {
+        if self.is_syntax_only_mode() {
+            let builder = SharedFunctionBodyScopeBuilder::new();
+            self.builder_stack.push_syntax_only_function_body(builder);
+            return;
+        }
+
+        let var_index = self.scopes.allocate();
+        let lexical_index = self.scopes.allocate();
+        debug_assert!(lexical_index == var_index.next());
+
+        let builder = FunctionBodyScopeBuilder::new(var_index, lexical_index);
+        self.non_global.insert(body, var_index);
+
+        self.builder_stack.push_function_body(builder);
+    }
+
+    fn add_closed_over_bindings(&mut self) {
+        self.function_stencil_builder.add_closed_over_bindings(
+            self.builder_stack
+                .closed_over_bindings_for_lazy
+                .pop()
+                .expect("Vector should be pushed by before_function_parameters"),
+        );
+    }
+
+    fn update_function_stencil(
+        &mut self,
+        parameter_scope_builder: &SharedFunctionParametersScopeBuilder,
+        body_scope_builder: &SharedFunctionBodyScopeBuilder,
+    ) {
+        let has_extra_body_var_scope = parameter_scope_builder.has_parameter_expressions;
+
+        let bindings_accessed_dynamically =
+            parameter_scope_builder.base.bindings_accessed_dynamically;
+
+        let needs_environment_object = if has_extra_body_var_scope {
+            bindings_accessed_dynamically || parameter_scope_builder.is_parameter_closed_over()
+        } else {
+            bindings_accessed_dynamically
+                || parameter_scope_builder.is_parameter_closed_over()
+                || body_scope_builder.is_var_closed_over()
+        };
+
+        let fun_stencil = self.function_stencil_builder.current_mut();
+
+        if needs_environment_object {
+            fun_stencil.set_needs_function_environment_objects();
+        }
+
+        if has_extra_body_var_scope {
+            if body_scope_builder.var_names.len() > 0 {
+                fun_stencil.set_function_has_extra_body_var_scope();
+            }
+        }
+
+        let strict = parameter_scope_builder.strict;
+        let simple_parameter_list = parameter_scope_builder.simple_parameter_list;
+        let has_mapped_arguments = !strict && simple_parameter_list;
+        if has_mapped_arguments {
+            fun_stencil.set_has_mapped_args_obj();
+        }
+
+        if !fun_stencil.is_arrow_function() {
+            let has_used_this = parameter_scope_builder
+                .base
+                .name_tracker
+                .is_used_or_closed_over(CommonSourceAtomSetIndices::this())
+                || bindings_accessed_dynamically;
+
+            if has_used_this {
+                fun_stencil.set_function_has_this_binding();
+            }
+
+            let has_used_arguments = parameter_scope_builder
+                .base
+                .name_tracker
+                .is_used_or_closed_over(CommonSourceAtomSetIndices::arguments())
+                || bindings_accessed_dynamically;
+
+            let mut uses_arguments = false;
+            let mut try_declare_arguments = has_used_arguments;
+
+            let parameter_has_arguments = parameter_scope_builder.parameter_has_arguments;
+
+            let var_names_has_arguments = body_scope_builder
+                .var_names
+                .contains(&CommonSourceAtomSetIndices::arguments());
+
+            let body_has_defined_arguments =
+                var_names_has_arguments || body_scope_builder.function_or_lexical_has_arguments;
+
+            // FunctionDeclarationInstantiation ( func, argumentsList )
+            // https://tc39.es/ecma262/#sec-functiondeclarationinstantiation
+            //
+            // Step 17 (Else if "arguments" is an element of parameterNames...)
+            // and step 18 (Else if hasParameterExpressions is false...) say
+            // formal parameters, lexical bindings, and body-level functions
+            // named 'arguments' shadow the arguments object.
+            //
+            // So even if there wasn't a free use of 'arguments' but there is a
+            // var binding of 'arguments', we still might need the arguments
+            // object.
+            //
+            // If we have an extra var scope due to parameter expressions and
+            // the body declared 'var arguments', we still need to declare
+            // 'arguments' in the function scope.
+            //
+            // NOTE: This is implementation-specfic optimization, and has
+            //       no corresponding steps in the spec.
+            if var_names_has_arguments {
+                if has_extra_body_var_scope {
+                    try_declare_arguments = true;
+                } else if !parameter_has_arguments {
+                    uses_arguments = true;
+                }
+            }
+
+            if try_declare_arguments {
+                // if extra body var scope exists, the existence of `arguments`
+                // binding in function body doesn't affect.
+                let declare_arguments = !parameter_has_arguments
+                    && (has_extra_body_var_scope || !body_has_defined_arguments);
+
+                if declare_arguments {
+                    fun_stencil.set_should_declare_arguments();
+                    uses_arguments = true;
+                }
+            }
+
+            if uses_arguments {
+                fun_stencil.set_needs_args_obj();
+
+                if has_used_this {
+                    // FIXME
+                    // IsLikelyConstructorWrapper should be set if
+                    // `.apply()` is used and `return` isn't used.
+                    self.set_error(ScopeBuildError::NotImplemented(
+                        "IsLikelyConstructorWrapper condition",
+                    ));
+                }
+            }
+        }
+    }
+
+    pub fn after_function_body(&mut self) {
+        self.scope_kind_stack
+            .pop(ScopeKind::FunctionParametersAndBody);
+
+        if self.is_syntax_only_mode() {
+            let (parameter_scope_builder, body_scope_builder) = self
+                .builder_stack
+                .pop_syntax_only_function_parameters_and_body(
+                    &mut self.function_declaration_properties,
+                    &mut self.possibly_annex_b_functions,
+                );
+            self.possibly_annex_b_functions.clear();
+            self.add_closed_over_bindings();
+            self.update_function_stencil(&parameter_scope_builder, &body_scope_builder);
+
+            self.maybe_exit_syntax_only_mode();
+            return;
+        }
+
+        let (parameter_scope_builder, body_scope_builder) =
+            self.builder_stack.pop_function_parameters_and_body(
+                &mut self.function_declaration_properties,
+                &mut self.possibly_annex_b_functions,
+            );
+        self.possibly_annex_b_functions.clear();
+        self.add_closed_over_bindings();
+        self.update_function_stencil(&parameter_scope_builder.shared, &body_scope_builder.shared);
+
+        let enclosing = self.builder_stack.current_scope_index();
+
+        let function_scope_index = parameter_scope_builder.scope_index;
+        let var_scope_index = body_scope_builder.var_scope_index;
+        let lexical_scope_index = body_scope_builder.lexical_scope_index;
+
+        // Runtime Semantics: EvaluateBody
+        // https://tc39.es/ecma262/#sec-function-definitions-runtime-semantics-evaluatebody
+        //
+        // With parameters functionObject and List argumentsList.
+        //
+        // FunctionBody : FunctionStatementList
+        //
+        // Step 1. Perform ? FunctionDeclarationInstantiation(functionObject,
+        //         argumentsList).
+        let scope_data_set =
+            parameter_scope_builder.into_scope_data_set(enclosing, body_scope_builder);
+
+        self.scopes
+            .populate(function_scope_index, scope_data_set.function);
+        self.scopes
+            .populate(var_scope_index, scope_data_set.extra_body_var);
+        self.scopes
+            .populate(lexical_scope_index, scope_data_set.lexical);
+    }
+
+    pub fn before_catch_clause(&mut self) {
+        // FIXME: NewDeclarativeEnvironment for catch parameter.
+        self.set_error(ScopeBuildError::NotImplemented("try-catch"));
+    }
+
+    pub fn on_direct_eval(&mut self) {
+        // FIXME: Propagate to script flags.
+        self.set_error(ScopeBuildError::NotImplemented(
+            "direct eval (script flags)",
+        ));
+
+        if let Some(parameter_scope_builder) =
+            self.builder_stack.maybe_innermost_function_parameters()
+        {
+            parameter_scope_builder.has_direct_eval = true;
+        }
+
+        self.builder_stack
+            .innermost()
+            .base_mut()
+            .bindings_accessed_dynamically = true;
+    }
+
+    pub fn on_class(&mut self) {
+        // FIXME: NewDeclarativeEnvironment for class tail.
+        self.set_error(ScopeBuildError::NotImplemented("class"));
+    }
+
+    pub fn on_with(&mut self) {
+        // FIXME: Propagate to script flags.
+        self.set_error(ScopeBuildError::NotImplemented("with statement"));
+    }
+
+    pub fn on_delete(&mut self) {
+        // FIXME: Propagate to script flags.
+        self.set_error(ScopeBuildError::NotImplemented("delete operator"));
+    }
+
+    pub fn on_lexical_for(&mut self) {
+        // FIXME: NewDeclarativeEnvironment in for statement
+        self.set_error(ScopeBuildError::NotImplemented("lexical for"));
+    }
+
+    pub fn on_switch(&mut self) {
+        // FIXME: NewDeclarativeEnvironment in for case block
+        self.set_error(ScopeBuildError::NotImplemented("switch"));
+    }
+
+    pub fn on_new_target(&mut self) {
+        if let Some(fun_stencil) = self.function_stencil_builder.maybe_current_mut() {
+            fun_stencil.set_function_has_new_target_binding()
+        }
+    }
+}
+
+pub struct ScopeDataMapAndScriptStencilList {
+    pub scope_data_map: ScopeDataMap,
+    pub function_stencil_indices: AssociatedData<ScriptStencilIndex>,
+    pub function_declaration_properties: FunctionDeclarationPropertyMap,
+    pub scripts: ScriptStencilList,
+    pub error: Option<ScopeBuildError>,
+}
+
+impl From<ScopeDataMapBuilder> for ScopeDataMapAndScriptStencilList {
+    fn from(builder: ScopeDataMapBuilder) -> ScopeDataMapAndScriptStencilList {
+        ScopeDataMapAndScriptStencilList {
+            scope_data_map: ScopeDataMap::new(
+                builder.scopes,
+                builder.global.expect("There should be global scope data"),
+                builder.non_global,
+            ),
+            function_stencil_indices: builder.function_stencil_builder.function_stencil_indices,
+            function_declaration_properties: builder.function_declaration_properties,
+            scripts: builder.function_stencil_builder.scripts,
+            error: builder.error,
+        }
+    }
+}
diff --git a/third_party/rust/jsparagus-scope/src/data.rs b/third_party/rust/jsparagus-scope/src/data.rs
new file mode 100644
index 0000000000..1baeffe097
--- /dev/null
+++ b/third_party/rust/jsparagus-scope/src/data.rs
@@ -0,0 +1,65 @@
+//! Data generated by scope analysis, and consumed only by emitter
+
+use std::collections::HashMap;
+use stencil::script::ScriptStencilIndex;
+
+/// Data associated to a function.
+#[derive(Debug)]
+pub struct FunctionProperty {
+    is_annex_b: bool,
+}
+
+impl FunctionProperty {
+    fn is_annex_b_default() -> bool {
+        false
+    }
+
+    pub fn new() -> Self {
+        Self {
+            is_annex_b: Self::is_annex_b_default(),
+        }
+    }
+
+    pub fn mark_annex_b(&mut self) {
+        self.is_annex_b = true;
+    }
+
+    pub fn is_annex_b(&self) -> bool {
+        self.is_annex_b
+    }
+}
+
+/// Map from function to associated data.
+#[derive(Debug)]
+pub struct FunctionDeclarationPropertyMap {
+    /// This map is populated lazily, only for functions with non-default
+    /// property.
+    props: HashMap<ScriptStencilIndex, FunctionProperty>,
+}
+
+impl FunctionDeclarationPropertyMap {
+    pub fn new() -> Self {
+        Self {
+            props: HashMap::new(),
+        }
+    }
+
+    pub fn mark_annex_b(&mut self, index: ScriptStencilIndex) {
+        if !self.props.contains_key(&index) {
+            self.props.insert(index, FunctionProperty::new());
+        }
+
+        self.props
+            .get_mut(&index)
+            .expect("Should exist")
+            .mark_annex_b();
+    }
+
+    pub fn is_annex_b(&self, index: ScriptStencilIndex) -> bool {
+        if !self.props.contains_key(&index) {
+            return FunctionProperty::is_annex_b_default();
+        }
+
+        self.props.get(&index).expect("Should exist").is_annex_b()
+    }
+}
diff --git a/third_party/rust/jsparagus-scope/src/free_name_tracker.rs b/third_party/rust/jsparagus-scope/src/free_name_tracker.rs
new file mode 100644
index 0000000000..e376e5a955
--- /dev/null
+++ b/third_party/rust/jsparagus-scope/src/free_name_tracker.rs
@@ -0,0 +1,129 @@
+//! Code to track free names in scopes, to compute which bindings are closed
+//! over.
+//!
+//! A binding is closed-over if it is defined in a scope in one `JSScript` and
+//! can be used in another `JSScript` (a nested function or direct eval).
+//!
+//! In our single pass over the AST, we compute which bindings are closed-over
+//! using a `FreeNameTracker` for each scope.
+
+use ast::source_atom_set::SourceAtomSetIndex;
+use std::collections::hash_map::RandomState;
+use std::collections::hash_set::{Difference, Intersection};
+use std::collections::HashSet;
+
+/// Tracks free names in a scope.
+///
+/// Usage:
+///
+/// *   Create this when entering a scope.
+///
+/// *   Call `.note_use(name)` when a name is used and `.note_def(name)` when
+///     one is defined.
+///
+/// *   Call `.propagate_from_inner_script(inner)` or
+///     `.propagate_from_inner_non_script(inner)` when leaving an inner
+///     scope. These methods do the real work of marking bindings as
+///     closed-over.
+///
+/// The gist of the algorithm is tracking name *uses* and propagating them
+/// outward to the scope where the name is *defined*. When we propagate a use
+/// out of a function, we put it in `closed_over_names`; when that use is
+/// matched with a binding, the binding is closed-over.
+///
+/// **Why we do all the work when exiting a scope** - It would save a lot of
+/// work if we could mark a def as closed-over as soon as we see a matching
+/// use.  We could deal with each use as we encounter it. We wouldn't have to
+/// track them. The problem is hoisting. Bindings can be used anywhere in a
+/// scope, even before their definition. We can't mark a def that we haven't
+/// seen yet. The end of scope is the first point where we have definitely seen
+/// all uses and defs in that scope.
+///
+#[derive(Debug)]
+pub struct FreeNameTracker {
+    /// Names closed over in inner script-scopes, that's not yet
+    /// defined up to (excluding) the current scope.
+    /// The name might be defined in the current scope.
+    ///
+    /// The name defined in this or outer scope is marked "closed over", and
+    /// no more propagated to outer scope.
+    closed_over_names: HashSet<SourceAtomSetIndex>,
+
+    /// Names used in the current scope, and nested non-script scopes.
+    /// The name might be defined in the current scope.
+    used_names: HashSet<SourceAtomSetIndex>,
+
+    /// Names defined in the current scope.
+    def_names: HashSet<SourceAtomSetIndex>,
+}
+
+impl FreeNameTracker {
+    pub fn new() -> Self {
+        Self {
+            closed_over_names: HashSet::new(),
+            used_names: HashSet::new(),
+            def_names: HashSet::new(),
+        }
+    }
+
+    fn note_closed_over(&mut self, atom: SourceAtomSetIndex) {
+        self.closed_over_names.insert(atom);
+    }
+
+    /// Note that the given name is used in this scope.
+    pub fn note_use(&mut self, atom: SourceAtomSetIndex) {
+        self.used_names.insert(atom);
+    }
+
+    pub fn note_def(&mut self, atom: SourceAtomSetIndex) {
+        self.def_names.insert(atom);
+    }
+
+    pub fn is_used_or_closed_over(&self, atom: SourceAtomSetIndex) -> bool {
+        self.used_names.contains(&atom) || self.closed_over_names.contains(&atom)
+    }
+
+    /// Names closed over in inner script-scopes, that's not yet defined.
+    pub fn closed_over_freevars(&self) -> Difference<'_, SourceAtomSetIndex, RandomState> {
+        self.closed_over_names.difference(&self.def_names)
+    }
+
+    /// Names defined in this scope and closed over by inner script-scopes.
+    pub fn defined_and_closed_over_vars(
+        &self,
+    ) -> Intersection<'_, SourceAtomSetIndex, RandomState> {
+        self.def_names.intersection(&self.closed_over_names)
+    }
+
+    /// Names used in this and inner non-script scopes, that's not yet defined.
+    pub fn used_freevars(&self) -> Difference<'_, SourceAtomSetIndex, RandomState> {
+        self.used_names.difference(&self.def_names)
+    }
+
+    pub fn is_closed_over_def(&self, atom: &SourceAtomSetIndex) -> bool {
+        return self.def_names.contains(atom) && self.closed_over_names.contains(atom);
+    }
+
+    /// Propagate free closed over names and used names from the inner
+    /// non-script scope.
+    pub fn propagate_from_inner_non_script(&mut self, inner: &FreeNameTracker) {
+        for atom in inner.closed_over_freevars() {
+            self.note_closed_over(*atom);
+        }
+        for atom in inner.used_freevars() {
+            self.note_use(*atom);
+        }
+    }
+
+    #[allow(dead_code)]
+    /// Propagate free closed over names and used names from the inner
+    /// script scope, converting everything into free closed over names
+    pub fn propagate_from_inner_script(&mut self, inner: &FreeNameTracker) {
+        for atom in inner.closed_over_freevars() {
+            self.note_closed_over(*atom);
+        }
+        for atom in inner.used_freevars() {
+            self.note_closed_over(*atom);
+        }
+    }
+}
diff --git a/third_party/rust/jsparagus-scope/src/lib.rs b/third_party/rust/jsparagus-scope/src/lib.rs
new file mode 100644
index 0000000000..919776ee38
--- /dev/null
+++ b/third_party/rust/jsparagus-scope/src/lib.rs
@@ -0,0 +1,36 @@
+//! Collect information about scopes and bindings, used by the emitter.
+//!
+//! Scope analysis happens in a separate pass after the AST is built:
+//!
+//! 1.  Parse the script, check for early errors, and build an AST.
+//! 2.  Traverse the AST and do scope analysis (this crate).
+//! 3.  Traverse the AST and emit bytecode.
+//!
+//! The output of this analysis is a `ScopeDataMapAndFunctionMap`
+//! describing each scope, binding, and function in the AST.
+
+mod builder;
+pub mod data;
+pub mod free_name_tracker;
+mod pass;
+
+extern crate jsparagus_ast as ast;
+extern crate jsparagus_stencil as stencil;
+
+use ast::visit::Pass;
+
+pub use builder::ScopeBuildError;
+pub use pass::ScopePassResult;
+
+/// Visit all nodes in the AST, and create a scope data.
+///
+/// `ast` must already have been checked for early errors. This analysis does
+/// not check for errors, even scope-related errors like redeclaration of a
+/// `let` variable.
+pub fn generate_scope_data<'alloc, 'a>(
+    ast: &'alloc ast::types::Program<'alloc>,
+) -> ScopePassResult {
+    let mut scope_pass = pass::ScopePass::new();
+    scope_pass.visit_program(ast);
+    scope_pass.into()
+}
diff --git a/third_party/rust/jsparagus-scope/src/pass.rs b/third_party/rust/jsparagus-scope/src/pass.rs
new file mode 100644
index 0000000000..34bede940e
--- /dev/null
+++ b/third_party/rust/jsparagus-scope/src/pass.rs
@@ -0,0 +1,373 @@
+//! Code to traverse the AST and drive the rest of scope analysis.
+//!
+//! This module is responsible for walking the AST. Other modules do the actual
+//! analysis.
+//!
+//! Scope analysis is currently a second pass, after parsing, using the AST,
+//! but the goal is to do this analysis as part of the parse phase, even when
+//! no AST is built. So we try to keep AST use separate from the analysis code.
+
+use crate::builder::{ScopeBuildError, ScopeDataMapAndScriptStencilList, ScopeDataMapBuilder};
+use crate::data::FunctionDeclarationPropertyMap;
+use ast::arena;
+use ast::associated_data::AssociatedData;
+use ast::source_atom_set::CommonSourceAtomSetIndices;
+use ast::{types::*, visit::Pass};
+use std::collections::HashMap;
+use stencil::scope::ScopeDataMap;
+use stencil::script::{ScriptStencilIndex, ScriptStencilList};
+
+/// The result of scope analysis.
+pub struct ScopePassResult<'alloc> {
+    pub scope_data_map: ScopeDataMap,
+    pub function_declarations: HashMap<ScriptStencilIndex, &'alloc Function<'alloc>>,
+    pub function_stencil_indices: AssociatedData<ScriptStencilIndex>,
+    pub function_declaration_properties: FunctionDeclarationPropertyMap,
+    pub scripts: ScriptStencilList,
+    pub error: Option<ScopeBuildError>,
+}
+
+/// The top-level struct responsible for extracting the necessary information
+/// from the AST. The analysis itself is done mainly by the `ScopeDataMapBuilder`,
+/// which has very limited interaction with the AST.
+///
+/// FIXME: This should be rewritten as a grammar extension.
+#[derive(Debug)]
+pub struct ScopePass<'alloc> {
+    builder: ScopeDataMapBuilder,
+    function_declarations: HashMap<ScriptStencilIndex, &'alloc Function<'alloc>>,
+}
+
+impl<'alloc> ScopePass<'alloc> {
+    pub fn new() -> Self {
+        Self {
+            builder: ScopeDataMapBuilder::new(),
+            function_declarations: HashMap::new(),
+        }
+    }
+}
+
+impl<'alloc> From<ScopePass<'alloc>> for ScopePassResult<'alloc> {
+    fn from(pass: ScopePass<'alloc>) -> ScopePassResult<'alloc> {
+        let ScopeDataMapAndScriptStencilList {
+            scope_data_map,
+            function_stencil_indices,
+            function_declaration_properties,
+            scripts,
+            error,
+        } = pass.builder.into();
+        ScopePassResult {
+            scope_data_map,
+            function_declarations: pass.function_declarations,
+            function_stencil_indices,
+            function_declaration_properties,
+            scripts,
+            error,
+        }
+    }
+}
+
+impl<'alloc> Pass<'alloc> for ScopePass<'alloc> {
+    fn enter_script(&mut self, _ast: &'alloc Script<'alloc>) {
+        self.builder.before_script();
+    }
+
+    fn leave_script(&mut self, _ast: &'alloc Script<'alloc>) {
+        self.builder.after_script();
+    }
+
+    fn enter_enum_statement_variant_block_statement(&mut self, block: &'alloc Block<'alloc>) {
+        self.builder.before_block_statement(block);
+    }
+
+    fn leave_enum_statement_variant_block_statement(&mut self, _block: &'alloc Block<'alloc>) {
+        self.builder.after_block_statement();
+    }
+
+    fn enter_variable_declaration(&mut self, ast: &'alloc VariableDeclaration<'alloc>) {
+        match ast.kind {
+            VariableDeclarationKind::Var { .. } => {
+                self.builder.before_var_declaration();
+            }
+            VariableDeclarationKind::Let { .. } => {
+                self.builder.before_let_declaration();
+            }
+            VariableDeclarationKind::Const { .. } => {
+                self.builder.before_const_declaration();
+            }
+        }
+    }
+
+    fn leave_variable_declaration(&mut self, ast: &'alloc VariableDeclaration<'alloc>) {
+        match ast.kind {
+            VariableDeclarationKind::Var { .. } => {
+                self.builder.after_var_declaration();
+            }
+            VariableDeclarationKind::Let { .. } => {
+                self.builder.after_let_declaration();
+            }
+            VariableDeclarationKind::Const { .. } => {
+                self.builder.after_const_declaration();
+            }
+        }
+    }
+
+    fn visit_binding_identifier(&mut self, ast: &'alloc BindingIdentifier) {
+        self.builder.on_binding_identifier(ast.name.value);
+    }
+
+    // Given we override `visit_binding_identifier` above,
+    // visit_identifier is not called for Identifier inside BindingIdentifier,
+    // and this is called only for references, either
+    // IdentifierExpression or AssignmentTargetIdentifier.
+    fn visit_identifier(&mut self, ast: &'alloc Identifier) {
+        self.builder.on_non_binding_identifier(ast.value);
+    }
+
+    fn visit_enum_expression_variant_this_expression(&mut self) {
+        self.builder
+            .on_non_binding_identifier(CommonSourceAtomSetIndices::this());
+    }
+
+    fn enter_enum_statement_variant_function_declaration(&mut self, ast: &'alloc Function<'alloc>) {
+        if !self.builder.is_syntax_only_mode() {
+            self.builder.enter_syntax_only_mode();
+        }
+
+        let name = if let Some(ref name) = ast.name {
+            name.name.value
+        } else {
+            panic!("FunctionDeclaration should have name");
+        };
+        let fun_index =
+            self.builder
+                .before_function_declaration(name, ast, ast.is_generator, ast.is_async);
+        self.function_declarations.insert(fun_index, ast);
+    }
+
+    fn leave_enum_statement_variant_function_declaration(&mut self, ast: &'alloc Function<'alloc>) {
+        self.builder.after_function_declaration(ast);
+    }
+
+    fn enter_enum_expression_variant_function_expression(&mut self, ast: &'alloc Function<'alloc>) {
+        if !self.builder.is_syntax_only_mode() {
+            self.builder.enter_syntax_only_mode();
+        }
+
+        self.builder
+            .before_function_expression(ast, ast.is_generator, ast.is_async);
+    }
+
+    fn leave_enum_expression_variant_function_expression(&mut self, ast: &'alloc Function<'alloc>) {
+        self.builder.after_function_expression(ast);
+    }
+
+    fn visit_formal_parameters(&mut self, ast: &'alloc FormalParameters<'alloc>) {
+        self.builder.before_function_parameters(ast);
+
+        self.enter_formal_parameters(ast);
+        for item in &ast.items {
+            self.builder.before_parameter();
+            self.visit_parameter(item);
+        }
+        if let Some(item) = &ast.rest {
+            self.builder.before_rest_parameter();
+            self.visit_binding(item);
+        }
+        self.leave_formal_parameters(ast);
+
+        self.builder.after_function_parameters();
+    }
+
+    fn enter_enum_method_definition_variant_method(&mut self, ast: &'alloc Method<'alloc>) {
+        self.builder
+            .before_method(ast, ast.is_generator, ast.is_async);
+        // FIXME: Call self.builder.on_function_name
+    }
+
+    fn leave_enum_method_definition_variant_method(&mut self, ast: &'alloc Method<'alloc>) {
+        self.builder.after_method(ast);
+    }
+
+    /// Getter doesn't have FormalParameters.
+    /// Call builder methods just before body.
+    fn visit_getter(&mut self, ast: &'alloc Getter<'alloc>) {
+        self.builder.before_getter(ast);
+        // FIXME: Call self.builder.on_function_name
+
+        self.enter_getter(ast);
+        self.visit_class_element_name(&ast.property_name);
+
+        // FIXME: Pass something that points `()` part of getter.
+        self.builder.on_getter_parameter(ast);
+
+        self.visit_function_body(&ast.body);
+        self.leave_getter(ast);
+
+        self.builder.after_getter(ast);
+    }
+
+    /// Setter doesn't have FormalParameters, but single Parameter.
+    /// Call builder methods around it.
+    fn visit_setter(&mut self, ast: &'alloc Setter<'alloc>) {
+        self.builder.before_setter(ast);
+        // FIXME: Call self.builder.on_function_name
+
+        self.enter_setter(ast);
+        self.visit_class_element_name(&ast.property_name);
+
+        // FIXME: Pass something that points `(param)` part of setter,
+        // including `(` and `)`.
+        self.builder.before_setter_parameter(&ast.param);
+        self.visit_parameter(&ast.param);
+        self.builder.after_setter_parameter();
+
+        self.visit_function_body(&ast.body);
+        self.leave_setter(ast);
+
+        self.builder.after_setter(ast);
+    }
+
+    fn leave_binding_with_default(&mut self, _ast: &'alloc BindingWithDefault<'alloc>) {
+        self.builder.after_initializer();
+    }
+
+    fn enter_enum_property_name_variant_computed_property_name(
+        &mut self,
+        _ast: &'alloc ComputedPropertyName<'alloc>,
+    ) {
+        self.builder.before_computed_property_name();
+    }
+
+    fn enter_binding_pattern(&mut self, _ast: &'alloc BindingPattern<'alloc>) {
+        self.builder.before_binding_pattern();
+    }
+
+    fn enter_function_body(&mut self, ast: &'alloc FunctionBody<'alloc>) {
+        self.builder.before_function_body(ast);
+    }
+
+    fn leave_function_body(&mut self, _ast: &'alloc FunctionBody<'alloc>) {
+        self.builder.after_function_body();
+    }
+
+    fn enter_enum_expression_variant_arrow_expression(
+        &mut self,
+        is_async: &'alloc bool,
+        params: &'alloc FormalParameters<'alloc>,
+        _body: &'alloc ArrowExpressionBody<'alloc>,
+    ) {
+        self.builder.before_arrow_function(*is_async, params);
+    }
+
+    fn leave_enum_expression_variant_arrow_expression(
+        &mut self,
+        _is_async: &'alloc bool,
+        _params: &'alloc FormalParameters<'alloc>,
+        body: &'alloc ArrowExpressionBody<'alloc>,
+    ) {
+        self.builder.after_arrow_function(body);
+    }
+
+    /// Arrow function with expression body.
+    /// Use the expression as the node for function body.
+    fn enter_enum_arrow_expression_body_variant_expression(
+        &mut self,
+        ast: &'alloc arena::Box<'alloc, Expression<'alloc>>,
+    ) {
+        let expr: &Expression = ast;
+        self.builder.before_function_body(expr);
+    }
+
+    fn leave_enum_arrow_expression_body_variant_expression(
+        &mut self,
+        _ast: &'alloc arena::Box<'alloc, Expression<'alloc>>,
+    ) {
+        self.builder.after_function_body();
+    }
+
+    fn enter_catch_clause(&mut self, _ast: &'alloc CatchClause<'alloc>) {
+        self.builder.before_catch_clause();
+    }
+
+    fn enter_call_expression(&mut self, ast: &'alloc CallExpression<'alloc>) {
+        match &ast.callee {
+            ExpressionOrSuper::Expression(expr) => match &**expr {
+                Expression::IdentifierExpression(IdentifierExpression { name, .. }) => {
+                    if name.value == CommonSourceAtomSetIndices::eval() {
+                        self.builder.on_direct_eval();
+                    }
+                }
+                _ => {}
+            },
+            _ => {}
+        }
+    }
+
+    fn enter_class_declaration(&mut self, _ast: &'alloc ClassDeclaration<'alloc>) {
+        self.builder.on_class();
+    }
+
+    fn enter_class_expression(&mut self, _ast: &'alloc ClassExpression<'alloc>) {
+        self.builder.on_class();
+    }
+
+    fn enter_enum_statement_variant_with_statement(
+        &mut self,
+        _object: &'alloc arena::Box<'alloc, Expression<'alloc>>,
+        _body: &'alloc arena::Box<'alloc, Statement<'alloc>>,
+    ) {
+        self.builder.on_with();
+    }
+
+    fn visit_enum_unary_operator_variant_delete(&mut self) {
+        self.builder.on_delete();
+    }
+
+    fn enter_enum_statement_variant_for_statement(
+        &mut self,
+        init: &'alloc Option<VariableDeclarationOrExpression<'alloc>>,
+        _test: &'alloc Option<arena::Box<'alloc, Expression<'alloc>>>,
+        _update: &'alloc Option<arena::Box<'alloc, Expression<'alloc>>>,
+        _block: &'alloc arena::Box<'alloc, Statement<'alloc>>,
+    ) {
+        match init {
+            Some(VariableDeclarationOrExpression::VariableDeclaration(decl)) => match decl.kind {
+                VariableDeclarationKind::Let { .. } | VariableDeclarationKind::Const { .. } => {
+                    self.builder.on_lexical_for();
+                }
+                _ => {}
+            },
+            _ => {}
+        }
+    }
+
+    fn enter_enum_statement_variant_for_in_statement(
+        &mut self,
+        left: &'alloc VariableDeclarationOrAssignmentTarget<'alloc>,
+        _right: &'alloc arena::Box<'alloc, Expression<'alloc>>,
+        _block: &'alloc arena::Box<'alloc, Statement<'alloc>>,
+    ) {
+        match left {
+            VariableDeclarationOrAssignmentTarget::VariableDeclaration(decl) => match decl.kind {
+                VariableDeclarationKind::Let { .. } | VariableDeclarationKind::Const { .. } => {
+                    self.builder.on_lexical_for();
+                }
+                _ => {}
+            },
+            _ => {}
+        }
+    }
+
+    fn enter_enum_statement_variant_switch_statement(
+        &mut self,
+        _discriminant: &'alloc arena::Box<'alloc, Expression<'alloc>>,
+        _cases: &'alloc arena::Vec<'alloc, SwitchCase<'alloc>>,
+    ) {
+        self.builder.on_switch();
+    }
+
+    fn visit_enum_expression_variant_new_target_expression(&mut self) {
+        self.builder.on_new_target();
+    }
+}