refactor(semantic): remove ScopeTree::child_ids (#5232)

closes #5244

crates/oxc_semantic/src/post_transform_checker.rs

@@ -420,13 +420,6 @@ impl<'s> PostTransformChecker<'s> {
                 self.errors.push_mismatch("Scope parent mismatch", scope_ids, parent_ids);
             }
 
-            // Check children match
-            let child_ids = self
-                .get_pair(scope_ids, |data, scope_id| data.scopes.get_child_ids(scope_id).to_vec());
-            if self.remap_scope_ids_sets(&child_ids).is_mismatch() {
-                self.errors.push_mismatch("Scope children mismatch", scope_ids, child_ids);
-            }
-
             // NB: Skip checking node IDs match - transformer does not set `AstNodeId`s
         }
     }
@@ -592,29 +585,6 @@ impl<'s> PostTransformChecker<'s> {
         Pair::new(self.scope_ids_map.get(scope_ids.after_transform), Some(scope_ids.rebuilt))
     }
 
-    /// Remap pair of arrays of `ScopeId`s.
-    /// Map `after_transform` IDs to `rebuilt` IDs.
-    /// Sort both sets.
-    fn remap_scope_ids_sets<V: AsRef<Vec<ScopeId>>>(
-        &self,
-        scope_ids: &Pair<V>,
-    ) -> Pair<Vec<Option<ScopeId>>> {
-        let mut after_transform = scope_ids
-            .after_transform
-            .as_ref()
-            .iter()
-            .map(|&scope_id| self.scope_ids_map.get(scope_id))
-            .collect::<Vec<_>>();
-        let mut rebuilt =
-            scope_ids.rebuilt.as_ref().iter().copied().map(Option::Some).collect::<Vec<_>>();
-
-        after_transform.sort_unstable();
-        rebuilt.sort_unstable();
-
-        Pair::new(after_transform, rebuilt)
-    }
-
-    /// Remap pair of arrays of `SymbolId`s.
     /// Map `after_transform` IDs to `rebuilt` IDs.
     /// Sort both sets.
     fn remap_symbol_ids_sets<V: AsRef<Vec<SymbolId>>>(

crates/oxc_semantic/src/scope.rs

@@ -28,8 +28,6 @@ pub type UnresolvedReferences = FxHashMap<CompactStr, Vec<ReferenceId>>;
 pub struct ScopeTree {
     /// Maps a scope to the parent scope it belongs in.
     parent_ids: IndexVec<ScopeId, Option<ScopeId>>,
-    /// Maps a scope to direct children scopes.
-    child_ids: IndexVec<ScopeId, Vec<ScopeId>>,
     /// Maps a scope to its node id.
     node_ids: IndexVec<ScopeId, AstNodeId>,
     flags: IndexVec<ScopeId, ScopeFlags>,
@@ -67,46 +65,6 @@ impl ScopeTree {
         std::iter::successors(Some(scope_id), |scope_id| self.parent_ids[*scope_id])
     }
 
-    /// Iterate over scopes contained by a scope in breadth-first order.
-    ///
-    /// Unlike [`ancestors`], this iterator will not include the scope itself.
-    ///
-    /// [`ancestors`]: ScopeTree::ancestors
-    pub fn descendants(&self, scope_id: ScopeId) -> impl Iterator<Item = ScopeId> + '_ {
-        // Has to be a `fn` and pass arguments because we can't
-        // have recursive closures
-        fn add_to_list(
-            parent_id: ScopeId,
-            child_ids: &IndexVec<ScopeId, Vec<ScopeId>>,
-            items: &mut Vec<ScopeId>,
-        ) {
-            if let Some(children) = child_ids.get(parent_id) {
-                for child_id in children {
-                    items.push(*child_id);
-                    add_to_list(*child_id, child_ids, items);
-                }
-            }
-        }
-
-        let mut list = vec![];
-
-        add_to_list(scope_id, &self.child_ids, &mut list);
-
-        list.into_iter()
-    }
-
-    /// Get the child scopes of a scope
-    #[inline]
-    pub fn get_child_ids(&self, scope_id: ScopeId) -> &[ScopeId] {
-        &self.child_ids[scope_id]
-    }
-
-    /// Get a mutable reference to a scope's children
-    #[inline]
-    pub fn get_child_ids_mut(&mut self, scope_id: ScopeId) -> &mut Vec<ScopeId> {
-        &mut self.child_ids[scope_id]
-    }
-
     pub fn descendants_from_root(&self) -> impl Iterator<Item = ScopeId> + '_ {
         self.parent_ids.iter_enumerated().map(|(scope_id, _)| scope_id)
     }
@@ -173,9 +131,6 @@ impl ScopeTree {
 
     pub fn set_parent_id(&mut self, scope_id: ScopeId, parent_id: Option<ScopeId>) {
         self.parent_ids[scope_id] = parent_id;
-        if let Some(parent_id) = parent_id {
-            self.child_ids[parent_id].push(scope_id);
-        }
     }
 
     /// Get a variable binding by name that was declared in the top-level scope
@@ -266,12 +221,7 @@ impl ScopeTree {
         node_id: AstNodeId,
         flags: ScopeFlags,
     ) -> ScopeId {
-        let scope_id = self.add_scope_impl(Some(parent_id), node_id, flags);
-
-        // Set this scope as child of parent scope
-        self.child_ids[parent_id].push(scope_id);
-
-        scope_id
+        self.add_scope_impl(Some(parent_id), node_id, flags)
     }
 
     /// Create the root [`Program`] scope.
@@ -295,7 +245,6 @@ impl ScopeTree {
         flags: ScopeFlags,
     ) -> ScopeId {
         let scope_id = self.parent_ids.push(parent_id);
-        self.child_ids.push(vec![]);
         self.flags.push(flags);
         self.bindings.push(Bindings::default());
         self.node_ids.push(node_id);
@@ -317,7 +266,6 @@ impl ScopeTree {
     /// Reserve memory for an `additional` number of scopes.
     pub fn reserve(&mut self, additional: usize) {
         self.parent_ids.reserve(additional);
-        self.child_ids.reserve(additional);
         self.flags.reserve(additional);
         self.bindings.reserve(additional);
         self.node_ids.reserve(additional);

crates/oxc_semantic/tests/integration/scopes.rs

@@ -24,10 +24,6 @@ fn test_only_program() {
     // ancestors
     assert_eq!(scopes.ancestors(root).count(), 1);
     assert!(scopes.get_parent_id(root).is_none());
-
-    // children
-    assert_eq!(scopes.descendants(root).count(), 0);
-    assert!(scopes.get_child_ids(root).is_empty());
 }
 
 #[test]

crates/oxc_semantic/tests/main.rs

@@ -7,16 +7,23 @@ use oxc_semantic::{ScopeId, Semantic, SemanticBuilder};
 use oxc_span::SourceType;
 
 fn get_scope_snapshot(semantic: &Semantic, scopes: impl Iterator<Item = ScopeId>) -> String {
+    let scope_tree = semantic.scopes();
     let mut result = String::default();
 
     result.push('[');
     scopes.enumerate().for_each(|(index, scope_id)| {
         if index != 0 {
             result.push(',');
         }
-        let flags = semantic.scopes().get_flags(scope_id);
+        let flags = scope_tree.get_flags(scope_id);
         result.push('{');
-        let child_ids = semantic.scopes().get_child_ids(scope_id);
+        let child_ids = semantic
+            .scopes()
+            .descendants_from_root()
+            .filter(|id| {
+                scope_tree.get_parent_id(*id).is_some_and(|parent_id| parent_id == scope_id)
+            })
+            .collect::<Vec<_>>();
         result.push_str("\"children\":");
         result.push_str(&get_scope_snapshot(semantic, child_ids.iter().copied()));
         result.push(',');
@@ -25,12 +32,12 @@ fn get_scope_snapshot(semantic: &Semantic, scopes: impl Iterator<Item = ScopeId>
         result.push_str(
             format!(
                 "\"node\": {:?},",
-                semantic.nodes().kind(semantic.scopes().get_node_id(scope_id)).debug_name()
+                semantic.nodes().kind(scope_tree.get_node_id(scope_id)).debug_name()
             )
             .as_str(),
         );
         result.push_str("\"symbols\": ");
-        let bindings = semantic.scopes().get_bindings(scope_id);
+        let bindings = scope_tree.get_bindings(scope_id);
         result.push('[');
         bindings.iter().enumerate().for_each(|(index, (name, symbol_id))| {
             if index != 0 {

crates/oxc_traverse/src/context/scoping.rs

@@ -119,10 +119,6 @@ impl TraverseScoping {
     }
 
     fn insert_scope_below(&mut self, child_scope_ids: &[ScopeId], flags: ScopeFlags) -> ScopeId {
-        // Remove these scopes from parent's children
-        let current_child_scope_ids = self.scopes.get_child_ids_mut(self.current_scope_id);
-        current_child_scope_ids.retain(|scope_id| !child_scope_ids.contains(scope_id));
-
         // Create new scope as child of parent
         let new_scope_id = self.create_child_scope_of_current(flags);
 

crates/oxc_wasm/Cargo.toml

@@ -26,7 +26,7 @@ oxc_linter   = { workspace = true }
 oxc_prettier = { workspace = true }
 serde        = { workspace = true }
 
-wasm-bindgen       = { workspace = true }
-serde-wasm-bindgen = { workspace = true }
-tsify              = { workspace = true }
+wasm-bindgen             = { workspace = true }
+serde-wasm-bindgen       = { workspace = true }
+tsify                    = { workspace = true }
 console_error_panic_hook = "0.1.7"

crates/oxc_wasm/src/lib.rs

@@ -316,13 +316,21 @@ impl Oxc {
         ) {
             let space = " ".repeat(depth * 2);
 
+            let scope_tree = semantic.scopes();
             for scope_id in scope_ids {
-                let flags = semantic.scopes().get_flags(*scope_id);
-                let next_scope_ids = semantic.scopes().get_child_ids(*scope_id);
+                let flags = scope_tree.get_flags(*scope_id);
+                let child_scope_ids = scope_tree
+                    .descendants_from_root()
+                    .filter(|id| {
+                        scope_tree
+                            .get_parent_id(*id)
+                            .is_some_and(|parent_id| parent_id == *scope_id)
+                    })
+                    .collect::<Vec<_>>();
 
                 scope_text
                     .push_str(&format!("{space}Scope{:?} ({flags:?}) {{\n", scope_id.index() + 1));
-                let bindings = semantic.scopes().get_bindings(*scope_id);
+                let bindings = scope_tree.get_bindings(*scope_id);
                 let binding_space = " ".repeat((depth + 1) * 2);
                 if !bindings.is_empty() {
                     scope_text.push_str(&format!("{binding_space}Bindings: {{"));
@@ -335,7 +343,7 @@ impl Oxc {
                     scope_text.push_str(&format!("\n{binding_space}}}\n"));
                 }
 
-                write_scope_text(semantic, scope_text, depth + 1, next_scope_ids);
+                write_scope_text(semantic, scope_text, depth + 1, &child_scope_ids);
                 scope_text.push_str(&format!("{space}}}\n"));
             }
         }