Store _children in a WeakMap

src/compiler/_namespaces/ts.ts

@@ -21,6 +21,7 @@ export * from "../factory/nodeFactory";
 export * from "../factory/emitNode";
 export * from "../factory/emitHelpers";
 export * from "../factory/nodeTests";
+export * from "../factory/nodeChildren";
 export * from "../factory/utilities";
 export * from "../factory/utilitiesPublic";
 export * from "../parser";

src/compiler/factory/nodeChildren.ts

@@ -0,0 +1,27 @@
+import { Node } from "../_namespaces/ts";
+
+const nodeChildren = new WeakMap<Node, Node[] | undefined>();
+
+/** @internal */
+export function getNodeChildren(node: Node): Node[] | undefined {
+    return nodeChildren.get(node);
+}
+
+/** @internal */
+export function setNodeChildren(node: Node, children: Node[]) {
+    nodeChildren.set(node, children);
+}
+
+/** @internal */
+export function unsetNodeChildren(node: Node) {
+    nodeChildren.delete(node);
+}
+
+/** @internal */
+export function getOrSetNodeChildren(node: Node, fn: () => Node[]): Node[] {
+    let children = getNodeChildren(node);
+    if (children === undefined) {
+        setNodeChildren(node, children = fn());
+    }
+    return children;
+}

src/compiler/factory/nodeFactory.ts

@@ -387,6 +387,7 @@ import {
     setEmitFlags,
     setIdentifierAutoGenerate,
     setIdentifierTypeArguments,
+    setNodeChildren,
     setParent,
     setTextRange,
     ShorthandPropertyAssignment,
@@ -6210,7 +6211,7 @@ export function createNodeFactory(flags: NodeFactoryFlags, baseFactory: BaseNode
     // @api
     function createSyntaxList(children: Node[]) {
         const node = createBaseNode<SyntaxList>(SyntaxKind.SyntaxList);
-        node._children = children;
+        setNodeChildren(node, children);
         return node;
     }
 

src/compiler/parser.ts

@@ -387,6 +387,7 @@ import {
     unescapeLeadingUnderscores,
     UnionOrIntersectionTypeNode,
     UnionTypeNode,
+    unsetNodeChildren,
     UpdateExpression,
     VariableDeclaration,
     VariableDeclarationList,
@@ -10002,9 +10003,7 @@ namespace IncrementalParser {
 
             // Ditch any existing LS children we may have created.  This way we can avoid
             // moving them forward.
-            if (node._children) {
-                node._children = undefined;
-            }
+            unsetNodeChildren(node);
 
             setTextRangePosEnd(node, node.pos + delta, node.end + delta);
 
@@ -10160,7 +10159,7 @@ namespace IncrementalParser {
             const fullEnd = child.end;
             if (fullEnd >= changeStart) {
                 child.intersectsChange = true;
-                child._children = undefined;
+                unsetNodeChildren(child);
 
                 // Adjust the pos or end (or both) of the intersecting element accordingly.
                 adjustIntersectingElement(child, changeStart, changeRangeOldEnd, changeRangeNewEnd, delta);
@@ -10349,7 +10348,6 @@ namespace IncrementalParser {
 
     export interface IncrementalNode extends Node, IncrementalElement {
         hasBeenIncrementallyParsed: boolean;
-        _children: Node[] | undefined;
     }
 
     interface IncrementalNodeArray extends NodeArray<IncrementalNode>, IncrementalElement {

src/compiler/types.ts

@@ -9666,7 +9666,6 @@ export interface DiagnosticCollection {
 // SyntaxKind.SyntaxList
 export interface SyntaxList extends Node {
     kind: SyntaxKind.SyntaxList;
-    _children: Node[];
 }
 
 // dprint-ignore

src/compiler/utilities.ts

@@ -187,6 +187,7 @@ import {
     getLineStarts,
     getModeForUsageLocation,
     getNameOfDeclaration,
+    getNodeChildren,
     getNormalizedAbsolutePath,
     getNormalizedPathComponents,
     getOwnKeys,
@@ -510,7 +511,6 @@ import {
     SymbolFlags,
     SymbolTable,
     SyntaxKind,
-    SyntaxList,
     TaggedTemplateExpression,
     TemplateExpression,
     TemplateLiteral,
@@ -1161,8 +1161,11 @@ export function getTokenPosOfNode(node: Node, sourceFile?: SourceFileLike, inclu
     // the syntax list itself considers them as normal trivia. Therefore if we simply skip
     // trivia for the list, we may have skipped the JSDocComment as well. So we should process its
     // first child to determine the actual position of its first token.
-    if (node.kind === SyntaxKind.SyntaxList && (node as SyntaxList)._children.length > 0) {
-        return getTokenPosOfNode((node as SyntaxList)._children[0], sourceFile, includeJsDoc);
+    if (node.kind === SyntaxKind.SyntaxList) {
+        const first = firstOrUndefined(getNodeChildren(node));
+        if (first) {
+            return getTokenPosOfNode(first, sourceFile, includeJsDoc);
+        }
     }
 
     return skipTrivia(

src/services/services.ts

@@ -109,6 +109,7 @@ import {
     getNonAssignedNameOfDeclaration,
     getNormalizedAbsolutePath,
     getObjectFlags,
+    getOrSetNodeChildren,
     getQuotePreference,
     getScriptKind,
     getSetExternalModuleIndicator,
@@ -266,6 +267,7 @@ import {
     ScriptTarget,
     SelectionRange,
     SemanticClassificationFormat,
+    setNodeChildren,
     setObjectAllocator,
     Signature,
     SignatureDeclaration,
@@ -357,7 +359,6 @@ class NodeObject<TKind extends SyntaxKind> implements Node {
     public symbol!: Symbol; // Actually optional, but it was too annoying to access `node.symbol!` everywhere since in many cases we know it must be defined
     public jsDoc?: JSDoc[];
     public original?: Node;
-    private _children: Node[] | undefined;
     public id?: number;
     public emitNode?: EmitNode;
 
@@ -373,7 +374,6 @@ class NodeObject<TKind extends SyntaxKind> implements Node {
         this.parent = undefined!;
         this.original = undefined;
         this.emitNode = undefined;
-        this._children = undefined;
     }
 
     private assertHasRealPosition(message?: string) {
@@ -438,7 +438,7 @@ class NodeObject<TKind extends SyntaxKind> implements Node {
 
     public getChildren(sourceFile?: SourceFileLike): Node[] {
         this.assertHasRealPosition("Node without a real position cannot be scanned and thus has no token nodes - use forEachChild and collect the result if that's fine");
-        return this._children || (this._children = createChildren(this, sourceFile));
+        return getOrSetNodeChildren(this, () => createChildren(this, sourceFile));
     }
 
     public getFirstToken(sourceFile?: SourceFileLike): Node | undefined {
@@ -533,14 +533,15 @@ function addSyntheticNodes(nodes: Node[], pos: number, end: number, parent: Node
 
 function createSyntaxList(nodes: NodeArray<Node>, parent: Node): Node {
     const list = createNode(SyntaxKind.SyntaxList, nodes.pos, nodes.end, parent) as any as SyntaxList;
-    list._children = [];
+    const children: Node[] = [];
     let pos = nodes.pos;
     for (const node of nodes) {
-        addSyntheticNodes(list._children, pos, node.pos, parent);
-        list._children.push(node);
+        addSyntheticNodes(children, pos, node.pos, parent);
+        children.push(node);
         pos = node.end;
     }
-    addSyntheticNodes(list._children, pos, nodes.end, parent);
+    addSyntheticNodes(children, pos, nodes.end, parent);
+    setNodeChildren(list, children);
     return list;
 }
 

tests/baselines/reference/api/typescript.d.ts

@@ -7985,7 +7985,6 @@ declare namespace ts {
     }
     interface SyntaxList extends Node {
         kind: SyntaxKind.SyntaxList;
-        _children: Node[];
     }
     enum ListFormat {
         None = 0,