Fix emit for nested object rest in assignment pattern (#52922)

src/compiler/factory/nodeFactory.ts

@@ -58,6 +58,7 @@ import {
     ConstructorDeclaration,
     ConstructorTypeNode,
     ConstructSignatureDeclaration,
+    containsObjectRestOrSpread,
     ContinueStatement,
     createBaseNodeFactory,
     createNodeConverters,
@@ -114,7 +115,6 @@ import {
     getAllUnscopedEmitHelpers,
     getBuildInfo,
     getCommentRange,
-    getElementsOfBindingOrAssignmentPattern,
     getEmitFlags,
     getIdentifierTypeArguments,
     getJSDocTypeAliasName,
@@ -124,7 +124,6 @@ import {
     getSourceMapRange,
     getSyntheticLeadingComments,
     getSyntheticTrailingComments,
-    getTargetOfBindingOrAssignmentElement,
     getTextOfIdentifierOrLiteral,
     hasInvalidEscape,
     HasModifiers,
@@ -150,7 +149,6 @@ import {
     isArray,
     isArrayLiteralExpression,
     isArrowFunction,
-    isAssignmentPattern,
     isBinaryExpression,
     isCallChain,
     isClassDeclaration,
@@ -3326,24 +3324,7 @@ export function createNodeFactory(flags: NodeFactoryFlags, baseFactory: BaseNode
     }
 
     function propagateAssignmentPatternFlags(node: AssignmentPattern): TransformFlags {
-        if (node.transformFlags & TransformFlags.ContainsObjectRestOrSpread) return TransformFlags.ContainsObjectRestOrSpread;
-        if (node.transformFlags & TransformFlags.ContainsES2018) {
-            // check for nested spread assignments, otherwise '{ x: { a, ...b } = foo } = c'
-            // will not be correctly interpreted by the ES2018 transformer
-            for (const element of getElementsOfBindingOrAssignmentPattern(node)) {
-                const target = getTargetOfBindingOrAssignmentElement(element);
-                if (target && isAssignmentPattern(target)) {
-                    if (target.transformFlags & TransformFlags.ContainsObjectRestOrSpread) {
-                        return TransformFlags.ContainsObjectRestOrSpread;
-                    }
-                    if (target.transformFlags & TransformFlags.ContainsES2018) {
-                        const flags = propagateAssignmentPatternFlags(target);
-                        if (flags) return flags;
-                    }
-                }
-            }
-        }
-        return TransformFlags.None;
+        return containsObjectRestOrSpread(node) ? TransformFlags.ContainsObjectRestOrSpread : TransformFlags.None;
     }
 
     // @api

src/compiler/factory/utilities.ts

@@ -7,6 +7,7 @@ import {
     AssertionLevel,
     AssignmentExpression,
     AssignmentOperatorOrHigher,
+    AssignmentPattern,
     BinaryExpression,
     BinaryOperator,
     BinaryOperatorToken,
@@ -76,6 +77,7 @@ import {
     InternalEmitFlags,
     isAssignmentExpression,
     isAssignmentOperator,
+    isAssignmentPattern,
     isBlock,
     isCommaListExpression,
     isComputedPropertyName,
@@ -174,6 +176,7 @@ import {
     TextRange,
     ThisTypeNode,
     Token,
+    TransformFlags,
     TypeNode,
 } from "../_namespaces/ts";
 
@@ -1742,3 +1745,31 @@ export function flattenCommaList(node: Expression) {
     flattenCommaListWorker(node, expressions);
     return expressions;
 }
+
+/**
+ * Walk an AssignmentPattern to determine if it contains object rest (`...`) syntax. We cannot rely on
+ * propagation of `TransformFlags.ContainsObjectRestOrSpread` since it isn't propagated by default in
+ * ObjectLiteralExpression and ArrayLiteralExpression since we do not know whether they belong to an
+ * AssignmentPattern at the time the nodes are parsed.
+ *
+ * @internal
+ */
+export function containsObjectRestOrSpread(node: AssignmentPattern): boolean {
+    if (node.transformFlags & TransformFlags.ContainsObjectRestOrSpread) return true;
+    if (node.transformFlags & TransformFlags.ContainsES2018) {
+        // check for nested spread assignments, otherwise '{ x: { a, ...b } = foo } = c'
+        // will not be correctly interpreted by the ES2018 transformer
+        for (const element of getElementsOfBindingOrAssignmentPattern(node)) {
+            const target = getTargetOfBindingOrAssignmentElement(element);
+            if (target && isAssignmentPattern(target)) {
+                if (target.transformFlags & TransformFlags.ContainsObjectRestOrSpread) {
+                    return true;
+                }
+                if (target.transformFlags & TransformFlags.ContainsES2018) {
+                    if (containsObjectRestOrSpread(target)) return true;
+                }
+            }
+        }
+    }
+    return false;
+}

src/compiler/transformers/es2018.ts

@@ -19,6 +19,7 @@ import {
     concatenate,
     ConciseBody,
     ConstructorDeclaration,
+    containsObjectRestOrSpread,
     createForOfBindingStatement,
     createSuperAccessVariableStatement,
     Debug,
@@ -577,7 +578,7 @@ export function transformES2018(context: TransformationContext): (x: SourceFile
      * expression of an `ExpressionStatement`).
      */
     function visitBinaryExpression(node: BinaryExpression, expressionResultIsUnused: boolean): Expression {
-        if (isDestructuringAssignment(node) && node.left.transformFlags & TransformFlags.ContainsObjectRestOrSpread) {
+        if (isDestructuringAssignment(node) && containsObjectRestOrSpread(node.left)) {
             return flattenDestructuringAssignment(
                 node,
                 visitor,
@@ -703,7 +704,8 @@ export function transformES2018(context: TransformationContext): (x: SourceFile
      */
     function visitForOfStatement(node: ForOfStatement, outermostLabeledStatement: LabeledStatement | undefined): VisitResult<Statement> {
         const ancestorFacts = enterSubtree(HierarchyFacts.IterationStatementExcludes, HierarchyFacts.IterationStatementIncludes);
-        if (node.initializer.transformFlags & TransformFlags.ContainsObjectRestOrSpread) {
+        if (node.initializer.transformFlags & TransformFlags.ContainsObjectRestOrSpread ||
+            isAssignmentPattern(node.initializer) && containsObjectRestOrSpread(node.initializer)) {
             node = transformForOfStatementWithObjectRest(node);
         }
         const result = node.awaitModifier ?