Fix handling of aruments in the emitter

Two problems are fixed:

* `isArgumentsLocalBinding` did only `PropertyAccessExpression`, now
  it's also doing `PropertyAssignment` (doesn't affect other files,
  since it's only used in the emitter).

* `visitShorthandPropertyAssignment` should call `visitIdentifier` on
  the synthesized id.  (For completion it might be better to make it
  visit the the original?)

Fixes #38594.

src/compiler/checker.ts

@@ -36095,15 +36095,16 @@ namespace ts {
         // Emitter support
 
         function isArgumentsLocalBinding(nodeIn: Identifier): boolean {
-            if (!isGeneratedIdentifier(nodeIn)) {
-                const node = getParseTreeNode(nodeIn, isIdentifier);
-                if (node) {
-                    const isPropertyName = node.parent.kind === SyntaxKind.PropertyAccessExpression && (<PropertyAccessExpression>node.parent).name === node;
-                    return !isPropertyName && getReferencedValueSymbol(node) === argumentsSymbol;
-                }
-            }
-
-            return false;
+            // Note: does not handle isShorthandPropertyAssignment (and probably a few more)
+            if (isGeneratedIdentifier(nodeIn)) return false;
+            const node = getParseTreeNode(nodeIn, isIdentifier);
+            if (!node) return false;
+            const parent = node.parent;
+            if (!parent) return false;
+            const isPropertyName = ((isPropertyAccessExpression(parent)
+                                     || isPropertyAssignment(parent))
+                                    && parent.name === node);
+            return !isPropertyName && getReferencedValueSymbol(node) === argumentsSymbol;
         }
 
         function moduleExportsSomeValue(moduleReferenceExpression: Expression): boolean {

src/compiler/transformers/es2015.ts

@@ -583,13 +583,10 @@ namespace ts {
             if (!convertedLoopState) {
                 return node;
             }
-            if (isGeneratedIdentifier(node)) {
-                return node;
+            if (resolver.isArgumentsLocalBinding(node)) {
+                return convertedLoopState.argumentsName || (convertedLoopState.argumentsName = createUniqueName("arguments"));
             }
-            if (node.escapedText !== "arguments" || !resolver.isArgumentsLocalBinding(node)) {
-                return node;
-            }
-            return convertedLoopState.argumentsName || (convertedLoopState.argumentsName = createUniqueName("arguments"));
+            return node;
         }
 
         function visitBreakOrContinueStatement(node: BreakOrContinueStatement): Statement {
@@ -3517,7 +3514,7 @@ namespace ts {
             return setTextRange(
                 createPropertyAssignment(
                     node.name,
-                    getSynthesizedClone(node.name)
+                    visitIdentifier(getSynthesizedClone(node.name))
                 ),
                 /*location*/ node
             );

tests/baselines/reference/argumentsAsPropertyName2.js

@@ -0,0 +1,29 @@
+//// [argumentsAsPropertyName2.ts]
+// target: es5
+
+function foo() {
+    for (let x = 0; x < 1; ++x) {
+        let i : number;
+        [].forEach(function () { i });
+        ({ arguments: 0 });
+        ({ arguments });
+        ({ arguments: arguments });
+    }
+}
+
+
+//// [argumentsAsPropertyName2.js]
+// target: es5
+function foo() {
+    var _loop_1 = function (x) {
+        var i;
+        [].forEach(function () { i; });
+        ({ arguments: 0 });
+        ({ arguments: arguments_1 });
+        ({ arguments: arguments_1 });
+    };
+    var arguments_1 = arguments;
+    for (var x = 0; x < 1; ++x) {
+        _loop_1(x);
+    }
+}

tests/baselines/reference/argumentsAsPropertyName2.symbols

@@ -0,0 +1,31 @@
+=== tests/cases/compiler/argumentsAsPropertyName2.ts ===
+// target: es5
+
+function foo() {
+>foo : Symbol(foo, Decl(argumentsAsPropertyName2.ts, 0, 0))
+
+    for (let x = 0; x < 1; ++x) {
+>x : Symbol(x, Decl(argumentsAsPropertyName2.ts, 3, 12))
+>x : Symbol(x, Decl(argumentsAsPropertyName2.ts, 3, 12))
+>x : Symbol(x, Decl(argumentsAsPropertyName2.ts, 3, 12))
+
+        let i : number;
+>i : Symbol(i, Decl(argumentsAsPropertyName2.ts, 4, 11))
+
+        [].forEach(function () { i });
+>[].forEach : Symbol(Array.forEach, Decl(lib.es5.d.ts, --, --))
+>forEach : Symbol(Array.forEach, Decl(lib.es5.d.ts, --, --))
+>i : Symbol(i, Decl(argumentsAsPropertyName2.ts, 4, 11))
+
+        ({ arguments: 0 });
+>arguments : Symbol(arguments, Decl(argumentsAsPropertyName2.ts, 6, 10))
+
+        ({ arguments });
+>arguments : Symbol(arguments, Decl(argumentsAsPropertyName2.ts, 7, 10))
+
+        ({ arguments: arguments });
+>arguments : Symbol(arguments, Decl(argumentsAsPropertyName2.ts, 8, 10))
+>arguments : Symbol(arguments)
+    }
+}
+

tests/baselines/reference/argumentsAsPropertyName2.types

@@ -0,0 +1,45 @@
+=== tests/cases/compiler/argumentsAsPropertyName2.ts ===
+// target: es5
+
+function foo() {
+>foo : () => void
+
+    for (let x = 0; x < 1; ++x) {
+>x : number
+>0 : 0
+>x < 1 : boolean
+>x : number
+>1 : 1
+>++x : number
+>x : number
+
+        let i : number;
+>i : number
+
+        [].forEach(function () { i });
+>[].forEach(function () { i }) : void
+>[].forEach : (callbackfn: (value: any, index: number, array: any[]) => void, thisArg?: any) => void
+>[] : undefined[]
+>forEach : (callbackfn: (value: any, index: number, array: any[]) => void, thisArg?: any) => void
+>function () { i } : () => void
+>i : number
+
+        ({ arguments: 0 });
+>({ arguments: 0 }) : { arguments: number; }
+>{ arguments: 0 } : { arguments: number; }
+>arguments : number
+>0 : 0
+
+        ({ arguments });
+>({ arguments }) : { arguments: IArguments; }
+>{ arguments } : { arguments: IArguments; }
+>arguments : IArguments
+
+        ({ arguments: arguments });
+>({ arguments: arguments }) : { arguments: IArguments; }
+>{ arguments: arguments } : { arguments: IArguments; }
+>arguments : IArguments
+>arguments : IArguments
+    }
+}
+

tests/cases/compiler/argumentsAsPropertyName2.ts

@@ -0,0 +1,11 @@
+// target: es5
+
+function foo() {
+    for (let x = 0; x < 1; ++x) {
+        let i : number;
+        [].forEach(function () { i });
+        ({ arguments: 0 });
+        ({ arguments });
+        ({ arguments: arguments });
+    }
+}