Disallow destructuring in 'for...in'

src/compiler/checker.ts

@@ -8806,6 +8806,11 @@ module ts {
             //   VarDecl must be a variable declaration without a type annotation that declares a variable of type Any,
             //   and Expr must be an expression of type Any, an object type, or a type parameter type.                        
             if (node.initializer.kind === SyntaxKind.VariableDeclarationList) {
+                var variable = (<VariableDeclarationList>node.initializer).declarations[0];
+                if (variable && isBindingPattern(variable.name)) {
+                    error(variable.name, Diagnostics.The_left_hand_side_of_a_for_in_statement_cannot_be_a_destructuring_pattern);
+                }
+                
                 checkForInOrForOfVariableDeclaration(node);
             }
             else {
@@ -8815,7 +8820,10 @@ module ts {
                 //   and Expr must be an expression of type Any, an object type, or a type parameter type.
                 var varExpr = <Expression>node.initializer;
                 var leftType = checkExpression(varExpr);
-                if (!allConstituentTypesHaveKind(leftType, TypeFlags.Any | TypeFlags.StringLike)) {
+                if (varExpr.kind === SyntaxKind.ArrayLiteralExpression || varExpr.kind === SyntaxKind.ObjectLiteralExpression) {
+                    error(varExpr, Diagnostics.The_left_hand_side_of_a_for_in_statement_cannot_be_a_destructuring_pattern);
+                }
+                else if (!allConstituentTypesHaveKind(leftType, TypeFlags.Any | TypeFlags.StringLike)) {
                     error(varExpr, Diagnostics.The_left_hand_side_of_a_for_in_statement_must_be_of_type_string_or_any);
                 }
                 else {

src/compiler/diagnosticInformationMap.generated.ts

@@ -332,6 +332,7 @@ module ts {
         The_right_hand_side_of_a_for_of_statement_must_have_a_Symbol_iterator_method_that_returns_an_iterator: { code: 2488, category: DiagnosticCategory.Error, key: "The right-hand side of a 'for...of' statement must have a '[Symbol.iterator]()' method that returns an iterator." },
         The_iterator_returned_by_the_right_hand_side_of_a_for_of_statement_must_have_a_next_method: { code: 2489, category: DiagnosticCategory.Error, key: "The iterator returned by the right-hand side of a 'for...of' statement must have a 'next()' method." },
         The_object_returned_by_the_next_method_of_the_iterator_must_have_a_value_property: { code: 2490, category: DiagnosticCategory.Error, key: "The object returned by the next method of the iterator must have a 'value' property." },
+        The_left_hand_side_of_a_for_in_statement_cannot_be_a_destructuring_pattern: { code: 2491, category: DiagnosticCategory.Error, key: "The left-hand side of a 'for...in' statement cannot be a destructuring pattern." },
         Import_declaration_0_is_using_private_name_1: { code: 4000, category: DiagnosticCategory.Error, key: "Import declaration '{0}' is using private name '{1}'." },
         Type_parameter_0_of_exported_class_has_or_is_using_private_name_1: { code: 4002, category: DiagnosticCategory.Error, key: "Type parameter '{0}' of exported class has or is using private name '{1}'." },
         Type_parameter_0_of_exported_interface_has_or_is_using_private_name_1: { code: 4004, category: DiagnosticCategory.Error, key: "Type parameter '{0}' of exported interface has or is using private name '{1}'." },

src/compiler/diagnosticMessages.json

@@ -1320,6 +1320,10 @@
         "category": "Error",
         "code": 2490
     },
+    "The left-hand side of a 'for...in' statement cannot be a destructuring pattern.": {
+        "category": "Error",
+        "code": 2491
+    },
 
     "Import declaration '{0}' is using private name '{1}'.": {
         "category": "Error",
@@ -1596,7 +1600,7 @@
     "Exported type alias '{0}' has or is using private name '{1}'.": {
         "category": "Error",
         "code": 4081
-    },
+    },
     "The current host does not support the '{0}' option.": {
         "category": "Error",
         "code": 5001

src/compiler/utilities.ts

@@ -665,7 +665,7 @@ module ts {
     }
 
     export function isBindingPattern(node: Node) {
-        return node.kind === SyntaxKind.ArrayBindingPattern || node.kind === SyntaxKind.ObjectBindingPattern;
+        return !!node && (node.kind === SyntaxKind.ArrayBindingPattern || node.kind === SyntaxKind.ObjectBindingPattern);
     }
 
     export function isInAmbientContext(node: Node): boolean {

tests/baselines/reference/for-inStatementsDestructuring.errors.txt

@@ -0,0 +1,7 @@
+tests/cases/conformance/statements/for-inStatements/for-inStatementsDestructuring.ts(1,10): error TS2491: The left-hand side of a 'for...in' statement cannot be a destructuring pattern.
+
+
+==== tests/cases/conformance/statements/for-inStatements/for-inStatementsDestructuring.ts (1 errors) ====
+    for (var [a, b] in []) {}
+             ~~~~~~
+!!! error TS2491: The left-hand side of a 'for...in' statement cannot be a destructuring pattern.

tests/baselines/reference/for-inStatementsDestructuring.js

@@ -0,0 +1,5 @@
+//// [for-inStatementsDestructuring.ts]
+for (var [a, b] in []) {}
+
+//// [for-inStatementsDestructuring.js]
+for (var _a = void 0, a = _a[0], b = _a[1] in []) { }

tests/baselines/reference/for-inStatementsDestructuring2.errors.txt

@@ -0,0 +1,7 @@
+tests/cases/conformance/statements/for-inStatements/for-inStatementsDestructuring2.ts(1,10): error TS2491: The left-hand side of a 'for...in' statement cannot be a destructuring pattern.
+
+
+==== tests/cases/conformance/statements/for-inStatements/for-inStatementsDestructuring2.ts (1 errors) ====
+    for (var {a, b} in []) {}
+             ~~~~~~
+!!! error TS2491: The left-hand side of a 'for...in' statement cannot be a destructuring pattern.

tests/baselines/reference/for-inStatementsDestructuring2.js

@@ -0,0 +1,5 @@
+//// [for-inStatementsDestructuring2.ts]
+for (var {a, b} in []) {}
+
+//// [for-inStatementsDestructuring2.js]
+for (var _a = void 0, a = _a.a, b = _a.b in []) { }

tests/baselines/reference/for-inStatementsDestructuring3.errors.txt

@@ -0,0 +1,8 @@
+tests/cases/conformance/statements/for-inStatements/for-inStatementsDestructuring3.ts(2,6): error TS2491: The left-hand side of a 'for...in' statement cannot be a destructuring pattern.
+
+
+==== tests/cases/conformance/statements/for-inStatements/for-inStatementsDestructuring3.ts (1 errors) ====
+    var a, b;
+    for ([a, b] in []) { }
+         ~~~~~~
+!!! error TS2491: The left-hand side of a 'for...in' statement cannot be a destructuring pattern.

tests/baselines/reference/for-inStatementsDestructuring3.js

@@ -0,0 +1,7 @@
+//// [for-inStatementsDestructuring3.ts]
+var a, b;
+for ([a, b] in []) { }
+
+//// [for-inStatementsDestructuring3.js]
+var a, b;
+for ([a, b] in []) { }

tests/baselines/reference/for-inStatementsDestructuring4.errors.txt

@@ -0,0 +1,8 @@
+tests/cases/conformance/statements/for-inStatements/for-inStatementsDestructuring4.ts(2,6): error TS2491: The left-hand side of a 'for...in' statement cannot be a destructuring pattern.
+
+
+==== tests/cases/conformance/statements/for-inStatements/for-inStatementsDestructuring4.ts (1 errors) ====
+    var a, b;
+    for ({a, b} in []) { }
+         ~~~~~~
+!!! error TS2491: The left-hand side of a 'for...in' statement cannot be a destructuring pattern.

tests/baselines/reference/for-inStatementsDestructuring4.js

@@ -0,0 +1,7 @@
+//// [for-inStatementsDestructuring4.ts]
+var a, b;
+for ({a, b} in []) { }
+
+//// [for-inStatementsDestructuring4.js]
+var a, b;
+for ({ a: a, b: b } in []) { }

tests/baselines/reference/parserForStatement5.errors.txt

@@ -1,11 +1,11 @@
-tests/cases/conformance/parser/ecmascript5/Statements/parserForStatement5.ts(1,6): error TS2405: The left-hand side of a 'for...in' statement must be of type 'string' or 'any'.
+tests/cases/conformance/parser/ecmascript5/Statements/parserForStatement5.ts(1,6): error TS2491: The left-hand side of a 'for...in' statement cannot be a destructuring pattern.
 tests/cases/conformance/parser/ecmascript5/Statements/parserForStatement5.ts(1,12): error TS2304: Cannot find name 'b'.
 
 
 ==== tests/cases/conformance/parser/ecmascript5/Statements/parserForStatement5.ts (2 errors) ====
     for ({} in b) {
          ~~
-!!! error TS2405: The left-hand side of a 'for...in' statement must be of type 'string' or 'any'.
+!!! error TS2491: The left-hand side of a 'for...in' statement cannot be a destructuring pattern.
                ~
 !!! error TS2304: Cannot find name 'b'.
     }

tests/cases/conformance/statements/for-inStatements/for-inStatementsDestructuring.ts

@@ -0,0 +1 @@
+for (var [a, b] in []) {}

tests/cases/conformance/statements/for-inStatements/for-inStatementsDestructuring2.ts

@@ -0,0 +1 @@
+for (var {a, b} in []) {}

tests/cases/conformance/statements/for-inStatements/for-inStatementsDestructuring3.ts

@@ -0,0 +1,2 @@
+var a, b;
+for ([a, b] in []) { }

tests/cases/conformance/statements/for-inStatements/for-inStatementsDestructuring4.ts

@@ -0,0 +1,2 @@
+var a, b;
+for ({a, b} in []) { }