Addressing CR feedback

Author: ahejlsberg

src/compiler/checker.ts

@@ -1721,7 +1721,7 @@ module ts {
                 }
             }
             else {
-                // For an array binding element the specified or inferred type of the parent must be assignable to any[]
+                // For an array binding element the specified or inferred type of the parent must be an array-like type
                 if (!isArrayLikeType(parentType)) {
                     error(pattern, Diagnostics.Type_0_is_not_an_array_type, typeToString(parentType));
                     return unknownType;
@@ -4191,6 +4191,7 @@ module ts {
         }
 
         function isArrayLikeType(type: Type): boolean {
+            // A type is array-like if it is not the undefined or null type and if it is assignable to any[]
             return !(type.flags & (TypeFlags.Undefined | TypeFlags.Null)) && isTypeAssignableTo(type, anyArrayType);
         }
 

tests/baselines/reference/restElementWithNullInitializer.errors.txt

@@ -1,8 +1,24 @@
-tests/cases/conformance/es6/destructuring/restElementWithNullInitializer.ts(1,14): error TS2461: Type 'null' is not an array type.
+tests/cases/conformance/es6/destructuring/restElementWithNullInitializer.ts(1,15): error TS2461: Type 'null' is not an array type.
+tests/cases/conformance/es6/destructuring/restElementWithNullInitializer.ts(4,15): error TS2461: Type 'undefined' is not an array type.
+tests/cases/conformance/es6/destructuring/restElementWithNullInitializer.ts(7,15): error TS2461: Type '{ [x: number]: undefined; }' is not an array type.
 
 
-==== tests/cases/conformance/es6/destructuring/restElementWithNullInitializer.ts (1 errors) ====
-    function foo([...r] = null) { }
-                 ~~~~~~
+==== tests/cases/conformance/es6/destructuring/restElementWithNullInitializer.ts (3 errors) ====
+    function foo1([...r] = null) {
+                  ~~~~~~
 !!! error TS2461: Type 'null' is not an array type.
+    }
+    
+    function foo2([...r] = undefined) {
+                  ~~~~~~
+!!! error TS2461: Type 'undefined' is not an array type.
+    }
+    
+    function foo3([...r] = {}) {
+                  ~~~~~~
+!!! error TS2461: Type '{ [x: number]: undefined; }' is not an array type.
+    }
+    
+    function foo4([...r] = []) {
+    }
 

tests/baselines/reference/restElementWithNullInitializer.js

@@ -1,6 +1,27 @@
 //// [restElementWithNullInitializer.ts]
-function foo([...r] = null) { }
+function foo1([...r] = null) {
+}
+
+function foo2([...r] = undefined) {
+}
+
+function foo3([...r] = {}) {
+}
+
+function foo4([...r] = []) {
+}
 
 
 //// [restElementWithNullInitializer.js]
-function foo(_a) { }
+function foo1(_a) {
+    var _b = _a === void 0 ? null : _a, r = _b.slice(0);
+}
+function foo2(_a) {
+    var _b = _a === void 0 ? undefined : _a, r = _b.slice(0);
+}
+function foo3(_a) {
+    var _b = _a === void 0 ? {} : _a, r = _b.slice(0);
+}
+function foo4(_a) {
+    var _b = _a === void 0 ? [] : _a, r = _b.slice(0);
+}

tests/cases/conformance/es6/destructuring/restElementWithNullInitializer.ts

@@ -1 +1,11 @@
-function foo([...r] = null) { }
+function foo1([...r] = null) {
+}
+
+function foo2([...r] = undefined) {
+}
+
+function foo3([...r] = {}) {
+}
+
+function foo4([...r] = []) {
+}