Merge pull request #2101 from Microsoft/restElementNull

Fix crash on rest element destructuring with null initializer

Author: ahejlsberg

src/compiler/checker.ts

@@ -1721,8 +1721,8 @@ module ts {
                 }
             }
             else {
-                // For an array binding element the specified or inferred type of the parent must be assignable to any[]
-                if (!isTypeAssignableTo(parentType, anyArrayType)) {
+                // 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;
                 }
@@ -4190,6 +4190,11 @@ module ts {
             return type.flags & TypeFlags.Reference && (<TypeReference>type).target === globalArrayType;
         }
 
+        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);
+        }
+
         function isTupleLikeType(type: Type): boolean {
             return !!getPropertyOfType(type, "0");
         }
@@ -5466,7 +5471,7 @@ module ts {
 
         function checkSpreadElementExpression(node: SpreadElementExpression, contextualMapper?: TypeMapper): Type {
             var type = checkExpressionCached(node.expression, contextualMapper);
-            if (!isTypeAssignableTo(type, anyArrayType)) {
+            if (!isArrayLikeType(type)) {
                 error(node.expression, Diagnostics.Type_0_is_not_an_array_type, typeToString(type));
                 return unknownType;
             }
@@ -7074,7 +7079,7 @@ module ts {
 
         function checkArrayLiteralAssignment(node: ArrayLiteralExpression, sourceType: Type, contextualMapper?: TypeMapper): Type {
             // TODOO(andersh): Allow iterable source type in ES6
-            if (!isTypeAssignableTo(sourceType, anyArrayType)) {
+            if (!isArrayLikeType(sourceType)) {
                 error(node, Diagnostics.Type_0_is_not_an_array_type, typeToString(sourceType));
                 return sourceType;
             }

tests/baselines/reference/restElementWithNullInitializer.errors.txt

@@ -0,0 +1,24 @@
+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 (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

@@ -0,0 +1,27 @@
+//// [restElementWithNullInitializer.ts]
+function foo1([...r] = null) {
+}
+
+function foo2([...r] = undefined) {
+}
+
+function foo3([...r] = {}) {
+}
+
+function foo4([...r] = []) {
+}
+
+
+//// [restElementWithNullInitializer.js]
+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

@@ -0,0 +1,11 @@
+function foo1([...r] = null) {
+}
+
+function foo2([...r] = undefined) {
+}
+
+function foo3([...r] = {}) {
+}
+
+function foo4([...r] = []) {
+}