Update the entry point to return property symbol of destructuring assignment

Author: sheetalkamat

src/compiler/checker.ts

@@ -83,7 +83,7 @@ namespace ts {
             getShorthandAssignmentValueSymbol,
             getExportSpecifierLocalTargetSymbol,
             getTypeAtLocation: getTypeOfNode,
-            getTypeOfArrayLiteralOrObjectLiteralDestructuringAssignment,
+            getPropertySymbolOfDestructuringAssignment,
             typeToString,
             getSymbolDisplayBuilder,
             symbolToString,
@@ -16568,6 +16568,7 @@ namespace ts {
         // [ a ] from 
         //     [a] = [ some array ...]
         function getTypeOfArrayLiteralOrObjectLiteralDestructuringAssignment(expr: Expression): Type {
+            Debug.assert(expr.kind === SyntaxKind.ObjectLiteralExpression || expr.kind === SyntaxKind.ArrayLiteralExpression);
             // If this is from "for of"
             //     for ( { a } of elems) {
             //     }
@@ -16596,6 +16597,18 @@ namespace ts {
                 indexOf((<ArrayLiteralExpression>expr.parent).elements, expr), elementType || unknownType);
         }
 
+        // Gets the property symbol corresponding to the property in destructuring assignment
+        // 'property1' from 
+        //     for ( { property1: a } of elems) {
+        //     }
+        // 'property1' at location 'a' from: 
+        //     [a] = [ property1, property2 ]
+        function getPropertySymbolOfDestructuringAssignment(location: Identifier) {
+            // Get the type of the object or array literal and then look for property of given name in the type
+            const typeOfObjectLiteral = getTypeOfArrayLiteralOrObjectLiteralDestructuringAssignment(<Expression>location.parent.parent);
+            return typeOfObjectLiteral && getPropertyOfType(typeOfObjectLiteral, location.text);
+        }
+
         function getTypeOfExpression(expr: Expression): Type {
             if (isRightSideOfQualifiedNameOrPropertyAccess(expr)) {
                 expr = <Expression>expr.parent;

src/compiler/types.ts

@@ -1735,7 +1735,7 @@ namespace ts {
         getSymbolsOfParameterPropertyDeclaration(parameter: ParameterDeclaration, parameterName: string): Symbol[];
         getShorthandAssignmentValueSymbol(location: Node): Symbol;
         getExportSpecifierLocalTargetSymbol(location: ExportSpecifier): Symbol;
-        getTypeOfArrayLiteralOrObjectLiteralDestructuringAssignment(expression: Expression): Type;
+        getPropertySymbolOfDestructuringAssignment(location: Identifier): Symbol;
         getTypeAtLocation(node: Node): Type;
         typeToString(type: Type, enclosingDeclaration?: Node, flags?: TypeFormatFlags): string;
         symbolToString(symbol: Symbol, enclosingDeclaration?: Node, meaning?: SymbolFlags): string;

src/services/services.ts

@@ -5651,14 +5651,8 @@ namespace ts {
             }
 
             function getPropertySymbolOfDestructuringAssignment(location: Node) {
-                if (isArrayLiteralOrObjectLiteralDestructuringPattern(location.parent.parent)) {
-                    // Do work to determine if this is a property symbol corresponding to the search symbol
-                    const typeOfObjectLiteral = typeChecker.getTypeOfArrayLiteralOrObjectLiteralDestructuringAssignment(<Expression>location.parent.parent);
-                    if (typeOfObjectLiteral) {
-                        return typeChecker.getPropertyOfType(typeOfObjectLiteral, (<Identifier>location).text);
-                    }
-                }
-                return undefined;
+                return isArrayLiteralOrObjectLiteralDestructuringPattern(location.parent.parent) &&
+                    typeChecker.getPropertySymbolOfDestructuringAssignment(<Identifier>location);
             }
 
             function isObjectBindingPatternElementWithoutPropertyName(symbol: Symbol) {