feat: add support for the safe navigation (aka Elvis) operator

fixes #791

modules/angular2/test/change_detection/change_detector_spec.ts

@@ -151,7 +151,7 @@ export function main() {
               expect(executeWatch('const', '"a\n\nb"')).toEqual(['const=a\n\nb']);
             });
 
-            it('simple chained property access', () => {
+            it('should support simple chained property access', () => {
               var address = new Address('Grenoble');
               var person = new Person('Victor', address);
 
@@ -159,6 +159,18 @@ export function main() {
                   .toEqual(['address.city=Grenoble']);
             });
 
+            it('should support the safe navigation operator', () => {
+              var person = new Person('Victor', null);
+
+              expect(executeWatch('city', 'address?.city', person)).toEqual(['city=null']);
+              expect(executeWatch('city', 'address?.toString()', person)).toEqual(['city=null']);
+
+              person.address = new Address('MTV');
+
+              expect(executeWatch('city', 'address?.city', person)).toEqual(['city=MTV']);
+              expect(executeWatch('city', 'address?.toString()', person)).toEqual(['city=MTV']);
+            });
+
             it("should support method calls", () => {
               var person = new Person('Victor');
               expect(executeWatch('m', 'sayHi("Jim")', person)).toEqual(['m=Hi, Jim']);
@@ -976,7 +988,7 @@ class Address {
   city: string;
   constructor(city: string) { this.city = city; }
 
-  toString(): string { return this.city; }
+  toString(): string { return isBlank(this.city) ? '-' : this.city }
 }
 
 class Uninitialized {

modules/angular2/test/change_detection/parser/lexer_spec.ts

@@ -126,14 +126,14 @@ export function main() {
         expectIdentifierToken(tokens[1], 8, 'b');
       });
 
-      it('should tokenize quoted string', function() {
+      it('should tokenize quoted string', () => {
         var str = "['\\'', \"\\\"\"]";
         var tokens: List<Token> = lex(str);
         expectStringToken(tokens[1], 1, "'");
         expectStringToken(tokens[3], 7, '"');
       });
 
-      it('should tokenize escaped quoted string', function() {
+      it('should tokenize escaped quoted string', () => {
         var str = '"\\"\\n\\f\\r\\t\\v\\u00A0"';
         var tokens: List<Token> = lex(str);
         expect(tokens.length).toEqual(1);
@@ -203,7 +203,7 @@ export function main() {
       });
 
       // NOTE(deboer): NOT A LEXER TEST
-      //    it('should tokenize negative number', function() {
+      //    it('should tokenize negative number', () => {
       //      var tokens:List<Token> = lex("-0.5");
       //      expectNumberToken(tokens[0], 0, -0.5);
       //    });
@@ -240,6 +240,11 @@ export function main() {
         expectOperatorToken(tokens[0], 0, '#');
       });
 
+      it('should tokenize ?. as operator', () => {
+        var tokens: List<Token> = lex('?.');
+        expectOperatorToken(tokens[0], 0, '?.');
+      });
+
     });
   });
 }

modules/angular2/test/change_detection/parser/parser_spec.ts

@@ -1,4 +1,4 @@
-import {ddescribe, describe, it, xit, iit, expect, beforeEach} from 'angular2/test_lib';
+import {ddescribe, describe, it, xit, iit, expect, beforeEach, IS_DARTIUM} from 'angular2/test_lib';
 import {BaseException, isBlank, isPresent} from 'angular2/src/facade/lang';
 import {reflector} from 'angular2/src/reflection/reflection';
 import {MapWrapper, ListWrapper} from 'angular2/src/facade/collection';
@@ -202,6 +202,33 @@ export function main() {
            });
       });
 
+      describe('safe navigation operator', () => {
+        it('should parse field access', () => {
+          expectEval('a?.a', td(td(999))).toEqual(999);
+          expectEval('a.a?.a', td(td(td(999)))).toEqual(999);
+        });
+
+        it('should return null when accessing a field on null',
+           () => { expect(() => { expectEval('null?.a', td()).toEqual(null); }).not.toThrow(); });
+
+        it('should have the same priority as .', () => {
+          expect(() => { expectEval('null?.a.a', td()).toEqual(null); }).toThrowError();
+        });
+
+        if (!IS_DARTIUM) {
+          it('should return null when accessing a field on undefined', () => {
+            expect(() => { expectEval('_undefined?.a', td()).toEqual(null); }).not.toThrow();
+          });
+        }
+
+        it('should evaluate method calls',
+           () => { expectEval('a?.add(1,2)', td(td())).toEqual(3); });
+
+        it('should return null when accessing a method on null', () => {
+          expect(() => { expectEval('null?.add(1, 2)', td()).toEqual(null); }).not.toThrow();
+        });
+      });
+
       describe("method calls", () => {
         it("should evaluate method calls", () => {
           expectEval("fn()", td(0, 0, "constant")).toEqual("constant");