fix(router): handle urls with only secondary top-level segments

modules/@angular/router/test/recognize.spec.ts

@@ -494,6 +494,22 @@ describe('recognize', () => {
               checkActivatedRoute(c[1], 'c', {}, ComponentC, 'aux');
             });
       });
+
+      it('should work when split is at the root level', () => {
+        checkRecognize(
+            [
+              {path: '', component: ComponentA}, {path: 'b', component: ComponentB},
+              {path: 'c', component: ComponentC, outlet: 'aux'}
+            ],
+            '(aux:c)', (s: RouterStateSnapshot) => {
+              checkActivatedRoute(s.root, '', {}, RootComponent);
+
+              const children = s.children(s.root);
+              expect(children.length).toEqual(2);
+              checkActivatedRoute(children[0], '', {}, ComponentA);
+              checkActivatedRoute(children[1], 'c', {}, ComponentC, 'aux');
+            });
+      });
     });
 
     describe('split at the end (right child)', () => {

modules/@angular/router/test/url_serializer.spec.ts

@@ -6,7 +6,6 @@ describe('url serializer', () => {
 
   it('should parse the root url', () => {
     const tree = url.parse('/');
-
     expectSegment(tree.root, '');
     expect(url.serialize(tree)).toEqual('/');
   });
@@ -27,6 +26,26 @@ describe('url serializer', () => {
     expect(url.serialize(tree)).toEqual('/one/two(left:three//right:four)');
   });
 
+  it('should parse top-level nodes with only secondary segment', () => {
+    const tree = url.parse('/(left:one)');
+
+    expect(tree.root.numberOfChildren).toEqual(1);
+    expectSegment(tree.root.children['left'], 'one');
+
+    expect(url.serialize(tree)).toEqual('/(left:one)');
+  });
+
+  it('should parse nodes with only secondary segment', () => {
+    const tree = url.parse('/one/(left:two)');
+
+    const one = tree.root.children[PRIMARY_OUTLET];
+    expectSegment(one, 'one', true);
+    expect(one.numberOfChildren).toEqual(1);
+    expectSegment(one.children['left'], 'two');
+
+    expect(url.serialize(tree)).toEqual('/one/(left:two)');
+  });
+
   it('should not parse empty path segments with params', () => {
     expect(() => url.parse('/one/two/(;a=1//right:;b=2)'))
         .toThrowError(/Empty path url segment cannot have parameters/);
@@ -167,6 +186,9 @@ describe('url serializer', () => {
 });
 
 function expectSegment(segment: UrlSegment, expected: string, hasChildren: boolean = false): void {
+  if (segment.pathsWithParams.filter(s => s.path === '').length > 0) {
+    throw new Error(`UrlPathWithParams cannot be empty ${segment.pathsWithParams}`);
+  }
   const p = segment.pathsWithParams.map(p => serializePath(p)).join('/');
   expect(p).toEqual(expected);
   expect(Object.keys(segment.children).length > 0).toEqual(hasChildren);