fix(router): remove parenthesis for primary outlet segment after removing auxiliary outlet segment (#24656) (#37163)

For URLs that use auxiliary route outlets in the second or following path segments,
when removing the auxiliary route segment, parenthesis remain for the primary outlet segment.
This causes the following error when trying to reload an URL: "Cannot match any route".
The commit adds a check for this scenario, serializing the URL as "a/b" instead of "a/(b)".

PR Close #24656

PR Close #37163

packages/router/src/url_tree.ts

@@ -341,6 +341,11 @@ function serializeSegment(segment: UrlSegmentGroup, root: boolean): string {
       return [`${k}:${serializeSegment(v, false)}`];
     });
 
+    // use no parenthesis if the only child is a primary outlet route
+    if (Object.keys(segment.children).length === 1 && segment.children[PRIMARY_OUTLET] != null) {
+      return `${serializePaths(segment)}/${children[0]}`;
+    }
+
     return `${serializePaths(segment)}/(${children.join('//')})`;
   }
 }

packages/router/test/create_url_tree.spec.ts

@@ -128,6 +128,12 @@ describe('createUrlTree', () => {
     expect(serializer.serialize(t)).toEqual('/a');
   });
 
+  it('should support removing parenthesis for primary segment on second path element', () => {
+    const p = serializer.parse('/a/(b//right:c)');
+    const t = createRoot(p, ['a', {outlets: {right: null}}]);
+    expect(serializer.serialize(t)).toEqual('/a/b');
+  });
+
   it('should update matrix parameters', () => {
     const p = serializer.parse('/a;pp=11');
     const t = createRoot(p, ['/a', {pp: 22, dd: 33}]);

packages/router/test/integration.spec.ts

@@ -3351,7 +3351,7 @@ describe('Integration', () => {
              advance(fixture);
 
              expect(log.map((a: any) => a.path)).toEqual(['b']);
-             expect(location.path()).toEqual('/two-outlets/(a)');
+             expect(location.path()).toEqual('/two-outlets/a');
            })));
 
         it('works with a nested route',