fix(@angular-devkit/core): rename to itself should be a noop

Author: clydin

packages/angular_devkit/core/src/virtual-fs/host/record.ts

@@ -271,12 +271,16 @@ export class CordHost extends SimpleMemoryHost {
     ).pipe(
       toArray(),
       switchMap(([existTo, existFrom]) => {
-        if (existTo) {
-          return throwError(new FileAlreadyExistException(to));
-        }
         if (!existFrom) {
           return throwError(new FileDoesNotExistException(from));
         }
+        if (from === to) {
+          return of();
+        }
+
+        if (existTo) {
+          return throwError(new FileAlreadyExistException(to));
+        }
 
         // If we're renaming a file that's been created, shortcircuit to creating the `to` path.
         if (this._filesToCreate.has(from)) {

packages/angular_devkit/core/src/virtual-fs/host/record_spec.ts

@@ -101,6 +101,29 @@ describe('CordHost', () => {
     done();
   });
 
+  it('works (create -> rename (identity))', done => {
+    const base = new TestHost({
+      '/hello': 'world',
+    });
+
+    const host = new CordHost(base);
+    host.write(path`/blue`, fileBuffer`hi`).subscribe(undefined, done.fail);
+    host.rename(path`/blue`, path`/blue`).subscribe(undefined, done.fail);
+
+    const target = new TestHost();
+    host.commit(target).subscribe(undefined, done.fail);
+
+    // Check that there's only 1 write done.
+    expect(target.records.filter(x => mutatingTestRecord.includes(x.kind))).toEqual([
+      { kind: 'write', path: path`/blue` },
+    ]);
+
+    expect(target.$exists('/hello')).toBe(false);
+    expect(target.$exists('/blue')).toBe(true);
+
+    done();
+  });
+
   it('works (create -> rename -> rename)', done => {
     const base = new TestHost({
       '/hello': 'world',