refactor(ivy): ngcc - extract file writing out into a class (#29092)

This is in preparation of having different file writing strategies.

PR Close #29092

packages/compiler-cli/ngcc/src/writing/file_writer.ts

@@ -0,0 +1,19 @@
+
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+import {EntryPoint} from '../packages/entry_point';
+import {EntryPointBundle} from '../packages/entry_point_bundle';
+import {FileInfo} from '../rendering/renderer';
+
+
+/**
+ * Responsible for writing out the transformed files to disk.
+ */
+export interface FileWriter {
+  writeBundle(entryPoint: EntryPoint, bundle: EntryPointBundle, transformedFiles: FileInfo[]): void;
+}

packages/compiler-cli/ngcc/src/writing/in_place_file_writer.ts

@@ -0,0 +1,40 @@
+
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {dirname} from 'canonical-path';
+import {existsSync, writeFileSync} from 'fs';
+import {mkdir, mv} from 'shelljs';
+
+import {EntryPoint} from '../packages/entry_point';
+import {EntryPointBundle} from '../packages/entry_point_bundle';
+import {FileInfo} from '../rendering/renderer';
+
+import {FileWriter} from './file_writer';
+
+/**
+ * This FileWriter overwrites the transformed file, in-place, while creating
+ * a back-up of the original file with an extra `.bak` extension.
+ */
+export class InPlaceFileWriter implements FileWriter {
+  writeBundle(_entryPoint: EntryPoint, _bundle: EntryPointBundle, transformedFiles: FileInfo[]) {
+    transformedFiles.forEach(file => this.writeFileAndBackup(file));
+  }
+  protected writeFileAndBackup(file: FileInfo): void {
+    mkdir('-p', dirname(file.path));
+    const backPath = file.path + '.__ivy_ngcc_bak';
+    if (existsSync(backPath)) {
+      throw new Error(
+          `Tried to overwrite ${backPath} with an ngcc back up file, which is disallowed.`);
+    }
+    if (existsSync(file.path)) {
+      mv(file.path, backPath);
+    }
+    writeFileSync(file.path, file.contents, 'utf8');
+  }
+}