feat(@schematics/angular): add migration to remove emitDecoratorMetadata

Add migration to remove 'emitDecoratorMetadata' TypeScript compiler option. Decorator metadata is no longer needed by Angular.

Read more about this option here: https://www.typescriptlang.org/docs/handbook/decorators.html#metadata

packages/schematics/angular/migrations/migration-collection.json

@@ -134,6 +134,11 @@
       "version": "12.0.0-next.1",
       "factory": "./update-12/update-zonejs",
       "description": "Update 'zone.js' to version 0.11.x. Read more about this here: https://github.com/angular/angular/blob/master/packages/zone.js/CHANGELOG.md#breaking-changes-since-zonejs-v0111"
+    },
+    "remove-emit-decorator-metadata": {
+      "version": "12.0.0-next.2",
+      "factory": "./update-12/remove-emit-decorator-metadata",
+      "description": "Remove 'emitDecoratorMetadata' TypeScript compiler option. Decorator metadata is no longer needed by Angular. Read more about this here: https://www.typescriptlang.org/docs/handbook/decorators.html#metadata"
     }
   }
 }

packages/schematics/angular/migrations/update-12/remove-emit-decorator-metadata.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 { join } from '@angular-devkit/core';
+import { DirEntry, Rule } from '@angular-devkit/schematics';
+import { JSONFile } from '../../utility/json-file';
+
+function* visitJsonFiles(directory: DirEntry): IterableIterator<string> {
+  for (const path of directory.subfiles) {
+    if (!path.endsWith('.json')) {
+      continue;
+    }
+
+    yield join(directory.path, path);
+  }
+
+  for (const path of directory.subdirs) {
+    if (path === 'node_modules' || path.startsWith('.')) {
+      continue;
+    }
+
+    yield* visitJsonFiles(directory.dir(path));
+  }
+}
+
+export default function (): Rule {
+  return tree => {
+    for (const path of visitJsonFiles(tree.root)) {
+      const content = tree.read(path);
+      if (content?.toString().includes('"emitDecoratorMetadata"')) {
+        const json = new JSONFile(tree, path);
+        json.remove(['compilerOptions', 'emitDecoratorMetadata']);
+      }
+    }
+  };
+}

packages/schematics/angular/migrations/update-12/remove-emit-decorator-metadata_spec.ts

@@ -0,0 +1,69 @@
+/**
+ * @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 { EmptyTree } from '@angular-devkit/schematics';
+import { SchematicTestRunner, UnitTestTree } from '@angular-devkit/schematics/testing';
+import { parse as parseJson } from 'jsonc-parser';
+
+describe('Migration to remove "emitDecoratorMetadata" compiler option', () => {
+  const schematicName = 'remove-emit-decorator-metadata';
+
+  const schematicRunner = new SchematicTestRunner(
+    'migrations',
+    require.resolve('../migration-collection.json'),
+  );
+
+  // tslint:disable-next-line: no-any
+  function readJsonFile(tree: UnitTestTree, filePath: string): any {
+    return parseJson(tree.readContent(filePath).toString());
+  }
+
+  let tree: UnitTestTree;
+  beforeEach(() => {
+    tree = new UnitTestTree(new EmptyTree());
+  });
+
+  it(`should rename 'emitDecoratorMetadata' when set to false`, async () => {
+    tree.create('/tsconfig.json', JSON.stringify({
+      compilerOptions: {
+        emitDecoratorMetadata: false,
+        strict: true,
+      },
+    }, undefined, 2));
+
+    const newTree = await schematicRunner.runSchematicAsync(schematicName, {}, tree).toPromise();
+    const { compilerOptions } = readJsonFile(newTree, '/tsconfig.json');
+    expect(compilerOptions['emitDecoratorMetadata']).toBeUndefined();
+    expect(compilerOptions['strict']).toBeTrue();
+  });
+
+  it(`should rename 'emitDecoratorMetadata' when set to true`, async () => {
+    tree.create('/tsconfig.json', JSON.stringify({
+      compilerOptions: {
+        emitDecoratorMetadata: true,
+        strict: true,
+      },
+    }, undefined, 2));
+
+    const newTree = await schematicRunner.runSchematicAsync(schematicName, {}, tree).toPromise();
+    const { compilerOptions } = readJsonFile(newTree, '/tsconfig.json');
+    expect(compilerOptions['emitDecoratorMetadata']).toBeUndefined();
+    expect(compilerOptions['strict']).toBeTrue();
+  });
+
+  it(`should not rename 'emitDecoratorMetadata' when it's not under 'compilerOptions'`, async () => {
+    tree.create('/foo.json', JSON.stringify({
+      options: {
+        emitDecoratorMetadata: true,
+      },
+    }, undefined, 2));
+
+    const newTree = await schematicRunner.runSchematicAsync(schematicName, {}, tree).toPromise();
+    const { options } = readJsonFile(newTree, '/foo.json');
+    expect(options['emitDecoratorMetadata']).toBeTrue();
+  });
+});