feat: add support for preserving comments in code

Useful for preserving `/*#__PURE__*/` annotations that aid tree shaking.
facebook · Apr 19, 2023 · 227989b · 227989b
1 parent 6900e87
commit 227989b
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Showing 4 changed files with 30 additions and 3 deletions.
diff --git a/packages/metro-config/src/__tests__/__snapshots__/loadConfig-test.js.snap b/packages/metro-config/src/__tests__/__snapshots__/loadConfig-test.js.snap
@@ -151,6 +151,7 @@ Object {
     "unstable_dependencyMapReservedName": null,
     "unstable_disableModuleWrapping": false,
     "unstable_disableNormalizePseudoGlobals": false,
+    "unstable_preserveComments": false,
     "workerPath": "metro/src/DeltaBundler/Worker",
   },
   "transformerPath": "",
@@ -329,6 +330,7 @@ Object {
     "unstable_dependencyMapReservedName": null,
     "unstable_disableModuleWrapping": false,
     "unstable_disableNormalizePseudoGlobals": false,
+    "unstable_preserveComments": false,
     "workerPath": "metro/src/DeltaBundler/Worker",
   },
   "transformerPath": "",
@@ -507,6 +509,7 @@ Object {
     "unstable_dependencyMapReservedName": null,
     "unstable_disableModuleWrapping": false,
     "unstable_disableNormalizePseudoGlobals": false,
+    "unstable_preserveComments": false,
     "workerPath": "metro/src/DeltaBundler/Worker",
   },
   "transformerPath": "",
@@ -685,6 +688,7 @@ Object {
     "unstable_dependencyMapReservedName": null,
     "unstable_disableModuleWrapping": false,
     "unstable_disableNormalizePseudoGlobals": false,
+    "unstable_preserveComments": false,
     "workerPath": "metro/src/DeltaBundler/Worker",
   },
   "transformerPath": "",

diff --git a/packages/metro-config/src/defaults/index.js b/packages/metro-config/src/defaults/index.js
@@ -134,6 +134,7 @@ const getDefaultValues = (projectRoot: ?string): ConfigT => ({
     unstable_disableModuleWrapping: false,
     unstable_disableNormalizePseudoGlobals: false,
     unstable_compactOutput: false,
+    unstable_preserveComments: false,
   },
   watcher: {
     additionalExts,

diff --git a/packages/metro-transform-worker/src/__tests__/index-test.js b/packages/metro-transform-worker/src/__tests__/index-test.js
@@ -63,6 +63,7 @@ const baseConfig: JsTransformerConfig = {
   unstable_disableModuleWrapping: false,
   unstable_disableNormalizePseudoGlobals: false,
   unstable_allowRequireContext: false,
+  unstable_preserveComments: false,
 };
 
 beforeEach(() => {
@@ -583,3 +584,23 @@ it('counts all line endings correctly', async () => {
     standardEndingsResult.output[0].data.lineCount,
   );
 });
+
+it('allows preservation of comments', async () => {
+  const result = await Transformer.transform(
+    {...baseConfig, unstable_preserveComments: true},
+    '/root',
+    'local/file.js',
+    Buffer.from('/*#__PURE__*/arbitrary(code);', 'utf8'),
+    // $FlowFixMe[prop-missing] Added when annotating Transformer.
+    {
+      dev: false,
+      minify: false,
+      type: 'module',
+    },
+  );
+  expect(result.output[0].data.code).toMatchInlineSnapshot(`
+    "__d(function (global, _$$_REQUIRE, _$$_IMPORT_DEFAULT, _$$_IMPORT_ALL, module, exports, _dependencyMap) {
+      /*#__PURE__*/arbitrary(code);
+    });"
+  `);
+});
diff --git a/packages/metro-transform-worker/src/index.js b/packages/metro-transform-worker/src/index.js
@@ -96,6 +96,7 @@ export type JsTransformerConfig = $ReadOnly<{
   unstable_compactOutput: boolean,
   /** Enable `require.context` statements which can be used to import multiple files in a directory. */
   unstable_allowRequireContext: boolean,
+  unstable_preserveComments: boolean,
 }>;
 
 export type {CustomTransformOptions} from 'metro-babel-transformer';
@@ -299,7 +300,7 @@ async function transformJS(
       babelrc: false,
       code: false,
       configFile: false,
-      comments: false,
+      comments: config.unstable_preserveComments,
       filename: file.filename,
       plugins,
       sourceMaps: false,
@@ -322,7 +323,7 @@ async function transformJS(
         babelrc: false,
         code: false,
         configFile: false,
-        comments: false,
+        comments: config.unstable_preserveComments,
         filename: file.filename,
         plugins: [
           [metroTransformPlugins.constantFoldingPlugin, babelPluginOpts],
@@ -407,7 +408,7 @@ async function transformJS(
   const result = generate(
     wrappedAst,
     {
-      comments: false,
+      comments: config.unstable_preserveComments,
       compact: config.unstable_compactOutput,
       filename: file.filename,
       retainLines: false,