feat(babel): add includeChunks/excludeChunks to filter generated-code transforms by manual chunk name; docs + tests

Author: CharlieHelps

packages/babel/README.md

@@ -200,6 +200,30 @@ export default {
 
 The `include`, `exclude` and `extensions` options are ignored when using `getBabelOutputPlugin` and `createBabelOutputPluginFactory` will produce warnings, and there are a few more points to note that users should be aware of.
 
+When transforming generated code, you can instead control which chunks are processed by matching their manual chunk names via the `includeChunks`/`excludeChunks` options. These patterns are matched against `chunk.name` as provided to Rollup's `renderChunk` hook and are especially useful to skip already-transpiled/minified vendor chunks:
+
+```js
+// rollup.config.js
+import { getBabelOutputPlugin } from '@rollup/plugin-babel';
+
+export default {
+  input: 'main.js',
+  manualChunks(id) {
+    if (id.includes('big-library')) return 'vendor';
+  },
+  output: {
+    format: 'es',
+    plugins: [
+      getBabelOutputPlugin({
+        presets: ['@babel/preset-env'],
+        // Do not transform the 'vendor' manual chunk
+        excludeChunks: ['vendor']
+      })
+    ]
+  }
+};
+```
+
 You can also run the plugin twice on the code, once when processing the input files to transpile special syntax to JavaScript and once on the output to transpile to a lower compatibility target:
 
 ```js

packages/babel/src/index.js

@@ -209,6 +209,9 @@ function createBabelOutputPluginFactory(customCallback = returnObject) {
       overrides
     );
 
+    // cache for chunk name filter (includeChunks/excludeChunks)
+    let chunkNameFilter;
+
     return {
       name: 'babel',
 
@@ -234,6 +237,9 @@ function createBabelOutputPluginFactory(customCallback = returnObject) {
         /* eslint-disable no-unused-vars */
         const {
           allowAllFormats,
+          // new: allow filtering of generated chunks by name
+          includeChunks,
+          excludeChunks,
           exclude,
           extensions,
           externalHelpers,
@@ -243,6 +249,16 @@ function createBabelOutputPluginFactory(customCallback = returnObject) {
           ...babelOptions
         } = unpackOutputPluginOptions(pluginOptionsWithOverrides, outputOptions);
         /* eslint-enable no-unused-vars */
+        // If includeChunks/excludeChunks are specified, filter by chunk.name
+        if (includeChunks != null || excludeChunks != null) {
+          if (!chunkNameFilter) {
+            chunkNameFilter = createFilter(includeChunks, excludeChunks, { resolve: false });
+          }
+          if (!chunkNameFilter(chunk.name)) {
+            // Skip transforming this chunk
+            return null;
+          }
+        }
 
         return transformCode(code, babelOptions, overrides, customOptions, this);
       }

packages/babel/test/as-output-plugin.mjs

@@ -378,3 +378,34 @@ console.log(\`the answer is \${answer}\`);
 `
   );
 });
+
+test('allows excluding manual chunks from output transform via `excludeChunks`', async (t) => {
+  const bundle = await rollup({
+    input: `${FIXTURES}chunks/main.js`
+  });
+
+  const output = await getCode(
+    bundle,
+    {
+      format: 'es',
+      manualChunks(id) {
+        // Place the dependency into a named manual chunk
+        if (id.endsWith(`${nodePath.sep}chunks${nodePath.sep}dep.js`)) return 'vendor';
+        return undefined;
+      },
+      plugins: [
+        getBabelOutputPlugin({
+          // Transform generated code but skip the 'vendor' manual chunk
+          presets: ['@babel/env'],
+          excludeChunks: ['vendor']
+        })
+      ]
+    },
+    true
+  );
+
+  const codes = output.map(({ code }) => code);
+  // The vendor chunk should remain untransformed and contain the arrow function as-is
+  // Debug output intentionally omitted
+  t.true(codes.some((c) => c.includes('=> 42')));
+});

packages/babel/types/index.d.ts

@@ -48,6 +48,16 @@ export interface RollupBabelOutputPluginOptions
    * @default false
    */
   allowAllFormats?: boolean;
+  /**
+   * Limit transforming of generated code to specific manual chunks by name.
+   * These patterns are matched against the `chunk.name` value in Rollup's `renderChunk` hook.
+   */
+  includeChunks?: FilterPattern;
+  /**
+   * Exclude specific manual chunks by name from transforming the generated code.
+   * These patterns are matched against the `chunk.name` value in Rollup's `renderChunk` hook.
+   */
+  excludeChunks?: FilterPattern;
 }
 
 export type RollupBabelCustomInputPluginOptions = (