fix: remove unnecessary chunks

Author: privatenumber

src/cli.ts

@@ -14,6 +14,7 @@ import { cleanDist } from './utils/clean-dist.js';
 import type { EntryPointValid } from './utils/get-entry-points/types.js';
 import type { SrcDistPair } from './types.js';
 import { entrySymbol } from './rollup/types';
+import { filterUnnecessaryOutputs } from './rollup/plugins/filter-unnecessary-outputs.js';
 
 const { stringify } = JSON;
 
@@ -217,32 +218,7 @@ if (tsconfigTarget) {
 				return Promise.all(rollupConfig.output.map(
 					(outputOption) => {
 						const inputNames = outputOption[entrySymbol].inputNames!;
-
-						/**
-						 * pkgroll merges shared configs, which causes it to build extra entry points
-						 * that weren't actually requested. We need to filter those out here to:
-						 * - Avoid generating unnecessary output files
-						 * - Prevent unexpected files from overwriting the ones we actually want
-						 */
-						outputOption.plugins = [{
-							name: 'filter-unnecessary-outputs',
-							generateBundle: (_options, bundle) => {
-								for (const fileName in bundle) {
-									if (!Object.hasOwn(bundle, fileName)) {
-										continue;
-									}
-
-									const chunk = bundle[fileName];
-									if (
-										'isEntry' in chunk
-										&& chunk.isEntry
-										&& !inputNames.includes(chunk.name)
-									) {
-										delete bundle[fileName];
-									}
-								}
-							},
-						}];
+						outputOption.plugins = [filterUnnecessaryOutputs(inputNames)];
 
 						return build.write(outputOption);
 					},

src/rollup/plugins/filter-unnecessary-outputs.ts

@@ -0,0 +1,53 @@
+import type { Plugin, OutputChunk } from 'rollup';
+
+/**
+ * pkgroll merges shared configs, which causes it to build extra entry points
+ * that weren't actually requested. We need to filter those out here to:
+ * - Avoid generating unnecessary output files
+ * - Prevent unexpected files from overwriting the ones we actually want
+ */
+export const filterUnnecessaryOutputs = (
+	inputNames: string[],
+): Plugin => ({
+	name: 'filter-unnecessary-outputs',
+	generateBundle: (_options, bundle) => {
+		const allChunkFileNames = Object.keys(bundle).filter(
+			fileName => bundle[fileName]!.type === 'chunk',
+		);
+
+		const queue: string[] = [];
+		for (const fileName of allChunkFileNames) {
+			const chunk = bundle[fileName] as OutputChunk;
+			if (
+				chunk.isEntry
+				&& inputNames.includes(chunk.name)
+			) {
+				queue.push(fileName);
+			}
+		}
+
+		const chunksToKeep = new Set<string>();
+		while (queue.length > 0) {
+			const fileName = queue.shift()!;
+			const chunk = bundle[fileName];
+			if (
+				// Can be an externalized import
+				!chunk
+				|| chunksToKeep.has(fileName)
+			) {
+				continue;
+			}
+
+			chunksToKeep.add(fileName);
+			for (const imported of (chunk as OutputChunk).dynamicImports) {
+				queue.push(imported);
+			}
+		}
+
+		for (const fileName of allChunkFileNames) {
+			if (!chunksToKeep.has(fileName)) {
+				delete bundle[fileName];
+			}
+		}
+	},
+});

tests/specs/builds/output-dual.ts

@@ -31,5 +31,45 @@ export default testSuite(({ describe }, nodePath: string) => {
 				'value.mjs',
 			]);
 		});
+
+		test('no unnecessary chunks', async () => {
+			await using fixture = await createFixture({
+				src: {
+					'index-a.js': 'import("./chunk-a.js")',
+					'chunk-a.js': 'console.log(1)',
+
+					'index-b.js': 'import("./chunk-b.js")',
+					'chunk-b.js': 'console.log(1)',
+
+					'index-c.js': 'import("./chunk-b.js")',
+				},
+				'package.json': createPackageJson({
+					exports: {
+						'./a': './dist/index-a.cjs',
+						'./b': './dist/index-b.mjs',
+						'./c': './dist/index-c.cjs',
+					},
+				}),
+			});
+
+			const pkgrollProcess = await pkgroll([], {
+				cwd: fixture.path,
+				nodePath,
+			});
+			expect(pkgrollProcess.exitCode).toBe(0);
+			expect(pkgrollProcess.stderr).toBe('');
+
+			const files = await fs.readdir(fixture.getPath('dist'));
+			files.sort();
+
+			expect(files).toStrictEqual([
+				'chunk-a-BeOsALY6.cjs',
+				'chunk-b-BeOsALY6.cjs',
+				'chunk-b-BrZXlwf9.mjs',
+				'index-a.cjs',
+				'index-b.mjs',
+				'index-c.cjs',
+			]);
+		});
 	});
 });