fix: make file name deterministic in parallel emits (fix rollup#4909)

src/utils/FileEmitter.ts

@@ -365,14 +365,23 @@ export class FileEmitter {
 		if (!fileName) {
 			const sourceHash = getSourceHash(source);
 			fileName = fileNamesBySource.get(sourceHash);
-			if (!fileName) {
-				fileName = generateAssetFileName(
-					consumedFile.name,
-					source,
-					sourceHash,
-					outputOptions,
-					bundle
-				);
+			const newFileName = generateAssetFileName(
+				consumedFile.name,
+				source,
+				sourceHash,
+				outputOptions,
+				bundle
+			);
+			// make sure file name deterministic in parallel emits, always use the shorter and smaller file name
+			if (
+				!fileName ||
+				fileName.length > newFileName.length ||
+				(fileName.length === newFileName.length && fileName.localeCompare(newFileName) > 0)
+			) {
+				if (fileName) {
+					delete bundle[fileName];
+				}
+				fileName = newFileName;
 				fileNamesBySource.set(sourceHash, fileName);
 			}
 		}

test/chunking-form/samples/emit-file/deduplicate-assets/_config.js

@@ -1,16 +1,35 @@
+function asyncify(callback) {
+	const time = Math.round(Math.random() * 100);
+
+	return new Promise(resolve => {
+		setTimeout(() => {
+			callback();
+			resolve();
+		}, time);
+	});
+}
 module.exports = {
 	description: 'deduplicates asset that have the same source',
+	solo: true,
 	options: {
 		input: ['main.js'],
 		plugins: {
-			buildStart() {
-				this.emitFile({ type: 'asset', name: 'string.txt', source: 'string' });
-				this.emitFile({ type: 'asset', name: 'stringSameSource.txt', source: 'string' });
-				this.emitFile({
-					type: 'asset',
-					name: 'sameStringAsBuffer.txt',
-					source: Buffer.from('string') // Test cross Buffer/string deduplication
-				});
+			async buildStart() {
+				await Promise.all([
+					asyncify(() => this.emitFile({ type: 'asset', name: 'string1.txt', source: 'string' })),
+					asyncify(() => this.emitFile({ type: 'asset', name: 'string2.txt', source: 'string' })),
+					asyncify(() =>
+						this.emitFile({ type: 'asset', name: 'stringSameSource.txt', source: 'string' })
+					),
+					asyncify(() =>
+						this.emitFile({
+							type: 'asset',
+							name: 'sameStringAsBuffer.txt',
+							source: Buffer.from('string') // Test cross Buffer/string deduplication
+						})
+					)
+				]);
+
 				// Different string source
 				this.emitFile({ type: 'asset', name: 'otherString.txt', source: 'otherString' });