feat: unify manualChunks implementation and support object form regular expressions #6106

maiieul · 2025-09-13T16:39:32Z

This PR contains:

Are tests included?

yes (bugfixes and features will not be merged without tests)
no

Breaking Changes?

yes (breaking changes will not be merged unless absolutely necessary)
no

List any relevant issue numbers:

resolves 'manualChunks' gives inconsistent results for object and function #5090

Description

Unifies manualChunks object and function form APIs into the function form implementation. As such, removes the addManualChunks logic of the object form and related error messages and tests. I only removed the obvious code, maybe more can be cleaned up.
Allows passing regular expressions in object form.

The idea is that when the developer passes

    manualChunks: {
      vendor: ['lodash-es', 'clsx'],
    },

Rollup then converts it to

    manualChunks: (id) => {
      if (id.includes('lodash-es')) return 'vendor';
      if (id.includes('clsx')) return 'vendor';
    },

and then always uses the assignManualChunks logic, without the addStaticDependenciesToManualChunk merge logic.

This will also reduce the changes needed for #6087, and simplify the implementation of onlyExplicitManualChunks.

⚠️ Edit: This can lead to non-deterministic behavior beucase of the .includes. See closing comment below.

vercel · 2025-09-13T16:39:36Z

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maiieul · 2025-09-13T16:49:33Z

src/ast/nodes/Program.ts

 	private hasLoggedEffect = false;

 	hasCachedEffects(): boolean {
-		if (!this.included) {


This was re-added in https://github.com/rollup/rollup/pull/4921/files to solve #4908. This solved the error message but also introduced a test that I think is incorrect. Discussing below on the test itself.

maiieul · 2025-09-13T16:56:49Z

test/chunking-form/samples/manual-chunk-not-included/_config.js

 module.exports = defineTest({
-	description: 'handles manual chunks where the root is not part of the module graph',
+	description:
+		'does not output a bundle for the manual chunks that are not part of the module graph',


I don't think this counts as a breaking change.

With the behavior after #4921, Rollup will artificially output a bundle for the manualChunks pattern provided if it was not in the module graph, but it won't be used by any bundle, unless Rollup merges some dependencies into it, which was the case in this test.

maiieul · 2025-09-13T16:58:52Z

test/function/samples/emit-chunk-manual-asset-source/main.js

@@ -1 +1,3 @@
+import './manual';


makes sure that manual.js is part of the module graph

maiieul · 2025-09-13T16:58:57Z

test/function/samples/emit-chunk-manual/main.js

@@ -1 +1,3 @@
+import './manual';


makes sure that manual.js is part of the module graph

maiieul · 2025-09-13T16:59:54Z

test/function/samples/manual-chunks-conflict/_config.js

-	},
-	generateError: {
-		code: 'INVALID_CHUNK',
-		message: 'Cannot assign "dep.js" to the "dep2" chunk as it is already in the "dep1" chunk.'


This won't happen anymore. I removed the related log error message code.

maiieul · 2025-09-13T17:00:37Z

test/function/samples/manual-chunks-include-external-modules/_config.js

-	},
-	generateError: {
-		code: 'EXTERNAL_MODULES_CANNOT_BE_INCLUDED_IN_MANUAL_CHUNKS',
-		message: `"${externalModule}" cannot be included in manualChunks because it is resolved as an external module by the "external" option or plugins.`


This won't happen anymore. I removed the related log error message code.

maiieul · 2025-09-13T17:00:50Z

test/function/samples/manual-chunks-include-external-modules3/_config.js

-	},
-	generateError: {
-		code: 'EXTERNAL_MODULES_CANNOT_BE_TRANSFORMED_TO_MODULES',
-		message: `${externalModule} is resolved as a module now, but it was an external module before. Please check whether there are conflicts in your Rollup options "external" and "manualChunks", manualChunks cannot include external modules.`


This won't happen anymore. I removed the related log error message code.

…ar expressions

maiieul · 2025-09-13T18:30:39Z

docs/configuration-options/index.md

 ```

-will put all lodash modules into a manual chunk even if you are only using imports of the form `import get from 'lodash/get'`.
+will put all lodash modules into a `lodash` chunk.


Removed the note about modules not needing to be part of the module graph since this is no longer true. See the manual-chunk-not-included test below.

The PR doesn't affect the behavior outlined in the docs though. I tested on a repro with lodash using import get from 'lodash/get' and the modules were properly grouped together into the lodash chunk. So I guess the statement wasn't really accurate to begin with.

maiieul · 2025-09-16T08:10:30Z

Closing, because this approach can lead to non-deterministic behavior.

It turns out that

    manualChunks: {
      vendor: ['lodash-es', 'clsx'],
    },

and

    manualChunks: (id) => {
      if (id.includes('lodash-es')) return 'vendor';
      if (id.includes('clsx')) return 'vendor';
    },

are not the same.

In basic use cases such as in this example it is the same and unlikely to pose a problem, but imagine that the developer passes vendor: [..., 'utils']; then that would be converted to if (id.includes('utils')) return 'vendor';, which would put all modules that include 'utils' in their path into the same chunk. The object form on the other hand would create an entry for the utils file if it can resolve it, and add it to the manualChunk alias.

We cannot use endsWith or similar because the id might not end with the pattern exactly (e.g. with lodash-es it is /.../node_modules/lodash-es/lodash.js, etc.)

I tried to play with some ways to solve the problem, but it seems the best way to be deterministic with the object form is to be through the current logic of addManualChunks -> getChunkAssignments -> getChunkDefinitionsFromManualChunks -> addStaticDependenciesToManualChunk.

vercel bot deployed to Preview September 13, 2025 16:40 View deployment

maiieul commented Sep 13, 2025

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vercel bot deployed to Preview September 13, 2025 17:18 View deployment

maiieul marked this pull request as ready for review September 13, 2025 17:54

maiieul added 4 commits September 13, 2025 20:23

docs: remove unnecessary note

fe6cea9

feat: unify manualChunks implementation and support object form regul…

75132a8

…ar expressions

refactor: clean up legacy code

2a909f7

test: object form regexp

17b8526

maiieul force-pushed the unify-manualChunks-impl-plus-support-obj-regexps branch from ffe5ca7 to e8682a5 Compare September 13, 2025 18:25

docs: add RegExp type

9c83296

maiieul force-pushed the unify-manualChunks-impl-plus-support-obj-regexps branch from e8682a5 to 9c83296 Compare September 13, 2025 18:26

vercel bot deployed to Preview September 13, 2025 18:28 View deployment

maiieul commented Sep 13, 2025

View reviewed changes

maiieul marked this pull request as draft September 14, 2025 09:42

maiieul closed this Sep 16, 2025

maiieul mentioned this pull request Sep 16, 2025

fix: manualChunks and non manualChunks shared dependencies are merged with the first manualChunk encountered alphabetically #6087

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feat: unify manualChunks implementation and support object form regular expressions #6106

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