Sandbox::https://redirect.github.com/rollup/rollup/issues/6230

lukastaegert · 2026-01-04T06:35:43Z

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:

Description

When looking into #6120, I found the current handling of module exports and namespaces very limiting. This PR implements several changes and improvements:

deduplicate logic between NamespaceVariable and Module
do not always include the entire namespace in certain situations when only some properties are needed to improve tree-shaking
establish a "live-connection" between dynamic imports and namespaces in some situations for improved tree-shaking
enforce consistent order of generated exports and re-exports based on their names. This only affects export { foo, bar } statements.

This implies the following changes:

When using const ns = await import(), you get full deep tree-shaking support for unused imports and object properties, even if the usages are elsewhere in the code.
When using import(…).then(ns => ), you only get top-level export tree-shaking. This is however a limit of the function property tree-shaking logic. If you use destructuring import(…).then(({ a, b: {c}}) => ), you instead get one-level deep property tree-shaking for the destructured variables depending on included variable usages.
When calling a namespace member via property access, i.e. ns.foo(), we now always include the entire namespace. The reason is that at the moment, we cannot easily track if ns.foo would access this, and if it did, it needs access to the entire namespace. This might be improved in the future.

vercel · 2026-01-04T06:35:47Z

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Project	Deployment	Review	Updated (UTC)
rollup	Ready	Preview, Comment	Jan 21, 2026 5:24am

github-actions · 2026-01-04T06:40:25Z

Thank you for your contribution! ❤️

You can try out this pull request locally by installing Rollup via

npm install rollup/rollup#refine-namespace-handling

Notice: Ensure you have installed the latest nightly Rust toolchain. If you haven't installed it yet, please see https://www.rust-lang.org/tools/install to learn how to download Rustup and install Rust.

or load it into the REPL:
https://rollup-hx9642wbb-rollup-js.vercel.app/repl/?pr=6230

github-actions · 2026-01-04T06:40:51Z

Performance report

BUILD: 7028ms, 830 MB (-3%)
- initialize: 0ms, 24.5 MB
- generate module graph: 2627ms, 637 MB
  - generate ast: 1380ms (+31ms, +2.3%), 626 MB
- sort and bind modules: 403ms, 702 MB
- mark included statements: 3978ms, 830 MB (-3%)
  - treeshaking pass 1: 2352ms, 829 MB
  - treeshaking pass 2: 458ms, 844 MB (+3%)
  - treeshaking pass 3: 394ms, 828 MB (-3%)
  - treeshaking pass 4: 382ms, 837 MB
  - treeshaking pass 5: 380ms, 830 MB (-3%)
GENERATE: 681ms, 910 MB
- initialize render: 0ms, 830 MB (-3%)
- generate chunks: 39ms (-11ms, -21.7%), 844 MB
  - optimize chunks: 0ms, 836 MB
- render chunks: 632ms (+13ms, +2.2%), 883 MB
- transform chunks: 17ms, 910 MB
- generate bundle: 0ms, 910 MB

codecov · 2026-01-04T06:53:00Z

Codecov Report

❌ Patch coverage is 99.46524% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 98.83%. Comparing base (6764d54) to head (2aadbf0).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/Module.ts	98.41%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6230      +/-   ##
==========================================
+ Coverage   98.81%   98.83%   +0.01%     
==========================================
  Files         272      273       +1     
  Lines       10717    10692      -25     
  Branches     2869     2849      -20     
==========================================
- Hits        10590    10567      -23     
+ Misses         85       82       -3     
- Partials       42       43       +1

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Copilot

Pull request overview

This PR refines namespace handling in Rollup with significant improvements to tree-shaking and module execution tracking for dynamic imports.

Changes:

Refactored namespace variable handling to deduplicate logic between NamespaceVariable and Module
Implemented smarter tree-shaking for namespaces by only including accessed properties instead of entire namespaces
Added "live-connection" tracking for dynamic imports via new PromiseHandler classes to improve tree-shaking of import().then() patterns
Restructured module export tracking using getExportedVariablesByName() instead of separate getAllExportNames() and getMemberVariables()

Reviewed changes

Copilot reviewed 151 out of 152 changed files in this pull request and generated 59 comments.

Show a summary per file

File	Description
src/ast/variables/PromiseHandler.ts	New file introducing `ObjectPromiseHandler` and `EmptyPromiseHandler` classes for tracking dynamic import promise chains
src/ast/variables/NamespaceVariable.ts	Refactored to use module's exported variables directly, added `includeMemberPath()` for selective inclusion, removed `getMemberVariables()`
src/ast/nodes/ImportExpression.ts	Major rewrite to track dynamic import resolution and establish live connections through promise handlers
src/Module.ts	Consolidated export tracking with `getExportedVariablesByName()`, removed `getAllExportNames()`, `getReexports()`, simplified `includeAllExports()`
src/ast/nodes/MemberExpression.ts	Added `promiseHandler` property to handle promise chain member access
test/function/samples/*	Multiple new test cases for namespace mutations and dynamic import tree-shaking
test/form/samples/*	Updated expected outputs reflecting improved tree-shaking
test/chunking-form/samples/*	New tests for dynamic import object property tree-shaking

Add general caching. The idea is to eventually merge this with the caching in NamespaceVariabe.getMemberVariables

This will make it easier to handle includes etc.

Instead of doing static analysis, this dynamically links the namespace to its usage. Currently, this is not as good, some test cases need to be analyzed if we can improve here.

* It was not easily to support optimizing (await import()).foo() because we cannot easily track if `foo` accesses `this`, in which case it could see the entire namespace. Added a regression test for this. * As .catch and .finally do not change property inclusion, we can now optimize cases where a .catch or .finally is followed by a .then * There was a bug in the synthetic namespace inclusion. Fixing this allows tree-shaking for synthetic namespaces.

This also simplifies return value deoptimization

github-actions · 2026-01-22T05:39:36Z

This PR has been released as part of rollup@4.56.0. You can test it via npm install rollup.

vercel Bot deployed to Preview January 4, 2026 06:36

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lukastaegert changed the title ~~Do not always include entire namespace when used as variable~~ Refine namespace handling Jan 4, 2026

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lukastaegert marked this pull request as ready for review January 16, 2026 15:41

Copilot AI review requested due to automatic review settings January 16, 2026 15:41

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TrickyPi mentioned this pull request Jan 17, 2026

Import expression effect check considers moduleSideEffects #6120

Closed

3 of 9 tasks

lukastaegert added 20 commits January 21, 2026 06:21

Do not always include entire namespace when used as variable

802889e

Refine export handling in module

057d534

Add general caching. The idea is to eventually merge this with the caching in NamespaceVariabe.getMemberVariables

Use cached exports in NamespaceVariable

09eafa9

Replace usages of cached namespace variables

573c600

Use cached map to get export names for variables

c5d61f4

Use cached map in more places

8b431d2

Use cached exports to replace list of export names

ee8a9d2

Separate namespace- and all-export-inclusion

bee81ab

Refine namespace inclusion

bdc9736

Break early in some loop

86a586e

Store ImportExpression resolution only on Node

6919203

This will make it easier to handle includes etc.

Dynamically include dynamic import members

973d609

Instead of doing static analysis, this dynamically links the namespace to its usage. Currently, this is not as good, some test cases need to be analyzed if we can improve here.

Ensure Promise handler return value is deoptimized for now

2672fec

Add test for deep object property tree-shaking

61390eb

Avoid some property accesses and improve names

1f9e2fc

Remove TODO

3175339

Ensure catch and finally handlers are always included and deoptimized

a4d6aa5

This also simplifies return value deoptimization

Reinstate system default export test

393da79

Clarify synthetic named export test

2aadbf0

lukastaegert force-pushed the refine-namespace-handling branch from 2241ea5 to 2aadbf0 Compare January 21, 2026 05:22

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lukastaegert merged commit 18ccab2 into master Jan 22, 2026
48 checks passed

lukastaegert deleted the refine-namespace-handling branch January 22, 2026 05:08

coderabbitai Bot mentioned this pull request May 6, 2026

ci: add-fixtures-and-generate-bundles ForgeRock/ping-javascript-sdk#627

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Refine namespace handling - #6230

Refine namespace handling#6230
lukastaegert merged 20 commits into
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