fix(mcs): `entriesAware` should calculate sizes without duplication by hyf0 · Pull Request #8887 · rolldown/rolldown

hyf0 · 2026-03-24T06:40:20Z

Summary

Fix: entriesAware subgroups no longer have duplicated shared dependencies, which inflated sizes and broke entriesAwareMergeThreshold comparisons
Refactor: module_groups uses IndexVec for regular groups; entries-aware groups stay in a Vec for flexible post-processing (split by bitset, merge, then push into IndexVec)
New test: entries_aware_merge_shared_deps — fails on main (shared deps duplicated → inflated sizes → no merge), passes after fix
Design doc: meta/design/manual-code-splitting.md — visual explanation of entriesAware flow

The bug

On main, ModuleGroupId includes each module's own bitset, creating separate subgroups during build. With includeDependenciesRecursively, shared dependencies get added to each subgroup independently:

lib-a.js (bits={A}) → subgroup {A}, deps add shared-dep.js
lib-b.js (bits={B}) → subgroup {B}, deps add shared-dep.js  ← DUPLICATE

subgroup {A} = [lib-a, shared-dep]  size: 150  (inflated)
subgroup {B} = [lib-b, shared-dep]  size: 150  (inflated)

Inflated sizes cause entriesAwareMergeThreshold to skip merges that should happen.

The fix

Build entries-aware groups as a flat group first, then split by bitset as post-processing. Each module appears in exactly one subgroup based on its own bits:

flat group = [lib-a, lib-b, shared-dep]

split by bits:
  {A}     → [lib-a]       size: 30   ← correct
  {B}     → [lib-b]       size: 30   ← correct
  {A, B}  → [shared-dep]  size: 100  ← counted once

Test plan

cargo test -p rolldown -- entries_aware (5 tests pass)
cargo test -p rolldown -- advanced_chunks (25 tests pass)
New test entries_aware_merge_shared_deps fails on main, passes on this branch

🤖 Generated with Claude Code

hyf0 · 2026-03-24T06:40:31Z

fix(mcs): entriesAware should calculate sizes without duplication #8887 👈 (View in Graphite)
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Copilot

Pull request overview

This PR fixes manualCodeSplitting.groups[].entriesAware size calculation so shared dependencies aren’t double-counted across per-entry subgroups, which previously caused incorrect entriesAwareMergeThreshold decisions.

Changes:

Refactors manual code splitting to collect a flat entriesAware group first, then split into bitset-based subgroups and merge small subgroups by threshold.
Adds an integration test fixture + snapshot ensuring shared deps don’t inflate subgroup sizes and incorrectly prevent merging.
Adds a design doc explaining entriesAware, why “flat-then-split” matters, and how subgroup merging works.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
`crates/rolldown/src/stages/generate_stage/manual_code_splitting.rs`	Implements flat collection for `entriesAware`, post-split subgroup sizing, and updated merge flow.
`crates/rolldown/tests/rolldown/function/advanced_chunks/entries_aware_merge_shared_deps/_config.json`	New regression test configuration for the shared-deps + merge-threshold scenario.
`crates/rolldown/tests/rolldown/function/advanced_chunks/entries_aware_merge_shared_deps/_test.mjs`	Asserts no per-entry vendor chunks are produced when subgroups should merge.
`crates/rolldown/tests/rolldown/function/advanced_chunks/entries_aware_merge_shared_deps/artifacts.snap`	Snapshot validating the expected chunk layout/output.
`crates/rolldown/tests/rolldown/function/advanced_chunks/entries_aware_merge_shared_deps/{entry-a.js,entry-b.js,lib-a.js,lib-b.js,shared-dep.js}`	Test fixture modules used to reproduce the duplication/inflated-size bug.
`meta/design/manual-code-splitting.md`	New documentation describing `entriesAware` mechanics and merge behavior.

crates/rolldown/src/stages/generate_stage/manual_code_splitting.rs

codspeed-hq · 2026-03-24T06:49:12Z

Merging this PR will not alter performance

✅ 4 untouched benchmarks
⏩ 10 skipped benchmarks¹

_{Comparing 03-24-fix_mcs_entriesaware_should_calculate_sizes_without_duplication (54e2cba) with main (efad975)}

10 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

netlify · 2026-03-24T07:02:49Z

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hyf0 · 2026-03-24T08:15:53Z

Merge activity

Mar 24, 8:15 AM UTC: The merge label 'graphite: merge-when-ready' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
Mar 24, 8:15 AM UTC: hyf0 added this pull request to the Graphite merge queue.
Mar 24, 8:20 AM UTC: Merged by the Graphite merge queue.

…8887) ## Summary - **Fix**: `entriesAware` subgroups no longer have duplicated shared dependencies, which inflated sizes and broke `entriesAwareMergeThreshold` comparisons - **Refactor**: `module_groups` uses `IndexVec` for regular groups; entries-aware groups stay in a `Vec` for flexible post-processing (split by bitset, merge, then push into IndexVec) - **New test**: `entries_aware_merge_shared_deps` — fails on `main` (shared deps duplicated → inflated sizes → no merge), passes after fix - **Design doc**: `meta/design/manual-code-splitting.md` — visual explanation of `entriesAware` flow ## The bug On `main`, `ModuleGroupId` includes each module's own bitset, creating separate subgroups during build. With `includeDependenciesRecursively`, shared dependencies get added to **each** subgroup independently: ``` lib-a.js (bits={A}) → subgroup {A}, deps add shared-dep.js lib-b.js (bits={B}) → subgroup {B}, deps add shared-dep.js ← DUPLICATE subgroup {A} = [lib-a, shared-dep] size: 150 (inflated) subgroup {B} = [lib-b, shared-dep] size: 150 (inflated) ``` Inflated sizes cause `entriesAwareMergeThreshold` to skip merges that should happen. ## The fix Build entries-aware groups as a **flat group first**, then split by bitset as post-processing. Each module appears in exactly one subgroup based on its own bits: ``` flat group = [lib-a, lib-b, shared-dep] split by bits: {A} → [lib-a] size: 30 ← correct {B} → [lib-b] size: 30 ← correct {A, B} → [shared-dep] size: 100 ← counted once ``` ## Test plan - [x] `cargo test -p rolldown -- entries_aware` (5 tests pass) - [x] `cargo test -p rolldown -- advanced_chunks` (25 tests pass) - [x] New test `entries_aware_merge_shared_deps` fails on `main`, passes on this branch 🤖 Generated with [Claude Code](https://claude.com/claude-code)

@hyf0

## [1.0.0-rc.12] - 2026-03-25 ### 🚀 Features - chunk-optimizer: skip circular dependency check when strict execution order is enabled (#8886) by @hyf0 ### 🐛 Bug Fixes - emit build warnings during watch mode rebuilds (#8897) by @IWANABETHATGUY - lazy-barrel: load import-then-export specifiers when barrel has local exports (#8895) by @shulaoda - correct execution order of transferred CJS init calls (#8877) by @IWANABETHATGUY - mcs: `entriesAware` should calculate sizes without duplication (#8887) by @hyf0 - non-deterministic chunk generation (#8882) by @sapphi-red - `is_top_level` incorrectly treats strict-mode scopes as top-level (#8878) by @Dunqing ### 🚜 Refactor - treeshake: migrate SideEffectDetector to Oxc's MayHaveSideEffects trait (#8624) by @Dunqing ### 🧪 Testing - make dev server tests deterministic by replacing fixed sleeps with event-driven polling (#8561) by @Boshen ### ⚙️ Miscellaneous Tasks - deps: update dependency vite-plus to v0.1.14 (#8902) by @camc314 - deps: update dependency oxfmt to ^0.42.0 (#8891) by @renovate[bot] - deps: update rust crate oxc_sourcemap to v6.1.1 (#8890) by @renovate[bot] - remove Rolldown MF plan (#8883) by @shulaoda - deps: update rollup submodule for tests to v4.60.0 (#8881) by @sapphi-red - deps: update test262 submodule for tests (#8880) by @sapphi-red - deps: upgrade oxc crates to 0.122.0 (#8879) by @shulaoda Co-authored-by: shulaoda <[email protected]>

github-actions bot assigned hyf0 Mar 24, 2026

hyf0 mentioned this pull request Mar 24, 2026

feat(chunk-optimizer): skip circular dependency check when strict execution order is enabled #8886

Merged

hyf0 marked this pull request as ready for review March 24, 2026 06:41

Copilot AI review requested due to automatic review settings March 24, 2026 06:41

Copilot started reviewing on behalf of hyf0 March 24, 2026 06:41 View session

hyf0 changed the base branch from 03-21-feat_chunk-optimizer_skip_circular_dependency_check_when_strict_execution_order_is_enabled to graphite-base/8887 March 24, 2026 06:42

hyf0 force-pushed the graphite-base/8887 branch from abe4f5b to efad975 Compare March 24, 2026 06:43

hyf0 force-pushed the 03-24-fix_mcs_entriesaware_should_calculate_sizes_without_duplication branch from 5ea0f64 to 071d65a Compare March 24, 2026 06:43

hyf0 changed the base branch from graphite-base/8887 to main March 24, 2026 06:43

Copilot AI reviewed Mar 24, 2026

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hyf0 force-pushed the 03-24-fix_mcs_entriesaware_should_calculate_sizes_without_duplication branch from 071d65a to 60ca9c0 Compare March 24, 2026 07:02

hyf0 requested review from IWANABETHATGUY, sapphi-red and shulaoda March 24, 2026 07:04

shulaoda approved these changes Mar 24, 2026

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graphite-app bot force-pushed the 03-24-fix_mcs_entriesaware_should_calculate_sizes_without_duplication branch from 54e2cba to 7833704 Compare March 24, 2026 08:16

graphite-app bot merged commit 7833704 into main Mar 24, 2026
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graphite-app bot deleted the 03-24-fix_mcs_entriesaware_should_calculate_sizes_without_duplication branch March 24, 2026 08:20

This was referenced Mar 25, 2026

release: v1.0.0-rc.12 #8894

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release: v1.0.0-rc.12 #8903

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fix(mcs): `entriesAware` should calculate sizes without duplication#8887

fix(mcs): `entriesAware` should calculate sizes without duplication#8887
graphite-app[bot] merged 1 commit intomainfrom
03-24-fix_mcs_entriesaware_should_calculate_sizes_without_duplication

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