feat: implement module tagging system for code splitting by hyf0 · Pull Request #9045 · rolldown/rolldown

hyf0 · 2026-04-09T02:55:51Z

Summary

Implements Phase 1 of the module tags design (#9017):

$initial tag — automatically computed during the entry BFS. Modules statically imported by user-defined entries (or in their dependency chain) are tagged $initial.
tags filter — manual code splitting groups can filter by tags with AND semantics. Only modules with all specified tags are captured.

Implementation

ModuleTagBitSet — u64-based bitset (Copy, single AND+CMP for contains_all). Supports up to 64 tags.
ModuleTagRegistry — sealed registry mapping tag names ($initial, future $lazy) to bit indices. All registration happens in new().
$initial tag is computed inside determine_reachable_modules_for_entry BFS — no separate pass needed.
Built-in tags use $ prefix to distinguish from user-defined tags.

Test plan

Integration test tags_initial — entry with static + dynamic imports, verifies tags: ['$initial'] captures only statically reachable modules
cargo check compiles
just lint-rust passes
just build-rolldown regenerates bindings
TypeScript types check

🤖 Generated with Claude Code

hyf0 · 2026-04-09T02:56:05Z

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Copilot

Pull request overview

Implements Phase 1 of module tags for manual code splitting by introducing a computed $initial tag and a tags filter for manual code splitting groups (AND semantics).

Changes:

Add $initial tagging during the per-entry static dependency BFS and propagate tag info into splitting metadata.
Add tags filtering to manual code splitting groups and wire it through TS options/validation, Rust options/bindings, and generated schemas.
Add an integration test fixture (tags_initial) to verify $initial selection vs dynamic-only modules.

Reviewed changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
packages/rolldown/src/utils/validator.ts	Adds `tags` field validation for advanced chunk group options.
packages/rolldown/src/options/output-options.ts	Documents/defines `BuiltinModuleTag` and adds `tags` to `CodeSplittingGroup`.
packages/rolldown/src/binding.d.cts	Updates generated binding typings to include `tags` on match groups.
crates/rolldown/src/stages/generate_stage/manual_code_splitting.rs	Applies `tags`-based filtering when matching modules into manual groups.
crates/rolldown/src/stages/generate_stage/code_splitting.rs	Computes `$initial` tag during static BFS and threads a tag registry into manual splitting.
crates/rolldown_common/src/types/module_tag.rs	Introduces `ModuleTagBitSet` and `ModuleTagRegistry` for tag compilation/checking.
crates/rolldown_common/src/types/mod.rs	Exposes the new `module_tag` module.
crates/rolldown_common/src/lib.rs	Re-exports `ModuleTagBitSet` / `ModuleTagRegistry`.
crates/rolldown_common/src/inner_bundler_options/types/manual_code_splitting_options.rs	Adds `tags` to `MatchGroup` and schema-only built-in tag enum for schemars.
crates/rolldown_binding/src/utils/normalize_binding_options.rs	Passes `tags` through binding option normalization.
crates/rolldown_binding/src/options/binding_output_options/binding_manual_code_splitting_options.rs	Adds `tags` to `BindingMatchGroup`.
crates/rolldown_testing/_config.schema.json	Extends test config schema with `tags` and a `BuiltinModuleTag` enum.
crates/rolldown/tests/rolldown/function/advanced_chunks/tags_initial/shared.js	Test fixture module for static import chain.
crates/rolldown/tests/rolldown/function/advanced_chunks/tags_initial/main.js	Test entry importing `shared` statically and `lazy` dynamically.
crates/rolldown/tests/rolldown/function/advanced_chunks/tags_initial/lazy.js	Test fixture for a dynamically imported module.
crates/rolldown/tests/rolldown/function/advanced_chunks/tags_initial/lazy-dep.js	Test fixture dependency for the lazy chunk.
crates/rolldown/tests/rolldown/function/advanced_chunks/tags_initial/artifacts.snap	Snapshot for expected chunk outputs.
crates/rolldown/tests/rolldown/function/advanced_chunks/tags_initial/_test.mjs	Asserts `$initial`-filtered chunk contents and file set.
crates/rolldown/tests/rolldown/function/advanced_chunks/tags_initial/_config.json	Configures a manual group filtered by `tags: ["$initial"]`.

netlify · 2026-04-09T07:08:53Z

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codspeed-hq · 2026-04-09T07:13:59Z

Merging this PR will not alter performance

✅ 4 untouched benchmarks
⏩ 10 skipped benchmarks¹

_{Comparing 04-09-feat_implement_module_tagging_system_for_code_splitting (c890eb4) with main (9dd533a)}

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. ↩

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commit: 2623771

hyf0 · 2026-04-09T15:33:47Z

Merge activity

Apr 9, 3:33 PM 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.
Apr 9, 3:33 PM UTC: hyf0 added this pull request to the Graphite merge queue.
Apr 9, 3:39 PM UTC: Merged by the Graphite merge queue.

## Summary Implements Phase 1 of the module tags design ([#9017](#9017)): - **`$initial` tag** — automatically computed during the entry BFS. Modules statically imported by user-defined entries (or in their dependency chain) are tagged `$initial`. - **`tags` filter** — manual code splitting groups can filter by tags with AND semantics. Only modules with all specified tags are captured. ## Implementation - `ModuleTagBitSet` — `u64`-based bitset (`Copy`, single AND+CMP for `contains_all`). Supports up to 64 tags. - `ModuleTagRegistry` — sealed registry mapping tag names (`$initial`, future `$lazy`) to bit indices. All registration happens in `new()`. - `$initial` tag is computed inside `determine_reachable_modules_for_entry` BFS — no separate pass needed. - Built-in tags use `$` prefix to distinguish from user-defined tags. ## Test plan - [x] Integration test `tags_initial` — entry with static + dynamic imports, verifies `tags: ['$initial']` captures only statically reachable modules - [x] `cargo check` compiles - [x] `just lint-rust` passes - [x] `just build-rolldown` regenerates bindings - [x] TypeScript types check 🤖 Generated with [Claude Code](https://claude.com/claude-code)

@Dunqing

## [1.0.0-rc.16] - 2026-04-16 ### 🚀 Features - const enum cross-module inlining support (#8796) by @Dunqing - implement module tagging system for code splitting (#9045) by @hyf0 ### 🐛 Bug Fixes - rolldown_plugin_vite_manifest: handle duplicate chunk names for CSS entries (#9059) by @sapphi-red - improve error message for invalid return values in function options (#9125) by @shulaoda - await async export-star init wrappers (#9101) by @thezzisu - never panic during diagnostic emission (#9091) by @IWANABETHATGUY - include array rest pattern in binding_identifiers (#9112) by @IWANABETHATGUY - rolldown: set worker thread count with ROLLDOWN_WORKER_THREADS (#9086) by @fpotter - rolldown_plugin_lazy_compilation: escape request ID in proxy modules (#9102) by @h-a-n-a - treat namespace member access as side-effect-free (#9099) by @IWANABETHATGUY - relax overly conservative side-effect leak check in chunk optimizer (#9085) by @IWANABETHATGUY - runtime: release `cb` reference after `__commonJS` factory initialization (#9067) by @hyf0-agent - `@__NO_SIDE_EFFECTS__` wrapper should not remove dynamic imports (#9075) by @IWANABETHATGUY - rolldown_plugin_vite_import_glob: use POSIX path join/normalize for glob resolution (#9077) by @shulaoda - emit REQUIRE_TLA error when require() loads a module with top-level await (#9071) by @jaehafe - emit namespace declaration for empty modules in manual chunks (#8993) by @privatenumber - rolldown_plugin_vite_import_glob: keep common base on path segment boundary (#9070) by @shulaoda - prevent circular runtime helper imports during facade elimination (#8989) (#9057) by @IWANABETHATGUY - correct circular dependency check in facade elimination (#9047) by @h-a-n-a - docs: correct dead link in CodeSplittingGroup.tags JSDoc (#9051) by @hyf0 - emit DUPLICATE_SHEBANG warning when banner contains shebang (#9026) by @IWANABETHATGUY ### 🚜 Refactor - use semantic reference flags for member write detection (#9060) by @Dunqing - extract UsedSymbolRefs newtype wrapper (#9130) by @IWANABETHATGUY - dedupe await wrapping in export-star init emit (#9119) by @IWANABETHATGUY - calculate side-effect-free function symbols on demand (#9120) by @IWANABETHATGUY - extract duplicated top-level await handling into shared helper (#9087) by @IWANABETHATGUY - rolldown_plugin_vite_import_glob: use split_first for get_common_base (#9069) by @shulaoda - simplify ESM init deduplication with idiomatic insert check (#9044) by @IWANABETHATGUY ### 📚 Documentation - document runtime module placement strategy in code-splitting design (#9062) by @IWANABETHATGUY - clarify `options` hook behavior difference with Rollup in watch mode (#9053) by @sapphi-red - meta/design: introduce module tags (#9017) by @hyf0 ### ⚡ Performance - convert `generate_transitive_esm_init` to iterative (#9046) by @IWANABETHATGUY ### 🧪 Testing - merge strict/non_strict test variants using configVariants (#9089) by @IWANABETHATGUY ### ⚙️ Miscellaneous Tasks - disable Renovate auto-updates for oxc packages (#9129) by @IWANABETHATGUY - upgrade oxc@0.126.0 (#9127) by @Dunqing - deps: update napi to v3.8.5 (#9126) by @renovate[bot] - deps: update dependency @napi-rs/cli to v3.6.2 (#9123) by @renovate[bot] - move lazy-compilation design doc (#9117) by @h-a-n-a - deps: update dependency vite-plus to v0.1.18 (#9118) by @renovate[bot] - deps: update dependency vite-plus to v0.1.17 (#9113) by @renovate[bot] - deps: update oxc to v0.125.0 (#9094) by @renovate[bot] - deps: update dependency follow-redirects to v1.16.0 [security] (#9103) by @renovate[bot] - deps: update test262 submodule for tests (#9097) by @sapphi-red - deps: update crate-ci/typos action to v1.45.1 (#9096) by @renovate[bot] - deps: update rust crates (#9081) by @renovate[bot] - deps: update npm packages (#9080) by @renovate[bot] - remove outdated TODO in determine_module_exports_kind (#9072) by @jaehafe - rust/test: support `extendedTests: false` shorthand in test config (#9050) by @hyf0 - ci: extract shared infra-changes anchor in path filters (#9054) by @hyf0 - add docs build check to catch dead links in PRs (#9052) by @hyf0 ### ❤️ New Contributors * @thezzisu made their first contribution in [#9101](#9101) * @fpotter made their first contribution in [#9086](#9086) * @jaehafe made their first contribution in [#9071](#9071) * @privatenumber made their first contribution in [#8993](#8993) Co-authored-by: shulaoda <165626830+shulaoda@users.noreply.github.com>

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docs(meta/design): introduce module tags #9017

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chore(rust/test): support extendedTests: false shorthand in test config #9050

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release: v1.0.0-rc.16 #9111

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release: v1.0.0-rc.16 #9131

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[Bug]: rc.16 hoists shared chunks (react-dom in particular) into main entry instead of auto-extracting #9323

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feat: implement module tagging system for code splitting#9045

feat: implement module tagging system for code splitting#9045
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