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…ce object `import * as ns from "./a.css"` prints the CSS file's namespace object, which calls the runtime's `__export`, but the runtime itself was missing from the output unless some JS module happened to need it too, so the bundle threw `ReferenceError: __export is not defined` at load. A CSS file keeps its JS side (namespace object, default export, wrapper) in the same source index as the stylesheet, unlike esbuild, which gives it a separate source. Two passes still treated CSS files as having no JS parts: - mark_file_reachable_for_code_splitting skipped their part dependencies, so the runtime never received the entry point's bit and was left out of the chunk (with --splitting it was printed into an orphan chunk that nothing imported). - compute_cross_chunk_dependencies only walks files_with_parts_in_chunk, which never contains CSS files; their JS parts are copied into every chunk that imports them, so with --splitting those chunks did not import `__export` from the chunk holding the runtime. Walk the part dependencies of CSS files like any other file, and record the symbol uses of the CSS copies printed into a chunk as imports of that chunk (without assigning their declarations to a chunk, since every chunk has its own copy). The now unused CodeSplitCtx::css_reprs is removed.
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Status: reproduced on the current release build ( 20868a0 narrows the reachability change to the live parts of a CSS file after CI ( |
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WalkthroughChangesThe bundler now traverses CSS dependencies during code splitting and computes cross-chunk dependencies for copied CSS files. Tests cover CSS namespace exports, CSS modules, separate outputs, and shared CSS across entries. CSS code-splitting support
Suggested reviewers: 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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In `@src/bundler/linker_context/computeCrossChunkDependencies.rs`:
- Around line 144-146: Update the chunk processing flow around the
Content::Javascript match so only the file-and-part walk is restricted to
JavaScript content; do not return from the entire function for non-JavaScript
chunks. Ensure entry-point dependency collection, including resolved exports,
exports_ref, and wrapper_ref updates to chunk_meta.imports, runs for every
entry-point chunk.
In `@test/bundler/bundler_splitting.test.ts`:
- Around line 273-297: Parameterize the splitting/NamespaceImportOfCSS test at
test/bundler/bundler_splitting.test.ts lines 273-297 to run for both “bun” and
“browser” targets. Apply the same target parameterization to the multi-entry
shared CSS Module test at test/bundler/bundler_splitting.test.ts lines 299-328,
preserving each test’s existing assertions and behavior.
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Fix all unresolved CodeRabbit comments on this PR:
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- Create a new PR with the fixes
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I reviewed this PR and didn't find any bugs. Because it changes two core linker passes (mark_file_reachable_for_code_splitting and the cross-chunk symbol walk) with a user-observable chunk-layout side effect noted in the description, a human look would still be worthwhile.
What was reviewed:
- Verified
files_in_chunk_orderis populated (incompute_chunks→find_all_imported_parts_in_js_order) beforecompute_cross_chunk_dependenciesreads it, and that CSS files are pushed there via thehas_intersectionbranch. - Confirmed
compute_chunksexcludes CSS files fromfiles_with_parts_in_chunk, sois_css_copycleanly partitions the chained iterator with no double-visits. - Confirmed the early return for non-JS chunks is behavior-preserving: the entry-point block was already JS-gated pre-PR and
compute_cross_chunk_dependencies_with_chunk_metasskips non-JS chunks. - Confirmed
css_reprsremains used byTreeShakeCtx; only theCodeSplitCtxfield was dead after thecontinueremoval.
Extended reasoning...
Overview
This PR fixes ReferenceError: __export is not defined when bundling import * as ns from "./x.css" where nothing else in the bundle needs the runtime. Two changes:
src/bundler/LinkerContext.rs(mark_file_reachable_for_code_splitting): removes thecontinuefor CSS files so their JS parts' dependencies (notably the runtime's__exportpart) receive the entry point's reachability bit. Also drops the now-unusedCodeSplitCtx::css_reprsfield.src/bundler/linker_context/computeCrossChunkDependencies.rs: chains CSS files fromjs.files_in_chunk_orderonto the per-chunk symbol-use walk so their uses of__exportbecome cross-chunk imports; skipsassign_chunk_indexfor those files' declared symbols (each importing chunk prints its own copy). The redundant per-filechunk.contentcheck becomes an earlylet else return, and the entry-point block below is de-indented (git diff -w shows it unchanged).
Tests: 2 loader tests (bun/browser × plain+module CSS) and 2×2 splitting tests (bun/browser × single/multi entry). The PR description states all fail on the release build and pass with the fix, and lists ~12 related suites that pass unchanged.
Security risks
None. This is a bundler linker reachability/dependency-tracking fix; no untrusted input parsing, auth, crypto, or filesystem-path handling is touched.
Level of scrutiny
High. The two functions touched are core linker passes that run for every bun build. Change 1 removes a guard that affects reachability marking for all CSS files (not just namespace-imported ones), and the PR description acknowledges a user-observable chunk-layout change for one edge case (an entry that only side-effect-imports CSS alongside another entry that uses the runtime now imports a shared runtime chunk instead of not importing it). Change 2 introduces a subtle invariant: CSS-declared symbols get no chunk_index, and the PR relies on "a symbol without a chunk index is ignored when cross-chunk imports are generated" for the JS-in-same-chunk-uses-CSS-local case to keep working.
Other factors
- I traced the ordering:
compute_chunkscallsfind_all_imported_parts_in_js_order(populatingjs.files_in_chunk_order) beforecompute_cross_chunk_dependenciesruns, so the new read is safe. - I confirmed
computeChunks.rs:293skips CSS files when buildingfiles_with_parts_in_chunk, so the two halves of the chained iterator are disjoint andis_css_copycorrectly identifies only the chained CSS files. - The
visitedmap in the JS-order visitor dedups source indices, so a CSS file appears at most once per chunk infiles_in_chunk_order. - The
import_recordsmutation inside the loop now runs for CSS files too (potentially across multiple chunks for the same source index), but the walk is sequential and CSS files' import records are@importstatements, not dynamic imports, sois_external_dynamic_importis false and the branch is a no-op. - CodeRabbit's two concerns were addressed (bun-target parametrization in 6ad6206; the early-return concern was refuted and CodeRabbit agreed). The remaining comment-cop hits are on pre-existing esbuild-derived comments that only moved with the de-indent.
TreeShakeCtx::css_reprsand themark_file_live_stepearly return are intentionally left in place per the PR description (separate bug forrequire("./x.module.css")).
Given the subtlety of the assign_chunk_index skip and the acknowledged layout side effect on previously-working bundles, I'm deferring so someone familiar with the linker's chunk-membership invariants can confirm.
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The #38307 needs the same runtime reachability for |
…bility Following every part made a stylesheet's dead namespace-export part mark the runtime reachable from every entry point with a stylesheet, which printed live-for-other-reasons helpers (the server's __jsonParse) into the browser chunks of HTML imports. Only the live parts of a CSS file's JS side are printed, so only they need to make their dependencies reachable.
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I reviewed this PR and didn't find any bugs. Because it changes bundler linking internals (reachability marking + cross-chunk dependency collection), had a mid-PR approach change after a CI failure in html-import-manifest.test.ts, and the last comment notes it touches the same lines as #38307, a human look would still be worthwhile to confirm CI is green on 20868a0 and to coordinate merge order.
What was reviewed:
mark_file_reachable_for_code_splitting: verifiedparts_liveis populated by tree-shaking before this runs (LinkerContext.rs:892-939), so gating CSS parts on liveness is sound.compute_cross_chunk_dependencies: the early return for non-JS chunks is behavior-preserving (the entry-point block was already JS-gated); the!is_css_copyskip onassign_chunk_indexmatches the per-chunk-copy printing model described.- Checked that CSS files never appear in
files_with_parts_in_chunk, so no double-visit within a chunk from the.chain(copied_css_files)iteration.
Extended reasoning...
Overview
This PR fixes import * as ns from "./style.css" producing bundles that throw ReferenceError: __export is not defined. Two changes: (1) mark_file_reachable_for_code_splitting in src/bundler/LinkerContext.rs now walks the live JS-part dependencies of CSS files instead of skipping them entirely, so the runtime file receives the entry point's reachability bit; (2) compute_cross_chunk_dependencies in computeCrossChunkDependencies.rs now also visits the CSS files listed in a JS chunk's files_in_chunk_order (whose JS parts are copied into the chunk) so their symbol uses become cross-chunk imports, while skipping assign_chunk_index for their declarations since each importing chunk prints its own copy. Tests are added in bundler_loader.test.ts and bundler_splitting.test.ts covering plain/module CSS × bun/browser × single/multi-entry × splitting on/off.
Security risks
None. This is bundler graph-traversal logic operating on already-parsed ASTs; no untrusted input parsing, auth, crypto, or filesystem-escape surface is touched.
Level of scrutiny
High. Bundler linking (reachability, chunk assignment, cross-chunk symbol import/export) is one of the most invariant-heavy subsystems in the repo, ported from esbuild with Bun-specific divergence (CSS files carry a JS side in the same source index — the exact divergence this PR reasons about). The change is small in line count but the correctness argument depends on several non-local invariants: tree-shaking runs before code-splitting reachability (verified at LinkerContext.rs:892-939), CSS files are excluded from files_with_parts_in_chunk by compute_chunks, and symbols without a chunk index are treated as local when cross-chunk imports are generated. These are the kinds of assumptions a bundler-knowledgeable reviewer should sign off on.
Other factors
- Mid-PR CI regression and approach change: The initial version walked all parts of CSS files (matching esbuild's shape for JS files). robobun's last comment (00:57:34Z) reported this broke
test/bundler/html-import-manifest.test.tsin CI because every ESM-imported CSS file has a namespace-export part depending on__export, so the runtime got every entry's bit even when unused. Commit 20868a0 switched to walking only live parts. There is no timeline confirmation that CI is green after this change, and the PR description is now partially stale (it still says "the pass walks dead parts too, as in esbuild" and thatCodeSplitCtx::css_reprswas deleted — neither is true in the current diff). - Overlap with #38307: The last comment explicitly says #38307 touches the same lines in
mark_file_reachable_for_code_splittingfor a related bug (require("./x.module.css")). Merge order needs human coordination. - The
!is_css_copyguard onassign_chunk_index: Skipping chunk-index assignment for symbols declared by copied CSS parts is the right call given the stated printing model (each chunk prints its own copy, andassign_chunk_indexdebug-asserts single ownership), but it means uses of those symbols by JS in the same chunk rely on the "no chunk index → local" fallback incompute_cross_chunk_dependencies_with_chunk_metas. The PR description covers this and cites an existing test (css-module/BundleTwoFilesWithCodeSplitting) that already exercises the pattern; still, it's a subtle enough design point that a reviewer familiar with the linker should confirm. - Test coverage: Good — the four new test cases (× 2 targets each for splitting) run the bundled output and assert stdout, plus one asserts the exact set of emitted files. All bot review threads are resolved.
…_for_code_splitting
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Re the overlap with #38307: as of 20868a0 this PR follows only the live parts of a CSS file as well, which is what fixed |
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I reviewed this PR and didn't find any bugs. Because it changes linker reachability and cross-chunk symbol assignment (an area where the first revision already tripped html-import-manifest.test.ts), and the last comment notes #38307 touches the same lines in mark_file_reachable_for_code_splitting, a human look from a bundler maintainer would still be worthwhile.
What was reviewed:
- Call ordering:
parts_liveis populated by tree shaking beforemark_file_reachable_for_code_splittingreads it, andfiles_in_chunk_orderis filled bycompute_chunksbeforecompute_cross_chunk_dependenciesreads it. files_in_chunk_orderdoes contain CSS files for JS chunks (the visitor useshas_intersectionfor CSS regardless of splitting), so the newcopied_css_filesfilter walks the right set.- The early return for non-JS chunks is behavior-preserving (
git diff -wshows the entry-point block only de-indented;compute_cross_chunk_dependencies_with_chunk_metasskips non-JS chunks anyway). - Repeated visits to the same CSS
source_indexfrom multiple chunks are sequential and the import-record rewrite in the loop body is idempotent (guarded bysource_index.is_valid()), and CSS synthetic parts have no dynamic imports.
Extended reasoning...
Overview
The PR fixes import * as ns from "./x.css" bundling to output that references __export without emitting the runtime that defines it. Two changes:
src/bundler/LinkerContext.rs(mark_file_reachable_for_code_splitting): CSS files no longer skip the part-dependency walk; instead only their live parts' dependencies are followed, so the runtime picks up the entry bit(s) of chunks that print the namespace object without leaking live runtime helpers into unrelated chunks (the__jsonParse-in-browser-chunk regression the first revision hit).src/bundler/linker_context/computeCrossChunkDependencies.rs: the per-chunk symbol-use walk now also visits the CSS files copied into the chunk (viajs.files_in_chunk_order), recording their symbol uses so__exportbecomes a cross-chunk import when the runtime lands in a shared chunk.assign_chunk_indexis skipped for these copies because each importing chunk prints its own copy of the CSS file's declarations, so they must not be pinned to one chunk. The redundant per-iterationchunk.contentchecks became a single early return; the entry-point block below is only de-indented.
Six new itBundled tests cover plain and module CSS, bun/browser targets, and single/multi-entry --splitting; the description says all fail on the release build and pass with the fix, and the unchanged-output side is pinned by existing hash/snapshot tests.
Security risks
None. This is bundler chunk-layout logic; no untrusted input parsing, no auth/crypto/permissions.
Level of scrutiny
High. The linker's reachability and cross-chunk import machinery decides what code ends up in which output file for every splitting build. The first version of this PR already caused a subtle regression (server-only __jsonParse printed into browser chunks) that only a hash-based test caught. The fix is narrow and well-argued, but the invariants ("CSS declarations must not get a chunk index because every importer prints its own copy", "only live parts, so bundles that already worked are byte-identical") are the kind a bundler maintainer should confirm.
Other factors
- The last timeline comment notes PR #38307 touches the same lines in
mark_file_reachable_for_code_splittingfor therequire("./x.module.css")case; a maintainer should decide sequencing. - I verified pass ordering: tree shaking populates
parts_livebefore code-splitting reachability reads it;compute_chunks→find_all_imported_parts_in_js_orderpopulatesfiles_in_chunk_orderbeforecompute_cross_chunk_dependenciesreads it. - I verified
findAllImportedPartsInJSOrder.rs:272-283useshas_intersectionfor CSS files even under code splitting, so CSS source indices do appear in each intersecting JS chunk'sfiles_in_chunk_order, which is what the new walk relies on. - Repeated sequential visits to the same CSS source from multiple chunks are safe: the only mutation in the loop body (
import_record.path/source_indexrewrite for external dynamic imports) is guarded bysource_index.is_valid()and CSS synthetic parts don't carry dynamic imports. - All CodeRabbit and comment-cop threads are resolved; the remaining flagged comments are pre-existing esbuild-derived comments that only moved via de-indent.
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Updated 5:05 AM PT - Aug 14th, 2026
❌ @robobun, your commit a7d795c has 1 failures in
🧪 To try this PR locally: bunx bun-pr 38286That installs a local version of the PR into your bun-38286 --bun |
…e runtime into - a stylesheet that is only imported does not pull a live runtime into its entry point, with and without splitting - an entry point whose chunk prints another entry's namespace object (reached through @import plus the import record of a tree-shaken package) gets the runtime too - entries sharing a JS module import __export for their copies of the namespace object from the shared chunk
| // `compute_chunks` gives CSS files no chunk of their own; `find_imported_parts_in_js_order` | ||
| // copies their live JS parts into every chunk importing them instead. |
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If you need a paragraph-long comment to justify why the workaround is OK, the code is wrong — fix the code
There was a problem hiding this comment.
I reviewed this PR and didn't find any bugs. Because it changes reachability propagation and cross-chunk symbol collection in the linker's code-splitting path — logic whose first revision here already needed a live-parts-only refinement after CI caught over-propagation — a human look from someone familiar with the bundler would still be worthwhile. Build #95289 on 3127bcc was also reported red; worth confirming that's unrelated.
What was reviewed:
mark_file_reachable_for_code_splitting: verified the live-parts-only gate matches whatfind_imported_parts_in_js_orderactually prints for CSS files (both key onparts_live), so the runtime's entry bits track the printed copies.compute_cross_chunk_dependencies: confirmedfiles_in_chunk_orderis populated bycompute_chunksbefore this runs, that CSS files are excluded from JS-chunkfiles_with_parts_in_chunk(so the two iterators are disjoint), and that skippingassign_chunk_indexfor CSS copies leaves per-chunk uses of those symbols resolving locally (no chunk index → skipped in cross-chunk import generation).- Checked the
import_recordswrite in the walk is dead for CSS parts (no dynamic imports) and the loop is sequential regardless, so the same CSS file appearing in multiple chunks'files_in_chunk_orderis safe. - The early return for non-JS chunks and the de-indented entry-point block are behavior-preserving vs. main (
git diff -w).
Extended reasoning...
Overview
The PR fixes import * as ns from "./style.css" producing bundles that throw ReferenceError: __export is not defined. Two bundler-core files change: mark_file_reachable_for_code_splitting in src/bundler/LinkerContext.rs now follows the part-dependencies of a CSS file's live JS parts (previously it continued for CSS files entirely, so the runtime never got the entry bit), and compute_cross_chunk_dependencies in src/bundler/linker_context/computeCrossChunkDependencies.rs now walks the CSS files copied into each JS chunk (from files_in_chunk_order) so their symbol uses (e.g. __export) become cross-chunk imports when the runtime lands in a shared chunk. Nine new itBundled tests cover single-/multi-entry, bun/browser, plain/.module.css, and two negative tests pin that non-namespace CSS imports do not newly pull in the runtime.
Security risks
None. This is bundler linking/tree-shaking control flow over already-parsed ASTs; no untrusted input parsing, auth, crypto, or filesystem-path handling is touched.
Level of scrutiny
High. Entry-bit propagation and cross-chunk symbol assignment decide chunk membership and generated imports for every code-splitting build; a mistake here changes output layout or produces broken bundles across the ecosystem. The PR's own history demonstrates the subtlety: the first revision (following all CSS parts) leaked a live __jsonParse helper into browser chunks of HTML imports and was caught by html-import-manifest.test.ts, prompting the live-parts-only rule. I verified the fix's invariants against find_imported_parts_in_js_order (CSS files use has_intersection on entry bits and only live parts are pushed to part_ranges, so gating on parts_live here matches what is printed), confirmed compute_chunks excludes CSS files from JS-chunk files_with_parts_in_chunk (line 293) so the chained iterator has no duplicates, confirmed files_in_chunk_order is populated inside compute_chunks before compute_cross_chunk_dependencies runs, and checked that skipping assign_chunk_index for CSS-declared symbols is required (each importing chunk prints its own copy) and harmless for local uses (symbols without a chunk index are ignored when generating cross-chunk imports in compute_cross_chunk_dependencies_with_chunk_metas).
Other factors
- Test coverage is thorough: positive cases for both targets with and without splitting, a shared-JS-module case asserting the exact
import { __export, shared }clause, an@import-reachability edge case, and two...DoesNot...inline-snapshot tests pinning that unaffected bundles stay byte-identical. The description lists a broad set of existing bundler suites re-run clean. - All CodeRabbit and comment-cop threads are resolved; the one remaining unresolved comment-cop hit (07:13 on
computeCrossChunkDependencies.rs) targets pre-existing esbuild-derived comments that only re-indented when the redundantchunk.contentguard was removed — the two comments this PR actually adds are one line each. - Build #95289 on 3127bcc was reported as failing; the two commits since (a2db253, a7d795c) are a test addition and a comment tweak, so if that failure was in-scope it likely still applies. I could not determine what failed from the timeline alone.
- There is a coordinated overlap with #38307 (the
mark_file_reachable_for_code_splittinghunk is intentionally identical in both). A maintainer should confirm the merge-order plan. - Given the blast radius of chunk-layout changes and the CI/companion-PR coordination, deferring rather than approving.
Following a CSS file's live parts from a traversal rooted at a stylesheet entry point (an explicit one, or an import()ed stylesheet under splitting) gave the runtime an entry bit that corresponds to no JS chunk, which under --splitting split the runtime away from the chunk printing the stylesheet's wrapper or namespace object. Skip the parts when the root is a stylesheet, and spell the live-parts filter the way #38286 does.
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One more shape this fixes, found separately and verified by applying this diff on top of current main (032b8db): printf '.foo{color:red}' > x.module.css
printf 'import * as ns from "./x.module.css"; console.log(JSON.stringify(ns));' > c.ts
printf 'export * from "./x.module.css";' > d.ts
bun build ./c.ts ./d.ts --outdir out && bun out/d.jsOn main, Unrelated to this PR and left alone: |
…f a stylesheet The namespace object of a stylesheet needs the __export helper, and nothing makes the runtime reachable for it (#38286). Such a bundle runs on main while another namespace object keeps the helper. A declaration that takes copies was the last such object in one fixture, and the bundle then threw ReferenceError: __export is not defined.
Problem
import * as ns from "./style.css"bundles to a file that throws at load:ReferenceError: __export is not defined. The CSS file's namespace object (__export(exports_style, { default: () => style_default })) is printed, but the runtime that defines__exportis not. Same for.module.css, for--target bunandbrowser, with and without--splitting.import style from "./style.css"is fine.--splittingit only works today when some JS module in the same bundle happens to need the runtime too (any file with anexportdoes), so cause 1 below shows up in small bundles. With--splittingand more than one entry point it fails even then (cause 2), because the runtime sits in a shared chunk that the entry chunks do not import from; that is the shape real apps hit.src/bundler/LinkerContext.rs(mark_file_reachable_for_code_splitting): CSS filescontinued before the loop over their parts' dependencies. The CSS file's namespace export part depends on the runtime's__exportpart, so the runtime never received the entry point's bit andfind_imported_parts_in_js_orderleft it out of the chunk. With--splittingthe live runtime parts ended up in a chunk with no entry bits at all, which nothing imported (the strayentry-<hash>.jsin the new splitting test's fail-before output).src/bundler/linker_context/computeCrossChunkDependencies.rs: the walk that records which symbols a chunk uses only visitschunk.files_with_parts_in_chunk, andcompute_chunksnever puts CSS files in there. So with--splittingand more than one entry point, even once the runtime lands in a shared chunk, the entry chunks that print a copy of the namespace object do notimport { __export }from it.Fix
mark_file_reachable_for_code_splittingnow also follows the part dependencies of CSS files, but only those of their live parts. Correct because, unlike esbuild (whose CSS files have no JS parts, which is where the skip came from), a CSS file in bun carries its JS side in the same source index, and its live parts are printed into the chunk, so whatever they depend on has to be reachable from the same entry points. Dead parts are not printed, and following them is harmful: every stylesheet has a (usually dead) namespace export part depending on the runtime, so the first version of this PR marked the runtime reachable from every entry point with a stylesheet, which printed the server's live__jsonParsehelper into the browser chunk of an HTML import (test/bundler/html-import-manifest.test.tscaught it, see details). JS files keep following every part as before (esbuild parity, and changing it would move chunks around in existing builds).require()s) a stylesheet, because otherwise no stylesheet has a live part with a runtime dependency. Checked by diffing such builds (HTML import, side-effect and default imports next to an entry that does use the runtime, with and without--splitting) against the release build: byte-identical, and pinned by the two...DoesNot...tests below.@import. That is deliberate: the printer (find_imported_parts_in_js_order) prints the live namespace object into any chunk whose bit the stylesheet carries once it reaches the file through any import record, including one of a tree-shaken module, so the entry bits of the file itself are the only thing that is guaranteed to cover every chunk printing it.bun/loader-css-namespace-object-printed-for-another-entryis exactly that case (entry B reaches the stylesheet through@import, the printer through asideEffects: falsepackage) and currently throws theReferenceErrorin B's output; propagating only along JS import edges would leave it broken. The cost is the__exportprelude (or, with--splitting, an import of the chunk holding it) in an entry that reaches such a stylesheet via@importbut never prints the object; an entry point containing any module with anexportalready gets every live helper printed into it today for the same reason, so this only affects entries without one.compute_cross_chunk_dependenciesalso walks the CSS files in the chunk'sfiles_in_chunk_order, i.e. exactly the CSS files whose JS parts the chunk prints. Their symbol uses become imports of the chunk like everyone else's; their declarations are not assigned a chunk index, since every importing chunk prints its own copy of them (the existing behavior, seecss-module/BundleTwoFilesWithCodeSplitting) andassign_chunk_indexasserts a symbol lives in one chunk. Uses of those per-chunk copies by JS in the same chunk resolve to the local copy as before, because a symbol without a chunk index is ignored when cross-chunk imports are generated. Unchanged and out of scope here: the copies are still not members offiles_with_parts_in_chunk, so their bytes are not attributed to any input in the metafile, and each chunk has its own copy of the objects (a default import from two chunks yields two objects), as on main.chunk.contentchecks in that walk became an early return (the entry-point block below it is only re-indented,git diff -wshows it unchanged).mark_file_live_stephas the same esbuild-shaped early return for CSS files. It causes a different bug (require("./x.module.css")bundles to an empty wrapper), fixed in bundler: emit the module.exports body of a require()d CSS file #38307. That PR needs the same reachability hunk as this one; both carry it with identical text (see the comment there), so they merge in either order, and the rest of the two diffs does not overlap.ReferenceErrorabove and passing with this change: intest/bundler/bundler_loader.test.ts,bun/loader-css-namespace-import-{bun,browser}(plain and module CSS, no other runtime user in the bundle) andbun/loader-css-namespace-object-printed-for-another-entry(the@importcase described above); intest/bundler/bundler_splitting.test.ts,splitting/NamespaceImportOfCSS-{bun,browser}(single entry: runtime joins the entry chunk, exact output file list),splitting/MultipleEntryPointsWithNamespaceImportOfSharedCSS-{bun,browser}(runtime alone in a shared chunk, needs both changes) andsplitting/NamespaceImportOfCSSNextToSharedModule(the usual shape: a shared JS module, asserts the entry chunksimport { __export, shared }from the shared chunk and that it exports them).bun/loader-css-plain-import-does-not-pull-in-runtime(side-effect and default imports next to an entry with a live__export, inline snapshot of the untouched entry) andsplitting/PlainImportOfCSSDoesNotShareTheRuntime(same with--splitting: exact output file list, no shared chunk, snapshot of the untouched entry), plus the existinghtml-import-manifest.test.tscontent hashes.test/bundler/{bundler_loader,bundler_splitting,html-import-manifest,bundler_regressions,bundler_html,bundler_html_server,bun-build-api,bundler_defer,bundler_compile_splitting,metafile}.test.ts,test/bundler/css/css-modules.test.ts,test/bundler/esbuild/{css,splitting,metafile,loader,default}.test.ts,test/js/bun/http/bun-serve-html{,-manifest}.test.ts,test/bake/dev-and-prod.test.ts;bun run rust:clippyandcargo fmt --all --checkare clean.Background
Index::RUNTIME) holding helpers such as__export,__commonJS,__toESM. Its parts are printed at the top of whichever chunk they belong to; nothing imports it through import records, it is only reached through part dependencies.(source, part)dependencies. Step 5 of the linker gives every file a "namespace export part" that builds theimport * asobject with__export, and makes it depend on the runtime's__exportpart.var x_default = {...}or the CSS module class map, a__commonJSwrapper ifrequire()d). esbuild instead gives that JS a separate source index, which is why its CSS-only branches in these passes were wrong to port as-is.mark_file_reachable_for_code_splittingmarks every file each entry point can reach (via import records and part dependencies) with that entry's bit.compute_chunksgroups files by their bits into chunks, andfind_imported_parts_in_js_orderprints a file's live parts into a chunk only if its bits match the chunk's. CSS files are excluded from chunk membership and are instead printed into every chunk whose bits intersect theirs.--splittingonly): for each chunk, the symbols used by the parts it prints are collected; any of them declared in another chunk becomes animport { x } from "./other-chunk.js"plus anexport { x }there. A symbol not declared by any chunk member is assumed local and skipped.Repro and output before / after
Before:
After: the
var __defProp = ...; var __export = ...prelude is emitted first and the script prints[ "default" ] {}.With
--splittingand two entriesa.ts/b.tsboth importing* asthe stylesheet, before:a-<hash>.jscontains the runtime but neithera.jsnorb.jsimports it. After:and
a-nb39b5ae.jsends withexport { __export };.Why only live parts (superseded first version of this PR, 9a7b1d0, followed every part of a CSS file): with
the server entry uses the runtime's
__jsonParse(the HTML manifest), so that part is live.home.csshas a dead namespace export part depending on the runtime, and following it gave the runtime thehome.htmlentry's bit, so the browser chunk becameinstead of just the
home.jsline, changing its content hash (test/bundler/html-import-manifest.test.ts,html-import/multiple-manifests). With the live-parts rule (20868a0, reshaped in 3127bcc) the browser chunk is byte-identical to the release build again. The same rule also means a multi-entry--splittingbuild whose entries only side-effect-import or default-import stylesheets keeps its chunk layout.