fix(esm-library): handle CSS modules in preserveModules#13670
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Pull request overview
Fixes output.library.preserveModules behavior when CSS-only modules/chunks are present, preventing ESM library rendering from emitting JS imports/requires for chunks that have no JavaScript asset and enabling per-chunk CSS filename overrides to take effect (including with CssExtractRspackPlugin).
Changes:
- Classify
preserveModulessplitting by modulesource_types, preserving.cssextension and applyingchunk.css_filename_templatefor CSS output. - Skip CSS-only modules/chunks during ESM render so JS output no longer references CSS-only chunks as JS imports/requires.
- Make
CssExtractRspackPluginrespectchunk.css_filename_templateand add new ESM output test fixtures for native CSS + extract-css.
Reviewed changes
Copilot reviewed 18 out of 18 changed files in this pull request and generated 2 comments.
Show a summary per file
| File | Description |
|---|---|
| crates/rspack_plugin_extract_css/src/plugin.rs | Honors per-chunk CSS filename overrides (chunk.css_filename_template) when emitting extracted CSS assets. |
| crates/rspack_plugin_esm_library/src/render.rs | Skips emitting JS requires/imports for CSS-only modules and chunks in ESM rendering. |
| crates/rspack_plugin_esm_library/src/preserve_modules.rs | Splits modules by kind (JS vs CSS), preserves .css names, and sets css_filename_template for CSS chunks. |
| crates/rspack_core/src/chunk.rs | Adds set_css_filename_template setter to support per-chunk CSS naming updates. |
| tests/rspack-test/esmOutputCases/preserve-modules/css/test.config.js | New esm-output case config for native CSS + preserveModules. |
| tests/rspack-test/esmOutputCases/preserve-modules/css/rspack.config.js | Enables experiments.css and preserveModules for native CSS fixture. |
| tests/rspack-test/esmOutputCases/preserve-modules/css/src/index.js | Imports CSS and a nested JS module for the native CSS fixture. |
| tests/rspack-test/esmOutputCases/preserve-modules/css/src/style.css | Native CSS fixture stylesheet. |
| tests/rspack-test/esmOutputCases/preserve-modules/css/src/components/button/index.js | Nested JS module used by the native CSS fixture. |
| tests/rspack-test/esmOutputCases/preserve-modules/css/src/components/button/style.css | Nested native CSS fixture stylesheet. |
| tests/rspack-test/esmOutputCases/preserve-modules/css/snapshots/esm.snap.txt | Snapshot for native CSS preserveModules fixture. |
| tests/rspack-test/esmOutputCases/preserve-modules/css-extract/test.config.js | New esm-output case config for extract-css + preserveModules. |
| tests/rspack-test/esmOutputCases/preserve-modules/css-extract/rspack.config.js | Configures CssExtractRspackPlugin and preserveModules for extract-css fixture. |
| tests/rspack-test/esmOutputCases/preserve-modules/css-extract/src/index.js | Imports CSS and a nested JS module for the extract-css fixture. |
| tests/rspack-test/esmOutputCases/preserve-modules/css-extract/src/style.css | Extract-css fixture stylesheet. |
| tests/rspack-test/esmOutputCases/preserve-modules/css-extract/src/components/button/index.js | Nested JS module used by the extract-css fixture. |
| tests/rspack-test/esmOutputCases/preserve-modules/css-extract/src/components/button/style.css | Nested extract-css fixture stylesheet. |
| tests/rspack-test/esmOutputCases/preserve-modules/css-extract/snapshots/esm.snap.txt | Snapshot for extract-css preserveModules fixture. |
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CSS modules (native `experiments.css` or mini-css-extract) under `output.library.preserveModules` caused either "chunk xxx should have at least one file" or "Multiple assets emit different content to the same filename". preserveModules set the JS filename_template on CSS chunks, left chunks nameless so multiple CSS files collapsed onto `.css`, and the ESM render phase emitted `import "__RSPACK_ESM_CHUNK_<id>"` placeholders pointing at CSS-only chunks with no JS file. Classify modules in preserve_modules by source_types and set css_filename_template for CSS modules (preserving the `.css` extension and source path), skip CSS-only modules/chunks in the ESM render paths that emit JS-side requires / cross-chunk imports, and make CssExtractRspackPlugin honor chunk.css_filename_template so preserveModules can override its per-chunk filename.
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Summary
output.library.preserveModulespanic when CSS modules are involved — both native CSS (experiments.css: true) andCssExtractRspackPlugin. The build previously died with "chunk xxx should have at least one file" or "Multiple assets emit different content to the same filename".preserve_modulesbysource_types, preserve the.cssextension and source path for CSS modules, and setcss_filename_templateinstead of the JSfilename_template.__webpack_require__('style.css')calls orimport \"__RSPACK_ESM_CHUNK_<id>\"placeholders that point at chunks with no JS file.CssExtractRspackPluginhonorchunk.css_filename_template, sopreserveModules' per-chunk CSS filename overrides actually take effect.Test plan