[intellild]

Superseded by #22, which passes the source map through PrinterOptions.

Summary

• Add a SourceMap trait and a standalone custom_sourcemap feature.
• Keep parcel_sourcemap behind the existing sourcemap feature and provide its trait adapter.
• Make printer and bundler source-map handling generic over the selected implementation.
• Use the source-index fix from fix: preserve output source indices when bundling CSS #23 with custom map writers, including writers that deduplicate paths or allocate non-contiguous IDs.
• Add benchmarks and focused bundler regression tests.

Example

Consumers can provide their own source-map writer:

let mut map = MySourceMap::default();
let result = stylesheet.to_css(PrinterOptions::default(), Some(&mut map))?;

For example, a bundler can canonicalize two imported paths to one output source index while mappings still point to the correct source content.

Validation

• cargo check --locked --workspace --all-features
• cargo test --locked -p rspack-lightningcss --all-features (189 passed)
• cargo test --locked -p rspack-lightningcss --no-default-features --features bundler --test test_bundler_source_map (3 passed with the custom implementation)
• cargo check --locked -p rspack-lightningcss --no-default-features --features visitor --example custom_at_rule --test test_custom_parser

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by OpenAI Codex

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[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-11-04T06:55:31.838580Z	6c2c168	PR opened

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[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 6c2c168591

ℹ️ About Codex in GitHub

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• Open a pull request for review
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• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

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[chatgpt-codex-connector]

Preserve input-map support through mutable-reference adapters

When a caller passes a mutable-reference wrapper as the writer (for example, Some(&mut map_ref) where map_ref: &mut ParcelSourceMap), this implementation silently disables inline source-map remapping even though the underlying implementation supports it. Both StyleSheet::to_css_impl and Bundler::load_file use S::from_data_url, so choosing S = &mut T loses the original source locations. If bundling used the concrete writer and printing subsequently uses the reference adapter, the bundled CSS source was never registered and the fallback mappings can even reference nonexistent output sources. Preserve access to an owned input-map reader rather than making the reference adapter unconditionally report that input maps are unreadable.

Useful? React with 👍 / 👎.

[codspeed]

Merging this PR will not alter performance

✅ 12 untouched benchmarks
⏩ 4 skipped benchmarks¹

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_{Comparing codex/rstack-custom-sourcemap-trait (d710de8) with codex/rstack-rename-sourcemap-feature (43b17bc)}

Footnotes

1. 4 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. ↩