[intellild]

Summary

• Introduce the sealed PrinterTrait abstraction with scoped access to printer internals.
• Change ToCss and related serialization helpers to accept PrinterTrait rather than one concrete Printer<W> type.
• Keep the .map_err(Into::into) to ? cleanup in the prerequisite printer PR, so this diff focuses on the trait migration.
• Preserve the existing parcel_sourcemap API in this layer.
• Reuse the existing scoped context helpers for nesting and @scope. Keep mapping feature gates and serializer state transitions aligned with the base branch.

Example

The same serializer now works with any internal printer variant implementing PrinterTrait:

fn to_css<P: PrinterTrait>(&self, dest: &mut P) -> Result<(), PrinterError> {
  dest.write_str("example")?;
  Ok(())
}

This is the prerequisite for adding a source-map-generic printer in the final PR without duplicating every ToCss implementation.

Validation

• cargo check --locked --workspace --all-features
• cargo test --locked -p rspack-lightningcss --all-features (184 passed)
• cargo check --locked -p rspack-lightningcss --no-default-features --features visitor --example custom_at_rule --test test_custom_parser

Stack

1. Fix bundled source-map indices
2. Use std::fmt::Write for printer output
3. This PR
4. Introduce the custom_sourcemap feature flag
5. Custom source maps through generic PrinterOptions

---

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 2026-11-04T06:55:47.669437Z	c6503a0	PR opened

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[codspeed]

Merging this PR will not alter performance

✅ 8 untouched benchmarks
⏩ 8 skipped benchmarks¹

---

_{Comparing codex/rstack-to-css-printer-trait (62d0547) with codex/rstack-printer-write (f077386)}

Footnotes

1. 8 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. ↩

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: c6503a0d3a

ℹ️ About Codex in GitHub

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• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

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[chatgpt-codex-connector]

Prevent lifetime-erased printer state from escaping

A safe custom ToCss implementation can call std::mem::swap(dest.state_mut(), other.state_mut()) with another printer because both returned states have lifetimes shortened to the temporary borrows. This allows borrowed CSS-module data, or the stack-backed nesting context, to move into a printer that outlives the original serialization. Subsequent serialization through that printer can then dereference dangling references or context pointers. Sealing PrinterTrait does not prevent callers from using its public methods this way. Keep mutable state inaccessible to external implementations, or expose operations that preserve its actual lifetimes rather than transmuting a mutable reference.

Useful? React with 👍 / 👎.