[cargo-zerocopy] Pass --cfg __ZEROCOPY_INTERNAL_USE_ONL_TOOLCHAIN=...

[joshlf]

This allows testing code to detect the current named toolchain. Unlike
the rustversion crate, it won't require us to update use sites when we
update pinned toolchain versions.

---

• 　  [derive] Implement #[zerocopy(on_error = skip/fail)] #2982
• 👉 [cargo-zerocopy] Pass --cfg __ZEROCOPY_INTERNAL_USE_ONL_TOOLCHAIN=... #2983

Latest Update: v3 — Compare vs v2

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[gemini-code-assist]

Summary of Changes

Hello @joshlf, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the cargo-zerocopy build process by introducing a new configuration flag that exposes the active Rust toolchain's name. This modification allows internal testing infrastructure to reliably detect the specific toolchain being used, offering a more resilient and less maintenance-intensive approach than previous methods.

Highlights

• Toolchain Detection: A new cfg flag, __ZEROCOPY_INTERNAL_USE_ONLY_TOOLCHAIN, is now passed during the build process of cargo-zerocopy.
• Dynamic Toolchain Name: This flag dynamically includes the name of the currently active Rust toolchain, allowing internal testing code to identify it.
• Improved Maintainability: This change provides a more stable method for toolchain detection compared to relying on the rustversion crate, which would require updates with pinned toolchain versions.

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Changelog

• tools/cargo-zerocopy/src/main.rs
  • Added a line to append a cfg flag containing the current toolchain's name to the rustflags.

Activity

• The pull request description was automatically generated by GHerrit.
• The PR is part of a stacked series, linking to [derive] Implement #[zerocopy(on_error = skip/fail)] #2982 and [cargo-zerocopy] Pass --cfg __ZEROCOPY_INTERNAL_USE_ONL_TOOLCHAIN=... #2983.
• Instructions for interacting with the PR branch (fetch, checkout, cherry-pick, pull) are provided.

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[gemini-code-assist]

Code Review

This pull request adds a --cfg flag to pass the current toolchain name to rustc, which is useful for conditional compilation. The change is correct and achieves its goal. I've included one suggestion to refactor the string construction for the flags, which improves readability and can be slightly more efficient.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.02%. Comparing base (78088c4) to head (9e964fb).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2983   +/-   ##
=======================================
  Coverage   92.02%   92.02%           
=======================================
  Files          19       19           
  Lines        6029     6029           
=======================================
  Hits         5548     5548           
  Misses        481      481           

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