[derive] In tests, assert hygiene of output

[joshlf]

When testing, perform a post-processing pass on all derive output which
checks for hygiene violations. Eventually, we may want to extend this
machinery to check for other violations as well.

Follows up on #2915 and #2917

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• 👉 [derive] In tests, assert hygiene of output #2918

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 testing infrastructure for the zerocopy-derive macro by introducing a mechanism to automatically check for hygiene violations in the generated code. This improvement aims to prevent subtle bugs related to identifier resolution, ensuring the macro's output is robust and behaves as expected across different usage contexts, particularly during development and testing.

Highlights

• Hygiene Check Implementation: Introduced a new testing utility to perform hygiene checks on the output of derive macros, specifically targeting ambiguous Self references.
• Dependency Update: Added syn with the visit feature as a new dependency to enable parsing and traversing the generated Rust syntax tree.
• Macro Integration: Integrated the hygiene check into the main derive! macro, ensuring that all generated code is validated for hygiene violations when compiled in test configurations.

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[gemini-code-assist]

Code Review

This pull request introduces a valuable hygiene check for generated code in tests. By adding a syn::visit pass, it ensures that ambiguous paths like Self::Item are caught, preventing potential hygiene issues. The implementation is straightforward and correctly gated behind the test configuration.

I've found one critical issue in the implementation of the visitor which would cause it to incorrectly flag valid code. My review includes a suggestion to fix this. Otherwise, the changes look good.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.91%. Comparing base (6a8db84) to head (0d8f01e).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2918   +/-   ##
=======================================
  Coverage   91.91%   91.91%           
=======================================
  Files          20       20           
  Lines        5888     5888           
=======================================
  Hits         5412     5412           
  Misses        476      476           

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