Replace unsafe_with_size_eq! with transmute_with

[joshlf]

Ptr::transmute_with allows us to transmute without SizeEq impls.

---

• 　 Permit shrinking transmutes in transmute machinery #2912
• 　 [transmute] Encode cast in TryTransmuteFromPtr params #2921
• 👉 Replace unsafe_with_size_eq! with transmute_with #2923

Latest Update: v8 — Compare vs v7

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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 refactors the internal mechanism for pointer transmutations by migrating from a macro-based approach to utilizing the Ptr::transmute_with method. This change streamlines the code responsible for handling type conversions without SizeEq constraints, resulting in improved maintainability and a reduction in boilerplate. The primary impact is a cleaner and more direct way to perform necessary unsafe pointer operations.

Highlights

• Refactoring Pointer Transmutation: The unsafe_with_size_eq! macro has been replaced with the more flexible Ptr::transmute_with method, simplifying the underlying pointer transmutation logic.
• Reduced Boilerplate: The change eliminates the need for explicit SizeEq implementations in contexts where pointer transmutations occur, leading to cleaner and more concise code.
• Macro Removal: The unsafe_with_size_eq! macro, along with its associated boilerplate for generating SizeEq implementations, has been entirely removed from the codebase.

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[gemini-code-assist]

Code Review

This pull request is a nice simplification, replacing the complex unsafe_with_size_eq! macro with direct calls to Ptr::transmute_with. This makes the transmutation logic for TransmuteRefDst and TransmuteMutDst much more straightforward and easier to understand. The changes are correct and improve the maintainability of the code. I have only a couple of minor suggestions to improve the precision of the safety comments.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.88%. Comparing base (6a8db84) to head (d65cc63).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2923      +/-   ##
==========================================
- Coverage   91.91%   91.88%   -0.04%     
==========================================
  Files          20       20              
  Lines        5888     5875      -13     
==========================================
- Hits         5412     5398      -14     
- Misses        476      477       +1     

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