[cast] Fix safety comment bug for CastUnsized

[joshlf]

The decorated unsafe impl block is still sound, but the proof
previously proved too much (namely, that the cast preserves referent
size, when in fact it may shrink referent size).

---

• 　 Make SizeEq safe #2907
• 　 [ci] Check for orphaned UI test .stderr files #2909
• 👉 [cast] Fix safety comment bug for CastUnsized #2908

Latest Update: v5 — Compare vs v4

📚 Full Patch History

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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 provides a crucial clarification to a safety comment within the src/pointer/mod.rs file. The update addresses the behavior of the CastUnsized implementation, specifically detailing how pointer metadata relates to the sizes of Src and Dst types, thereby ensuring the documentation precisely reflects that referent size can be preserved or reduced.

Highlights

• Safety Comment Clarification: The safety comment for the CastUnsized unsafe impl block has been updated to accurately reflect that the project operation may shrink the referent size, rather than strictly preserving it. This ensures the documentation correctly describes the conditions for soundness.

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[gemini-code-assist]

Code Review

This pull request corrects a safety comment for CastUnsized to accurately reflect that it can perform shrinking casts, not just size-preserving ones. The change is correct and improves the accuracy of the documentation. I've found a small typo in the updated comment.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.90%. Comparing base (5c67d2c) to head (f902320).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2908   +/-   ##
=======================================
  Coverage   91.90%   91.90%           
=======================================
  Files          20       20           
  Lines        5877     5877           
=======================================
  Hits         5401     5401           
  Misses        476      476           

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