[projection] Clarify comment explaining fallibility

[joshlf]

---

• 　 Simplify try_transmute! (and friends) internals #2938
• 　 [derive] Allow TryFromBytes on non-Immutable unions #2876
• 　 Use ReadOnly in TryFromBytes::is_bit_valid #2873
• 👉 [projection] Clarify comment explaining fallibility #2939

Latest Update: v3 — Compare vs v2

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v1			vs Base

[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 focuses on improving the clarity of an important code comment within src/lib.rs. The change aims to provide a more accurate and understandable explanation of how Uninit and Initialized validity invariants behave when projecting fields from enum variants, particularly emphasizing their independence from the enum's tag. This enhancement will help future developers better grasp the underlying memory safety principles.

Highlights

• Code Comment Clarity: The existing comment explaining the fallibility of projecting fields from Uninit or Initialized union variants has been rewritten to be more precise. The new text clarifies that these validity invariants are independent of the enum's tag, meaning that the specific variant does not matter when dealing with uninitialized or initialized memory.

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.44%. Comparing base (4f2643c) to head (237fc29).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2939   +/-   ##
=======================================
  Coverage   92.44%   92.44%           
=======================================
  Files          19       19           
  Lines        5825     5825           
=======================================
  Hits         5385     5385           
  Misses        440      440           

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[gemini-code-assist]

Code Review

The pull request clarifies a comment in src/lib.rs regarding the fallibility of field projection in enums, specifically concerning Uninit and Initialized validity kinds. The change enhances the explanation of why these validity invariants do not depend on the enum's tag.

[jswrenn]

I like this phrasing a lot; I struggled to find the right framing.