[WIP] Wrapped projections

[joshlf]

Makes progress on #2336

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• 　 [derive] Allow TryFromBytes on non-Immutable unions #2876
• 　 Use ReadOnly in TryFromBytes::is_bit_valid #2873
• 👉 [WIP] Wrapped projections #2919

Latest Update: v9 — Compare vs v8

📚 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 introduces foundational traits and implementations to support 'wrapped projections' within the pointer casting system. The primary goal is to enable the projection mechanism to correctly handle types that encapsulate other types, such as MaybeUninit or Wrapping, by defining how to 'unwrap' them for projection and then 're-wrap' the projected field. This is a significant preparatory step towards more robust and flexible pointer manipulation, particularly in scenarios involving low-level memory management or specialized arithmetic types.

Highlights

• Introduction of Wrapped and HasWrappedField traits: Two new unsafe traits, Wrapped and HasWrappedField, have been introduced. These traits define how types that 'wrap' another type can be unwrapped and re-wrapped for projection purposes, enabling the projection mechanism to traverse through such wrappers.
• Implementations for standard library wrappers: The Wrapped and HasWrappedField traits are now implemented for core::mem::MaybeUninit and core::num::Wrapping. This allows the projection system to correctly handle these common standard library types.
• Definition of WrappedProjection: A new type alias, WrappedProjection, has been added. This alias is designed to facilitate transitive projections that involve wrapped types, streamlining the process of projecting through multiple layers of type wrappers.
• Support for ReadOnly wrapper: The custom ReadOnly type now also implements the Wrapped and HasWrappedField traits, extending the new wrapped projection capabilities to this specific wrapper type.

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[gemini-code-assist]

Code Review

This pull request introduces new Wrapped and HasWrappedField traits, along with their implementations for MaybeUninit, Wrapping, and ReadOnly types. It also defines a WrappedProjection type alias. The changes aim to extend the library's capabilities for pointer casting and projection. A critical aspect of this review is the presence of several TODO comments, particularly regarding safety justifications for unsafe traits and unsafe impl blocks. Given that zerocopy is a library focused on memory safety, these justifications are crucial and must be thoroughly documented. Additionally, the complex WrappedProjection type alias would benefit from a detailed doc comment to enhance maintainability and understanding.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.33%. Comparing base (1a21b6d) to head (c713b4d).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2919   +/-   ##
=======================================
  Coverage   91.33%   91.33%           
=======================================
  Files          20       20           
  Lines        5918     5918           
=======================================
  Hits         5405     5405           
  Misses        513      513           

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[joshlf]

Squashed into #2873