[WIP]

[joshlf]

---

• 👉 [WIP] #2864
• 　 [WIP] ReadOnly + TryFromBytes::is_bit_valid #2863
• 　 [pointer] Add generic projection/cast framework #2860

Latest Update: v7 — Compare vs v6

📚 Full Patch History

Links show the diff between the row version and the column version.

Version	v6	v5	v4	v3	v2	v1	Base
v7	vs v6	vs v5	vs v4	vs v3	vs v2	vs v1	vs Base
v6		vs v5	vs v4	vs v3	vs v2	vs v1	vs Base
v5			vs v4	vs v3	vs v2	vs v1	vs Base
v4				vs v3	vs v2	vs v1	vs Base
v3					vs v2	vs v1	vs Base
v2						vs v1	vs Base
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 introduces a significant refactoring of the is_bit_valid function within the zerocopy crate. The primary goal is to simplify the function's API by removing an unnecessary generic parameter, enhance the clarity and safety of aliasing semantics through the consistent use of ReadOnly wrappers, and enforce a KnownLayout requirement for all types implementing TryFromBytes. These changes collectively aim to make the bit validity checking mechanism more robust, consistent, and easier to reason about, especially for complex data structures and automatically derived implementations.

Highlights

• Simplified is_bit_valid Signature: The is_bit_valid function across the crate, including the TryFromBytes trait, its implementations, and associated macros, has been simplified by removing the invariant::Reference generic parameter from its Maybe candidate argument. This streamlines the API and reduces complexity.
• Refined UnsafeCell Bit Validity Handling: The implementation of is_bit_valid for UnsafeCell<T> now utilizes transmute_unchecked with ReadOnly<T> instead of relying on an exclusive aliasing requirement. This change simplifies the logic for UnsafeCell and potentially broadens its applicability for bit validity checks.
• TryFromBytes Requires KnownLayout: The TryFromBytes trait now includes a supertrait bound KnownLayout, ensuring that any type implementing TryFromBytes has a well-defined memory layout. This adds a crucial constraint for types that can be checked for bit validity.
• Consistent ReadOnly Wrapper Usage: Derived and manual implementations of is_bit_valid now consistently employ transmute_unchecked with ReadOnly wrappers to handle the Maybe candidate. This standardizes how bit validity checks are performed across various types and contexts.

🧠 New Feature in Public Preview: You can now enable Memory to help Gemini Code Assist learn from your team's feedback. This makes future code reviews more consistent and personalized to your project's style. Click here to enable Memory in your admin console.

Using Gemini Code Assist

The full guide for Gemini Code Assist can be found on our documentation page, here are some quick tips.

Invoking Gemini

You can request assistance from Gemini at any point by creating a comment using either /gemini <command> or @gemini-code-assist <command>. Below is a summary of the supported commands on the current page.

Feature	Command	Description
Code Review	/gemini review	Performs a code review for the current pull request in its current state.
Pull Request Summary	/gemini summary	Provides a summary of the current pull request in its current state.
Comment	@gemini-code-assist	Responds in comments when explicitly tagged, both in pull request comments and review comments.
Help	/gemini help	Displays a list of available commands.

Customization

To customize Gemini Code Assist for GitHub experience, repository maintainers can create a configuration file and/or provide a custom code review style guide (such as PEP-8 for Python) by creating and adding files to a .gemini/ folder in the base of the repository. Detailed instructions can be found here.

Limitations & Feedback

Gemini Code Assist may make mistakes. Please leave feedback on any instances where its feedback is incorrect or counter productive. You can react with 👍 and 👎 on @gemini-code-assist comments. If you're interested in giving your feedback about your experience with Gemini Code Assist for Github and other Google products, sign up here.

You can also get AI-powered code generation, chat, as well as code reviews directly in the IDE at no cost with the Gemini Code Assist IDE Extension.

Footnotes

1. Review the Privacy Notices, Generative AI Prohibited Use Policy, Terms of Service, and learn how to configure Gemini Code Assist in GitHub here. Gemini can make mistakes, so double check it and use code with caution. ↩

[gemini-code-assist]

Code Review

This pull request refactors the TryFromBytes::is_bit_valid method by removing its generic parameter for aliasing invariants. This simplifies the trait's API. The new implementation approach uses ReadOnly<T> to handle types with interior mutability like UnsafeCell, which seems like a sound refactoring.

My review has identified a few minor issues, mostly related to duplicated #[inline] attributes and some formatting inconsistencies in generated code within macros. These are likely leftovers from the refactoring and should be straightforward to fix.

[gemini-code-assist]

The #[inline] attribute is duplicated. Please remove one of them.

[gemini-code-assist]

The #[inline] attribute is duplicated. Please remove one of them.

[gemini-code-assist]

There's an extra space at the beginning of this line, causing inconsistent indentation within the unsafe block. Please remove it for better code formatting.

Suggested change

	field_candidate.transmute_unchecked::<
	#zerocopy_crate::wrappers::ReadOnly<#field_tys>,
	_,
	#zerocopy_crate::pointer::cast::CastUnsized
	>()
	field_candidate.transmute_unchecked::<
	#zerocopy_crate::wrappers::ReadOnly<#field_tys>,
	_,
	#zerocopy_crate::pointer::cast::CastUnsized
	>()