Someday Maybe

[joshlf]

This issue tracks ideas which we might want to tackle some day, but which don't have enough detail to warrant their own separate issues.

Feature additions

• Track all parser ideas somewhere in the zerocopy repo, including this prototype; also link to Support mid-level byte slice and buffer operations #1315
• If two slice DSTs have the same slice offset, element size, and alignment, then we can support transmute_ref! and transmute_mut! for these types - just need to figure out how to encode all of these in the type system (e.g. associated types on KnownLayout)
• As part of a broader trend towards teaching zerocopy to express more powerful transmutations, could we add trait AsInitialized<T>? We could use it to replace the existing Src: IntoBytes bound in transmute!, try_transmute!, etc
• Look at the nolife crate's API for inspiration
• Look at the binary_layout crate's API for inspiration
• Add method to Ref to change the type parameter (ie, perform a transmutation); we could use this to make new_sized a thin wrapper around new
• Support stdlib's new generic NonZero<T>
  • Add a trait that marks T for which size_of::<T>() == size_of::<Option<T>>() (see Support generic NonZero<T> #2255)
• Support transmuting T to MaybeUninit<T> (or maybe even MaybeUninit<U>) even when T: ?IntoBytes
• Once generic_const_exprs and associated_const_equality are stabilized, we can use KnownLayout::LAYOUT to guarantee layout equality, supporting both size equality and slice DST equality (e.g., T: KnownLayout, U: KnownLayout<LAYOUT = {T::LAYOUT}>); see playground example
• Add Unalign::replace or swap (which returns the original) and maybe deprecate Unalign::set. Strictly more powerful.

Safety

• Audit for &slice[0] as *const per rust-lang/unsafe-code-guidelines#134
• Audit for &mut as *const per rust-lang/rust#56604 - see also rust-lang/clippy#12791
• In Ptr's internal invariants, do we need to separately say that the pointer is derived from a valid allocation and that it has provenance for that allocation? Is the latter alone sufficient?
• Use Rudra in CI?

Performance

• When deriving TryFromBytes, if we're deriving it thanks to #[derive(FromBytes)], emit an empty is_bit_valid impl; this will be more optimizable, and should cut down on compile times
  • Derive trivial is_bit_valid when possible #1303
• cargo-llvm-lines

Developer experience

• Consider using cargo nextest to speed up CI execution times
• Cargo docs published to google.github.io/zerocopy could include link to the commit that generated it
  • One idea for how to do this: programmatically edit the crate-root doc comment with a link
  • Maybe publish each commit's docs in a subdirectory named for that commit's hash so we have a historical record of all documentation?
• Publish cargo docs to google.github.io/zerocopy for every PR (see this StackOverflow question)
  • Looks like GitHub might eventually support this natively
  • Feature request: Partial upload/deploy actions/deploy-pages#349
  • Here's a suggestion for working around the current issue
• Consider using cargo release
• Consider using larger GitHub Actions runners
• In CI, confirm that MSRV is lower than any version we use for version detection. This will naturally trigger us to clean up the codebase when we bump MSRV.
• Only generate roll PRs (for pinned stable and nightly toolchains) on week days
• Allow setting repository-wide "vacation mode" that causes rollers to pause

Documentation

• Write documentation post on zerocopy's values
• Be consistent about our use of "interpret" vs "reinterpret" in doc comments
• Compile for multiple targets on docs.rs using the package.metadata.docs.rs.targets Cargo.toml key (see e.g. usage in syn)?
• Use permalinks when quoting Rust documentation; e.g., "https://doc.rust-lang.org/1.54.0/std/" instead of "https://doc.rust-lang.org/stable/std/"
• Make zerocopy-derive docs link to zerocopy traits

Testing

• Use kani::cover! (e.g. to more thoroughly test Derive trivial is_bit_valid when possible #1303)
• Test our tests using mutagen

Community engagement and outside contributions

• Post research projects on edu Zulip

Miscellaneous

• Check for missing copyright header comments in CI
• Use invariant lifetimes to achieve a sort of dependent typing? E.g., here's a function where the returned byte array is guaranteed to be n bytes long:
  • fn take_bytes<'a>(&mut self, n: Usize<'a>) -> Option<Bytes<'a>>
• Put lints in Cargo.toml once that's stable on our MSRV: Tracking Issue for [lints] table RFC 3389 rust-lang/cargo#12115
• Use freeze API once it lands/stabilizes: RFC: Add freeze intrinsic and related library functions rust-lang/rfcs#3605
• Use inline const in zerocopy? Stabilise inline_const rust-lang/rust#104087
• Any use for return-position impl trait in traits (RPITT) in zerocopy or downstream libraries like packet?
• Any use for variadic generics?
• Any use for slice_flatten?

Done

• Add GitHub Action - to be triggered manually - that submits a PR that releases a new zerocopy version
  • Add "release new crate version" workflow #1172
• Publish cargo docs (with private/hidden items documented) for main at google.github.io/zerocopy
  • Done: [ci] Publish cargo doc to GitHub Pages #1227