Add tests for compilation failure

[joshlf]

We use the trybuild crate to test that zerocopy-derive correctly rejects code that it ought to. We have the same running for zerocopy itself, but no tests have been written to make use of it. zerocopy's API uses trait bounds to make certain illegal code impossible to express; we should write trybuild tests that make sure that each illegal code pattern actually fails to compile.

Contributing

If you'd like to contribute to this issue, just look through zerocopy's API, find unsound behavior that ought to be impossible to express, and write a test to confirm that it's inexpressible!

If you're not sure where to start, consider:

• Does the API have any documented preconditions which ought to be enforced at compile time?
• Does the API have any trait bounds?

Write a test which fails to uphold one of these requirements.

Here's a list of all of the APIs in zerocopy that have preconditions or trait bounds:

• FromBytes (@IsaacCloos assigned)
  • read_from
  • read_from_prefix
  • read_from_suffix
• AsBytes
  • as_bytes_mut
  • write_to
  • write_to_prefix
  • write_to_suffix
• LayoutVerified
  • new
  • new_from_prefix
  • new_from_suffix
  • new_slice
  • new_slice_from_prefix
  • new_slice_from_suffix
  • new_zeroed
  • new_from_prefix_zeroed
  • new_from_suffix_zeroed
  • new_slice_zeroed
  • new_slice_from_prefix_zeroed
  • new_slice_from_suffix_zeroed
  • new_unaligned
  • new_unaligned_from_prefix
  • new_unaligned_from_suffix
  • new_slice_unaligned
  • new_slice_unaligned_from_prefix
  • new_slice_unaligned_from_suffix
  • new_unaligned_zeroed
  • new_unaligned_from_prefix_zeroed
  • new_unaligned_from_suffix_zeroed
  • new_slice_unaligned_zeroed
  • new_slice_unaligned_from_prefix_zeroed
  • new_slice_unaligned_from_suffix_zeroed
  • into_ref
  • into_mut
  • into_slice
  • into_mut_slice
  • bytes
  • bytes_mut
  • read
  • write
  • Debug for LayoutVerified<B, T>
  • Debug for LayoutVerified<B, [T]>
  • Deref for LayoutVerified<B, T>
  • Deref for LayoutVerified<B, [T]>
  • DerefMut for LayoutVerified<B, T>
  • DerefMut for LayoutVerified<B, [T]>
  • Display for LayoutVerified<B, T>
  • Display for LayoutVerified<B, [T]>
  • Ord for LayoutVerified<B, T>
  • Ord for LayoutVerified<B, [T]>
  • PartialOrd for LayoutVerified<B, T>
  • PartialOrd for LayoutVerified<B, [T]>
  • Eq for LayoutVerified<B, T>
  • Eq for LayoutVerified<B, [T]>
  • PartialEq for LayoutVerified<B, T>
  • PartialEq for LayoutVerified<B, [T]>
• Unalign
  • get
  • AsBytes for Unalign<T>
  • FromBytes for Unalign<T>
  • Copy for Unalign<T>
  • Clone for Unalign<T>
• extend_vec_zeroed
• insert_vec_zeroed
• transmute! macro

[IsaacCloos]

Hello, this issue wasn't referenced in This Week in Rust 464, but if you're open to assistance I'd be happy to contribute however might be valuable 😄

[joshlf]

Awesome, thanks @IsaacCloos! Welcome to zerocopy 😃

I've updated the description with more detailed instructions. Let me know which of the APIs you're planning on tackling so I can put your username next to them - we might have multiple people tackling different APIs. Let me know if you have any questions!

[IsaacCloos]

Wow! Documentation eruption 🌋 You can put me down for the FromBytes trait to start. I do have a few questions brewing, but I'll let them marinate before following up 👍🏻

Also, if at any point the timeline of completing this work isn't to your liking, just lmk and take me off 😄

[joshlf]

Will do! And no rush - this is just "nice to have" stuff. There's no time pressure 😃

[Atixx]

Hey there! Seems like there's plenty to do here, if it seems like something more than one person can tackle, I'd like to take on another API

[joshlf]

Definitely! Just lmk which you'd like to take and I'll put your name next to it.

[IsaacCloos]

I see since making my draft you have further defined the expected layout of the ui tests for zerocopy. I will adapt my tests to your format in a new PR after work today.

Feedback on the initial few I made would mean a lot, and help improve the quality of the rest to come 😄

[joshlf]

At this point, we have the tests that we need. We could always add more, but it doesn't make sense to leave this as a standing TODO.