Commits on Sep 12, 2023

1. Add TryFromBytes trait …

   `TryFromBytes` can be implemented for types which are not `FromZeroes`
   or `FromBytes`; it supports performing a runtime check to determine
   whether a given byte sequence contains a valid instance of `Self`.
   
   This is the first step of #5. Future commits will add support for a
   custom derive and for implementing `TryFromBytes` on unsized types.
   
   TODO:
   - More thorough tests for non-FromBytes types (bool, char, etc)
   - Tests that go through the `TryFromBytes` public methods rather than
     testing `is_bit_valid` directly
   - Pick public TryFromBytes method names that are more consistent with
     FromBytes? In particular:
     - try_from_ref -> try_from_bytes
     - try_from_mut -> try_from_bytes_mut
   
   Makes progress on #5

   

   joshlf committed Sep 12, 2023
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2. Add try_transmute!, try_transmute_{ref,mut}! …

   TODO: Commit message body
   
   TODO:
   - In `try_transmute!`, should the argument be dropped or forgotten (ie,
     `mem::forget`) when the transmute fails? We could also return the
     original value in a `Result::Error`, but that would be inconsistent
     with `TryFrom`. Then again, `TryFrom` provides a custom error type, so
     in theory implementers could do that if they wanted to. Most of the
     types that don't consume Copy types.
   
   Makes progress on #5

   

   joshlf committed Sep 12, 2023
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3. [derive] Support TryFromBytes for structs …

   TODO:
   - Should DataExt::fields have a different shape? Extracting field names
     for enums doesn't really make sense
   - Lots and lots of tests
   - If we manage to land derive(KnownLayout) first, replace manual impls
     of KnownLayout with the derive
   - Is there any way to make sure the code we emit doesn't emit warnings?
     I tested with an earlier version of the code that had lots of code
     smells like pointer coercions that emitted warnings, and even after
     emitting `#[deny(...)]` attributes, I couldn't get code which made use
     of the derive to complain at all - the compiler just happily accepted
     it.
   
   Makes progress on #5

   

   joshlf committed Sep 12, 2023
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4. [WIP][derive] Support custom TryFromBytes validator …

   TODO:
   - Cleaner way to pass name of validator to `impl_block`?
   - Cleaner way to parse validator attribute?
   - Safety comment in emitted call to `validate`
   - Tests (especially including tests for the error message resulting from
     passing a validator with the wrong type signature - test for both
     argument types and return types)
     - Also test for invalid zerocopy attributes
     - Also test for hygiene - that the validator can't access variables
       from the `is_bit_valid` function body scope
   - Other misc TODO comments in code

   

   joshlf committed Sep 12, 2023
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5. [WIP] TryFromBuild derive support for enums …

   TODO:
   - Clean up repr computation
   - Support enums with fields
   - If we don't support enums with fields, enforce that
   - Should enum variants be considered "used" in the sense of dead code?
     It's possible to never construct an enum variant from Rust's
     perspective even though it is constructed via TryFromBytes.
   - Confirm that we reject uninhabited enums. Currently Rust doesn't let
     you put a repr on these enums, so we would reject them for lack of a
     repr, but we should probably have a more reliable check than that.

   

   joshlf committed Sep 12, 2023
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