rust/tests/ui/transmutability/maybeuninit.stderr
Jack Wrenn 3aa14e3b2e Compute transmutability from rustc_target::abi::Layout
In its first step of computing transmutability, `rustc_transmutability`
constructs a byte-level representation of type layout (`Tree`). Previously, this
representation was computed for ADTs by inspecting the ADT definition and
performing our own layout computations. This process was error-prone, verbose,
and limited our ability to analyze many types (particularly default-repr types).

In this PR, we instead construct `Tree`s from `rustc_target::abi::Layout`s. This
helps ensure that layout optimizations are reflected our analyses, and increases
the kinds of types we can now analyze, including:
- default repr ADTs
- transparent unions
- `UnsafeCell`-containing types

Overall, this PR expands the expressvity of `rustc_transmutability` to be much
closer to the transmutability analysis performed by miri. Future PRs will work
to close the remaining gaps (e.g., support for `Box`, raw pointers, `NonZero*`,
coroutines, etc.).
2024-04-08 15:36:52 +00:00

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error[E0277]: `MaybeUninit<u8>` cannot be safely transmuted into `u8`
--> $DIR/maybeuninit.rs:21:54
|
LL | assert::is_maybe_transmutable::<MaybeUninit<u8>, u8>();
| ^^ at least one value of `MaybeUninit<u8>` isn't a bit-valid value of `u8`
|
note: required by a bound in `is_maybe_transmutable`
--> $DIR/maybeuninit.rs:12:14
|
LL | pub fn is_maybe_transmutable<Src, Dst>()
| --------------------- required by a bound in this function
LL | where
LL | Dst: BikeshedIntrinsicFrom<Src, { Assume::SAFETY }>
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `is_maybe_transmutable`
error: aborting due to 1 previous error
For more information about this error, try `rustc --explain E0277`.