transmute: use diagnostic item
closes#66075, we now have no remaining uses of `match_def_path` in the compiler while some uses still remain in `clippy`.
cc @RalfJung
Remove unused feature gates from library/ crates
Removes some unused feature gates from library crates. It's likely not a complete list as I only tested a subset for which it's more likely that it is unused.
Stabilize some Result methods as const
Stabilize the following methods of Result as const:
- `is_ok`
- `is_err`
- `as_ref`
A test is also included, analogous to the test for `const_option`.
These methods are currently const under the unstable feature `const_result` (tracking issue: #67520).
I believe these methods to be eligible for stabilization because of the stabilization of #49146 (Allow if and match in constants) and the trivial implementations, see also: [PR#75463](https://github.com/rust-lang/rust/pull/75463) and [PR#76135](https://github.com/rust-lang/rust/pull/76135).
Note: these methods are the only methods currently under the `const_result` feature, thus this PR results in the removal of the feature.
Related: #76225
This made too many assumptions about platforms, breaking some things.
Will need to be added later with a better way of gating on proper
alignment, without hardcoding cfg(target_arch)s.
Add associated constant `BITS` to all integer types
Recently I've regularly come across this snippet (in a few different crates, including `core` and `std`):
```rust
std::mem::size_of<usize>() * 8
```
I think it's time for a `usize::BITS`.
do not inline black_box when building for Miri
We cannot do the assembly trick in Miri, but let's at least make sure MIR inlining does not circumvent the black_box.
Also use black_box instead of local optimization barriers in a few const tests.
Add array_windows fn
This mimicks the functionality added by array_chunks, and implements a const-generic form of
`windows`. It makes egregious use of `unsafe`, but by necessity because the array must be
re-interpreted as a slice of arrays, and unlike array_chunks this cannot be done by casting the
original array once, since each time the index is advanced it needs to move one element, not
`N`.
I'm planning on adding more tests, but this should be good enough as a premise for the functionality.
Notably: should there be more functions overwritten for the iterator implementation/in general?
~~I've marked the issue as #74985 as there is no corresponding exact issue for `array_windows`, but it's based of off `array_chunks`.~~
Edit: See Issue #75027 created by @lcnr for tracking issue
~~Do not merge until I add more tests, please.~~
r? @lcnr
