- Either explicitly annotate `let x: () = expr;` where `x` has unit
type, or remove the unit binding to leave only `expr;` instead.
- Fix disjoint-capture-in-same-closure test
When constant evaluation fails because its MIR is tainted by errors,
suppress note indicating that erroneous constant was used, since those
errors have to be fixed regardless of the constant being used or not.
Add suggestion to use closure argument instead of a capture on borrowck error
Fixes#109271
r? `@compiler-errors`
This should probably be refined a bit, but opening a PR so that I don't forget anything.
Updates `interpret`, `codegen_ssa`, and `codegen_cranelift` to consume the new cast instead of the intrinsic.
Includes `CastTransmute` for custom MIR building, to be able to test the extra UB.
I was looking into `array::IntoIter` optimization, and noticed that it wasn't annotating the loads with `noundef` for simple things like `array::IntoIter<i32, N>`.
Turned out to be a more general problem as `MaybeUninit::assume_init_read` isn't marking the load as initialized (<https://rust.godbolt.org/z/Mxd8TPTnv>), which is unfortunate since that's basically its reason to exist.
This PR lowers `ptr::read(p)` to `copy *p` in MIR, which fortuitiously also improves the IR we give to LLVM for things like `mem::replace`.
An `assume` would definitely not be worth it, but since the flag is almost free we might as well tell LLVM this, especially on `_unchecked` calls where there's no obvious way for it to deduce it.
(Today neither safe nor unsafe indexing gets it: <https://rust.godbolt.org/z/G1jYT548s>)
lint: don't suggest MaybeUninit::assume_init for uninhabited types
Creating a zeroed uninhabited type such as `!` or an empty enum with `mem::zeroed()` (or transmuting `()` to `!`) currently triggers this lint:
```rs
warning: the type `!` does not permit zero-initialization
--> test.rs:5:23
|
5 | let _val: ! = mem::zeroed();
| ^^^^^^^^^^^^^
| |
| this code causes undefined behavior when executed
| help: use `MaybeUninit<T>` instead, and only call `assume_init` after initialization is done
|
= note: the `!` type has no valid value
```
The `MaybeUninit` suggestion in the help message seems confusing/useless for uninhabited types, as such a type cannot be fully initialized in the first place (as the note implies).
This PR limits this help message to inhabited types which can be initialized
