Rollup merge of #65485 - ecstatic-morse:const-validation-mismatch-ugliness, r=eddyb

Suppress ICE when validators disagree on `LiveDrop`s in presence of `&mut`

Resolves #65394.

This hack disables the validator mismatch ICE in cases where a `MutBorrow` error has been emitted by both validators, but they don't agree on the number of `LiveDrop` errors.

The new validator is more conservative about whether a value is moved from in the presence of mutable borrows. For example, the new validator will emit a `LiveDrop` error on the following code.

```rust
const _: Vec<i32> = {
    let mut x = Vec::new();
    let px = &mut x as *mut _;
    let y = x;
    unsafe { ptr::write(px, Vec::new()); }
    y
};
```

This code is not UB AFAIK (it passes MIRI at least). The current validator does not emit a `LiveDrop` error for `x` upon exit from the initializer. `x` is not actually dropped, so I think this is correct? A proper fix for this would require a new `MaybeInitializedLocals` dataflow analysis or maybe a relaxation of the existing `IndirectlyMutableLocals` one.

r? @RalfJung

0 files changed, 0 insertions, 0 deletions