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Do not promote values with const drop that need to be dropped #89988

Merged
merged 2 commits into from
Oct 19, 2021
Merged

Do not promote values with const drop that need to be dropped #89988

merged 2 commits into from
Oct 19, 2021

Commits on Oct 18, 2021

  1. Rename needs_drop to needs_non_const_drop

    @tmiasko
    tmiasko committed Oct 18, 2021
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  2. Do not promote values with const drop that need to be dropped 

    Changes from rust-lang#88558 allowed using `~const Drop` in constants by
introducing a new `NeedsNonConstDrop` qualif.

The new qualif was also used for promotion purposes, and allowed
promotion to happen for values that needs to be dropped but which
do have a const drop impl.

Since for promoted the drop implementation is never executed,
this lead to observable change in behaviour. For example:

```rust

struct Panic();

impl const Drop for Panic {
    fn drop(&mut self) {
        panic!();
    }
}

fn main() {
    let _ = &Panic();
}
```

Restore the use of `NeedsDrop` qualif during promotion to avoid the issue.
    @tmiasko
    tmiasko committed Oct 18, 2021
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