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Rollup merge of #72194 - doctorn:dispatch-from-dyn-ice, r=estebank

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Don't ICE on missing `Unsize` impl

Previously code of the form

```rust
#![feature(unsize, dispatch_from_dyn)]

use std::marker::Unsize;
use std::ops::DispatchFromDyn;

pub struct Foo<'a, T: ?Sized> {
    _inner: &'a &'a T,
}

impl<'a, T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Foo<'a, U>> for Foo<'a, T> {}
```

would generate an ICE due to the missing `Unsize` impl being run through the `suggest_change_mut` suggestion. This PR adds an early exit and a pointer to the appropriate docs regarding `Unsize` instead:

```
error[E0277]: the trait bound `&'a T: std::marker::Unsize<&'a U>` is not satisfied
  --> src/test/ui/issues/issue-71036.rs:11:1
   |
11 | impl<'a, T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Foo<'a, U>> for Foo<'a, T> {}
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `std::marker::Unsize<&'a U>` is not implemented for `&'a T`
   |
   = note: all implementations of `Unsize` are provided automatically by the compiler, see <https://doc.rust-lang.org/stable/std/marker/trait.Unsize.html> for more information
   = note: required because of the requirements on the impl of `std::ops::DispatchFromDyn<&'a &'a U>` for `&'a &'a T`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.
```

r? @estebank

Resolves #71036
This commit is contained in:
Dylan DPC 2020-05-14 18:21:59 +02:00 • committed by GitHub
commit 7b5bc61e99
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17
src/test/ui/issues/issue-71036.rs Normal file
View file

@ -0,0 +1,17 @@
#![feature(unsize, dispatch_from_dyn)]
use std::marker::Unsize;
use std::ops::DispatchFromDyn;
#[allow(unused)]
struct Foo<'a, T: ?Sized> {
_inner: &'a &'a T,
}
impl<'a, T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Foo<'a, U>> for Foo<'a, T> {}
//~^ ERROR the trait bound `&'a T: std::marker::Unsize<&'a U>` is not satisfied
//~| NOTE the trait `std::marker::Unsize<&'a U>` is not implemented for `&'a T`
//~| NOTE all implementations of `Unsize` are provided automatically by the compiler
//~| NOTE required because of the requirements on the impl
fn main() {}

12
src/test/ui/issues/issue-71036.stderr Normal file
View file

@ -0,0 +1,12 @@
error[E0277]: the trait bound `&'a T: std::marker::Unsize<&'a U>` is not satisfied
--> $DIR/issue-71036.rs:11:1
|
LL | impl<'a, T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Foo<'a, U>> for Foo<'a, T> {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `std::marker::Unsize<&'a U>` is not implemented for `&'a T`
|
= note: all implementations of `Unsize` are provided automatically by the compiler, see <https://doc.rust-lang.org/stable/std/marker/trait.Unsize.html> for more information
= note: required because of the requirements on the impl of `std::ops::DispatchFromDyn<&'a &'a U>` for `&'a &'a T`
error: aborting due to previous error
For more information about this error, try `rustc --explain E0277`.