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GAT: lifetime is inconsistently required with Higher-Rank Trait Bounds #93262
Description
I'm getting weird error messages by combining GATs with HRTBs. Here is an example:
#![feature(generic_associated_types)]
pub trait Trait {
type Assoc<'a> where Self: 'a;
}
pub trait Foo<T: Trait>
where
for<'a> T::Assoc<'a>: Clone
{}
pub struct Type;
impl<T: Trait> Foo<T> for Type
where
for<'a> T::Assoc<'a>: Clone
{}This was working fine with rustc 1.58. Now with 1.60 I get the following error message:
error[E0311]: the parameter type `T` may not live long enough
--> src/lib.rs:13:16
|
13 | impl<T: Trait> Foo<T> for Type
| -- ^^^^^^ ...so that the type `T` will meet its required lifetime bounds...
| |
| help: consider adding an explicit lifetime bound...: `T: 'a +`
|
note: ...that is required by this bound
--> src/lib.rs:8:38
|
8 | for<'a> <T as Trait>::Assoc<'a>: Clone
| ^^^^^
There are a couple of weird things going on:
- First, it was my understanding that the
for<'a> <T as Trait>::Assoc<'a>: ...bound is well formed and should be accepted by the compiler even though thewhere Self: 'abound onTrait::Assocmeans thatTmust outlive'a. I might be wrong here. - The error message disappears if we remove the HRTB from the trait definition but not from the trait implementation.
- We can define a function with the same HRTB, and it compiles fine:
pub fn foo<T: Trait>()
where
for<'a> T::Assoc<'a>: Clone
{}
Activity
compiler-errors commentedon Apr 14, 2022
This is due to #92191
Rollup merge of rust-lang#96593 - jackh726:issue-93262, r=compiler-er…
Auto merge of rust-lang#96593 - jackh726:issue-93262, r=compiler-errors