Closed
Description
Given the following code (playground link):
trait Foo {
const ASSOC: bool = true;
}
impl<T> Foo for fn(T) {}
fn foo(_x: i32) {}
fn impls_foo<T: Foo>(_x: T) {}
fn main() {
// Works, but if the below code is present, it is shown as failed
impls_foo(foo as fn(i32));
// Fails as expected, see https://github.com/rust-lang/rust/issues/56105
<fn(&u8) as Foo>::ASSOC;
}The current (nightly ec55c61 2022-06-10, regressed in the past week) output is:
Compiling playground v0.0.1 (/playground)
error: implementation of `Foo` is not general enough
--> src/main.rs:12:5
|
12 | impls_foo(foo as fn(i32));
| ^^^^^^^^^^^^^^^^^^^^^^^^^ implementation of `Foo` is not general enough
|
= note: `Foo` would have to be implemented for the type `for<'r> fn(&'r u8)`
= note: ...but `Foo` is actually implemented for the type `fn(&'0 u8)`, for some specific lifetime `'0`
error: implementation of `Foo` is not general enough
--> src/main.rs:15:5
|
15 | <fn(&u8) as Foo>::ASSOC;
| ^^^^^^^^^^^^^^^^^^^^^^^ implementation of `Foo` is not general enough
|
= note: `Foo` would have to be implemented for the type `for<'r> fn(&'r u8)`
= note: ...but `Foo` is actually implemented for the type `fn(&'0 u8)`, for some specific lifetime `'0`
error: could not compile `playground` due to 2 previous errors
Ideally the output should look like:
Compiling playground v0.0.1 (/playground)
error: implementation of `Foo` is not general enough
--> src/main.rs:15:5
|
15 | <fn(&u8) as Foo>::ASSOC;
| ^^^^^^^^^^^^^^^^^^^^^^^ implementation of `Foo` is not general enough
|
= note: `Foo` would have to be implemented for the type `for<'r> fn(&'r u8)`
= note: ...but `Foo` is actually implemented for the type `fn(&'0 u8)`, for some specific lifetime `'0`
error: could not compile `playground` due to previous error
The desired result can be achieved by swapping the order of the two statements <fn(&u8) as Foo>::ASSOC; and impls_foo(foo as fn(i32));.