"implement the missing item: …" helper does not substitute type parameter

[Tamschi]

This seems distinct from #10326.

Given

trait A<T> {
    fn a(&self) -> &T;
}
struct B {}

impl<'a, T> A<B> for T {} // <-- not all trait items implemented, missing: `a` in implementation

, applying the "implement the missing item: …" helper leads to the following code (after formatting):

trait A<T> {
    fn a(&self) -> &T;
}
struct B {}

impl<'a, T> A<B> for T {
    fn a(&self) -> &T { // <-- method `a` has an incompatible type for trait\nexpected fn pointer `fn(&T) -> &B`\n found fn pointer `fn(&T) -> &T`
        todo!()
    }
}

This should instead be

trait A<T> {
    fn a(&self) -> &T;
}
struct B {}

impl<'a, T> A<B> for T {
    fn a(&self) -> &B { // <-- Ok
        todo!()
    }
}

as with the "Implement missing members" helper.

[Veykril]

We do not have control over the rustc diagnostic fixes, we only apply what rustc suggests in that case.

[Tamschi]

We do not have control over the rustc diagnostic fixes, we only apply what rustc suggests in that case.

Ah sorry, that explains the different capitalisation and why it appears later. I'll close this and file it with rustc.