When suggesting associated fn with type parameters, include in the structured suggestion

[estebank]

Address #50734.

error[E0046]: not all trait items implemented, missing: `foo`, `bar`, `baz`
  --> file.rs:14:1
   |
14 | impl TraitA<()> for S {
   | ^^^^^^^^^^^^^^^^^^^^^ missing `foo`, `bar`, `baz` in implementation
   |
   = help: implement the missing item: `fn foo<T>(_: T) -> Self where T: TraitB, TraitB::Item = A { unimplemented!() }`
   = help: implement the missing item: `fn bar<T>(_: T) -> Self { unimplemented!() }`
   = help: implement the missing item: `fn baz<T>(_: T) -> Self where T: TraitB, <T as TraitB>::Item: std::marker::Copy { unimplemented!() }`

It doesn't work well for associated types with ty::Predicate::Projections as we need to resugar T: Trait, Trait::Assoc = K → T: Trait<Assoc = K>.

[rust-highfive]

r? @varkor

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[estebank]

This should be

fn from_iter<T>(_: T) -> Self where T: std::iter::IntoIterator<Item = A> { unimplemented!() }

[estebank]

Filed #68982 to track this

[estebank]

cc @rust-lang/compiler in order for this suggestion to be accurate we would need a way to resugar ty::Predicate::Trait and ty::Predicate::Projection into a single thing, at least on a best effort basis. Does anyone have any reservations on doing so? Do we already have that anywhere?

[eddyb]

@estebank There's some code like that in rustdoc, might be nice to share that between the two usecases (if this is even a good idea).

[estebank]

might be nice to share that between the two usecases

Definitely.

if this is even a good idea

It's categorically not a good idea, but we might need to do it anyways.

[estebank]

For reference for future me, src/librustdoc/clean/inline.rs seems to have the rustdoc logic to do this in build_external_trait.

[varkor]

r=me after fixing the comment.

[estebank]

@bors r=varkor

[bors]

📌 Commit 3cdd7ae has been approved by varkor

[bors]

⌛ Testing commit 3cdd7ae with merge 64ea639...

[bors]

☀️ Test successful - checks-azure
Approved by: varkor
Pushing 64ea639 to master...