Incorrect help suggestion on E0790 with parameterized traits

[polina4096]

Given the following code:

trait TraitA<T> {
    fn func();
}

struct StructA {}

impl TraitA<i32> for StructA {
    fn func() {}
}

fn main() {
    TraitA::<i32>::func();
}

The current output is:

error[E0790]: cannot call associated function on trait without specifying the corresponding `impl` type
  --> src/main.rs:12:5
   |
2  |     fn func();
   |     ---------- `TraitA::func` defined here
...
12 |     TraitA::<i32>::func();
   |     ^^^^^^^^^^^^^^^^^^^ cannot call associated function of trait
   |
help: use the fully-qualified path to the only available implementation
   |
12 |     <::StructA as TraitA>::<i32>::func();
   |     +++++++++++++       +

error: aborting due to previous error

For more information about this error, try `rustc --explain E0790`.

Ideally the output should look like:

error[E0790]: cannot call associated function on trait without specifying the corresponding `impl` type
  --> src/main.rs:12:5
   |
2  |     fn func();
   |     ---------- `TraitA::func` defined here
...
12 |     TraitA::<i32>::func();
   |     ^^^^^^^^^^^^^^^^^^^ cannot call associated function of trait
   |
help: use the fully-qualified path to the only available implementation
   |
12 |     <StructA as TraitA<i32>>::func();
   |     ++++++++++++           +

error: aborting due to previous error

For more information about this error, try `rustc --explain E0790`.

The suggested code when trying to call associated function on trait without specifying the corresponding impl type does not compile, as the type parameter is in the wrong place.

[Rageking8]

@rustbot label +D-invalid-suggestion

[lyming2007]

@rustbot claim

[lyming2007]

I can generate diagnostic information like

error[E0790]: cannot call associated function on trait without specifying the corresponding `impl` type
  --> main.rs:15:5
   |
2  |     fn func();
   |     ---------- `TraitA::func` defined here
...
15 |     TraitA::<i32>::func();
   |     ^^^^^^^^^^^^^^^^^^^ cannot call associated function of trait
   |
help: use the fully-qualified path to the only available implementation
   |
15 |     <::StructA as TraitA::<i32>>::func();
   |     +++++++++++++              +

error: aborting due to previous error

Which is close to

   |
15 |     <::StructA as TraitA<i32>>::func();
   |     +++++++++++++              +

the only difference is the :: between TraitA and <i32>.
The code to generate this suggestion is:

                           err.multipart_suggestion(
                                message,
                                vec![
                                    (trait_path_segment.ident.span.shrink_to_lo(), format!("<{} as ", self.tcx.def_path(impl_def_id).to_string_no_crate_verbose())),
                                   // (trait_path_segment.ident.span.shrink_to_hi(), format!(">"))
                                    (generic_arg.span_ext.shrink_to_hi(), format!(">")),
                                ],
                                Applicability::MaybeIncorrect
                            );

now I even got span for :: by this code:

let between_span = trait_path_segment.ident.span.between(generic_arg.span_ext);

@estebank
Could you give me some suggestions how I can remove the between_span from err above?
Thus we can generate

   |
15 |     <::StructA as TraitA<i32>>::func();
   |     +++++++++++++              +

[lyming2007]

the fix was created:
#102421

[polina4096]

Should I close the issue?

[lyming2007]

yes please.