For E0223, suggest associated functions that are similar to the path, even if the base type has multiple inherent impl blocks.

[zachs18]

Currently, the "help: there is an associated function with a similar name from_utf8" suggestion for String::from::utf8 is only given if String has exactly one inherent impl item. This PR makes the suggestion be emitted even if the base type has multiple inherent impl items.

Example:

struct Foo;
impl Foo {
    fn bar_baz() {}
}
impl Foo {} // load-bearing
fn main() {
    Foo::bar::baz;
}

Nightly/stable output:

error[E0223]: ambiguous associated type
 --> f.rs:7:5
  |
7 |     Foo::bar::baz;
  |     ^^^^^^^^
  |
help: if there were a trait named `Example` with associated type `bar` implemented for `Foo`, you could use the fully-qualified path
  |
7 |     <Foo as Example>::bar::baz;
  |     ~~~~~~~~~~~~~~~~~~~~~

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0223`.

Output with this PR, or without the load-bearing empty impl on nightly/stable:

error[E0223]: ambiguous associated type
 --> f.rs:7:5
  |
7 |     Foo::bar::baz;
  |     ^^^^^^^^
  |
help: there is an associated function with a similar name: `bar_baz`
  |
7 |     Foo::bar_baz;
  |          ~~~~~~~

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0223`.

Ideally, this suggestion would also work for non-ADT types like str::char::indices (edit: latest commit makes this work with primitives) or <dyn Any>::downcast::mut_unchecked, but that seemed to be a harder change.

@rustbot label +A-diagnostics

[rustbot]

r? @compiler-errors

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[rustbot]

HIR ty lowering was modified

cc @fmease

[zachs18]

(Latest commit also works for primitives, but not <dyn Any>::downcast::mut_unchecked)