Compiler suggests [type error] when encountering placeholder in fn return type

[spookyvision]

Given the following code:

fn make() -> Option<_> {}

The current output is:

error[E0121]: the type placeholder `_` is not allowed within types on item signatures for return types
 --> src/lib.rs:1:21
  |
1 | fn make() -> Option<_> {}
  |              -------^-
  |              |      |
  |              |      not allowed in type signatures
  |              help: replace with the correct return type: `Option<[type error]>`

Ideally the output should look like:

error[E0121]: the type placeholder `_` is not allowed within types on item signatures for return types
 --> src/lib.rs:1:21
  |
1 | fn make() -> Option<_> {}
  |              -------^-
  |              |      |
  |              |      not allowed in type signatures
  |              help: put a fully specified type here

this issue might be related/helpful.

[hkmatsumoto]

@rustbot claim