error help suggests writing down a closure type, which would be a syntax error

[jendrikw]

Given the following code: play

fn f() {
    vec!['a'].iter().map(|c| c)
}

The current output is:

error[E0308]: mismatched types
 --> src/lib.rs:2:5
  |
2 |     vec!['a'].iter().map(|c| c)
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `()`, found struct `Map`
  |
  = note: expected unit type `()`
                found struct `Map<std::slice::Iter<'_, char>, [closure@src/lib.rs:2:26: 2:31]>`
help: consider using a semicolon here
  |
2 |     vec!['a'].iter().map(|c| c);
  |                                +
help: try adding a return type
  |
1 | fn f() -> Map<std::slice::Iter<'_, char>, [closure@src/lib.rs:2:26: 2:31]> {
  |        +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Ideally the output should look like:

Don't suggest adding -> Map<std::slice::Iter<'_, char>, [closure@src/lib.rs:2:26: 2:31]> if that's not going to compile.

[compiler-errors]

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