"Expected type, found {x}" message could be more helpful

[wesleywiser]

I mistyped a ; as a : because it was following a ) which requires holding the shift key on American keyboards. It would be nice if the error message mentioned why it was expecting a type.

Sample code:

fn main() {
    println!("test"):
    0;
}

Current error:

rustc 1.17.0 (56124baa9 2017-04-24)
error: expected type, found `0`
 --> <anon>:3:5
  |
3 |     0;
  |     ^

error: aborting due to previous error

It would be nice if it said something like this:

rustc 1.17.0 (56124baa9 2017-04-24)
error: expected type, found `0`
 --> <anon>:3:5
  |
3 |     0;
  |     ^

error: aborting due to previous error

--> <anon>:2:21
  |
2 |   println!("test"):
  |                   ^

hint: expecting a type because of type ascription here

[Mark-Simulacrum]

There's lots of similar issues to this one, and I believe #42057 tracks the unique part of this issue, closing.