External macro invocation errors print internals but not invocation site

[arielb1]

The code

fn main() {}
// ...
// lots of code
// ...
fn some_random_function() {
    // lots of code here
    let unused = vec![];
    // even more code
}

gives an error message which does not even hint about the error's location:

<std macros>:5:9: 5:22 error: unable to infer enough type information about `_`; type annotations required
<std macros>:5         xs.into_vec()
                       ^~~~~~~~~~~~~
<std macros>:1:1: 8:2 note: in expansion of vec!
<anon>:4:5: 4:12 note: expansion site

Which makes finding the offending statement require quite a bit of effort.

[sfackler]

The last line of the message has the location of the offending statement.

[steveklabnik]

Triage: no change. This does point at where the error is, but it's still a worse error than we could give.

[nagisa]

Duplicate of #25633. Duping into a newer issue, because the other issue has more descriptive title and shows the underlying issue of compiler being unable to figure out the generic parameters for calls.

[arielb1]

Not that sure of it - the error coming out of a vec![] macro wasn't my problem, more that we span the interior of vec![] rather than the actual source.

[keeperofdakeys]

On rust 1.13, this now shows the following:

error[E0282]: unable to infer enough type information about `_`
 --> temp.rs:2:16
  |
2 |   let unused = vec![];
  |                ^^^^^^ cannot infer type for `_`
  |
  = note: type annotations or generic parameter binding required
  = note: this error originates in a macro outside of the current crate

error: aborting due to previous error

This now points at the right span, and any improvement of the error message would probably be part a of #25633. So this issue can probably be closed.