check_for_deref_method suggestion introduces a parse error

[jruderman]

Given the following code (playground):

fn main() {
    let length = <&[u32]>::len;
    assert_eq!(length(&[1,3]), 2);
}

The current output is:

error[E0599]: the function or associated item `len` exists for reference `&[u32]`, but its trait bounds were not satisfied
 --> src/main.rs:2:28
  |
2 |     let length = <&[u32]>::len;
  |                            ^^^ function or associated item cannot be called on `&[u32]` due to unsatisfied trait bounds
  |
  = note: the following trait bounds were not satisfied:
          `&[u32]: ExactSizeIterator`
          which is required by `&mut &[u32]: ExactSizeIterator`
help: the function `len` is implemented on `[u32]`
  |
2 |     let length = <<[u32]>>::len;
  |                   ~~~~~~~

This suggestion is on the right track, but unfortunately it introduces a parse error. It should be:

help: the function `len` is implemented on `[u32]`
  |
2 |     let length = <[u32]>::len;
  |                   ~~~~~

This suggestion is in check_for_deref_method. It suggests adding <> around the type because the type is a slice, but I already have <> in my program (and the span doesn't include the existing <>).

[lyming2007]

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