Improve error message for one named, one anonymous lifetimes - underline correct source

[gaurikholkar-zz]

fn foo<'a>(x: &'a i32, y: Vec<&i32>) {
                       - consider changing the type of `y` to `std::vec::Vec<&'a i32>`
    y.push(x);
           ^ this reference must have lifetime 'a
}

The error message wrongly underlines x. It should underline y, which is the source of the error. The refined message will be like this

fn foo<'a>(x: &'a i32, y: Vec<&i32>) {
                       - consider changing the type of `y` to `std::vec::Vec<&'a i32>`
    y.push(x);
    ^ this reference must have lifetime 'a
}

cc @nikomatsakis

[gaurikholkar-zz]

cc @nikomatsakis
Status:

11 | fn foo<'a>((x, y): (&'a i32, &i32)) -> &'a i32 {
   |                              ---- consider changing type to `(&'a i32, &'a i32)`
12 |     if x > y { x } else { y }
   |                           ^ lifetime `'a` required

error: aborting due to previous error

Notice that the &'a i32 is being underlined while it says
consider changing type to (&'a i32, &'a i32) , pointing to the tuple (&'a i32, &'a i32) here.

Option 1

11 | fn foo<'a>((x, y): (&'a i32, &i32)) -> &'a i32 {
   |                     ------------- consider changing type to `(&'a i32, &'a i32)`
12 |     if x > y { x } else { y }
   |                           ^ lifetime `'a` required

Option 2

11 | fn foo<'a>((x, y): (&'a i32, &i32)) -> &'a i32 {
   |                              ---- consider changing type to `&'a i32`
12 |     if x > y { x } else { y }
   |                           ^ lifetime `'a` required

Closed the PR for now.

[estebank]

Current output, added structured suggestion:

error[E0621]: explicit lifetime required in the type of `y`
 --> file.rs:2:12
  |
1 | fn foo<'a>(x: &'a i32, y: Vec<&i32>) {
  |                           --------- help: add explicit lifetime `'a` to the type of `y`: `std::vec::Vec<&'a i32>`
2 |     y.push(x);
  |            ^ lifetime `'a` required

error[E0621]: explicit lifetime required in parameter type
 --> file.rs:2:27
  |
1 | fn foo<'a>((x, y): (&'a i32, &i32)) -> &'a i32 {
  |                    --------------- help: add explicit lifetime `'a` to type: `(&'a i32, &'a i32)`
2 |     if x > y { x } else { y }
  |                           ^ lifetime `'a` required

I don't think there's anything else for us to do here.