properly handle anonymous regions appearing in return type - anon-anon conflicts

[gaurikholkar-zz]

For the following example, currently E0623 is disabled right now. This is how the error message will now look like.

fn foo<'a>(&self, x: &i32) -> &i32 {
    //               -----    ---- these references must have the same lifetime
    if true { &self.field } else { x }
    //                             ^ data from `x` is returned here
}

cc @nikomatsakis

[gaurikholkar-zz]

@nikomatsakis this is the output I get

  --> $DIR/ex3-both-anon-regions-return-type-is-anon.rs:17:5
   |
16 |   fn foo<'a>(&self, x: &i32) -> &i32 {
   |              -----     ---- this parameter and the return type are
                            declared with different lifetimes...
17 |     x
   |     ^ ...but data from `x` flows into `self` here

error: aborting due to previous error

How do we want this?

[gaurikholkar-zz]

@nikomatsakis @arielb1 @estebank @GuillaumeGomez I needed some help to extract the span of the return type. I was thinking of getting it from the fndecl.output.span. Is there a better way?

[arielb1]

There isn't.