Point at fn bound that introduced lifetime obligation

[estebank]

The last note is new

error[E0597]: `c` does not live long enough
  --> $DIR/without-precise-captures-we-are-powerless.rs:19:20
   |
LL | fn simple<'a>(x: &'a i32) {
   |           -- lifetime `'a` defined here
...
LL |     let c = async move || { println!("{}", *x); };
   |         - binding `c` declared here
LL |     outlives::<'a>(c());
   |     ---------------^---
   |     |              |
   |     |              borrowed value does not live long enough
   |     argument requires that `c` is borrowed for `'a`
LL |     outlives::<'a>(call_once(c));
LL | }
   | - `c` dropped here while still borrowed
   |
note: requirement that `c` is borrowed for `'a` introduced here
  --> $DIR/without-precise-captures-we-are-powerless.rs:7:33
   |
LL | fn outlives<'a>(_: impl Sized + 'a) {}
   |                                 ^^

When encountering a ConstraintCategory::Predicate in a funtion call, point at the Span for that Predicate to explain where the lifetime obligation originates from.

CC #55307.

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[lcnr]

what is a requirement for 'a, I feel like the requirement is for the APIT here, not 'a. Is it not possible to keep sth like "requirement that outlives " introduced here"?

[estebank]

Changed to "requirement that the value outlives 'a introduced here".

[lcnr]

how come this doesn't actually show the predicate which caused this?

[lcnr]

if we report this for all preds while always using region_name it'd be reported twice here, would it?

fn outlives_indir<'a: 'b, 'b, T: 'a>(x: T) {}

fn foo<'b>() {
    outlives_indir::<'_, 'b, _>(&mut 1u32);
}

in a sense it would be

• requirement that the value outlives {other_region} introduced here
• requirement that {other_region} outlives {region_name} introduced here

ahhh. you break. please make this a if let Some(pred_span) = ... :<

[lcnr]

r=me after nit

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