Point at fn bound that introduced lifetime obligation

```
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.

2 files changed, 10 insertions, 1 deletions

diff --git a/compiler/rustc_borrowck/src/borrowck_errors.rs b/compiler/rustc_borrowck/src/borrowck_errors.rs
index c9be5575da5..bc985cbe133 100644
--- a/compiler/rustc_borrowck/src/borrowck_errors.rs
+++ b/compiler/rustc_borrowck/src/borrowck_errors.rs
@@ -426,7 +426,7 @@ impl<'infcx, 'tcx> crate::MirBorrowckCtxt<'_, 'infcx, 'tcx> {
     }
 
     pub(crate) fn path_does_not_live_long_enough(&self, span: Span, path: &str) -> Diag<'infcx> {
-        struct_span_code_err!(self.dcx(), span, E0597, "{} does not live long enough", path,)
+        struct_span_code_err!(self.dcx(), span, E0597, "{} does not live long enough", path)
     }
 
     pub(crate) fn cannot_return_reference_to_local(
diff --git a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
index 7e20a5133e0..3b268f538cf 100644
--- a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
@@ -3031,6 +3031,15 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
 
         let mut err = self.path_does_not_live_long_enough(borrow_span, &name);
 
+        if let BorrowExplanation::MustBeValidFor { ref path, region_name, .. } = explanation {
+            for constraint in path {
+                if let ConstraintCategory::Predicate(pred) = constraint.category
+                    && !pred.is_dummy()
+                {
+                    err.span_note(pred, format!("requirement that {name} is borrowed for `{region_name}` introduced here"));
+                }
+            }
+        }
         if let Some(annotation) = self.annotate_argument_and_return_for_borrow(borrow) {
             let region_name = annotation.emit(self, &mut err);