Auto merge of #89249 - Aaron1011:higher-ranked-cause, r=estebank

Improve cause information for NLL higher-ranked errors

This PR has several interconnected pieces:

1. In some of the NLL region error code, we now pass
   around an `ObligationCause`, instead of just a plain `Span`.
   This gets forwarded into `fulfill_cx.register_predicate_obligation`
   during error reporting.
2. The general InferCtxt error reporting code is extended to
   handle `ObligationCauseCode::BindingObligation`
3. A new enum variant `ConstraintCategory::Predicate` is added.
   We try to avoid using this as the 'best blame constraint' - instead,
   we use it to enhance the `ObligationCause` of the `BlameConstraint`
   that we do end up choosing.

As a result, several NLL error messages now contain the same
"the lifetime requirement is introduced here" message as non-NLL
errors.

Having an `ObligationCause` available will likely prove useful
for future improvements to NLL error messages.

6 files changed, 40 insertions, 0 deletions

diff --git a/src/test/ui/associated-types/higher-ranked-projection.bad.nll.stderr b/src/test/ui/associated-types/higher-ranked-projection.bad.nll.stderr
index e3bd0c2276e..de254b7a163 100644
--- a/src/test/ui/associated-types/higher-ranked-projection.bad.nll.stderr
+++ b/src/test/ui/associated-types/higher-ranked-projection.bad.nll.stderr
@@ -6,6 +6,11 @@ LL |     foo(());
    |
    = note: expected reference `&'a ()`
               found reference `&()`
+note: the lifetime requirement is introduced here
+  --> $DIR/higher-ranked-projection.rs:15:33
+   |
+LL |     where for<'a> &'a T: Mirror<Image=U>
+   |                                 ^^^^^^^
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/generator/resume-arg-late-bound.nll.stderr b/src/test/ui/generator/resume-arg-late-bound.nll.stderr
index 25bc6afc550..b5144c607a8 100644
--- a/src/test/ui/generator/resume-arg-late-bound.nll.stderr
+++ b/src/test/ui/generator/resume-arg-late-bound.nll.stderr
@@ -6,6 +6,11 @@ LL |     test(gen);
    |
    = note: expected type `for<'a> Generator<&'a mut bool>`
               found type `Generator<&mut bool>`
+note: the lifetime requirement is introduced here
+  --> $DIR/resume-arg-late-bound.rs:8:17
+   |
+LL | fn test(a: impl for<'a> Generator<&'a mut bool>) {}
+   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/lifetimes/issue-79187-2.nll.stderr b/src/test/ui/lifetimes/issue-79187-2.nll.stderr
index 907b43d6762..04d9b64d64f 100644
--- a/src/test/ui/lifetimes/issue-79187-2.nll.stderr
+++ b/src/test/ui/lifetimes/issue-79187-2.nll.stderr
@@ -38,6 +38,11 @@ note: this closure does not fulfill the lifetime requirements
    |
 LL |     take_foo(|a| a);
    |              ^^^^^
+note: the lifetime requirement is introduced here
+  --> $DIR/issue-79187-2.rs:5:21
+   |
+LL | fn take_foo(_: impl Foo) {}
+   |                     ^^^
 
 error[E0308]: mismatched types
   --> $DIR/issue-79187-2.rs:9:5
@@ -47,6 +52,11 @@ LL |     take_foo(|a: &i32| a);
    |
    = note: expected reference `&i32`
               found reference `&i32`
+note: the lifetime requirement is introduced here
+  --> $DIR/issue-79187-2.rs:5:21
+   |
+LL | fn take_foo(_: impl Foo) {}
+   |                     ^^^
 
 error[E0308]: mismatched types
   --> $DIR/issue-79187-2.rs:10:5
@@ -56,6 +66,11 @@ LL |     take_foo(|a: &i32| -> &i32 { a });
    |
    = note: expected reference `&i32`
               found reference `&i32`
+note: the lifetime requirement is introduced here
+  --> $DIR/issue-79187-2.rs:5:21
+   |
+LL | fn take_foo(_: impl Foo) {}
+   |                     ^^^
 
 error: aborting due to 6 previous errors
 
diff --git a/src/test/ui/lifetimes/issue-79187.nll.stderr b/src/test/ui/lifetimes/issue-79187.nll.stderr
index 725b132e83a..3a993e88d8a 100644
--- a/src/test/ui/lifetimes/issue-79187.nll.stderr
+++ b/src/test/ui/lifetimes/issue-79187.nll.stderr
@@ -11,6 +11,11 @@ note: this closure does not fulfill the lifetime requirements
    |
 LL |     let f = |_| ();
    |             ^^^^^^
+note: the lifetime requirement is introduced here
+  --> $DIR/issue-79187.rs:1:18
+   |
+LL | fn thing(x: impl FnOnce(&u32)) {}
+   |                  ^^^^^^^^^^^^
 
 error: implementation of `FnOnce` is not general enough
   --> $DIR/issue-79187.rs:5:5
diff --git a/src/test/ui/lifetimes/lifetime-errors/issue_74400.nll.stderr b/src/test/ui/lifetimes/lifetime-errors/issue_74400.nll.stderr
index 5a1294f948f..5509226cb1c 100644
--- a/src/test/ui/lifetimes/lifetime-errors/issue_74400.nll.stderr
+++ b/src/test/ui/lifetimes/lifetime-errors/issue_74400.nll.stderr
@@ -14,6 +14,11 @@ LL |     f(data, identity)
    |
    = note: expected type `for<'r> Fn<(&'r T,)>`
               found type `Fn<(&T,)>`
+note: the lifetime requirement is introduced here
+  --> $DIR/issue_74400.rs:8:34
+   |
+LL | fn f<T, S>(data: &[T], key: impl Fn(&T) -> S) {
+   |                                  ^^^^^^^^^^^
 
 error: implementation of `FnOnce` is not general enough
   --> $DIR/issue_74400.rs:12:5
diff --git a/src/test/ui/mismatched_types/closure-mismatch.nll.stderr b/src/test/ui/mismatched_types/closure-mismatch.nll.stderr
index f29126e6afc..bd36fab9288 100644
--- a/src/test/ui/mismatched_types/closure-mismatch.nll.stderr
+++ b/src/test/ui/mismatched_types/closure-mismatch.nll.stderr
@@ -20,6 +20,11 @@ note: this closure does not fulfill the lifetime requirements
    |
 LL |     baz(|_| ());
    |         ^^^^^^
+note: the lifetime requirement is introduced here
+  --> $DIR/closure-mismatch.rs:5:11
+   |
+LL | fn baz<T: Foo>(_: T) {}
+   |           ^^^
 
 error: aborting due to 2 previous errors