From 93c6c0445db7f33d3fd85edbfb64768a88cef5ba Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Tue, 26 Mar 2024 13:35:13 -0400
Subject: [PATCH] Restore error messaging

---
 compiler/rustc_hir_typeck/src/method/probe.rs         | 11 +++++++++++
 tests/ui/mismatched_types/issue-36053-2.stderr        | 10 ++++------
 tests/ui/traits/method-on-unbounded-type-param.stderr |  2 +-
 tests/ui/typeck/issue-31173.stderr                    |  2 +-
 4 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/compiler/rustc_hir_typeck/src/method/probe.rs b/compiler/rustc_hir_typeck/src/method/probe.rs
index 1dcda06a349..cfeb0792d9f 100644
--- a/compiler/rustc_hir_typeck/src/method/probe.rs
+++ b/compiler/rustc_hir_typeck/src/method/probe.rs
@@ -1465,6 +1465,17 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                         ocx.register_obligation(obligation);
                     } else {
                         result = ProbeResult::NoMatch;
+                        if let Ok(Some(candidate)) = self.select_trait_candidate(trait_ref) {
+                            for nested_obligation in candidate.nested_obligations() {
+                                if !self.infcx.predicate_may_hold(&nested_obligation) {
+                                    possibly_unsatisfied_predicates.push((
+                                        self.resolve_vars_if_possible(nested_obligation.predicate),
+                                        Some(self.resolve_vars_if_possible(obligation.predicate)),
+                                        Some(nested_obligation.cause),
+                                    ));
+                                }
+                            }
+                        }
                     }
 
                     trait_predicate = Some(ty::Binder::dummy(trait_ref).to_predicate(self.tcx));
diff --git a/tests/ui/mismatched_types/issue-36053-2.stderr b/tests/ui/mismatched_types/issue-36053-2.stderr
index 5b8332016de..ffaa276b62e 100644
--- a/tests/ui/mismatched_types/issue-36053-2.stderr
+++ b/tests/ui/mismatched_types/issue-36053-2.stderr
@@ -21,16 +21,14 @@ error[E0599]: the method `count` exists for struct `Filter<Fuse<Once<&str>>, {cl
 LL |     once::<&str>("str").fuse().filter(|a: &str| true).count();
    |                                       ---------       ^^^^^ method cannot be called due to unsatisfied trait bounds
    |                                       |
-   |                                       doesn't satisfy `_: FnMut<(&&str,)>` or `_: FnOnce<(&&str,)>`
+   |                                       doesn't satisfy `<_ as FnOnce<(&&str,)>>::Output = bool` or `_: FnMut<(&&str,)>`
    |
    = note: the following trait bounds were not satisfied:
-           `{closure@$DIR/issue-36053-2.rs:7:39: 7:48}: FnMut<(&&str,)>`
-           which is required by `Filter<Fuse<std::iter::Once<&str>>, {closure@$DIR/issue-36053-2.rs:7:39: 7:48}>: Iterator`
-           `{closure@$DIR/issue-36053-2.rs:7:39: 7:48}: FnOnce<(&&str,)>`
+           `<{closure@$DIR/issue-36053-2.rs:7:39: 7:48} as FnOnce<(&&str,)>>::Output = bool`
            which is required by `Filter<Fuse<std::iter::Once<&str>>, {closure@$DIR/issue-36053-2.rs:7:39: 7:48}>: Iterator`
            `{closure@$DIR/issue-36053-2.rs:7:39: 7:48}: FnMut<(&&str,)>`
-           which is required by `&mut Filter<Fuse<std::iter::Once<&str>>, {closure@$DIR/issue-36053-2.rs:7:39: 7:48}>: Iterator`
-           `{closure@$DIR/issue-36053-2.rs:7:39: 7:48}: FnOnce<(&&str,)>`
+           which is required by `Filter<Fuse<std::iter::Once<&str>>, {closure@$DIR/issue-36053-2.rs:7:39: 7:48}>: Iterator`
+           `Filter<Fuse<std::iter::Once<&str>>, {closure@$DIR/issue-36053-2.rs:7:39: 7:48}>: Iterator`
            which is required by `&mut Filter<Fuse<std::iter::Once<&str>>, {closure@$DIR/issue-36053-2.rs:7:39: 7:48}>: Iterator`
 
 error: aborting due to 2 previous errors
diff --git a/tests/ui/traits/method-on-unbounded-type-param.stderr b/tests/ui/traits/method-on-unbounded-type-param.stderr
index 38537619365..4d968e7bee1 100644
--- a/tests/ui/traits/method-on-unbounded-type-param.stderr
+++ b/tests/ui/traits/method-on-unbounded-type-param.stderr
@@ -70,7 +70,7 @@ LL |     x.cmp(&x);
            which is required by `Box<dyn T>: Iterator`
            `dyn T: Ord`
            which is required by `Box<dyn T>: Ord`
-           `dyn T: Iterator`
+           `Box<dyn T>: Iterator`
            which is required by `&mut Box<dyn T>: Iterator`
            `dyn T: Iterator`
            which is required by `&mut dyn T: Iterator`
diff --git a/tests/ui/typeck/issue-31173.stderr b/tests/ui/typeck/issue-31173.stderr
index 5fee16b5e89..0983147a5f0 100644
--- a/tests/ui/typeck/issue-31173.stderr
+++ b/tests/ui/typeck/issue-31173.stderr
@@ -39,7 +39,7 @@ LL | |         .collect();
    = note: the following trait bounds were not satisfied:
            `<TakeWhile<&mut std::vec::IntoIter<u8>, {closure@$DIR/issue-31173.rs:7:21: 7:25}> as Iterator>::Item = &_`
            which is required by `Cloned<TakeWhile<&mut std::vec::IntoIter<u8>, {closure@$DIR/issue-31173.rs:7:21: 7:25}>>: Iterator`
-           `<TakeWhile<&mut std::vec::IntoIter<u8>, {closure@$DIR/issue-31173.rs:7:21: 7:25}> as Iterator>::Item = &_`
+           `Cloned<TakeWhile<&mut std::vec::IntoIter<u8>, {closure@$DIR/issue-31173.rs:7:21: 7:25}>>: Iterator`
            which is required by `&mut Cloned<TakeWhile<&mut std::vec::IntoIter<u8>, {closure@$DIR/issue-31173.rs:7:21: 7:25}>>: Iterator`
 
 error: aborting due to 2 previous errors