Restore error messaging

Author: compiler-errors

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));

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

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`

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