Deduplicate unsatisfied trait bounds

src/librustc_typeck/check/method/suggest.rs

@@ -424,10 +424,12 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                 }
 
                 if !unsatisfied_predicates.is_empty() {
-                    let bound_list = unsatisfied_predicates.iter()
+                    let mut bound_list = unsatisfied_predicates.iter()
                         .map(|p| format!("`{} : {}`", p.self_ty(), p))
-                        .collect::<Vec<_>>()
-                        .join("\n");
+                        .collect::<Vec<_>>();
+                    bound_list.sort();
+                    bound_list.dedup_by(|a, b| a == b);  // #35677
+                    let bound_list = bound_list.join("\n");
                     err.note(&format!("the method `{}` exists but the following trait bounds \
                                        were not satisfied:\n{}",
                                       item_name,

src/test/ui/issues/issue-31173.stderr

@@ -14,8 +14,8 @@ LL |         .collect(); //~ ERROR no method named `collect`
    |          ^^^^^^^
    |
    = note: the method `collect` exists but the following trait bounds were not satisfied:
-           `std::iter::Cloned<std::iter::TakeWhile<&mut std::vec::IntoIter<u8>, [closure@$DIR/issue-31173.rs:16:39: 19:6 found_e:_]>> : std::iter::Iterator`
            `&mut std::iter::Cloned<std::iter::TakeWhile<&mut std::vec::IntoIter<u8>, [closure@$DIR/issue-31173.rs:16:39: 19:6 found_e:_]>> : std::iter::Iterator`
+           `std::iter::Cloned<std::iter::TakeWhile<&mut std::vec::IntoIter<u8>, [closure@$DIR/issue-31173.rs:16:39: 19:6 found_e:_]>> : std::iter::Iterator`
 
 error: aborting due to 2 previous errors
 

src/test/ui/issues/issue-35677.rs

@@ -0,0 +1,5 @@
+use std::collections::HashMap;
+fn intersect_map<K, V>(this: &mut HashMap<K, V>, other: HashMap<K, V>) -> bool {
+    this.drain()
+    //~^ ERROR no method named
+}

src/test/ui/issues/issue-35677.stderr

@@ -0,0 +1,18 @@
+error[E0601]: `main` function not found in crate `issue_35677`
+   |
+   = note: consider adding a `main` function to `$DIR/issue-35677.rs`
+
+error[E0599]: no method named `drain` found for type `&mut std::collections::HashMap<K, V>` in the current scope
+  --> $DIR/issue-35677.rs:3:10
+   |
+LL |     this.drain()
+   |          ^^^^^
+   |
+   = note: the method `drain` exists but the following trait bounds were not satisfied:
+           `K : std::cmp::Eq`
+           `K : std::hash::Hash`
+
+error: aborting due to 2 previous errors
+
+Some errors occurred: E0599, E0601.
+For more information about an error, try `rustc --explain E0599`.

src/test/ui/mismatched_types/issue-36053-2.stderr

@@ -5,8 +5,8 @@ LL |     once::<&str>("str").fuse().filter(|a: &str| true).count();
    |                                                       ^^^^^
    |
    = note: the method `count` exists but the following trait bounds were not satisfied:
-           `std::iter::Filter<std::iter::Fuse<std::iter::Once<&str>>, [closure@$DIR/issue-36053-2.rs:17:39: 17:53]> : std::iter::Iterator`
            `&mut std::iter::Filter<std::iter::Fuse<std::iter::Once<&str>>, [closure@$DIR/issue-36053-2.rs:17:39: 17:53]> : std::iter::Iterator`
+           `std::iter::Filter<std::iter::Fuse<std::iter::Once<&str>>, [closure@$DIR/issue-36053-2.rs:17:39: 17:53]> : std::iter::Iterator`
 
 error[E0631]: type mismatch in closure arguments
   --> $DIR/issue-36053-2.rs:17:32