Make unsatisfied trait bounds note multiline

Make diagnostic note for existing method with unsatisfied trait bounds
multiline for cleaner output.

```
  = note: the method `count` exists but the following trait bounds were not satisfied:
          `[closure@../../src/test/compile-fail/issue-36053-2.rs:17:39: 17:53] : std::ops::FnMut<(&_,)>`
          `std::iter::Filter<std::iter::Fuse<std::iter::Once<&str>> [closure@../../src/test/compile-fail/issue-36053-2.rs:17:39: 17:53]> : std::iter::Iterator`

Before:

```
  = note: the method `count` exists but the following trait bounds were not satisfied: `[closure@../../src/test/compile-fail/issue-36053-2.rs:17:39: 17:53] : std::ops::FnMut<(&_,)>`, `std::iter::Filter<std::iter::Fuse<std::iter::Once<&str>>, [closure@../../src/test/compile-fail/issue-36053-2.rs:17:39: 17:53]> : std::iter::Iterator`
```

4 files changed, 17 insertions, 4 deletions

diff --git a/src/librustc_typeck/check/method/suggest.rs b/src/librustc_typeck/check/method/suggest.rs
index c7ec379b0de..7e70bb92cd6 100644
--- a/src/librustc_typeck/check/method/suggest.rs
+++ b/src/librustc_typeck/check/method/suggest.rs
@@ -251,9 +251,9 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                     let bound_list = unsatisfied_predicates.iter()
                         .map(|p| format!("`{} : {}`", p.self_ty(), p))
                         .collect::<Vec<_>>()
-                        .join(", ");
+                        .join("\n");
                     err.note(&format!("the method `{}` exists but the following trait bounds \
-                                       were not satisfied: {}",
+                                       were not satisfied:\n{}",
                                       item_name,
                                       bound_list));
                 }
diff --git a/src/test/ui/mismatched_types/issue-36053-2.stderr b/src/test/ui/mismatched_types/issue-36053-2.stderr
index adc229aaacc..78e0f7e619b 100644
--- a/src/test/ui/mismatched_types/issue-36053-2.stderr
+++ b/src/test/ui/mismatched_types/issue-36053-2.stderr
@@ -4,7 +4,9 @@ error: no method named `count` found for type `std::iter::Filter<std::iter::Fuse
 17 |     once::<&str>("str").fuse().filter(|a: &str| true).count();
    |                                                       ^^^^^
    |
-   = note: the method `count` exists but the following trait bounds were not satisfied: `[closure@$DIR/issue-36053-2.rs:17:39: 17:53] : std::ops::FnMut<(&_,)>`, `std::iter::Filter<std::iter::Fuse<std::iter::Once<&str>>, [closure@$DIR/issue-36053-2.rs:17:39: 17:53]> : std::iter::Iterator`
+   = note: the method `count` exists but the following trait bounds were not satisfied:
+           `[closure@$DIR/issue-36053-2.rs:17:39: 17:53] : std::ops::FnMut<(&_,)>`
+           `std::iter::Filter<std::iter::Fuse<std::iter::Once<&str>>, [closure@$DIR/issue-36053-2.rs:17:39: 17:53]> : std::iter::Iterator`
 
 error[E0281]: type mismatch: `[closure@$DIR/issue-36053-2.rs:17:39: 17:53]` implements the trait `for<'r> std::ops::FnMut<(&'r str,)>`, but the trait `for<'r> std::ops::FnMut<(&'r &str,)>` is required
   --> $DIR/issue-36053-2.rs:17:32
diff --git a/src/test/compile-fail/method-help-unsatisfied-bound.rs b/src/test/ui/mismatched_types/method-help-unsatisfied-bound.rs
index 6416d5467c8..a4eb4455551 100644
--- a/src/test/compile-fail/method-help-unsatisfied-bound.rs
+++ b/src/test/ui/mismatched_types/method-help-unsatisfied-bound.rs
@@ -14,5 +14,5 @@ fn main() {
     let a: Result<(), Foo> = Ok(());
     a.unwrap();
     //~^ ERROR no method named `unwrap` found for type `std::result::Result<(), Foo>`
-    //~| NOTE the following trait bounds were not satisfied: `Foo : std::fmt::Debug`
+    //~| NOTE the method `unwrap` exists but the following trait bounds were not satisfied
 }
diff --git a/src/test/ui/mismatched_types/method-help-unsatisfied-bound.stderr b/src/test/ui/mismatched_types/method-help-unsatisfied-bound.stderr
new file mode 100644
index 00000000000..2bd786c20fe
--- /dev/null
+++ b/src/test/ui/mismatched_types/method-help-unsatisfied-bound.stderr
@@ -0,0 +1,11 @@
+error: no method named `unwrap` found for type `std::result::Result<(), Foo>` in the current scope
+  --> $DIR/method-help-unsatisfied-bound.rs:15:7
+   |
+15 |     a.unwrap();
+   |       ^^^^^^
+   |
+   = note: the method `unwrap` exists but the following trait bounds were not satisfied:
+           `Foo : std::fmt::Debug`
+
+error: aborting due to previous error
+