Suggest derivable trait on E0277

src/test/ui/error-codes/E0277-3.rs

@@ -0,0 +1,8 @@
+fn foo<T: PartialEq>(_: T) {}
+
+struct S;
+
+fn main() {
+    foo(S);
+    //~^ ERROR can't compare `S` with `S`
+}

src/test/ui/error-codes/E0277-3.stderr

@@ -0,0 +1,22 @@
+error[E0277]: can't compare `S` with `S`
+  --> $DIR/E0277-3.rs:6:9
+   |
+LL |     foo(S);
+   |     --- ^ no implementation for `S == S`
+   |     |
+   |     required by a bound introduced by this call
+   |
+   = help: the trait `PartialEq` is not implemented for `S`
+note: required by a bound in `foo`
+  --> $DIR/E0277-3.rs:1:11
+   |
+LL | fn foo<T: PartialEq>(_: T) {}
+   |           ^^^^^^^^^ required by this bound in `foo`
+help: consider annotating `S` with `#[derive(PartialEq)]`
+   |
+LL | #[derive(PartialEq)]
+   |
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.