test doc comment

Author: cijiugechu

tests/ui/parser/where-clause-doc-comment-without-predicate.rs

@@ -0,0 +1,10 @@
+#![crate_type = "lib"]
+#![feature(where_clause_attrs)]
+
+fn f<T>()
+where
+    T: Copy,
+    /// dangling
+    //~^ ERROR found a documentation comment that doesn't document anything
+{
+}

tests/ui/parser/where-clause-doc-comment-without-predicate.stderr

@@ -0,0 +1,11 @@
+error[E0585]: found a documentation comment that doesn't document anything
+  --> $DIR/where-clause-doc-comment-without-predicate.rs:7:5
+   |
+LL |     /// dangling
+   |     ^^^^^^^^^^^^
+   |
+   = help: doc comments must come before what they document, if a comment was intended use `//`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0585`.