Show suggestion for <SelfTy as Trait>::assoc_fn in more cases and fmt code

compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs

@@ -27,7 +27,7 @@ use std::iter;
 
 pub enum TypeAnnotationNeeded {
     /// ```compile_fail,E0282
-    /// let x = "hello".chars().rev().collect();
+    /// let x;
     /// ```
     E0282,
     /// An implementation cannot be chosen unambiguously because of lack of information.