Suggest replacing patterns with underscores

Author: varkor

src/librustc_passes/ast_validation.rs

@@ -344,8 +344,11 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                                         trait_item.id, span,
                                         "patterns aren't allowed in methods without bodies");
                                 } else {
-                                    struct_span_err!(self.session, span, E0642,
-                                        "patterns aren't allowed in methods without bodies").emit();
+                                    let mut err = struct_span_err!(self.session, span, E0642,
+                                        "patterns aren't allowed in methods without bodies");
+                                    err.span_suggestion(span,
+                                        "use an underscore to ignore the name", "_".to_owned());
+                                    err.emit();
                                 }
                             });
                         }

src/test/ui/E0642.stderr

@@ -2,7 +2,7 @@ error[E0642]: patterns aren't allowed in methods without bodies
   --> $DIR/E0642.rs:12:12
    |
 LL |     fn foo((x, y): (i32, i32)); //~ ERROR patterns aren't allowed in methods without bodies
-   |            ^^^^^^
+   |            ^^^^^^ help: use an underscore to ignore the name: `_`
 
 error: aborting due to previous error