Rollup merge of #117298 - clubby789:fn-missing-params, r=petrochenkov

Recover from missing param list in function definitions

Addresses the other issue mentioned in #108109

compiler/rustc_parse/src/errors.rs

@@ -1551,6 +1551,14 @@ pub(crate) enum AmbiguousMissingKwForItemSub {
     HelpMacro,
 }
 
+#[derive(Diagnostic)]
+#[diag(parse_missing_fn_params)]
+pub(crate) struct MissingFnParams {
+    #[primary_span]
+    #[suggestion(code = "()", applicability = "machine-applicable", style = "short")]
+    pub span: Span,
+}
+
 #[derive(Diagnostic)]
 #[diag(parse_missing_trait_in_trait_impl)]
 pub(crate) struct MissingTraitInTraitImpl {