Use parse_param_general when parsing (T, U)->R in parse_path_segment

Signed-off-by: xizheyin <xizheyin@smail.nju.edu.cn>

Co-authored-by: Vadim Petrochenkov <vadim.petrochenkov@gmail.com>

compiler/rustc_parse/src/errors.rs

@@ -1591,6 +1591,30 @@ pub(crate) struct ExpectedFnPathFoundFnKeyword {
     pub fn_token_span: Span,
 }
 
+#[derive(Diagnostic)]
+#[diag(parse_path_found_named_params)]
+pub(crate) struct FnPathFoundNamedParams {
+    #[primary_span]
+    #[suggestion(applicability = "machine-applicable", code = "")]
+    pub named_param_span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_path_found_c_variadic_params)]
+pub(crate) struct PathFoundCVariadicParams {
+    #[primary_span]
+    #[suggestion(applicability = "machine-applicable", code = "")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(parse_path_found_attribute_in_params)]
+pub(crate) struct PathFoundAttributeInParams {
+    #[primary_span]
+    #[suggestion(applicability = "machine-applicable", code = "")]
+    pub span: Span,
+}
+
 #[derive(Diagnostic)]
 #[diag(parse_path_double_colon)]
 pub(crate) struct PathSingleColon {