[gcc r13-4380] c++: simple-requirement starting with 'typename' [PR101733]

[Jason Merrill <jason@gcc.gnu.org>]

https://gcc.gnu.org/g:2b0ae7fb91f64fb005abf7d7903fd4c0764bb45c

commit r13-4380-g2b0ae7fb91f64fb005abf7d7903fd4c0764bb45c
Author: Jason Merrill <jason@redhat.com>
Date:   Sat Nov 26 11:13:55 2022 -0500

    c++: simple-requirement starting with 'typename' [PR101733]
    
    Usually a requirement starting with 'typename' is a type-requirement, but it
    might be a simple-requirement such as a functional cast to a typename-type.
    
            PR c++/101733
    
    gcc/cp/ChangeLog:
    
            * parser.cc (cp_parser_requirement): Parse tentatively for the
            'typename' case.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp2a/concepts-requires32.C: New test.

Diff:
---
 gcc/cp/parser.cc                                 | 15 ++++++++++++++-
 gcc/testsuite/g++.dg/cpp2a/concepts-requires32.C | 11 +++++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index 82459b7683a..a13fbe41309 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -30737,7 +30737,20 @@ cp_parser_requirement (cp_parser *parser)
   if (cp_lexer_next_token_is (parser->lexer, CPP_OPEN_BRACE))
     return cp_parser_compound_requirement (parser);
   else if (cp_lexer_next_token_is_keyword (parser->lexer, RID_TYPENAME))
-    return cp_parser_type_requirement (parser);
+    {
+      /* It's probably a type-requirement.  */
+      cp_parser_parse_tentatively (parser);
+      tree req = cp_parser_type_requirement (parser);
+      if (cp_parser_parse_definitely (parser))
+	return req;
+      /* No, maybe it's something like typename T::type(); */
+      cp_parser_parse_tentatively (parser);
+      req = cp_parser_simple_requirement (parser);
+      if (cp_parser_parse_definitely (parser))
+	return req;
+      /* Non-tentative for the error.  */
+      return cp_parser_type_requirement (parser);
+    }
   else if (cp_lexer_next_token_is_keyword (parser->lexer, RID_REQUIRES))
     return cp_parser_nested_requirement (parser);
   else
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-requires32.C b/gcc/testsuite/g++.dg/cpp2a/concepts-requires32.C
new file mode 100644
index 00000000000..117b8920787
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-requires32.C
@@ -0,0 +1,11 @@
+// PR c++/101733
+// { dg-do compile { target c++20 } }
+
+template<class T>
+requires requires {
+    typename T::type;
+    (typename T::type()); // (1)
+    T::type();            // (2)
+    typename T::type();   // (3)
+}
+void f(T) { }