[gcc r10-9469] c++: Fix endless errors on invalid requirement seq [PR97742]

[Jakub Jelinek]

https://gcc.gnu.org/g:a7237df0aa26f74cc52103f5c8dba5f0efbb198f

commit r10-9469-ga7237df0aa26f74cc52103f5c8dba5f0efbb198f
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Feb 12 09:55:46 2021 +0100

    c++: Fix endless errors on invalid requirement seq [PR97742]
    
    As the testcase shows, if we reach CPP_EOF during parsing of requirement
    sequence, we end up with endless loop where we always report invalid
    requirement expression, don't consume any token (as we are at eof) and
    repeat.
    
    This patch stops the loop when we reach CPP_EOF.
    
    2021-02-12  Jakub Jelinek  <jakub@redhat.com>
    
            PR c++/97742
            * parser.c (cp_parser_requirement_seq): Stop iterating after reaching
            CPP_EOF.
    
            * g++.dg/cpp2a/concepts-requires24.C: New test.
    
    (cherry picked from commit cf059e1c099ed45c97f740c030dcb8e146ac7d4a)

Diff:
---
 gcc/cp/parser.c                                  | 4 +++-
 gcc/testsuite/g++.dg/cpp2a/concepts-requires24.C | 4 ++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index ba75c4797e4..40af0de95e4 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -27895,7 +27895,9 @@ cp_parser_requirement_seq (cp_parser *parser)
       tree req = cp_parser_requirement (parser);
       if (req != error_mark_node)
 	result = tree_cons (NULL_TREE, req, result);
-    } while (cp_lexer_next_token_is_not (parser->lexer, CPP_CLOSE_BRACE));
+    }
+  while (cp_lexer_next_token_is_not (parser->lexer, CPP_CLOSE_BRACE)
+	 && cp_lexer_next_token_is_not (parser->lexer, CPP_EOF));
 
   /* If there are no valid requirements, this is not a valid expression. */
   if (!result)
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-requires24.C b/gcc/testsuite/g++.dg/cpp2a/concepts-requires24.C
new file mode 100644
index 00000000000..597528b49f8
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-requires24.C
@@ -0,0 +1,4 @@
+// PR c++/97742
+// { dg-do compile { target c++20 } }
+
+template <int = requires { true	// { dg-error "expected" }