[gcc r12-6879] c++: ->template and using-decl [PR104235]

[Jason Merrill]

https://gcc.gnu.org/g:00d8321124123daf41f7c51526355a5a610cdeb8

commit r12-6879-g00d8321124123daf41f7c51526355a5a610cdeb8
Author: Jason Merrill <jason@redhat.com>
Date:   Wed Jan 26 10:40:42 2022 -0500

    c++: ->template and using-decl [PR104235]
    
    cp_parser_template_id wasn't prepared to handle getting a USING_DECL back
    from cp_parser_template_name.  Let's defer that case to instantiation time,
    as well.
    
            PR c++/104235
    
    gcc/cp/ChangeLog:
    
            * parser.cc (cp_parser_template_name): Repeat lookup of USING_DECL.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/parse/template-keyword2.C: New test.

Diff:
---
 gcc/cp/parser.cc                               | 3 ++-
 gcc/testsuite/g++.dg/parse/template-keyword2.C | 8 ++++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index ed219d79dc9..8b38165020f 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -18680,7 +18680,8 @@ cp_parser_template_name (cp_parser* parser,
 	  cp_parser_error (parser, "expected template-name");
 	  return error_mark_node;
 	}
-      else if (!DECL_P (decl) && !is_overloaded_fn (decl))
+      else if ((!DECL_P (decl) && !is_overloaded_fn (decl))
+	       || TREE_CODE (decl) == USING_DECL)
 	/* Repeat the lookup at instantiation time.  */
 	decl = identifier;
     }
diff --git a/gcc/testsuite/g++.dg/parse/template-keyword2.C b/gcc/testsuite/g++.dg/parse/template-keyword2.C
new file mode 100644
index 00000000000..ecd066787bc
--- /dev/null
+++ b/gcc/testsuite/g++.dg/parse/template-keyword2.C
@@ -0,0 +1,8 @@
+// PR c++/104235
+
+template <class M>
+struct L: M {
+  using M::a;
+  void a();
+  void p() { this->template a<>(); }
+};