[gcc r11-3688] c++: typename in out-of-class member function definitions [PR97297]

[gcc r11-3688] c++: typename in out-of-class member function definitions [PR97297]

[Marek Polacek]

https://gcc.gnu.org/g:85307b4e938d42201d6c232f5d9259f91133a303

commit r11-3688-g85307b4e938d42201d6c232f5d9259f91133a303
Author: Marek Polacek <polacek@redhat.com>
Date:   Mon Oct 5 17:48:19 2020 -0400

    c++: typename in out-of-class member function definitions [PR97297]
    
    I was notified that our P0634R3 (Down with typename) implementation has
    a flaw: when we have an out-of-class member function definition, we
    still required 'typename' for its parameters.  For example here:
    
      template <typename T> struct S {
        int simple(T::type);
      };
      template <typename T>
      int S<T>::simple(/* typename */T::type) { return 0; }
    
    the 'typename' isn't necessary per [temp.res]/5.2.4.  We have a qualified
    name here ("S<T>::simple") so we know it's already been declared so we
    can look it up to see if it's a function template or a variable
    template.
    
    In this case, the P0634R3 code in cp_parser_direct_declarator wasn't
    looking into uninstantiated templates and didn't find the member
    function 'simple' -- cp_parser_lookup_name returned a SCOPE_REF which
    means that the qualifying scope was dependent.  With this fix, we find
    the BASELINK for 'simple', don't clear CP_PARSER_FLAGS_TYPENAME_OPTIONAL
    from the flags, and the typename is implicitly assumed.
    
    gcc/cp/ChangeLog:
    
            PR c++/97297
            * parser.c (cp_parser_direct_declarator): When checking if a
            name is a function template declaration for the P0634R3 case,
            look in uninstantiated templates too.
    
    gcc/testsuite/ChangeLog:
    
            PR c++/97297
            * g++.dg/cpp2a/typename18.C: New test.

Diff:
---
 gcc/cp/parser.c                         | 10 ++++++++--
 gcc/testsuite/g++.dg/cpp2a/typename18.C | 21 +++++++++++++++++++++
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index cb4422764ed..2002c05fdb5 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -21788,8 +21788,14 @@ cp_parser_direct_declarator (cp_parser* parser,
 		       templates, assume S::p to name a type.  Otherwise,
 		       don't.  */
 		    tree decl
-		      = cp_parser_lookup_name_simple (parser, unqualified_name,
-						      token->location);
+		      = cp_parser_lookup_name (parser, unqualified_name,
+					       none_type,
+					       /*is_template=*/false,
+					       /*is_namespace=*/false,
+					       /*check_dependency=*/false,
+					       /*ambiguous_decls=*/NULL,
+					       token->location);
+
 		    if (!is_overloaded_fn (decl)
 			/* Allow
 			   template<typename T>
diff --git a/gcc/testsuite/g++.dg/cpp2a/typename18.C b/gcc/testsuite/g++.dg/cpp2a/typename18.C
new file mode 100644
index 00000000000..99468661491
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/typename18.C
@@ -0,0 +1,21 @@
+// PR c++/97297
+// { dg-do compile { target c++20 } }
+
+template <typename T>
+struct S {
+    int simple(T::type);
+
+    template <typename U>
+    int member(U::type);
+};
+
+template <typename T>
+int S<T>::simple(T::type) {
+    return 1;
+}
+
+template <typename T>
+template <typename U>
+int S<T>::member(U::type) {
+    return 2;
+}