C++ PATCH for DR 2413 - typename in conversion-function-ids

[Jason Merrill]

OK.

On Mon, Aug 5, 2019 at 8:03 PM Marek Polacek <polacek@redhat.com> wrote:
>
> While updating the C++ DR table, I noticed that one of the new DRs, DR 2413,
> is trivial:
> ---
> The “Down with typename!” paper, P0634R3, overlooked the case of a conversion-type-id
> in a conversion-function-id:
>
>   template<class T> struct S {
>     operator typename T::X(); // typename is not helpful here.
>   };
>
> This context should be added to the list of contexts in which a qualified-id is assumed
> to name a type.
> ---
>
> It's still in "drafting", but it looks like a shoo-in to me.
>
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
>
> 2019-08-05  Marek Polacek  <polacek@redhat.com>
>
>         DR 2413 - typename in conversion-function-ids.
>         * parser.c (cp_parser_conversion_type_id): Call
>         cp_parser_type_specifier_seq with CP_PARSER_FLAGS_TYPENAME_OPTIONAL
>         instead of CP_PARSER_FLAGS_NONE.
>
>         * g++.dg/cpp2a/typename17.C: New test.
>
> diff --git gcc/cp/parser.c gcc/cp/parser.c
> index 86857e7d468..83e6d24a9c1 100644
> --- gcc/cp/parser.c
> +++ gcc/cp/parser.c
> @@ -14844,8 +14844,9 @@ cp_parser_conversion_type_id (cp_parser* parser)
>    parser->type_definition_forbidden_message
>      = G_("types may not be defined in a conversion-type-id");
>
> -  /* Parse the type-specifiers.  */
> -  cp_parser_type_specifier_seq (parser, CP_PARSER_FLAGS_NONE,
> +  /* Parse the type-specifiers.  DR 2413 clarifies that `typename' is
> +     optional in conversion-type-id.  */
> +  cp_parser_type_specifier_seq (parser, CP_PARSER_FLAGS_TYPENAME_OPTIONAL,
>                                 /*is_declaration=*/false,
>                                 /*is_trailing_return=*/false,
>                                 &type_specifiers);
> diff --git gcc/testsuite/g++.dg/cpp2a/typename17.C gcc/testsuite/g++.dg/cpp2a/typename17.C
> new file mode 100644
> index 00000000000..bf534f1717f
> --- /dev/null
> +++ gcc/testsuite/g++.dg/cpp2a/typename17.C
> @@ -0,0 +1,6 @@
> +// DR 2413 - typename in conversion-function-ids.
> +// { dg-do compile { target c++2a } }
> +
> +template<class T> struct S {
> +  operator T::X();
> +};