Re: [committed] libstdc++: Find make_error_code and make_error_condition via ADL only

["Daniel Krügler" <daniel.kruegler@gmail.com>]

Am Do., 8. Sept. 2022 um 20:30 Uhr schrieb Jonathan Wakely via
Libstdc++ <libstdc++@gcc.gnu.org>:
>
> Tested powerpc64le-linux, pushed to trunk.
>
> -- >8 --
>
> The new proposed resolution for LWG 3629 says that std::error_code and
> std::error_condition should only use ADL to find their customization
> points. This means we need to use a poison pill to prevent lookup from
> finding overloads in the enclosing namespaces.
>
> We can also remove the forward declarations of std::make_error_code and
> std::make_error_condition, because they aren't needed now. ADL can find
> them anyway (when std is an associated namespace), and unqualified name
> lookup will not (and should not) find them.
>
> libstdc++-v3/ChangeLog:
>
>         * include/std/system_error (__adl_only::make_error_code): Add
>         deleted function.
>         (__adl_only::make_error_condition): Likewise.
>         (error_code::error_code(ErrorCodeEnum)): Add using-declaration
>         for deleted function.
>         (error_condition::error_condition(ErrorConditionEnum)):
>         Likewise.
>         * testsuite/19_diagnostics/error_code/cons/lwg3629.cc: New test.
>         * testsuite/19_diagnostics/error_condition/cons/lwg3629.cc: New test.
> ---
[..]
> +// { dg-do compile { target c++11 } }
> +
> +// 3629. make_error_code and make_error_condition are customization points
> +// Verify that make_error_code is looked up using ADL only.
> +
> +namespace user
> +{
> +  struct E1;
> +}
> +
> +// N.B. not in associated namespace of E1, and declared before <system_error>.
> +user::E1 make_error_code(user::E1);
> +
> +#include <future> // declares std::make_error_code(future_errc)
> +#include <system_error>
> +
> +namespace user
> +{
> +  struct E1
> +  {
> +    operator std::error_code() const;
> +  };
> +
> +  struct E2
> +  {
> +    operator std::future_errc() const;
> +  };
> +
> +  struct E3
> +  {
> +    operator std::errc() const;
> +  };
> +}
> +
> +template<> struct std::is_error_code_enum<user::E1> : std::true_type { };
> +template<> struct std::is_error_code_enum<user::E2> : std::true_type { };
> +template<> struct std::is_error_code_enum<user::E3> : std::true_type { };
> +
> +// ::make_error_code(E1) should not be found by name lookup.
> +std::error_code e1( user::E1{} ); // { dg-error "here" }
> +
> +// std::make_error_code(errc) should not be found by name lookup.
> +std::error_code e2( user::E2{} ); // { dg-error "here" }

(1) Unless I'm misunderstanding something here, the comment above
doesn't match here, it should mention (std::)future_errc instead.

> +// std::make_error_code(future_errc) should not be found by name lookup.
> +std::error_code e3( user::E3{} ); // { dg-error "here" }

(2) Unless I'm misunderstanding something here, the comment above
doesn't match here, it should mention (std::)errc instead.

> +// { dg-error "use of deleted function" "" { target *-*-* } 0 }
> diff --git a/libstdc++-v3/testsuite/19_diagnostics/error_condition/cons/lwg3629.cc b/libstdc++-v3/testsuite/19_diagnostics/error_condition/cons/lwg3629.cc
> new file mode 100644
> index 00000000000..e34b53de8a1
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/19_diagnostics/error_condition/cons/lwg3629.cc
> @@ -0,0 +1,48 @@
> +// { dg-do compile { target c++11 } }
> +
> +// 3629. make_error_code and make_error_condition are customization points
> +// Verify that make_error_condition is looked up using ADL only.
> +
> +namespace user
> +{
> +  struct E1;
> +}
> +
> +// N.B. not in associated namespace of E1, and declared before <system_error>.
> +user::E1 make_error_condition(user::E1);
> +
> +#include <future> // declares std::make_error_condition(future_errc)
> +#include <system_error>
> +
> +namespace user
> +{
> +  struct E1
> +  {
> +    operator std::error_code() const;
> +  };
> +
> +  struct E2
> +  {
> +    operator std::future_errc() const;
> +  };
> +
> +  struct E3
> +  {
> +    operator std::errc() const;
> +  };
> +}
> +
> +template<> struct std::is_error_condition_enum<user::E1> : std::true_type { };
> +template<> struct std::is_error_condition_enum<user::E2> : std::true_type { };
> +template<> struct std::is_error_condition_enum<user::E3> : std::true_type { };
> +
> +// ::make_error_condition(E1) should not be found by name lookup.
> +std::error_condition e1( user::E1{} ); // { dg-error "here" }
> +
> +// std::make_error_condition(errc) should not be found by name lookup.
> +std::error_condition e2( user::E2{} ); // { dg-error "here" }

Ditto here (1)

> +// std::make_error_condition(future_errc) should not be found by name lookup.
> +std::error_condition e3( user::E3{} ); // { dg-error "here" }

Ditto here (2)

> +// { dg-error "use of deleted function" "" { target *-*-* } 0 }
> --
> 2.37.3

- Daniel