On Mon, 10 Oct 2022, Jonathan Wakely via Libstdc++ wrote:
> Tested powerpc64le-linux. Pushed to trunk.
>
> -- >8 --
>
> Currently we only reject std::make_signed_t<bool> but not cv bool.
> Similarly for std::make_unsigned_t<cv bool>.
>
> As well as making those ill-formed, this adds a requires-clause to the
> make_signed and make_unsigned primary templates. This makes
> non-integral, non-enum cases fail immediately with a clear error, rather
> than giving an error about __make_signed_selector<T, false, false> being
> incomplete.
IIUC the requires-clause turns what was once a hard error into a SFINAE
error, so e.g. for
template<class T> typename make_signed<T>::type f(int);
template<class T> void f(...);
int main() { f<void>(0); }
the call to f would previously be rejected due to an error outside the
immediate context about incomplete __make_signed_selector, and now with
the requires-clause resolves to the second overload. I wonder if this
new behavior is conforming -- the examples in [structure.specifications]
of how to implement 'Mandates' suggest that a failed 'Mandates' should
yield a hard error?
>
> libstdc++-v3/ChangeLog:
>
> * include/std/type_traits (make_signed, make_unsigned): Add
> specializations for cv bool. Add requires-clause for C++20 to
> improve diagnostics for non-integral, non-enum cases.
> * testsuite/20_util/make_signed/requirements/typedefs_neg.cc:
> Check cv bool.
> * testsuite/20_util/make_unsigned/requirements/typedefs_neg.cc:
> Likewise.
> * testsuite/24_iterators/range_access/range_access_cpp20_neg.cc:
> Adjust expected errors for C++20 and later.
> * testsuite/lib/prune.exp: Prune "in requirements [with ...]"
> lines from diagnostics.
> ---
> libstdc++-v3/include/std/type_traits | 18 ++++++++++---
> .../make_signed/requirements/typedefs_neg.cc | 27 +++++++++----------
> .../requirements/typedefs_neg.cc | 25 ++++++++---------
> .../range_access/range_access_cpp20_neg.cc | 3 ++-
> libstdc++-v3/testsuite/lib/prune.exp | 1 +
> 5 files changed, 40 insertions(+), 34 deletions(-)
>
> diff --git a/libstdc++-v3/include/std/type_traits
> b/libstdc++-v3/include/std/type_traits
> index b74565eb521..6108b98aa6a 100644
> --- a/libstdc++-v3/include/std/type_traits
> +++ b/libstdc++-v3/include/std/type_traits
> @@ -1802,12 +1802,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> // Primary template.
> /// make_unsigned
> template<typename _Tp>
> +#if __cpp_concepts
> + requires is_integral<_Tp>::value || __is_enum(_Tp)
> +#endif
> struct make_unsigned
> { typedef typename __make_unsigned_selector<_Tp>::__type type; };
>
> // Integral, but don't define.
> - template<>
> - struct make_unsigned<bool>;
> + template<> struct make_unsigned<bool>;
> + template<> struct make_unsigned<bool const>;
> + template<> struct make_unsigned<bool volatile>;
> + template<> struct make_unsigned<bool const volatile>;
>
> /// @cond undocumented
>
> @@ -1932,12 +1937,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> // Primary template.
> /// make_signed
> template<typename _Tp>
> +#if __cpp_concepts
> + requires is_integral<_Tp>::value || __is_enum(_Tp)
> +#endif
> struct make_signed
> { typedef typename __make_signed_selector<_Tp>::__type type; };
>
> // Integral, but don't define.
> - template<>
> - struct make_signed<bool>;
> + template<> struct make_signed<bool>;
> + template<> struct make_signed<bool const>;
> + template<> struct make_signed<bool volatile>;
> + template<> struct make_signed<bool const volatile>;
>
> #if __cplusplus > 201103L
> /// Alias template for make_signed
> diff --git
> a/libstdc++-v3/testsuite/20_util/make_signed/requirements/typedefs_neg.cc
> b/libstdc++-v3/testsuite/20_util/make_signed/requirements/typedefs_neg.cc
> index 051bb64c710..88b8ae887ef 100644
> --- a/libstdc++-v3/testsuite/20_util/make_signed/requirements/typedefs_neg.cc
> +++ b/libstdc++-v3/testsuite/20_util/make_signed/requirements/typedefs_neg.cc
> @@ -20,31 +20,28 @@
> // <http://www.gnu.org/licenses/>.
>
> #include <type_traits>
> -#include <testsuite_character.h>
>
> -enum test_enum { first_selection };
> +struct pod_class { };
>
> void test01()
> {
> using std::make_signed;
>
> // Negative tests.
> - typedef make_signed<bool>::type test1_type;
> + using T1 = make_signed<bool>::type; // { dg-error "incomplete" }
> + using T2 = make_signed<const bool>::type; // { dg-error "incomplete" }
> + using T3 = make_signed<volatile bool>::type; // { dg-error "incomplete" }
> + using T4 = make_signed<const volatile bool>::type; // { dg-error
> "incomplete" }
>
> - typedef make_signed<__gnu_test::pod_uint>::type test2_type;
> + using T5 = make_signed<pod_class>::type; // { dg-error "here" }
>
> - typedef make_signed<int[4]>::type test3_type;
> + using T6 = make_signed<int[4]>::type; // { dg-error "here" }
>
> - typedef void (fn_type) ();
> - typedef make_signed<fn_type>::type test4_type;
> + using fn_type = void ();
> + using T7 = make_signed<fn_type>::type; // { dg-error "here" }
>
> - typedef make_signed<float>::type test5_type;
> + using T8 = make_signed<float>::type; // { dg-error "here" }
> }
>
> -// { dg-error "invalid use of incomplete type" "" { target *-*-* } 32 }
> -// { dg-error "required from here" "" { target *-*-* } 34 }
> -// { dg-error "required from here" "" { target *-*-* } 36 }
> -// { dg-error "required from here" "" { target *-*-* } 39 }
> -// { dg-error "required from here" "" { target *-*-* } 41 }
> -
> -// { dg-error "invalid use of incomplete type" "" { target *-*-* } 0 }
> +// { dg-error "invalid use of incomplete type" "" { target c++17_down } 0 }
> +// { dg-error "constraint failure" "" { target c++20 } 0 }
> diff --git
> a/libstdc++-v3/testsuite/20_util/make_unsigned/requirements/typedefs_neg.cc
> b/libstdc++-v3/testsuite/20_util/make_unsigned/requirements/typedefs_neg.cc
> index ff98cc42ef7..50f15e7037c 100644
> ---
> a/libstdc++-v3/testsuite/20_util/make_unsigned/requirements/typedefs_neg.cc
> +++
> b/libstdc++-v3/testsuite/20_util/make_unsigned/requirements/typedefs_neg.cc
> @@ -21,7 +21,6 @@
>
> #include <type_traits>
>
> -enum test_enum { first_selection };
> struct pod_class { };
>
> void test01()
> @@ -29,22 +28,20 @@ void test01()
> using std::make_unsigned;
>
> // Negative tests.
> - typedef make_unsigned<bool>::type test1_type;
> + using T1 = make_unsigned<bool>::type; // { dg-error "incomplete" }
> + using T2 = make_unsigned<const bool>::type; // { dg-error "incomplete" }
> + using T3 = make_unsigned<volatile bool>::type; // { dg-error "incomplete" }
> + using T4 = make_unsigned<const volatile bool>::type; // { dg-error
> "incomplete" }
>
> - typedef make_unsigned<pod_class>::type test2_type;
> + using T5 = make_unsigned<pod_class>::type; // { dg-error "here" }
>
> - typedef make_unsigned<int[4]>::type test3_type;
> + using T6 = make_unsigned<int[4]>::type; // { dg-error "here" }
>
> - typedef void (fn_type) ();
> - typedef make_unsigned<fn_type>::type test4_type;
> + using fn_type = void ();
> + using T7 = make_unsigned<fn_type>::type; // { dg-error "here" }
>
> - typedef make_unsigned<float>::type test5_type;
> + using T8 = make_unsigned<float>::type; // { dg-error "here" }
> }
>
> -// { dg-error "invalid use of incomplete type" "" { target *-*-* } 32 }
> -// { dg-error "required from here" "" { target *-*-* } 34 }
> -// { dg-error "required from here" "" { target *-*-* } 36 }
> -// { dg-error "required from here" "" { target *-*-* } 39 }
> -// { dg-error "required from here" "" { target *-*-* } 41 }
> -
> -// { dg-error "invalid use of incomplete type" "" { target *-*-* } 0 }
> +// { dg-error "invalid use of incomplete type" "" { target c++17_down } 0 }
> +// { dg-error "constraint failure" "" { target c++20 } 0 }
> diff --git
> a/libstdc++-v3/testsuite/24_iterators/range_access/range_access_cpp20_neg.cc
> b/libstdc++-v3/testsuite/24_iterators/range_access/range_access_cpp20_neg.cc
> index c0825a58587..26c8ae0ee1e 100644
> ---
> a/libstdc++-v3/testsuite/24_iterators/range_access/range_access_cpp20_neg.cc
> +++
> b/libstdc++-v3/testsuite/24_iterators/range_access/range_access_cpp20_neg.cc
> @@ -46,4 +46,5 @@ test03()
> C c;
> std::ssize(c); // { dg-error "no matching function" }
> }
> -// { dg-error "incomplete type .*make_signed.*S" "" { target *-*-* } 0 }
> +// { dg-error "incomplete type .*make_signed.*S" "" { target c++17_down } 0 }
> +// { dg-error "constraint failure" "" { target c++20 } 0 }
> diff --git a/libstdc++-v3/testsuite/lib/prune.exp
> b/libstdc++-v3/testsuite/lib/prune.exp
> index d457e975218..6d0b77a8ccd 100644
> --- a/libstdc++-v3/testsuite/lib/prune.exp
> +++ b/libstdc++-v3/testsuite/lib/prune.exp
> @@ -51,6 +51,7 @@ proc libstdc++-dg-prune { system text } {
> regsub -all "(^|\n)\[^\n\]*: (recursively )?required \[^\n\]*" $text
> "" text
> regsub -all "(^|\n)\[^\n\]*: . skipping \[0-9\]* instantiation
> contexts \[^\n\]*" $text "" text
> regsub -all "(^|\n)\[^\n\]*: in .constexpr. expansion \[^\n\]*" $text
> "" text
> + regsub -all "(^|\n)\[^\n\]*: in requirements .with\[^\n\]*" $text ""
> text
> regsub -all "(^|\n) inlined from \[^\n\]*" $text "" text
> # Why doesn't GCC need these to strip header context?
> regsub -all "(^|\n)In file included from \[^\n\]*" $text "" text
> --
> 2.37.3
>
>
