Tested aarch64-linux. Pushed to trunk.
-- >8 --
This was just approved in Tokyo as a DR for C++23. It doesn't affect us
yet, because we don't implement the __cpp_lib_format_ranges features. We
can add the disabled specializations and add a testcase now though.
libstdc++-v3/ChangeLog:
* include/std/format (formatter): Disable specializations that
would allow sequences of narrow characters to be formatted as
wchar_t without conversion, as per LWG 3944.
* testsuite/std/format/formatter/lwg3944.cc: New test.
---
libstdc++-v3/include/std/format | 23 ++++++++++++++
.../testsuite/std/format/formatter/lwg3944.cc | 31 +++++++++++++++++++
2 files changed, 54 insertions(+)
create mode 100644 libstdc++-v3/testsuite/std/format/formatter/lwg3944.cc
diff --git a/libstdc++-v3/include/std/format b/libstdc++-v3/include/std/format
index 613016d1a10..22dcb5f24bd 100644
--- a/libstdc++-v3/include/std/format
+++ b/libstdc++-v3/include/std/format
@@ -2478,6 +2478,29 @@ namespace __format
};
/// @}
+#if defined _GLIBCXX_USE_WCHAR_T && __cpp_lib_format_ranges
+ // _GLIBCXX_RESOLVE_LIB_DEFECTS
+ // 3944. Formatters converting sequences of char to sequences of wchar_t
+
+ namespace __format { struct __disabled; }
+
+ // std::formatter<__disabled, C> uses the primary template, which is
disabled.
+ template<>
+ struct formatter<char*, wchar_t>
+ : private formatter<__format::__disabled, wchar_t> { };
+ template<>
+ struct formatter<const char*, wchar_t>
+ : private formatter<__format::__disabled, wchar_t> { };
+ template<size_t _Nm>
+ struct formatter<char[_Nm], wchar_t>
+ : private formatter<__format::__disabled, wchar_t> { };
+ template<class _Traits, class _Allocator>
+ struct formatter<basic_string<char, _Traits, _Allocator>, wchar_t>
+ : private formatter<__format::__disabled, wchar_t> { };
+ template<class _Traits>
+ struct formatter<basic_string_view<char, _Traits>, wchar_t>
+ : private formatter<__format::__disabled, wchar_t> { };
+#endif
/// @cond undocumented
namespace __format
diff --git a/libstdc++-v3/testsuite/std/format/formatter/lwg3944.cc
b/libstdc++-v3/testsuite/std/format/formatter/lwg3944.cc
new file mode 100644
index 00000000000..ff5f075bcc8
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/format/formatter/lwg3944.cc
@@ -0,0 +1,31 @@
+// { dg-do compile { target c++20 } }
+// { dg-options "-Wno-unused-result" }
+
+// LWG 3944. Formatters converting sequences of char to sequences of wchar_t
+
+#include <format>
+
+void test_lwg3944()
+{
+ // Ill-formed in C++20 and C++23
+ const char* cstr = "hello";
+ char* str = const_cast<char*>(cstr);
+ std::format(L"{}", str); // { dg-error "here" }
+ std::format(L"{}",cstr); // { dg-error "here" }
+
+ // Ill-formed in C++20
+ // In C++23 they give L"['h', 'e', 'l', 'l', 'o']"
+ std::format(L"{}", "hello"); // { dg-error "here" }
+ std::format(L"{}", std::string_view("hello")); // { dg-error "here" }
+ std::format(L"{}", std::string("hello")); // { dg-error "here" }
+#ifdef __cpp_lib_format_ranges
+ // LWG 3944 does not change this, it's still valid.
+ std::format(L"{}", std::vector{'h', 'e', 'l', 'l', 'o'});
+#endif
+}
+
+// { dg-error "std::formatter must be specialized" "" { target *-*-* } 0 }
+// { dg-prune-output "use of deleted function" }
+// { dg-prune-output "no matching function" }
+// { dg-prune-output "has no member named 'parse'" }
+// { dg-prune-output "not a constant expression" }
--
2.44.0
