List of changes:

 - Define macro unconditionally when the compiler is clang.
 - Remove preprocessor logic that isn't needed anymore.
 - Define new libcxx test feature for the AIX platform.
 - Mark tests as xfail in the platforms whose C library doesn't support
   the char8_t functions.

Author: vhscampos

libcxx/include/__config

@@ -1021,27 +1021,16 @@ typedef __char32_t char32_t;
 // the latter depends on internal GNU libc details that are not appropriate
 // to depend on here, so any declarations present when __cpp_char8_t is not
 // defined are ignored.
-//
-// picolibc 1.8.9 and newer declare the two functions unconditionally.
-//
-// Apple C library, Microsoft C Runtime, AIX C library and FreeBSD libc do not
-// yet support these functions.
 #  if defined(_LIBCPP_GLIBC_PREREQ)
-#    if defined(__cpp_char8_t) && _LIBCPP_GLIBC_PREREQ(2, 36)
-#      define _LIBCPP_HAS_C8RTOMB_MBRTOC8 1
-#    else
-#      define _LIBCPP_HAS_C8RTOMB_MBRTOC8 0
-#    endif
-#  elif defined(_LIBCPP_PICOLIBC_PREREQ)
-#    if _LIBCPP_PICOLIBC_PREREQ(1, 8, 9)
+#    if _LIBCPP_GLIBC_PREREQ(2, 36) && defined(__cpp_char8_t)
 #      define _LIBCPP_HAS_C8RTOMB_MBRTOC8 1
 #    else
 #      define _LIBCPP_HAS_C8RTOMB_MBRTOC8 0
 #    endif
-#  elif defined(__APPLE__) || defined(_MSC_VER) || defined(_LIBCPP_UCRT) || defined(_AIX) || defined(__FreeBSD__)
-#    define _LIBCPP_HAS_C8RTOMB_MBRTOC8 0
-#  else
+#  elif defined(__clang__)
 #    define _LIBCPP_HAS_C8RTOMB_MBRTOC8 1
+#  else
+#    define _LIBCPP_HAS_C8RTOMB_MBRTOC8 0
 #  endif
 
 // There are a handful of public standard library types that are intended to

libcxx/include/__configuration/platform.h

@@ -47,17 +47,6 @@
 //       user code. Move code paths that need _NEWLIB_VERSION to another customization mechanism.
 #if __has_include(<picolibc.h>)
 #  include <picolibc.h>
-#  define _LIBCPP_PICOLIBC_VERSION_INT(maj, min, patch) (maj * 10000 + min * 100 + patch)
-#  define _LIBCPP_PICOLIBC_PREREQ(maj, min, patch)                                                                     \
-    _LIBCPP_PICOLIBC_VERSION_INT(__PICOLIBC__, __PICOLIBC_MINOR__, __PICOLIBC_PATCHLEVEL__) >=                         \
-        _LIBCPP_PICOLIBC_VERSION_INT(maj, min, patch)
-#endif
-
-#if __has_include(<corecrt.h>)
-#  include <corecrt.h>
-#  if defined(_UCRT)
-#    define _LIBCPP_UCRT
-#  endif
 #endif
 
 #ifndef __BYTE_ORDER__

libcxx/test/std/depr/depr.c.headers/uchar_h.compile.pass.cpp

@@ -11,6 +11,11 @@
 // Apple platforms don't provide <uchar.h> yet, so these tests fail.
 // XFAIL: target={{.+}}-apple-{{.+}}
 
+// The following platforms do not provide mbrtoc8 and c8rtomb so the tests fail
+// XFAIL: aix
+// XFAIL: freebsd
+// XFAIL: windows
+
 // mbrtoc16 not defined.
 // XFAIL: LIBCXX-PICOLIBC-FIXME
 

libcxx/test/std/strings/c.strings/cuchar.compile.pass.cpp

@@ -11,6 +11,11 @@
 // Apple platforms don't provide <uchar.h> yet, so these tests fail.
 // XFAIL: target={{.+}}-apple-{{.+}}
 
+// The following platforms do not provide mbrtoc8 and c8rtomb so the tests fail
+// XFAIL: aix
+// XFAIL: freebsd
+// XFAIL: windows
+
 // mbrtoc16 not defined.
 // XFAIL: LIBCXX-PICOLIBC-FIXME
 

libcxx/test/std/strings/c.strings/no_c8rtomb_mbrtoc8.verify.cpp

@@ -8,6 +8,12 @@
 
 // UNSUPPORTED: c++03
 
+// The following platforms do not provide mbrtoc8 and c8rtomb so the tests fail
+// XFAIL: aix
+// XFAIL: darwin
+// XFAIL: freebsd
+// XFAIL: windows
+
 #include <uchar.h>
 
 #include "test_macros.h"

libcxx/utils/libcxx/test/features.py

@@ -669,6 +669,7 @@ def _getLocaleFlagsAction(cfg, locale, alts, members):
             """,
         ),
     ),
+    Feature(name="aix", when=lambda cfg: "_AIX" in compilerMacros(cfg)),
 ]
 
 # Add features representing the build host platform name.