HAVE_CPP_ATTRIBUTE_FALLTHROUGH is always true now

...but for safety, leave the configure.ac check in for some longer.

Also, save removing now-redundant SAL_FALLTHROUGH for a follow-up commit.

Change-Id: I9bf42d237aea4c09459f28275568cf340e588607
Reviewed-on: https://gerrit.libreoffice.org/64770
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

config_host/config_global.h.in

@@ -21,9 +21,6 @@ Any change in this header will cause a rebuild of almost everything.
 /* Compiler supports __attribute__((warn_unused)). */
 #define HAVE_GCC_ATTRIBUTE_WARN_UNUSED 0
 
-/* [[fallthrough]] (C++17), __has_cpp_attribute(fallthrough) (C++2a): */
-#define HAVE_CPP_ATTRIBUTE_FALLTHROUGH 0
-
 /* [[nodiscard]] (C++17), __has_cpp_attribute(nodiscard) (C++2a): */
 #define HAVE_CPP_ATTRIBUTE_NODISCARD 0
 

configure.ac

@@ -6413,7 +6413,8 @@ if test "$GCC" = yes; then
 fi
 AC_SUBST([HAVE_GCC_FNO_SIZED_DEALLOCATION])
 
-AC_MSG_CHECKING([[whether $CXX supports [[fallthrough]]]])
+dnl This check can eventually be removed completely (e.g., after libreoffice-6-3 branch off):
+AC_MSG_CHECKING([[that $CXX supports [[fallthrough]]]])
 AC_LANG_PUSH([C++])
 save_CXXFLAGS=$CXXFLAGS
 CXXFLAGS="$CXXFLAGS $CXXFLAGS_CXX11"
@@ -6441,10 +6442,8 @@ AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
             }
         }
         #endif
-    ]])], [
-        AC_DEFINE([HAVE_CPP_ATTRIBUTE_FALLTHROUGH],[1])
-        AC_MSG_RESULT([yes])
-    ], [AC_MSG_RESULT([no])])
+    ]])],
+    AC_MSG_RESULT([yes]), AC_MSG_ERROR([$CXX lacks required [[fallthrough]] support]))
 CXXFLAGS=$save_CXXFLAGS
 AC_LANG_POP([C++])
 

include/sal/types.h

@@ -410,15 +410,7 @@ namespace css = ::com::sun::star;
 #endif
 
 #if defined LIBO_INTERNAL_ONLY
-#if HAVE_CPP_ATTRIBUTE_FALLTHROUGH
 #define SAL_FALLTHROUGH [[fallthrough]]
-#elif defined __clang__
-    /* before Clang 3.9, according to
-       <https://en.cppreference.com/w/cpp/compiler_support#C.2B.2B17_features> */
-#define SAL_FALLTHROUGH [[clang::fallthrough]]
-#else
-#define SAL_FALLTHROUGH
-#endif
 #endif
 
 #endif /* __cplusplus */