config_host/config_global.h.in | 1 +
configure.ac | 15 +++++++++++++++
include/vcl/vclptr.hxx | 19 +++++++++++++++++++
3 files changed, 35 insertions(+)
New commits:
commit dc01bb6306016346e52d654c3c46e4d21211964e
Author: Stephan Bergmann <stephan.bergm...@collabora.com>
AuthorDate: Mon Jul 21 16:42:28 2025 +0200
Commit: Stephan Bergmann <stephan.bergm...@collabora.com>
CommitDate: Mon Jul 21 18:11:10 2025 +0200
Silence new GCC 16 trunk -Wsfinae-incomplete for now
...which was introduced in
<https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=117782e0c2a81a4b8170f87f0fe7190ee22548e2>
"c++: add -Wsfinae-incomplete" and causes warnings like
> In file included from include/vcl/event.hxx:28,
> from libreofficekit/source/gtk/lokdocview.cxx:26:
> include/vcl/outdev.hxx:160:37: error: defining ‘OutputDevice’, which
previously failed to be complete in a SFINAE context
[-Werror=sfinae-incomplete=]
> 160 | class SAL_WARN_UNUSED VCL_DLLPUBLIC OutputDevice : public virtual
VclReferenceBase
> | ^~~~~~~~~~~~
> In file included from include/vcl/vclevent.hxx:24,
> from include/svtools/colorcfg.hxx:29,
> from include/vcl/themecolors.hxx:12,
> from include/vcl/settings.hxx:26,
> from include/vcl/event.hxx:26:
> include/vcl/vclptr.hxx:44:13: note: here. Use ‘-Wsfinae-incomplete=2’
for a diagnostic at that point
> 44 | int (*)[sizeof(T)])
> | ^~~~~~~~~
because
> include/vcl/vclptr.hxx:44:13: error: failed to complete ‘OutputDevice’ in
SFINAE context [-Werror=sfinae-incomplete=]
> 44 | int (*)[sizeof(T)])
> | ^~~~~~~~~
> include/vcl/vclptr.hxx: In substitution of ‘template<class T> constexpr
bool vcl::detail::isIncompleteOrDerivedFromVclReferenceBase(int (*)[sizeof
(T)]) [with T = VirtualDevice]’:
> include/vcl/vclptr.hxx:60:79: required from ‘class
VclPtr<VirtualDevice>’
> 60 |
vcl::detail::isIncompleteOrDerivedFromVclReferenceBase<reference_type>(
> |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
> 61 | nullptr),
> | ~~~~~~~~
> include/vcl/outdev.hxx:188:37: required from here
> 188 | VclPtr<VirtualDevice> mpAlphaVDev;
> | ^~~~~~~~~~~
As discussed in the newly added comment in include/vcl/vclptr.hxx, until we
can
address this with C++26 reflection, "use a HACK of (globally) ignoring that
warning". (Which required adding a new HAVE_GCC_WSFINAE_INCOMPLETE
configure
check.)
Change-Id: Ie1b44e730cf6b6269572158f6bd50e8911c15846
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/188115
Reviewed-by: Stephan Bergmann <stephan.bergm...@collabora.com>
Tested-by: Jenkins
diff --git a/config_host/config_global.h.in b/config_host/config_global.h.in
index 5b42b2c5a8bd..6580fdfd0af7 100644
--- a/config_host/config_global.h.in
+++ b/config_host/config_global.h.in
@@ -13,6 +13,7 @@ Any change in this header will cause a rebuild of almost
everything.
#define CONFIG_GLOBAL_H
#define HAVE_GCC_BUILTIN_ATOMIC 0
+#define HAVE_GCC_WSFINAE_INCOMPLETE 0
#define HAVE_SYSLOG_H 0
// Compiler supports C++20
<http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1073r3.html>
diff --git a/configure.ac b/configure.ac
index f3761d0eeca6..f8433c6655a2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -8013,6 +8013,21 @@ AC_SUBST(HARDENING_LDFLAGS)
AC_SUBST(HARDENING_CFLAGS)
AC_SUBST(HARDENING_OPT_CFLAGS)
+if test "$GCC" = yes && test "$COM_IS_CLANG" != TRUE; then
+ AC_MSG_CHECKING([whether $CXX_BASE supports -Wsfinae-incomplete])
+ AC_LANG_PUSH([C++])
+ save_CXXFLAGS=$CFLAGS
+ CXXFLAGS="$CXXFLAGS -Werror"
+ AC_COMPILE_IFELSE([AC_LANG_SOURCE([
+ #pragma GCC diagnostic warning "-Wsfinae-incomplete"
+ ])], [
+ AC_DEFINE([HAVE_GCC_WSFINAE_INCOMPLETE])
+ AC_MSG_RESULT([yes])
+ ], [AC_MSG_RESULT([no])])
+ CXXFLAGS=$save_CXXFLAGS
+ AC_LANG_POP([C++])
+fi
+
dnl ===================================================================
dnl Identify the C++ library
dnl ===================================================================
diff --git a/include/vcl/vclptr.hxx b/include/vcl/vclptr.hxx
index 228a14c27482..8333f1a1b1a4 100644
--- a/include/vcl/vclptr.hxx
+++ b/include/vcl/vclptr.hxx
@@ -22,6 +22,7 @@
#include <sal/config.h>
+#include <config_global.h>
#include <rtl/ref.hxx>
#include <utility>
@@ -44,6 +45,24 @@ template<typename T> constexpr bool
isIncompleteOrDerivedFromVclReferenceBase(
int (*)[sizeof(T)])
{ return std::is_base_of<VclReferenceBase, T>::value; }
+// The above isIncompleteOrDerivedFromVclReferenceBase will cause will cause
-Wsfinae-incomplete
+// warnings when e.g. OutputDevice (include/vcl/outdev.hxx) contains members
of type
+// VclPtr<OutputDevice>, so OutputDevice is not yet complete when
+// sIncompleteOrDerivedFromVclReferenceBase is instantiated, but will become
complete later on
+// ("warning: error: defining ‘OutputDevice’, which previously failed to be
complete in a SFINAE
+// context [-Werror=sfinae-incomplete=]"). A real solution would presumably
be using C++26
+// reflection and rewriting the above
isIncompleteOrDerivedFromVclReferenceBase as something like
+//
+// consteval bool isIncompleteOrDerivedFromVclReferenceBase(std::meta::info
type) {
+// return !std::meta::is_complete_type(type)
+// || std::meta::is_base_of_type(^^VclReferenceBase, type);
+// }
+//
+// But until then, use a HACK of (globally) ignoring that warning:
+#if defined __GNUC__ && !defined __clang__ && HAVE_GCC_WSFINAE_INCOMPLETE
+#pragma GCC diagnostic ignored "-Wsfinae-incomplete"
+#endif
+
} // namespace vcl::detail
/**
