tdf#124598 gtk3_kde5: Link gtk3 side against kf5 libs

The separate filepicker executable 'lo_kde5filepicker'
used by the gtk3_kde5 VCL plugin needs the KF5 libraries
(in particular the 'KFileWidget' class) in order to
provide custom controls in the Plasma-native QFileDialog.

The gtk3 side ('lo_kde5filepicker') itself doesn't use
any functionality from KF5 libraries itself and therefore
didn't link against those.

When determining which VCL plugin to use on LibreOffice
start, a 'dlopen()' is used on the libraries of the
potential VCL plugins, which fails if linked libraries
are not available, so unsuitable VCL plugin are skipped.

This mechanism didn't work for the gtk3_kde5 VCL plugin
if KF5 libraries were not installed, since the 'dlopen()'
on 'libvclplug_gtk3_kde5lo.so' would succeed, but starting
the 'lo_kde5filepicker' process would later fail at runtime
due to the missing libraries.

To avoid this, make 'libvclplug_gtk3_kde5lo.so' link
against KF5 libraries as well to prevent gtk3_kde5 from
being used unless all required libraries are actually present.

Add a dummy KFileWidget use in Gtk3KDE5FilePicker to prevent
smart linkers from not linking unused libraries despite linker
flags.

While this is a hack, it seems to be acceptable, in
particular since gtk3_kde5 is more meant as a temporary
solution supposed to be dropped at a later point in time
in favor of the pure kde5 VCL plugin.

Reviewed-on: https://gerrit.libreoffice.org/71237
Reviewed-by: Katarina Behrens <Katarina.Behrens@cib.de>
Tested-by: Jenkins
(cherry picked from commit 1674c6964b)

Change-Id: I3a37daaeb1307b4f24f6fd75d7b6ec5ffaade0fd
Reviewed-on: https://gerrit.libreoffice.org/71374
Tested-by: Jenkins
Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>

vcl/Library_vclplug_gtk3_kde5.mk

@@ -39,6 +39,7 @@ $(eval $(call gb_Library_add_cxxflags,vclplug_gtk3_kde5,\
 
 $(eval $(call gb_Library_add_defs,vclplug_gtk3_kde5,\
     -DVCLPLUG_GTK_IMPLEMENTATION -DVCLPLUG_GTK3_KDE5_IMPLEMENTATION \
+    $(KF5_CFLAGS) \
 ))
 
 $(eval $(call gb_Library_use_custom_headers,vclplug_gtk3_kde5,\
@@ -125,6 +126,7 @@ $(eval $(call gb_Library_add_libs,vclplug_gtk3_kde5,\
 	-lm \
 	-ldl \
 	-lpthread \
+	$(KF5_LIBS) \
 ))
 endif
 

vcl/unx/gtk3_kde5/gtk3_kde5_filepicker.cxx

@@ -17,6 +17,9 @@
  *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
  */
 
+#include <QUrl>
+#include <KFileWidget>
+
 #include "gtk3_kde5_filepicker.hxx"
 
 #include <com/sun/star/lang/DisposedException.hpp>
@@ -71,6 +74,11 @@ Gtk3KDE5FilePicker::Gtk3KDE5FilePicker(const uno::Reference<uno::XComponentConte
     : Gtk3KDE5FilePicker_Base(_helperMutex)
 {
     setMultiSelectionMode(false);
+
+    // tdf#124598 dummy KWidget use to make gtk3_kde5 VCL plugin link against KIO libraries
+    QString sDummyStr;
+    QUrl aUrl = KFileWidget::getStartUrl(QUrl(), sDummyStr);
+    aUrl.setPath("/dev/null");
 }
 
 Gtk3KDE5FilePicker::~Gtk3KDE5FilePicker() = default;