tdf#130857 qt weld: Implement QtBuilder + use it for first msg dialog

This implements an initial QtBuilder, which is used by
QtInstanceBuilder to create weld::Widget instances
using native Qt widgets.

This tries to be close to the VCL implementation (VclBuilder).
The selected approach is based on Caolán's suggestion in [1] to
rework VclBuilder to have overridable methods for widgets creation.

This way, we can have common code for the UI parser but the
function for widget creation is different.

Qt equivalents for Gtk's widget classes in the .ui files:

* GtkMessageDialog -> QMessageBox
* GtkBox -> QLayout (can be QVBoxLayout/QHBoxLayout based on
property in .ui file)
* GtkButtonBox -> QDialogButtonBox
* GtkButton -> QPushButton

As QMessageBox already comes with a layout and
a QDialogButtonBox, don't create new ones, but
return the existing ones in QtBuilder::makeObject.

This commit implements initial support for the
above-mentioned widget types and adds the first
message dialog to the list of supported .ui files
in QtInstanceBuilder::IsUIFileSupported,
so a native QMessageBox is used for it now, unless
environment variable SAL_VCL_QT_NO_WELDED_WIDGETS
is set when starting LibreOffice.

The dialog ("modules/swriter/ui/inforeadonlydialog.ui")
gets shown when taking the following steps:

* start Writer
* type "hello world"
* select text
* "Insert" -> "Section"
* tick the "Protect" checkbox in the "Write Protection" section
* close dialog via "Insert" button
* try to type in the protected section

The dialog can be dismissed using the default "OK" button.
(Handling for response codes for buttons is not implemented
yet, which will be needed when welding dialogs that have multiple
buttons resulting in different behavior depending on what button
gets clicked.)

This change was originally submitted as a WIP change as part of
Omkar Acharekar's Outreachy project "Implement Qt/KDE Frameworks
theming using native Qt widgets" (see [2]), then further refined
by Michael Weghorn.

[1] https://lists.freedesktop.org/archives/libreoffice/2023-December/091288.html
[2] https://lists.freedesktop.org/archives/libreoffice/2023-December/091281.html

Co-authored-by: Michael Weghorn <m.weghorn@posteo.de>
Change-Id: I6dd010a2138c245dc1e6d83dd08123898e9d9048
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/161831
Tested-by: Jenkins
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>

1 files changed, 17 insertions, 9 deletions

diff --git a/vcl/qt5/QtInstanceBuilder.cxx b/vcl/qt5/QtInstanceBuilder.cxx
index 938be55ecfbc..68386ec6d3d2 100644
--- a/vcl/qt5/QtInstanceBuilder.cxx
+++ b/vcl/qt5/QtInstanceBuilder.cxx
@@ -11,31 +11,39 @@
 
 #include <unordered_set>
 
-QtInstanceBuilder::QtInstanceBuilder(QWidget*, std::u16string_view, std::u16string_view) {}
+#include <QtBuilder.hxx>
+#include <QtInstanceMessageDialog.hxx>
+
+QtInstanceBuilder::QtInstanceBuilder(QWidget* pParent, std::u16string_view sUIRoot,
+                                     const OUString& rUIFile)
+    : m_xBuilder(std::make_unique<QtBuilder>(pParent, sUIRoot, rUIFile))
+{
+}
 
 QtInstanceBuilder::~QtInstanceBuilder() {}
 
 bool QtInstanceBuilder::IsUIFileSupported(const OUString& rUIFile)
 {
-    // set of supported UI files - none yet
+    // set of supported UI files
     //
     // The idea is to implement functionality needed for a specific UI file/dialog
     // in QtInstanceBuilder, then add it to the set of supported UI files here.
     // This allows looking at one .ui file at a time and only having to implement
     // what is relevant for that particular one, without having to implement the full
     // weld API at once.
-    //
-    // see demo/WIP change: https://gerrit.libreoffice.org/c/core/+/161831
-    // for an example
-    static std::unordered_set<OUString> aSupportedUIFiles = {};
+    static std::unordered_set<OUString> aSupportedUIFiles = {
+        u"modules/swriter/ui/inforeadonlydialog.ui"_ustr,
+    };
 
     return aSupportedUIFiles.contains(rUIFile);
 }
 
-std::unique_ptr<weld::MessageDialog> QtInstanceBuilder::weld_message_dialog(const OUString&)
+std::unique_ptr<weld::MessageDialog> QtInstanceBuilder::weld_message_dialog(const OUString& id)
 {
-    assert(false && "Not implemented yet");
-    return nullptr;
+    QMessageBox* pMessageBox = m_xBuilder->get<QMessageBox>(id);
+    std::unique_ptr<weld::MessageDialog> xRet(
+        pMessageBox ? std::make_unique<QtInstanceMessageDialog>(pMessageBox) : nullptr);
+    return xRet;
 }
 
 std::unique_ptr<weld::Dialog> QtInstanceBuilder::weld_dialog(const OUString&)