visibility of docks cannot be toggled when menubar is hidden

Bug description:

Visibility of docks cannot be toggled when menubar is hidden.

Reproducible:

Always.

Proposed solution:

I think this is a problem with Qt. As a workround I just toggle the height of the menubar between 0 and QWIDGETSIZE_MAX. In Gentoo I apply the following user patch:

diff --git a/sources/mainwindow.cpp b/sources/mainwindow.cpp
index 02ac3fd..707abe6 100644
--- a/sources/mainwindow.cpp
+++ b/sources/mainwindow.cpp
@@ -2227,7 +2227,7 @@ void MainWindow::on_toggleToolBars_triggered(bool checked)

 void MainWindow::on_toggleMenuBar_triggered(bool checked)
 {
- menuBar()->setVisible(checked);
+ menuBar()->setMaximumHeight(checked ? QWIDGETSIZE_MAX : 0);
 }

 void MainWindow::on_searchInitiated(const QString& text, bool modified)

To apply this manually in a non-git repository the patchfile can be placed in the root of the project directory and be applied as follows:

patch -p1 < qpdfview-0.4.18-qt-5.15.patch

System Information:

qpdfview version: 0.4.18
build-time options: CONFIG+="without_synctex without_ps"
operating system: Gentoo Linux
installed dependencies:

   -- net-print/cups-2.3.3_p2-r2 (net-print/cups) amd64
   -- app-text/djvu-3.5.28-r1 (app-text/djvu) amd64
   -- app-text/mupdf-1.18.0-r4 (>=app-text/mupdf-1.7) amd64
   -- app-text/libspectre-0.2.9 (app-text/libspectre) amd64
   -- dev-qt/qtconcurrent-5.15.2 (dev-qt/qtconcurrent) amd64
   -- dev-qt/qtcore-5.15.2-r2 (dev-qt/qtcore) amd64
   -- dev-qt/qtgui-5.15.2-r1 (dev-qt/qtgui) amd64
   -- dev-qt/qtprintsupport-5.15.2 (dev-qt/qtprintsupport) amd64 [cups?]
   -- dev-qt/qtwidgets-5.15.2 (dev-qt/qtwidgets) amd64
   -- dev-qt/qtdbus-5.15.2 (dev-qt/qtdbus) amd64
   -- app-text/poppler-21.05.0 (>=app-text/poppler-0.35) amd64 [qt5]
   -- dev-qt/qtxml-5.15.2 (dev-qt/qtxml) amd64
   -- dev-qt/qtsql-5.15.2 (dev-qt/qtsql) amd64 [sqlite]
   -- dev-qt/qtsvg-5.15.2 (dev-qt/qtsvg) amd64
   -- virtual/freedesktop-icon-theme-0-r4 (virtual/freedesktop-icon-theme) amd64
   -- app-text/texlive-core-2021 (app-text/texlive-core) amd64
   -- dev-util/desktop-file-utils-0.26-r1 (dev-util/desktop-file-utils) amd64
   -- x11-misc/shared-mime-info-2.0-r2 (x11-misc/shared-mime-info) amd64
   -- dev-qt/linguist-tools-5.15.2 (dev-qt/linguist-tools) amd64
   -- virtual/pkgconfig-2 (virtual/pkgconfig) amd64