Port QtVCP from PyQt5 to QtPy

[bgermann]

Replace all PyQt5-specific imports and idioms with their QtPy equivalents, making the codebase compatible with PyQt5 and PyQt6.

Import changes:

• Replace from PyQt5.XXX import with from qtpy.XXX import
• Replace bare from PyQt5 import XXX with from qtpy import XXX
• Replace pyqtSignal, pyqtSlot, pyqtProperty with the qtpy canonical names Signal, Slot, Property
• Port PyQt5.QtDesigner imports to qtpy.QtDesigner
• Port PyQt5.Qsci imports to qtpy.Qsci

PDFViewer: add QtPdf backend as Qt6 alternative to popplerqt5

• Try qtpy.QtPdf.QPdfDocument first; fall back to popplerqt5
• Use QPdfDocumentRenderOptions with Annotations flag for render quality matching the popplerqt5 Antialiasing/TextAntialiasing hints

sys_notify: make DBus main loop integration backend-agnostic

• Try dbus.mainloop.pyqt5, then pyqt6.

qtplasmac handlers: replace find_spec("PyQt5.QtWebEngineWidgets")

• Use a module-level _WEBENGINE_AVAILABLE flag set by try/import of qtpy.QtWebEngineWidgets in the qtplasmac handler

plugins/status_label_plugin: fix pyqtProperty descriptor check

• Replace fragile 'PyQt5.QtCore.pyqtProperty' in str(...) with isinstance(..., Property) to work across all Qt bindings

[andypugh]

@c-morley The description sounds like a good approach. What do you think?

[snowgoer540]

Made some time to apply this to the project and test it out.

After installing the necessary pyqt dependency, I get these in the terminal window when running the qtplasmac GUI:

QSocketNotifier: Can only be used with threads started with QThread
QSocketNotifier: Can only be used with threads started with QThread
QSocketNotifier: Can only be used with threads started with QThread
QSocketNotifier: Can only be used with threads started with QThread

[bgermann]

QSocketNotifier: Can only be used with threads started with QThread

I have removed the dbus.mainloop.glib fallback (which was added for PySide which we do not need to support) so this should be fixed.

[snowgoer540]

It still gave the same QSocketNotifier message. In order to fix it, I had to change the order of the import test to prefer testing pyqt5 first.

From:
for _mod in ('dbus.mainloop.pyqt6', 'dbus.mainloop.pyqt5'):

To:
for _mod in ('dbus.mainloop.pyqt5', 'dbus.mainloop.pyqt6'):

[bgermann]

It still gave the same QSocketNotifier message. In order to fix it, I had to change the order of the import test to prefer testing pyqt5 first.

Applied to the PR.

[snowgoer540]

From a QtPlasmaC standpoint this seems ok to merge. It will require RIP users to install the python3-qtpy dependency.

Will require @c-morley 's review prior to merging, he is much much more familiar with all of the core qtvcp stuff, and has many more affected GUIs.

[c-morley]

hmm on my system I get:

from qtpy.Qsci import QsciScintilla

ModuleNotFoundError: No module named 'qtpy.Qsci'

[c-morley]

if in gcode_editor, I change to:

try:
from qtpy.Qsci import QsciScintilla, QsciLexerCustom, QsciLexerPython
except ImportError as e:
from PyQt5.Qsci import QsciScintilla, QsciLexerCustom, QsciLexerPython

then dragon runs.
More testing needed...

[bgermann]

That is interesting because I have actually verified that module to work on Debian bookworm. Support for qtpy.Qsci was introduced in QtPy 2.3.0. So probably you are using an older version.

[snowgoer540]

If the goal of this pull request is to allow Debian to drop python3-poppler-qt5, then I think we should limit the changes to only what is necessary to support the necessary updates in PDFViewer.py.

I understand and appreciate the groundwork being done with this commit to support our future conversion to pyqt6, but that introduces additional changes that require extensive testing and review. Given that our master branch is approaching a release state, this may not be the right time to include the broader refactoring.

At this point, I recommend we focus only on the changes necessary to remove poppler from the codebase so Debian can proceed with dropping the package from Forky. The rest can be handled by Chris and myself in a separate effort where the changes can be reviewed and tested thoroughly (after 2.10 is released).

[snowgoer540]

After further consideration, I recommend changing this pull request to encompass only what is absolutely necessary to remove python3-poppler-qt5 from PDFViewer.py in support of dropping the package for Debian Forky.

[bgermann]

That is okay. The Debian package can just drop the optional dependency. There is nothing in this PR that suggests to integrate it very soon.