Add PySide6 dependency for Windows and MacOS

We're not yet adding them to Linux, since PySide6 is not yet available
in Linux distros' packages, whereas with Linux and macOS our packaging
process includes the shipped binaries.

Fixes #211

dangerzone/gui/__init__.py

@@ -4,12 +4,21 @@
 import platform
 import signal
 import sys
+import typing
 import uuid
 from typing import Dict, List, Optional
 
 import click
 import colorama
-from PySide2 import QtCore, QtGui, QtWidgets
+
+# FIXME: See https://github.com/freedomofpress/dangerzone/issues/320 for more details.
+if typing.TYPE_CHECKING:
+    from PySide2 import QtCore, QtGui, QtWidgets
+else:
+    try:
+        from PySide6 import QtCore, QtGui, QtWidgets
+    except ImportError:
+        from PySide2 import QtCore, QtGui, QtWidgets
 
 from .. import args, errors
 from ..document import Document

dangerzone/gui/logic.py

@@ -4,11 +4,20 @@
 import platform
 import shlex
 import subprocess
+import typing
 from pathlib import Path
 from typing import Dict
 
 from colorama import Fore
-from PySide2 import QtCore, QtGui, QtWidgets
+
+# FIXME: See https://github.com/freedomofpress/dangerzone/issues/320 for more details.
+if typing.TYPE_CHECKING:
+    from PySide2 import QtCore, QtGui, QtWidgets
+else:
+    try:
+        from PySide6 import QtCore, QtGui, QtWidgets
+    except ImportError:
+        from PySide2 import QtCore, QtGui, QtWidgets
 
 if platform.system() == "Linux":
     from xdg.DesktopEntry import DesktopEntry

dangerzone/gui/main_window.py

@@ -5,11 +5,20 @@
 import shutil
 import subprocess
 import tempfile
+import typing
 from multiprocessing.pool import ThreadPool
 from typing import List, Optional
 
 from colorama import Fore, Style
-from PySide2 import QtCore, QtGui, QtWidgets
+
+# FIXME: See https://github.com/freedomofpress/dangerzone/issues/320 for more details.
+if typing.TYPE_CHECKING:
+    from PySide2 import QtCore, QtGui, QtWidgets
+else:
+    try:
+        from PySide6 import QtCore, QtGui, QtWidgets
+    except ImportError:
+        from PySide2 import QtCore, QtGui, QtWidgets
 
 from .. import errors
 from ..document import SAFE_EXTENSION, Document
@@ -385,8 +394,10 @@ def __init__(self, dangerzone: DangerzoneGui) -> None:
         self.safe_extension_name_layout.addWidget(self.safe_extension_filename)
         self.safe_extension_name_layout.addWidget(self.safe_extension)
 
-        dot_pdf_regex = QtCore.QRegExp(r".*\.[Pp][Dd][Ff]")
-        self.safe_extension.setValidator(QtGui.QRegExpValidator(dot_pdf_regex))
+        dot_pdf_regex = QtCore.QRegularExpression(r".*\.[Pp][Dd][Ff]")
+        self.safe_extension.setValidator(
+            QtGui.QRegularExpressionValidator(dot_pdf_regex)
+        )
         self.safe_extension_layout = QtWidgets.QHBoxLayout()
         self.safe_extension_layout.addWidget(self.save_checkbox)
         self.safe_extension_layout.addWidget(self.safe_extension_label)

pyproject.toml

@@ -9,7 +9,8 @@ license = "MIT"
 python = ">=3.7,<3.11"
 click = "*"
 appdirs = "*"
-PySide2 = "5.15.2.1"
+PySide2 = {version = "5.15.2.1", platform = "linux"}
+PySide6 = {version = "^6.4.1", markers = "sys_platform == 'win32' or sys_platform == 'darwin'"}
 colorama = "*"
 pyxdg = {version = "*", platform = "linux"}