qt gui: qrreader: macos: add runtime requesting of camera permission

- we were already
  - statically declaring "NSCameraUsageDescription" in the Info.plist
    - this used to be enough in the past
  - codesigning with an entitlements.plist that declares "com.apple.security.device.camera"
    - I believe this is required for notarization to pass for an app that declares "NSCameraUsageDescription".
- previously this was enough to access the camera IIRC
  - in any case, if the user goes into "System Preferences">"Security & Privacy", they can manually modify permissions there
- now with this commit, we on-demand trigger at runtime the OS permission prompt
  - making it much easier for users to actually use the camera
  - note: if you run via the Terminal, e.g. `$ $HOME/Desktop/Electrum.app/Contents/MacOS/run_electrum`,
    then it will be the Terminal app that requires the camera permission. If you run by double-clicking Electrum.app,
    then Electrum.app will be the "app" that requires the camera permission.
  - `$ tccutil reset Camera` can be used to clear permissions for all apps (back to the Qt::PermissionStatus::Undetermined state)

ref https://doc.qt.io/qt-6.5/qcoreapplication.html#requestPermission-1

electrum/gui/qt/main_window.py

@@ -97,7 +97,7 @@ from .update_checker import UpdateCheck, UpdateCheckThread
 from .channels_list import ChannelsList
 from .confirm_tx_dialog import ConfirmTxDialog
 from .rbf_dialog import BumpFeeDialog, DSCancelDialog
-from .qrreader import scan_qrcode
+from .qrreader import scan_qrcode_from_camera
 from .swap_dialog import SwapDialog, InvalidSwapParameters
 from .balance_dialog import (BalanceToolButton, COLOR_FROZEN, COLOR_UNMATURED, COLOR_UNCONFIRMED, COLOR_CONFIRMED,
                              COLOR_LIGHTNING, COLOR_FROZEN_LIGHTNING)
@@ -2313,7 +2313,7 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, Logger, QtEventListener):
                 return
             self.show_transaction(tx)
 
-        scan_qrcode(parent=self.top_level_window(), config=self.config, callback=cb)
+        scan_qrcode_from_camera(parent=self.top_level_window(), config=self.config, callback=cb)
 
     def read_tx_from_file(self) -> Optional[Transaction]:
         fileName = getOpenFileName(

electrum/gui/qt/qrreader/__init__.py

@@ -26,7 +26,8 @@ from typing import Callable, Optional, TYPE_CHECKING, Mapping, Sequence
 
 from PyQt6.QtWidgets import QMessageBox, QWidget
 from PyQt6.QtGui import QImage, QPainter, QColor
-from PyQt6.QtCore import QRect
+from PyQt6.QtCore import QRect, QCoreApplication
+from PyQt6 import QtCore
 
 from electrum.i18n import _
 from electrum.util import UserFacingException
@@ -43,18 +44,24 @@ if TYPE_CHECKING:
 _logger = get_logger(__name__)
 
 
-def scan_qrcode(
+def scan_qrcode_from_camera(
         *,
         parent: Optional[QWidget],
         config: 'SimpleConfig',
         callback: Callable[[bool, str, Optional[str]], None],
 ) -> None:
-    """Scans QR code using camera."""
+    """Scans QR code using camera. It handles requesting camera access permission from the OS if needed."""
     assert parent is None or isinstance(parent, QWidget), f"parent should be a QWidget, not {parent!r}"
-    if sys.platform == 'darwin' or sys.platform in ('windows', 'win32'):
-        _scan_qrcode_using_qtmultimedia(parent=parent, config=config, callback=callback)
-    else:  # desktop Linux and similar
-        _scan_qrcode_using_zbar(parent=parent, config=config, callback=callback)
+    def do_scan():
+        _scan_qrcode_from_camera(parent=parent, config=config, callback=callback)
+
+    if _has_camera_permission():
+        do_scan()
+    else:
+        # Request permission now. This is only a thing on macOS atm.
+        # Note: this assumes we are running on the main thread. Permissions can only be requested from the main thread.
+        app = QCoreApplication.instance()
+        app.requestPermission(QtCore.QCameraPermission(), lambda _x: do_scan())
 
 
 def scan_qr_from_image(image: QImage) -> Sequence[QrCodeResult]:
@@ -181,3 +188,29 @@ def _scan_qrcode_using_qtmultimedia(
         _qr_dialog = None
         callback(False, repr(e), None)
 
+
+def _scan_qrcode_from_camera(
+        *,
+        parent: Optional[QWidget],
+        config: 'SimpleConfig',
+        callback: Callable[[bool, str, Optional[str]], None],
+) -> None:
+    """Scans QR code using camera."""
+    assert parent is None or isinstance(parent, QWidget), f"parent should be a QWidget, not {parent!r}"
+    if not _has_camera_permission():
+        callback(False, _("Missing camera permission."), None)
+        return
+    if sys.platform == 'darwin' or sys.platform in ('windows', 'win32'):
+        _scan_qrcode_using_qtmultimedia(parent=parent, config=config, callback=callback)
+    else:  # desktop Linux and similar
+        _scan_qrcode_using_zbar(parent=parent, config=config, callback=callback)
+
+
+def _has_camera_permission() -> bool:
+    if not hasattr(QtCore, "QCameraPermission"):  # requires Qt 6.5+
+        _logger.info(f"QtCore does not support QCameraPermission. This requires Qt 6.5+")
+        return True  # hope for the best
+    app = QCoreApplication.instance()
+    permission_status = app.checkPermission(QtCore.QCameraPermission())
+    return permission_status == QtCore.Qt.PermissionStatus.Granted
+

electrum/gui/qt/util.py

@@ -792,10 +792,10 @@ class GenericInputHandler:
             except Exception as e:
                 show_error(_('Invalid payment identifier in QR') + ':\n' + repr(e))
 
-        from .qrreader import scan_qrcode
+        from .qrreader import scan_qrcode_from_camera
         if parent is None:
             parent = self if isinstance(self, QWidget) else None
-        scan_qrcode(parent=parent, config=config, callback=cb)
+        scan_qrcode_from_camera(parent=parent, config=config, callback=cb)
 
     def input_qr_from_screenshot(
             self,