Code for #7131 - implementing SUPPORTS_BACKLOADING

src/calibre/devices/interface.py

@@ -39,6 +39,10 @@ class DevicePlugin(Plugin):
     #: Whether the metadata on books can be set via the GUI.
     CAN_SET_METADATA = ['title', 'authors', 'collections']
 
+    # Set this to True if the books on the device are files that the GUI can
+    # access in order to add the books from the device to the library
+    SUPPORTS_BACKLOADING = False
+
     #: Path separator for paths to books on device
     path_sep = os.sep
 

src/calibre/devices/usbms/device.py

@@ -94,6 +94,9 @@ class Device(DeviceConfig, DevicePlugin):
     EBOOK_DIR_CARD_B = ''
     DELETE_EXTS = []
 
+    # USB disk-based devices can see the book files on the device, so can
+    # copy these back to the library
+    SUPPORTS_BACKLOADING = True
 
     def reset(self, key='-1', log_packets=False, report_progress=None,
             detected_device=None):

src/calibre/gui2/actions/add_to_library.py

@@ -19,7 +19,12 @@ class AddToLibraryAction(InterfaceAction):
         self.qaction.triggered.connect(self.add_books_to_library)
 
     def location_selected(self, loc):
-        enabled = loc != 'library'
+        enabled = False
+        if loc != 'library':
+            if self.gui.device_manager.is_device_connected:
+                device = self.gui.device_manager.connected_device
+                if device is not None:
+                    enabled = getattr(device, 'SUPPORTS_BACKLOADING', False)
         self.qaction.setEnabled(enabled)
 
     def add_books_to_library(self, *args):