Add an option in Preferences->Look & feel to disable the new 'drag and drop to merge books feature'

src/calibre/gui2/__init__.py

@@ -168,6 +168,7 @@ def create_defs():
     defs['book_details_narrow_comments_layout'] = 'float'
     defs['book_list_split'] = False
     defs['wrap_toolbar_text'] = False
+    defs['dnd_merge'] = True
 
 
 create_defs()

src/calibre/gui2/library/alternate_views.py

@@ -201,6 +201,10 @@ def mouseMoveEvent(base_class, self, event):
     self.drag_start_pos = None
 
 
+def dnd_merge_ok(md):
+    return md.hasFormat('application/calibre+from_library') and gprefs['dnd_merge']
+
+
 def dragEnterEvent(self, event):
     if int(event.possibleActions() & Qt.CopyAction) + \
         int(event.possibleActions() & Qt.MoveAction) == 0:
@@ -208,13 +212,13 @@ def dragEnterEvent(self, event):
     paths = self.paths_from_event(event)
     md = event.mimeData()
 
-    if paths or md.hasFormat('application/calibre+from_library'):
+    if paths or dnd_merge_ok(md):
         event.acceptProposedAction()
 
 
 def dropEvent(self, event):
     md = event.mimeData()
-    if md.hasFormat('application/calibre+from_library'):
+    if dnd_merge_ok(md):
         ids = set(map(int, bytes(md.data('application/calibre+from_library')).decode('utf-8').split(' ')))
         row = self.indexAt(event.pos()).row()
         if row > -1 and ids:

src/calibre/gui2/preferences/look_feel.py

@@ -394,6 +394,7 @@ class ConfigWidget(ConfigWidgetBase, Ui_Form):
             self.opt_hidpi.setVisible(False), self.label_hidpi.setVisible(False)
         r('ui_style', gprefs, restart_required=True, choices=[(_('System default'), 'system'), (_('calibre style'), 'calibre')])
         r('book_list_tooltips', gprefs)
+        r('dnd_merge', gprefs)
         r('wrap_toolbar_text', gprefs, restart_required=True)
         r('show_layout_buttons', gprefs, restart_required=True)
         r('row_numbers_in_book_list', gprefs)

src/calibre/gui2/preferences/look_feel.ui

@@ -28,6 +28,16 @@
        <string>&amp;Main interface</string>
       </attribute>
       <layout class="QGridLayout" name="gridLayout_9">
+       <item row="0" column="0">
+        <widget class="QLabel" name="label_widget_style">
+         <property name="text">
+          <string>User interface style (&amp;needs restart):</string>
+         </property>
+         <property name="buddy">
+          <cstring>opt_ui_style</cstring>
+         </property>
+        </widget>
+       </item>
        <item row="2" column="0">
         <widget class="QLabel" name="label_17">
          <property name="text">
@@ -140,7 +150,7 @@
          </property>
         </widget>
        </item>
-       <item row="12" column="0">
+       <item row="13" column="0">
         <spacer name="verticalSpacer_3">
          <property name="orientation">
           <enum>Qt::Vertical</enum>
@@ -218,16 +228,6 @@
          </property>
         </widget>
        </item>
-       <item row="0" column="0">
-        <widget class="QLabel" name="label_widget_style">
-         <property name="text">
-          <string>User interface style (&amp;needs restart):</string>
-         </property>
-         <property name="buddy">
-          <cstring>opt_ui_style</cstring>
-         </property>
-        </widget>
-       </item>
        <item row="5" column="1">
         <widget class="QCheckBox" name="opt_disable_animations">
          <property name="toolTip">
@@ -284,6 +284,13 @@
          </property>
         </widget>
        </item>
+       <item row="12" column="0">
+        <widget class="QCheckBox" name="opt_dnd_merge">
+         <property name="text">
+          <string>Allow using &amp;drag and drop to merge books</string>
+         </property>
+        </widget>
+       </item>
       </layout>
      </widget>
      <widget class="QWidget" name="cover_grid_tab">