Add a tweak to not preselect the first completion in the new combobox

resources/default_tweaks.py

@@ -516,3 +516,11 @@ default_tweak_format = None
 #    enable_multicharacters_in_tag_browser = False
 enable_multicharacters_in_tag_browser = True
 
+#: Do not preselect a completion when editing authors/tags/series/etc.
+# This means that you can make changes and press Enter and your changes will
+# not be overwritten by a matching completion. However, if you wish to use the
+# completions you will now have to press Tab to select one before pressing
+# Enter. Which technique you prefer will depend on the state of metadata in
+# your library and your personal editing style.
+preselect_first_completion = False
+

src/calibre/gui2/complete2.py

@@ -16,6 +16,7 @@ from PyQt4.Qt import (QLineEdit, QAbstractListModel, Qt, pyqtSignal, QObject,
 from calibre.utils.icu import sort_key, primary_startswith
 from calibre.gui2 import NONE
 from calibre.gui2.widgets import EnComboBox, LineEditECM
+from calibre.utils.config import tweaks
 
 class CompleteModel(QAbstractListModel): # {{{
 
@@ -157,8 +158,8 @@ class Completer(QListView): # {{{
 
         p.setGeometry(pos.x(), pos.y(), w, h)
 
-        if (select_first and not self.currentIndex().isValid() and
-                self.model().rowCount() > 0):
+        if (tweaks['preselect_first_completion'] and select_first and not
+                self.currentIndex().isValid() and self.model().rowCount() > 0):
             self.setCurrentIndex(self.model().index(0))
 
         if not p.isVisible():