Make rename_tags handle splitting tags (1 -> many)

src/calibre/library/database2.py

@@ -1485,7 +1485,18 @@ class LibraryDatabase2(LibraryDatabase, SchemaUpgrade, CustomColumns):
         return result
 
     def rename_tag(self, old_id, new_name):
-        new_name = new_name.strip()
+        # It is possible that new_name is in fact a set of names. Split it on
+        # comma to find out. If it is, then rename the first one and append the
+        # rest
+        new_names = [t.strip() for t in new_name.strip().split(',') if t.strip()]
+        new_name = new_names[0]
+        new_names = new_names[1:]
+
+        # get the list of books that reference the tag being changed
+        books = self.conn.get('''SELECT book from books_tags_link
+                                 WHERE tag=?''', (old_id,))
+        books = [b[0] for b in books]
+
         new_id = self.conn.get(
                     '''SELECT id from tags
                        WHERE name=?''', (new_name,), all=False)
@@ -1501,9 +1512,7 @@ class LibraryDatabase2(LibraryDatabase, SchemaUpgrade, CustomColumns):
             # all the changes. To get around this, we first delete any links
             # to the new_id from books referencing the old_id, so that
             # renaming old_id to new_id will be unique on the book
-            books = self.conn.get('''SELECT book from books_tags_link
-                                     WHERE tag=?''', (old_id,))
-            for (book_id,) in books:
+            for book_id in books:
                 self.conn.execute('''DELETE FROM books_tags_link
                                      WHERE book=? and tag=?''', (book_id, new_id))
 
@@ -1512,7 +1521,13 @@ class LibraryDatabase2(LibraryDatabase, SchemaUpgrade, CustomColumns):
                                  WHERE tag=?''',(new_id, old_id,))
             # Get rid of the no-longer used publisher
             self.conn.execute('DELETE FROM tags WHERE id=?', (old_id,))
-        self.dirty_books_referencing('tags', new_id, commit=False)
+
+        if new_names:
+            # have some left-over names to process. Add them to the book.
+            for book_id in books:
+                self.set_tags(book_id, new_names, append=True, notify=False,
+                              commit=False)
+        self.dirtied(books, commit=False)
         self.conn.commit()
 
     def delete_tag_using_id(self, id):