ToC Editor: When generating ToCs using headings/xpath ignore duplicate entries at the same level that have the same text. Fixes #1735799 [[Enhancement] Filter dupes in TOC editor](https://bugs.launchpad.net/calibre/+bug/1735799)

src/calibre/ebooks/oeb/polish/toc.py

@@ -78,6 +78,19 @@ class TOC(object):
             for gc in child.iterdescendants():
                 yield gc
 
+    def remove_duplicates(self, only_text=True):
+        seen = set()
+        remove = []
+        for child in self:
+            key = child.title if only_text else (child.title, child.dest, (child.frag or None))
+            if key in seen:
+                remove.append(child)
+            else:
+                seen.add(key)
+                child.remove_duplicates()
+        for child in remove:
+            self.remove(child)
+
     @property
     def depth(self):
         """The maximum depth of the navigation tree rooted at this node."""

src/calibre/gui2/toc/main.py

@@ -933,6 +933,7 @@ class TOCView(QWidget):  # {{{
         if len(toc) == 0:
             return error_dialog(self, _('No items found'),
                 _('No items were found that could be added to the Table of Contents.'), show=True)
+        toc.remove_duplicates()
         self.insert_toc_fragment(toc)
 
     def create_from_links(self):