do not create 404 page for embedded (e.g. ePub)

notfound/extension.py

@@ -31,9 +31,9 @@ def html_collect_pages(app):
     :param app: Sphinx Application
     :type app: sphinx.application.Sphinx
     """
-    if app.config.notfound_pagename in app.env.titles:
-        # There is already a ``404.rst`` file rendered.
-        # Skip generating our default one.
+    if app.builder.embedded or app.config.notfound_pagename in app.env.titles:
+        # Building embedded (e.g. htmlhelp or ePub) or there is already a ``404.rst``
+        # file rendered. Skip generating our default one.
         return []
 
     return [(

tests/test_urls.py

@@ -46,6 +46,12 @@ def test_404_page_created(app, status, warning):
     path = app.outdir / '404.html'
     assert path.exists()
 
+@pytest.mark.sphinx('epub', srcdir=srcdir)
+def test_404_page_not_created(app, status, warning):
+    assert app.builder.embedded
+    app.build()
+    path = app.outdir / '404.html'
+    assert not path.exists()
 
 @pytest.mark.sphinx(srcdir=srcdir)
 def test_default_settings(app, status, warning):

tox.ini

@@ -10,6 +10,7 @@ envlist =
 deps =
   pytest
   pdbpp
+  defusedxml
   .
   sphinx5: sphinx<6.0
   sphinx6: sphinx<7.0