The arguments of Epub3Builder.build_navigation_doc() is deprecated.

CHANGES

@@ -61,6 +61,7 @@ Deprecated
 * The arguments of ``EpubBuilder.build_mimetype()``,
   ``EpubBuilder.build_container()``, ``EpubBuilder.bulid_content()``,
   ``EpubBuilder.build_toc()`` and ``EpubBuilder.build_epub()``
+* The arguments of ``Epub3Builder.build_navigation_doc()``
 * The ``encoding`` argument of ``autodoc.Documenter.get_doc()``,
   ``autodoc.DocstringSignatureMixin.get_doc()``,
   ``autodoc.DocstringSignatureMixin._find_signature()``, and

doc/extdev/index.rst

@@ -249,6 +249,11 @@ The following is a list of deprecated interfaces.
      - 4.0
      - N/A
 
+   * - arguments of ``Epub3Builder.build_navigation_doc()``
+     - 2.0
+     - 4.0
+     - N/A
+
    * - ``nodetype`` argument of
        ``sphinx.search.WordCollector.is_meta_keywords()``
      - 2.0

sphinx/builders/epub3.py

@@ -9,12 +9,14 @@
     :license: BSD, see LICENSE for details.
 """
 
+import warnings
 from collections import namedtuple
 from os import path
 
 from sphinx import package_dir
 from sphinx.builders import _epub_base
 from sphinx.config import ENUM
+from sphinx.deprecation import RemovedInSphinx40Warning
 from sphinx.locale import __
 from sphinx.util import logging, xmlname_checker
 from sphinx.util.fileutil import copy_asset_file
@@ -81,7 +83,7 @@ class Epub3Builder(_epub_base.EpubBuilder):
         self.build_mimetype()
         self.build_container()
         self.build_content()
-        self.build_navigation_doc(self.outdir, 'nav.xhtml')
+        self.build_navigation_doc()
         self.build_toc()
         self.build_epub()
 
@@ -202,9 +204,15 @@ class Epub3Builder(_epub_base.EpubBuilder):
         metadata['navlist'] = navlist
         return metadata
 
-    def build_navigation_doc(self, outdir, outname):
+    def build_navigation_doc(self, outdir=None, outname='nav.xhtml'):
         # type: (str, str) -> None
         """Write the metainfo file nav.xhtml."""
+        if outdir:
+            warnings.warn('The arguments of Epub3Builder.build_navigation_doc() '
+                          'is deprecated.', RemovedInSphinx40Warning, stacklevel=2)
+        else:
+            outdir = self.outdir
+
         logger.info(__('writing %s file...'), outname)
 
         if self.config.epub_tocscope == 'default':