debian: override default value for SPHINXBUILD in docs/makefile This is the recommended Debian approach. As suggested by Debian Developer Stephen Kitt, use the approach recommended by Debian for building Sphinx documentation. See https://wiki.debian.org/Python/LibraryStyleGuide#Sphinx_documentation Also belated credit to Zash on the #mercurial channel on the Freenode IRC network, who suggested the Make variable approach in the first place.

--- a/debian/rules	Fri May 03 03:52:44 2019 +0530
+++ b/debian/rules	Sun May 05 22:48:41 2019 +0530
@@ -7,7 +7,7 @@
 override_dh_auto_build:
 	dh_auto_build
 	# Workaround for Sphinx in Debian Buster defaulting to Python 3
-	SPHINXBUILD=/usr/share/sphinx/scripts/python2/sphinx-build $(MAKE) -C docs
+	SPHINXBUILD="python -m sphinx -bhtml" $(MAKE) -C docs
 
 hgsrc_defined:
 	# Use "! -z" instead of "-n", because "-n" without arguments is true