Sphinx can't find linuxdoc when building readthedocs project - python-sphinx

Question

I am creating some documentation using readthedocs. I can make the html files locally, and when I open the html files with my browser the documentation looks exactly as I want it to. So, I push the source to github and try to build the project there - but that fails with the following error:
Running Sphinx v4.1.2
loading translations [en]... done
Traceback (most recent call last):
File "/home/docs/checkouts/readthedocs.org/user_builds/compas-docs-readthedocs/envs/latest/lib/python3.7/site-packages/sphinx/registry.py", line 429, in load_extension
mod = import_module(extname)
File "/home/docs/checkouts/readthedocs.org/user_builds/compas-docs-readthedocs/envs/latest/lib/python3.7/importlib/__init__.py", line 127, in import_module
return _bootstrap._gcd_import(name[level:], package, level)
File "<frozen importlib._bootstrap>", line 1006, in _gcd_import
File "<frozen importlib._bootstrap>", line 983, in _find_and_load
File "<frozen importlib._bootstrap>", line 953, in _find_and_load_unlocked
File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
File "<frozen importlib._bootstrap>", line 1006, in _gcd_import
File "<frozen importlib._bootstrap>", line 983, in _find_and_load
File "<frozen importlib._bootstrap>", line 965, in _find_and_load_unlocked
ModuleNotFoundError: No module named 'linuxdoc'
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "/home/docs/checkouts/readthedocs.org/user_builds/compas-docs-readthedocs/envs/latest/lib/python3.7/site-packages/sphinx/cmd/build.py", line 279, in build_main
args.tags, args.verbosity, args.jobs, args.keep_going)
File "/home/docs/checkouts/readthedocs.org/user_builds/compas-docs-readthedocs/envs/latest/lib/python3.7/site-packages/sphinx/application.py", line 237, in __init__
self.setup_extension(extension)
File "/home/docs/checkouts/readthedocs.org/user_builds/compas-docs-readthedocs/envs/latest/lib/python3.7/site-packages/sphinx/application.py", line 393, in setup_extension
self.registry.load_extension(self, extname)
File "/home/docs/checkouts/readthedocs.org/user_builds/compas-docs-readthedocs/envs/latest/lib/python3.7/site-packages/sphinx/registry.py", line 433, in load_extension
err) from err
sphinx.errors.ExtensionError: Could not import extension linuxdoc.rstFlatTable (exception: No module named 'linuxdoc')
Extension error:
Could not import extension linuxdoc.rstFlatTable (exception: No module named 'linuxdoc')
I am using the linuxdoc.rstFlatTable module. I have installed linuxdoc locally and, as I mentioned, the local build of the html files works a treat, and the flat-tables appear as they should. But the build at readthedocs fails.
I suspect I may need to set the path to linuxdoc in conf.py, but I don't know what the path is.
I installed linuxdoc thus:
pip install git+http://github.com/return42/linuxdoc.git
I can't find where it was installed. Any guidance would be much appreciated.

Answer 1

Dependencies like that must be explicitly added to your requirements.txt file,
https://docs.readthedocs.io/en/stable/guides/reproducible-builds.html#using-a-configuration-file
# File: docs/requirements.txt
# Defining the exact version will make sure things don't break
sphinx==3.4.3
sphinx_rtd_theme==0.5.1
readthedocs-sphinx-search==0.1.0
linuxdoc==20210324