[LTP] [PATCH v5 2/3] doc: Add sphinx to requirements.txt

[Petr Vorel]

Although that slightly prolongs creating virtualenv (and CI job), but
it's probably better to handle it as the other requirements.

Use the same sphinx and sphinx-rtd-theme versions as on readthedocs.org.
That way we get doc generation tested by CI and by local build (to avoid
incompatibility changes).

Also don't install python3-sphinx via apt in CI job to keep usage the
same as in readthedocs.org.

Suggested-by: Andrea Cervesato <andrea.cervesato@suse.com>
Signed-off-by: Petr Vorel <pvorel@suse.cz>
---
Changes from v4:
* Use sphinx version used on readthedocs.org (to really test in devel
  and github CI what will be deployed).
* Don't install sphinx in github CI (python3-sphinx package)

 .github/workflows/ci-sphinx-doc.yml | 2 +-
 doc/developers/documentation.rst    | 2 --
 doc/requirements.txt                | 4 ++++
 3 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/.github/workflows/ci-sphinx-doc.yml b/.github/workflows/ci-sphinx-doc.yml
index a5f9d74d1f..e77c766871 100644
--- a/.github/workflows/ci-sphinx-doc.yml
+++ b/.github/workflows/ci-sphinx-doc.yml
@@ -23,7 +23,7 @@ jobs:
       - name: Install sphinx and autotools
         run: |
           sudo apt update
-          sudo apt install autoconf make python3-sphinx python3-virtualenv
+          sudo apt install autoconf make python3-virtualenv
 
       - name: Run configure
         run: |
diff --git a/doc/developers/documentation.rst b/doc/developers/documentation.rst
index 27c847e125..a303253693 100644
--- a/doc/developers/documentation.rst
+++ b/doc/developers/documentation.rst
@@ -23,8 +23,6 @@ Before building, make sure you have python3 ``virtualenv`` module installed.
     # prepare virtual environment
     python3 -m virtualenv .venv
     . .venv/bin/activate
-
-    pip install sphinx # usually packaged in distros
     pip install -r requirements.txt
 
     # build documentation
diff --git a/doc/requirements.txt b/doc/requirements.txt
index 742fb8b4bb..6302ecd9f2 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -1,3 +1,7 @@
+# Use the same sphinx as on readthedocs.org. When updated, make sure
+# sphinx-rtd-theme is compatible with sphinx.
+sphinx==5.3.0
 sphinx-rtd-theme==2.0.0
+
 linuxdoc==20231020
 sphinxcontrib-spelling==7.7.0
-- 
2.49.0