scripts: sphinx-pre-install: some adjustments related to venv

While nothing was really needed for virtualenv to work on most
distros, we had an issue with OpenMandriva.

While checking for it, it was noticed that there was no check if
python-virtualenv was installed.

This didn't solve the issues we faced there: at least with
the half-broken OpenMandriva Lx 4.0 docker container we used,
ensurepip was not available anywhere, causing venv to fail.

Add a distro-specific note about that.

Note: at least at the time we did our tests, OpenMandriva Lx 4.0
docker was shipped with wrong dnf repositories. Also, there
was no repos available for it anymore. So, we had to do some
hacks to upgrade to 4.3 before being able to run any tests.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/e3a0e5eccd50eb506846e3e8487a2d9124ef83e2.1754992972.git.mchehab+huawei@kernel.org

scripts/sphinx-pre-install

@@ -983,6 +983,22 @@ class SphinxDependencyChecker(MissingCheckers):
             # Tested on OpenMandriva Lx 4.3
             progs["convert"] = "imagemagick"
             progs["yaml"] = "python-pyyaml"
+            progs["python-virtualenv"] = "python-virtualenv"
+            progs["python-sphinx"] = "python-sphinx"
+
+            self.check_program("python-virtualenv", DepManager.PYTHON_MANDATORY)
+
+            # On my tests with openMandriva LX 4.0 docker image, upgraded
+            # to 4.3, python-virtualenv package is broken: it is missing
+            # ensurepip. Without it, the alternative would be to run:
+            # python3 -m venv --without-pip ~/sphinx_latest, but running
+            # pip there won't install sphinx at venv.
+            #
+            # Add a note about that.
+
+            if not self.distro_msg:
+                self.distro_msg = \
+                    "Note: for venv, ensurepip could be broken, preventing its install method."
 
         else:
             packager_cmd = "urpmi"