docs: drop the version constraints for sphinx and dependencies

As discussed (see Links), there is some inertia to move to the recent
Sphinx versions for the doc build environment.

As first step, drop the version constraints and the related comments. As
sphinx depends on jinja2, jinja2 is pulled in automatically. So drop that.
Then, the sphinx-pre-install script will fail though with:

Can't get default sphinx version from ./Documentation/sphinx/requirements.txt at ./scripts/sphinx-pre-install line 305.

The script simply expects to parse a version constraint with Sphinx in the
requirements.txt. That version is used in the script for suggesting the
virtualenv directory name.

To suggest a virtualenv directory name, when there is no version given in
the requirements.txt, one could try to guess the version that would be
downloaded with 'pip install -r Documentation/sphinx/requirements.txt'.
However, there seems no simple way to get that version without actually
setting up the venv and running pip. So, instead, name the directory with
the fixed name 'sphinx_latest'.

Finally update the Sphinx build documentation to reflect this directory
name change.

Link: https://lore.kernel.org/linux-doc/874jf4m384.fsf@meer.lwn.net/
Link: https://lore.kernel.org/linux-doc/20240226093854.47830-1-lukas.bulwahn@gmail.com/
Reviewed-by: Akira Yokosawa <akiyks@gmail.com>
Tested-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <20240301141800.30218-1-lukas.bulwahn@gmail.com>

Documentation: constrain alabaster package to older versions

The 'alabaster' theme dropped support for Sphinx < v3.4:

0.7.14 – 2024-01-08

* Dropped support for Python 3.8 and earlier.
* Dropped support for Sphinx 3.3 and earlier.
[...]

(Source: https://alabaster.readthedocs.io/en/latest/changelog.html)

This manifests as an error when running 'make htmldocs' in a virtualenv
constructed from Documentation/sphinx/requirements.txt:

Sphinx version error:
The alabaster extension used by this project needs at least Sphinx v3.4; it therefore cannot be built with this version.

Raising the Sphinx version is not really a good option at this point,
since 3.x through 6.x have horrible performance regressions (7.x still
does, but not quite as bad).

Instead, constrain the 'alabaster' package to versions that still support
Sphinx 2.4.4.

Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Link: https://lore.kernel.org/r/20240110104646.3647600-1-vegard.nossum@oracle.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation: add pyyaml to requirements.txt

Commit f061c9f7d058 ("Documentation: Document each netlink family") added
a new Python script that is invoked during 'make htmldocs' and which reads
the netlink YAML spec files.

Using the virtualenv from scripts/sphinx-pre-install, we get this new
error wen running 'make htmldocs':

Traceback (most recent call last):
File "./tools/net/ynl/ynl-gen-rst.py", line 26, in <module>
import yaml
ModuleNotFoundError: No module named 'yaml'
make[2]: *** [Documentation/Makefile:112: Documentation/networking/netlink_spec/rt_link.rst] Error 1
make[1]: *** [Makefile:1708: htmldocs] Error 2

Fix this by adding 'pyyaml' to requirements.txt.

Note: This was somehow present in the original patch submission:
<https://lore.kernel.org/all/20231103135622.250314-1-leitao@debian.org/>
I'm not sure why the pyyaml requirement disappeared in the meantime.

Fixes: f061c9f7d058 ("Documentation: Document each netlink family")
Cc: Breno Leitao <leitao@debian.org>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

docs: sphinx-pre-install: don't require the RTD theme

We don't default to the RTD theme anymore, so sphinx-pre-install need not
insist on installing it.

Acked-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

docs: sphinx/requirements: Limit jinja2<3.1

jinja2 release 3.1.0 (March 24, 2022) broke Sphinx<4.0.
This looks like the result of deprecating Python 3.6.
It has been tested against Sphinx 4.3.0 and later.

Setting an upper limit of <3.1 to junja2 can unbreak Sphinx<4.0
including Sphinx 2.4.4.

Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: stable@vger.kernel.org # v5.15+
Link: https://lore.kernel.org/r/7dbff8a0-f4ff-34a0-71c7-1987baf471f9@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

docs: sphinx-requirements: Move sphinx_rtd_theme to top

sphinx_rtd_theme 0.5.2 has "docutils<0.17" in its requirements.
docutils 0.17 released this April caused regression in
sphinx_rtd_theme 0.5.1 [1].

By removing docutils and moving sphinx_rtd_theme before Sphinx in
requirements.txt, the requirement of "docutils<0.17" can be met
naturally.

[1]: https://github.com/readthedocs/sphinx_rtd_theme/issues/1112

Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Acked-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Link: https://lore.kernel.org/r/75f14c88-6091-1072-41cb-16b886aee5a0@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Docs: drop Python 2 support

The kernel build system as a whole is dropping support for Python 2, so we
should do the same. The effects are rather small, especially considering
that much of the deleted code was not doing anything under any version of
Python anyway.

Signed-off-by: Jonathan Corbet <corbet@lwn.net>

docs: update requirements to install six module

On the update of Sphinx version to 2.4.4, the "six" library won't be
installed automatically. (which is required by kfigure.py)

Main reason of this issue were occurred by the requirements changed from
the sphinx library. In Sphinx v1.7.9, six was listed on the
install_requires, but it has been removed since 2.x

The kfigure.py uses six library explicitly, adding six to
requirements.txt seems reasonable

Signed-off-by: JaeSang Yoo <jsyoo5b@gmail.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/20201208014628.GA1361@JSYoo5B-Base.localdomain
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

docs: update recommended Sphinx version to 2.4.4

There are some docs that have nested tables. While this was
always part of the spec, only Sphinx version 2.4.x can
translate it to LaTeX.

In other words, if someone is using a Sphinx version < 2.4,
the LaTeX and PDF output won't work for some of the docs.

So, it seems that it is time to raise the bar again
for the recommented version.

The Sphinx check script is already smart enough to keep
working, with older versions, warning the users that
an upgrade is recommended (and explaining how):

Sphinx version 1.7.9
Warning: It is recommended at least Sphinx version 2.4.4.
Detected OS: Fedora release 31 (Thirty One).

To upgrade Sphinx, use:

/usr/bin/virtualenv sphinx_2.4.4
. sphinx_2.4.4/bin/activate
pip install -r ./Documentation/sphinx/requirements.txt

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/498f701c618f7d0cf5f0a37e5889ee926f7c8bf4.1586881715.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

docs: requirements.txt: recommend Sphinx 1.7.9

As discussed at the linux-doc ML, while we'll still support
version 1.3, it is time to recommend a more modern version.

So, let's switch the minimal requirements to Sphinx 1.7.9,
as it has the "-jauto" flag, with makes a lot faster when
building documentation.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

sphinx-pre-install: use a requirements file

Instead of using 3 commands to install a virtualenv, use
a single one, reading the requirements from this file:

Documentation/sphinx/requirements.txt

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>