Re: Bogus "is either too old or uses too old a Python version" from docs/meson.build

[Peter Maydell]

On Thu, 25 Feb 2021 at 12:23, Markus Armbruster <armbru@redhat.com> wrote:
>
> I just chanced on this one:
>
>     Program sphinx-build-3 found: YES
>     ../docs/meson.build:30: WARNING: /usr/bin/sphinx-build-3 is either too 
> old or uses too old a Python version
>
>     ../docs/meson.build:33:6: ERROR: Problem encountered: Install a Python 3 
> version of python-sphinx
>
>     A full log can be found at 
> /work/armbru/qemu/bld-x86/meson-logs/meson-log.txt
>
>     ERROR: meson setup failed
>
> My sphinx-build-3 is just fine, the problem is caused by me changing my
> tree so that
>
> 1. qapi-gen.py fails (because I messed up), and
>
> 2. make re-runs configure.
>
> Perhaps the test for a working sphinx-build-3 could be made a bit more
> robust.

I'm not sure what could reasonably be done. The Sphinx test is just
"try building a trivial document with our config (which is what
enforces the version requirement)". So yes, if you modify the QEMU sources
in a way that breaks the config file or one of the Sphinx plugins then
it'll trip the configure check. If you give the configure-check run
its own config file, then you end up with the version checks in two places
and they could get out of sync. One could try to have the conf.py have a
lot of conditionals to cut out things that the test-document doesn't use,
but then you run the risk that we no longer catch something for end-users
that we didn't anticipate that means we can't build the docs.

It seems more reasonable to me to assume that developers who are
actively modifying the QEMU code which is used in docs building
are able to read the log file that the error message points them
at, and can figure out what really happened from the log.

thanks
-- PMM