RE: RFC: Fix for sphinx setup message

[Bird, Tim]

> -----Original Message-----
> From: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
> 
> Em Sat, 22 Feb 2020 08:16:44 +0100
> Mauro Carvalho Chehab <mchehab@xxxxxxxxxx> escreveu:
> 
> > Hi Tim,
> >
> > Em Fri, 21 Feb 2020 22:15:36 +0000
> > "Bird, Tim" <Tim.Bird@xxxxxxxx> escreveu:
> >
> > > (Resend: Sorry for the dup.  I forgot to include the maintainers, and I had the LKML
> > > address wrong.)
> > >
> > > I was trying to set up my machine to do some documentation work,
> > > and I had some problems with the sphinx install.  I figured out how to work
> > > around the issue, but I have a question about how to add the information
> > > to scripts/sphinx-pre-install (or whether it should go somewhere else).
> > >
> > > Detailed messages below, but the TLl;DR is that I got the message:
> > > -------
> > > You should run:
> > >
> > >     sudo apt-get install dvipng fonts-noto-cjk latexmk librsvg2-bin texlive-xetex
> > >     /usr/bin/virtualenv sphinx_1.7.9
> > >     . sphinx_1.7.9/bin/activate
> > >     pip install -r ./Documentation/sphinx/requirements.txt
> > >     ...
> > > ------
> > >
> > > The pip install step didn't work, and I found that I needed to have everything
> > > based on python3 instead.  When I replaced:
> > >     /usr/bin/virtualenv sphinx_1.7.9
> > > with
> > >     /usr/bin/virtualenv -p python3 sphinx_1.7.9
> > > everything worked.
> > >
> > > This message is coming from scripts/sphinx-pre-install (I believe on line 708).
> > >
> > > Should I go ahead and submit a patch to add '-p python3' to that line?
> > >
> > > Are there any downsides to enforcing that the virtualenv used for the
> > > documentation build use python3 only?
> >
> > Actually, the script tries to detect if python3 is installed. Currently, it
> > does it by seeking for a python3 variant of virtualenv. If it finds, it
> > changes the recommendation accordingly. The actual code with does that is
> > this one:
> >
> > 	my $virtualenv = findprog("virtualenv-3");
> > 	$virtualenv = findprog("virtualenv-3.5") if (!$virtualenv);
> > 	$virtualenv = findprog("virtualenv") if (!$virtualenv);
> > 	$virtualenv = "virtualenv" if (!$virtualenv);
> >
> > This works fine on older Fedora distros (and probably CentOS/RHEL), where
> > there is a python3 variant of virtualenv. On Ubuntu (and Fedora 31), it
> > will just use virtualenv.
> >
> > So, perhaps if we add something like this (untested):
> >
> > 	my $python = findprog("python3");
> >
> > 	if ($python)
> > 		$virtualenv = "$virtualenv -p $python";
> >
> > it would make the trick. Please notice, however, that this could cause
> > troubles with some distros that might have a version of virtualenv that
> > won't work with the above. So, perhaps we should add something like the
> > above inside give_debian_hints(), and either ensure that other Debian and
> > Ubuntu LTS versions will work with such change, or add some checks for the
> > Ubuntu/Debian versions where we know this works.
> 
> Indeed it seems that, with some versions of python, virtualenv -p python3
> don't work:
> 
> 	https://stackoverflow.com/questions/23842713/using-python-3-in-virtualenv
> 
> This could well be something already solved on most distros, but I think it
> would be safer if we only add "-p python3" if it is Ubuntu 16.04 or upper
> (and doing a similar test for Debian).

OK - see the patch I will send shortly for what I came up with.
 -- Tim

> >
> > Note: the version of the distribution (and its name) is already stored
> > at the global var $system_release.
> >
> > Cheers,
> > Mauro