Re: Patch: allow the 'python' used to run gentpl.py to be configured

[Daniel Kiper]

On Tue, Jul 17, 2018 at 12:35:42PM -0700, Adam Williamson wrote:
> On Fri, 2018-07-06 at 13:19 -0700, Adam Williamson wrote:
> > On Fri, 2018-07-06 at 19:25 +0200, Daniel Kiper wrote:
> > > On Wed, Jul 04, 2018 at 10:08:53AM -0700, Adam Williamson wrote:
> > > > gentpl.py is python2/3-agnostic, but there's no way to cause it
> > > > to be run with any interpreter other than 'python', it's just
> > > > hard-coded into Makefile.common that way. Adjust that to allow
> > > > a make variable PYTHONBIN to be set to the desired interpreter.
> > > > This will make it easier in situations where we specifically
> > > > want to build with 'python2' or 'python3' or whatever.
> > > >
> > > > Signed-off-by: Adam Williamson <address@hidden>
> > >
> > > Thanks for the patch. However, I think that the configure should find
> > > correct python binary and set PYTHON variable (instead of PYTHONBIN)
> > > in the Makefile (good example is BUILD_CC variable in Makefile.in).
> >
> > That's possible, but it depends what you mean by "correct", doesn't it?
> > There could be many python interpreters installed on a system; which
> > are we to assume is "correct"?
> >
> > We could make it configurable with some sort of default heuristic, I
> > guess, I was just going for a simple patch approximately in line with
> > what was done for autogen.sh for now. (And I wouldn't want to reinvent
> > python interpreter discovery, which has been invented enough times
> > already; if we were to go that route it'd probably make sense to use an
> > existing autoconf extension or something).
>
> So I've just been looking into this, and it's actually very easy to do
> using AM_PATH_PYTHON, provided by autoconf. However, there's a rather
> funny wrinkle for grub's particular build process. AM_PATH_PYTHON has a
> documented behaviour where, if the 'PYTHON' env var is set when
> autoconf is run, it will *only* consider the value that env var is set
> to as a candidate for the Python interpreter - it won't do its usual
> attempt to discover one. And grub's autogen.sh already uses the PYTHON
> env var - setting it if it was not set already - and then calls
> autoreconf!
>
> So the practical effect of just applying this patch would be that only
> 'python', or whatever the env var PYTHON is set to when running
> autogen.sh, would be considered, when using autogen.sh. All the
> 'discovery' bits of AM_PATH_PYTHON wouldn't be used: if you just call
> 'autogen.sh' without setting PYTHON, but your Python binary is called
> 'python3' or 'python2.7' or whatever, it won't work.
>
> This seems a bit funny, but I'm not sure if it's really a
> *problem*...because autogen.sh *itself* will only work if whatever
> value PYTHON is set to is a working Python interpreter, anyway. We
> could in fact argue that the consequence is quite nice as it makes
> everything sort of consistent: whatever PYTHON is set to will be the
> interpreter used both by autogen.sh and for running gentpl.py. But I
> figured I should point it out.
>
> With that in mind, I'm attaching the updated patch in git format.
> Thanks!

> From 5fc0bb5f16a4189aa9581ebca4ea3abbc5c96593 Mon Sep 17 00:00:00 2001
> From: Adam Williamson <address@hidden>
> Date: Wed, 4 Jul 2018 09:55:52 -0700
> Subject: [PATCH] Use AM_PATH_PYTHON to determine interpreter for gentpl.py
>
> gentpl.py is python2/3-agnostic, but there's no way to cause it
> to be run with any interpreter other than 'python', it's just
> hard-coded into Makefile.common that way. Adjust that to use
> AM_PATH_PYTHON (provided by automake) to find an interpreter
> and run gentpl.py with that instead. This makes grub buildable
> when `python` does not exist (but rather `python3` or `python2`
> or `python2.7`, etc.) Minimum version is set to 2.6 as this is
> the first version with `__future__.print_function` available.
>
> Note, AM_PATH_PYTHON respects the PYTHON environment variable
> and will treat its value as the *only* candidate for a valid
> interpreter if it is set - when PYTHON is set, AM_PATH_PYTHON
> will not try to find any alternative interpreter, it will only
> check whether the interpreter set as the value of PYTHON meets
> the requirements and use it if so or fail if not. This means
> that when using grub's `autogen.sh`, as it too uses the value
> of the PYTHON environment variable (and if it is not set, just
> sets it to 'python') you cannot rely on AM_PATH_PYTHON
> interpreter discovery. If your desired Python interpreter is
> not just 'python', you must set the PYTHON environment variable,
> e.g. 'PYTHON=/usr/local/bin/python3 ./autogen.sh'. The specified
> interpreter will then be used both by autogen.sh itself and by
> the autotools-driven build scripts.
>
> Signed-off-by: Adam Williamson <address@hidden>

Reviewed-by: Daniel Kiper <address@hidden>

Daniel