Re: [PATCH v3 1/8] meson: stop discovering native version of Python

[Junio C Hamano <gitster@pobox.com>]

Patrick Steinhardt <ps@pks.im> writes:

> When Python features are enabled we search both for a native and
> non-native version of Python. This is wrong though: we don't use Python
> in our build process, so there is no need to search for it in the first
> place.
>
> There is one location where we use the native version of Python, namely
> when deciding whether or not we want to wire up git-p4(1). This check is
> invalid though, as we shouldn't check for the build host to have Python,
> but for the target host.
>
> Fix this invalid check to use the non-native version of Python and stop
> searching for a native version of Python altogether.
>
> Signed-off-by: Patrick Steinhardt <ps@pks.im>
> ---
>  meson.build | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)

The above explains the reasoning very nicely.

> -python = import('python').find_installation('python3', required: get_option('python'))
> -target_python = find_program('python3', native: false, required: python.found())
> -if python.found()
> +# Python is not used for our build system, but exclusively for git-p4.
> +# Consequently we only need to determine whether Python is available for the
> +# build target.
> +target_python = find_program('python3', native: false, required: get_option('python'))
> +if target_python.found()
>    build_options_config.set('NO_PYTHON', '')
>  else
>    libgit_c_args += '-DNO_PYTHON'

We ask explicitly for Python 3 here.

Does find_program() have some magic to deal with installations where
Python3 is simply called /usr/bin/python (and worse yet, not as a
symbolic link to /usr/bin/python3)?

I found

    "Since 0.50.0 if the "python3" program is requested and it is
    not found in the system, Meson will return its current
    interpreter",

which I suspect refers to the path to python3 used during the build
and is not what we want, at

https://mesonbuild.com/Reference-manual_functions.html#find_program

which got me a bit worried.

Perhaps everybody with Python3 has it at /usr/bin/python3 these
days, and my worries are unfounded? ;-)

Thanks.


> @@ -1979,7 +1981,7 @@ if perl_features_enabled
>    subdir('perl')
>  endif
>  
> -if python.found()
> +if target_python.found()
>    scripts_python = [
>      'git-p4.py'
>    ]
> @@ -2202,7 +2204,7 @@ summary({
>    'iconv': iconv.found(),
>    'pcre2': pcre2.found(),
>    'perl': perl_features_enabled,
> -  'python': python.found(),
> +  'python': target_python.found(),
>  }, section: 'Auto-detected features')
>  
>  summary({