Python 3 can't be found on NetBSD 8.0 or DragonFlyBSD 5.2

[nomis]

meson.build

...
python3 = import('python').find_installation('python3')
...

NetBSD 8.0

Version: 0.48.1
...
meson.build:79:0: ERROR:  python3 not found

$ echo $PATH
/home/simon/bin:/bin:/sbin:/usr/bin:/usr/sbin:/usr/X11R7/bin:/usr/pkg/bin:/usr/pkg/sbin:/usr/games:/usr/local/bin:/usr/local/sbin:/home/simon/.local/bin
$ which python3
$ which python3.6
/usr/pkg/bin/python3.6

DragonflyBSD 5.2

Version: 0.46.1
...
meson.build:79:0: ERROR:  python3 not found

$ echo $PATH
/sbin:/bin:/usr/sbin:/usr/bin:/usr/games:/usr/local/sbin:/usr/local/bin:/usr/pkg/sbin:/usr/pkg/bin:/home/simon/bin:/home/simon/.local/bin
$ which python3
$ which python3.6
/usr/local/bin/python3.6

[nomis]

It seems I'm confusing find_program() with pymod.find_installation()...

[nomis]

I've reopened this because pymod.find_installation() can't find python3 either.

The standard Python 3 package on these systems does not provide a python3 command.

[jpakkane]

Does this work:

python3 = import('python').find_installation()

[nomis]

Yes that works... I think I'll use that instead

[jtojnar]

IMHO, the fact that Meson uses Python 3 should be an implementation detail. Ideally, we would try to find any python3.x executable on PATH on BSDs but something like this might cover most use cases as it will make find_installation('python3') fall back to the same value as find_installation():

--- a/mesonbuild/modules/python.py
+++ b/mesonbuild/modules/python.py
@@ -534,6 +534,11 @@ class PythonModule(ExtensionModule):
             if not python.found() and name_or_path in ['python2', 'python3']:
                 python = ExternalProgram('python', silent=True)
 
+            # Even more dire effort, Meson must be using python3,
+            # even though it might be a minimal bootstrapping instance.
+            if not python.found() and name_or_path == 'python3':
+                python = ExternalProgram('python3', mesonlib.python_command, silent=True)
+
         if python.found() and want_modules:
             for mod in want_modules:
                 p, out, err = mesonlib.Popen_safe(

I am definitely against find_installation without arguments and would like to deprecate it: #7415

[arrowd]

This is still a problem for FreeBSD too:

python3 = import('python').find_installation('python3')

# which python3.7
/usr/local/bin/python3.7

Program python found: NO

meson.build:47:0: ERROR: python3 not found

[eli-schwartz]

This is still a FreeBSD bug, meson.build asked for the $PATH lookup key command -v python3 and you're bringing evidence that command -v python3.7 exists, which is an entirely different lookup key.

Moreover, it's conceptually broken because FreeBSD is directly refusing to comply with https://peps.python.org/pep-0394/ and as a result probing does not work, whether that probing is done by Meson or any other software.

You are of course welcome to use https://mesonbuild.com/Machine-files.html to override the locations of programs, for example by instructing meson to find the python3 program at /usr/local/bin/python3.7 - this is very similar to how with most autotools build systems you would override the path of python by setting the $PYTHON environment variable in the ./configure command line.

Meson could in theory fall back again to the python it knows exists due to having it as sys.executable, but this then makes people who have Meson installed with python 3.7 but want to build software for python 3.9, to be unhappy when it gets built for 3.7 instead...

[arrowd]

This is still a FreeBSD bug, meson.build asked for the $PATH lookup key command -v python3 and you're bringing evidence that command -v python3.7 exists, which is an entirely different lookup key.

Ah, I see. I had an expectation that find_installation('python3') means "find any Python 3 installation", not literally "find an executable named python3".

Moreover, it's conceptually broken because FreeBSD is directly refusing to comply with https://peps.python.org/pep-0394/ and as a result probing does not work, whether that probing is done by Meson or any other software.

It seems you're right. I'll bring this up on our side, thanks.

You are of course welcome to use https://mesonbuild.com/Machine-files.html to override the locations of programs, for example by instructing meson to find the python3 program at /usr/local/bin/python3.7 - this is very similar to how with most autotools build systems you would override the path of python by setting the $PYTHON environment variable in the ./configure command line.

Yep, this sounds like a most sane workaround for now, I'll try it.

Thanks for your input!