[gtk-osx] Conditionally set $PYTHON and libxml2's python-install-dir.

[John Ralls <jralls src gnome org>]

commit 9008438da32bd2c3d6092ffe92e52dc336c39c53
Author: John Ralls <jralls ceridwen us>
Date:   Mon Aug 17 12:37:55 2020 -0700

    Conditionally set $PYTHON and libxml2's python-install-dir.
    
    Depending on python3 or meta-gtk-osx-python3 being in the
    modules argument. As noted in the comment this is far from ideal.

 jhbuildrc-gtk-osx | 29 +++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)
---
diff --git a/jhbuildrc-gtk-osx b/jhbuildrc-gtk-osx
index 7892e64..4a6048e 100644
--- a/jhbuildrc-gtk-osx
+++ b/jhbuildrc-gtk-osx
@@ -590,21 +590,26 @@ if not _ran_recursively and _gtk_osx_prompt_prefix:
 # we're not building python because if it tries to install in the
 # virtenv site-packages jhbuild will refuse to install it. Ideally
 # we'd do this only if not building python because if we do then it
-# finds the right place and does the right thing. Unfortunately
-# there's no way to get the config object from the project to find out
-# if we're building python.
-
-# Note that this will break if the built python is a different major + minor
-# version from the virtenv one.
-_python_ver = _popen('bash -c "python -V"')
-if _python_ver:
-    _python_ver = 'python' + _python_ver.split(" ")[1][0:3]
-    _python_install_path = os.path.join(prefix, 'lib',
-                                        _python_ver, 'site-packages')
+# finds the right place and does the right thing.
+
+# Unfortunately there's no way to get the config object from the
+# project to find out if we're building python3. We test the modules
+# list here but that's not really reliable because python3 might be
+# pulled in as a dependency by another module.
+
+# Note that this will break if there's an undetected python3 build and
+# the built python is a different major + minor version from the
+# virtenv one.
+if 'python3' in modules or 'meta-gtk-osx-python3' in modules:
+    os.environ['PYTHON'] = os.path.join(prefix, 'bin', 'python3')
+else:
+    _python_ver = sys.version_info.major * 10 + sys.version_info.minor
+    _python_install_path = os.path.join(prefix, 'lib', _python_ver, 'site-packages')
     append_autogenargs('libxml2',
                        '--with-python-install-dir=' + _python_install_path)
     environ_append('PYTHONPATH', _python_install_path, ':')
-os.environ['PYTHON'] = '/usr/bin/env python3'
+    os.environ['PYTHON'] = sys.executable
+
 # Unset this so we don't mess with the check for not starting
 # recursively.
 os.unsetenv("JHB")