python module: stop using distutils schemes on sufficiently new Debian

Since 3.10.3, Debian finally started patching sysconfig with custom
paths, instead of just distutils. This means we can now go use that
instead. It reduces our reliance on the deprecated distutils module.

Partial fix for #7702

mesonbuild/scripts/python_info.py

@@ -13,7 +13,6 @@ if sys.path[0].endswith('scripts'):
     del sys.path[0]
 
 import json, os, sysconfig
-import distutils.command.install
 
 def get_distutils_paths(scheme=None, prefix=None):
     import distutils.dist
@@ -37,15 +36,32 @@ def get_distutils_paths(scheme=None, prefix=None):
 # default scheme to a custom one pointing to /usr/local and replacing
 # site-packages with dist-packages.
 # See https://github.com/mesonbuild/meson/issues/8739.
-# XXX: We should be using sysconfig, but Debian only patches distutils.
+#
+# We should be using sysconfig, but before 3.10.3, Debian only patches distutils.
+# So we may end up falling back.
 
-if 'deb_system' in distutils.command.install.INSTALL_SCHEMES:
+def get_install_paths():
+    if sys.version_info >= (3, 10):
+        scheme = sysconfig.get_default_scheme()
+    else:
+        scheme = sysconfig._get_default_scheme()
+
+    if sys.version_info >= (3, 10, 3):
+        if 'deb_system' in sysconfig.get_scheme_names():
+            scheme = 'deb_system'
+    else:
+        import distutils.command.install
+        if 'deb_system' in distutils.command.install.INSTALL_SCHEMES:
             paths = get_distutils_paths(scheme='deb_system')
             install_paths = get_distutils_paths(scheme='deb_system', prefix='')
-else:
+            return paths, install_paths
-    paths = sysconfig.get_paths()
+
+    paths = sysconfig.get_paths(scheme=scheme)
     empty_vars = {'base': '', 'platbase': '', 'installed_base': ''}
-    install_paths = sysconfig.get_paths(vars=empty_vars)
+    install_paths = sysconfig.get_paths(scheme=scheme, vars=empty_vars)
+    return paths, install_paths
+
+paths, install_paths = get_install_paths()
 
 def links_against_libpython():
     from distutils.core import Distribution, Extension