Use importlib when pkg_resources isn't available

pkg_resources is part of setuptools which is no longer included in
python environments by default in python3.12. Importlib.resources can be
used instead and is included in stdlib starting with python3.7.
Unfortunately the ability to extract directories isn't available until
python3.12 in importlib.resources and we rely on this functionality. We
address these problems by trying to use pkg_resources first which should
work for anything python3.11 and older and if not available use
importlib.resources which should work for python3.12 and newer.

Change-Id: I97d9150f92960f0e7ab5efb60523a67d750c7646

glean/install.py

@@ -16,16 +16,36 @@
 import argparse
 import logging
 import os
-import pkg_resources
 import subprocess
 import sys
 
 log = logging.getLogger("glean-install")
 
 
+# Define a proper class based context manager here for maximum cross
+# python compatibility (contextlib.nullcontext is what we want but not
+# available everywhere).
+class NullPathContext(object):
+    def __init__(self, path):
+        self.path = path
+
+    def __enter__(self):
+        return self.path
+
+    def __exit__(self, *args):
+        pass
+
+
 def _find_scripts_dir():
-    p = pkg_resources.resource_filename(__name__, "init")
-    return p
+    try:
+        import pkg_resources
+        p = pkg_resources.resource_filename(__name__, "init")
+        return NullPathContext(p)
+    except ImportError:
+        # This code only works on directories in python3.12 or newer
+        # and init/ is a directory.
+        import importlib.resources as ires
+        return ires.as_file(ires.files(__name__).joinpath('init'))
 
 
 def install(source_file, target_file, mode='0755', replacements=dict()):
@@ -43,15 +63,16 @@ def install(source_file, target_file, mode='0755', replacements=dict()):
 
     log.info("Installing %s -> %s" % (source_file, target_file))
 
-    script_dir = _find_scripts_dir()
+    res_mgr = _find_scripts_dir()
 
-    cmd = ('install -D -g root -o root'
-           ' -m {mode} {source_file} {target_file}').format(
-               source_file=os.path.join(script_dir, source_file),
-               target_file=target_file,
-               mode=mode)
-    log.info(cmd)
-    ret = os.system(cmd)
+    with res_mgr as script_dir:
+        cmd = ('install -D -g root -o root'
+               ' -m {mode} {source_file} {target_file}').format(
+                   source_file=os.path.join(script_dir, source_file),
+                   target_file=target_file,
+                   mode=mode)
+        log.info(cmd)
+        ret = os.system(cmd)
     if ret != 0:
         log.error("Failed to install %s!" % source_file)
         sys.exit(ret)
@@ -91,7 +112,6 @@ def main():
                              "it will be left unconfigured.")
 
     args = parser.parse_args()
-    p = _find_scripts_dir()
     extra_args = '--no-dhcp-fallback' if args.no_dhcp_fallback else ''
 
     if args.quiet:
@@ -99,18 +119,21 @@ def main():
     else:
         logging.basicConfig(level=logging.INFO)
 
-    replacements = {
-        'INTERP': sys.executable,
-        'GLEAN_SCRIPTS_DIR': p,
-        'EXTRA_ARGS': extra_args,
-    }
+    res_mgr = _find_scripts_dir()
+    with res_mgr as script_dir:
+        replacements = {
+            'INTERP': sys.executable,
+            'GLEAN_SCRIPTS_DIR': script_dir,
+            'EXTRA_ARGS': extra_args,
+        }
 
-    # Write the path of the currently executing interpreter into the
-    # scripts dir.  This means glean shell scripts can call the
-    # sibling python-glean and know that it's using the glean we
-    # installed, even in a virtualenv etc.
-    install('python-glean.template', os.path.join(p, 'python-glean'),
-            mode='0755', replacements=replacements)
+        # Write the path of the currently executing interpreter into the
+        # scripts dir.  This means glean shell scripts can call the
+        # sibling python-glean and know that it's using the glean we
+        # installed, even in a virtualenv etc.
+        install('python-glean.template',
+                os.path.join(script_dir, 'python-glean'),
+                mode='0755', replacements=replacements)
 
     # needs to go first because gentoo can have systemd along side openrc
     if os.path.exists('/etc/gentoo-release'):