*: Replace imp with importlib on py3

@Qubitium notes (https://github.com/navytux/pygolang/issues/1):

    Python 3.12 no longer support the imp module (fully deprecated) with note to use importlib as replacement.

    Please support python 3.12 by migrating from imp code to importlib. Thanks.

and indeed, even trying to build pygolang fails on py3.12:

    (py312.venv) kirr@deca:~/src/tools/go/pygolang-master$ python setup.py build_ext -i
    Traceback (most recent call last):
      File "/home/kirr/src/tools/go/pygolang-master/setup.py", line 40, in <module>
        exec(readfile('trun'), trun)
      File "<string>", line 41, in <module>
    ModuleNotFoundError: No module named 'imp'

-> Rework the code to use importlib instead, but keep using imp on py2
where there is practically no importlib functionality.

/reported-by @Qubitium (github)
/reviewed-by @jerome
/reviewed-on !23

golang/_gopath.py

-# Copyright (C) 2018-2019  Nexedi SA and Contributors.
+# Copyright (C) 2018-2024  Nexedi SA and Contributors.
 #                          Kirill Smelkov <kirr@nexedi.com>
 #
 # This program is free software: you can Use, Study, Modify and Redistribute
@@ -34,11 +34,7 @@ from __future__ import print_function, absolute_import
 
 import os, os.path
 import sys
-
-import warnings
-with warnings.catch_warnings():
-    warnings.simplefilter('ignore', DeprecationWarning)
-    import imp
+import six
 
 # _gopathv returns $GOPATH vector.
 def _gopathv():
@@ -51,11 +47,25 @@ def _gopathv():
 
 # gimport imports python module or package from fully-qualified module name under $GOPATH.
 def gimport(name):
-    imp.acquire_lock()
+    _gimport_lock()
     try:
         return _gimport(name)
     finally:
-        imp.release_lock()
+        _gimport_unlock()
+
+# on py2 there is global import lock
+# on py3 we need to organize our own gimport synchronization
+if six.PY2:
+    import imp
+    _gimport_lock   = imp.acquire_lock
+    _gimport_unlock = imp.release_lock
+else:
+    from importlib import machinery as imp_machinery
+    from importlib import util      as imp_util
+    from golang import sync
+    _gimport_mu = sync.Mutex()
+    _gimport_lock   = _gimport_mu.lock
+    _gimport_unlock = _gimport_mu.unlock
 
 def _gimport(name):
     # we will register imported module into sys.modules with adjusted path.
@@ -93,4 +103,16 @@ def _gimport(name):
 
 
     # https://stackoverflow.com/a/67692
+    return _imp_load_source(modname, modpath)
+
+def _imp_load_source(modname, modpath):
+    if six.PY2:
         return imp.load_source(modname, modpath)
+
+    # https://docs.python.org/3/whatsnew/3.12.html#imp
+    loader = imp_machinery.SourceFileLoader(modname, modpath)
+    spec   = imp_util.spec_from_file_location(modname, modpath, loader=loader)
+    mod    = imp_util.module_from_spec(spec)
+    sys.modules[modname] = mod
+    loader.exec_module(mod)
+    return mod

trun

 #!/usr/bin/env python
-# Copyright (C) 2019-2020  Nexedi SA and Contributors.
+# Copyright (C) 2019-2024  Nexedi SA and Contributors.
 #                          Kirill Smelkov <kirr@nexedi.com>
 #
 # This program is free software: you can Use, Study, Modify and Redistribute
@@ -34,12 +34,13 @@ trun cares to run python with LD_PRELOAD set appropriately to /path/to/libtsan.s
 
 from __future__ import print_function, absolute_import
 
-import os, sys, re, subprocess, pkgutil
-import warnings
-with warnings.catch_warnings():
-    warnings.simplefilter('ignore', DeprecationWarning)
-    import imp
+import os, sys, re, subprocess, types
 PY3 = (bytes is not str)
+if PY3:
+    from importlib import machinery as imp_machinery
+else:
+    import imp, pkgutil
+
 
 # env_prepend prepends value to ${name} environment variable.
 #
@@ -64,10 +65,13 @@ def grep1(pattern, text): # -> re.Match|None
 # to import e.g. golang.pyx.build, or locate golang._golang, without built/working golang.
 def ximport_empty_golangmod():
     assert 'golang' not in sys.modules
-    golang = imp.new_module('golang')
+    golang = types.ModuleType('golang')
     golang.__package__ = 'golang'
     golang.__path__    = ['golang']
     golang.__file__    = 'golang/__init__.py'
+    if PY3:
+        golang.__loader__ = imp_machinery.SourceFileLoader('golang', 'golang/__init__.py')
+    else:
         golang.__loader__ = pkgutil.ImpLoader('golang', None, 'golang/__init__.py',
                                               [None, None, imp.PY_SOURCE])
     sys.modules['golang'] = golang