Inherit environment from parent process.

colcon_core/package_identification/python.py

@@ -100,11 +100,15 @@ def get_setup_result(setup_py, *, env: Optional[dict]):
     :return: Dictionary of data describing the package.
     :raise: RuntimeError if the setup script encountered an error
     """
+    env_copy = os.environ.copy()
+    if env is not None:
+        env_copy.update(env)
+
     conn_recv, conn_send = multiprocessing.Pipe(duplex=False)
     with conn_send:
         p = multiprocessing.Process(
             target=_get_setup_result_target,
-            args=(os.path.abspath(str(setup_py)), env, conn_send)
+            args=(os.path.abspath(str(setup_py)), env_copy, conn_send),
         )
         p.start()
         p.join()
@@ -118,7 +122,7 @@ def get_setup_result(setup_py, *, env: Optional[dict]):
         .format(setup_py, result_or_exception_string))
 
 
-def _get_setup_result_target(setup_py: str, env: Optional[dict], conn_send):
+def _get_setup_result_target(setup_py: str, env: dict, conn_send):
     """
     Run setup.py in a modified environment.
 
@@ -136,11 +140,8 @@ def _get_setup_result_target(setup_py: str, env: Optional[dict], conn_send):
         # need to be in setup.py's parent dir to detect any setup.cfg
         os.chdir(os.path.dirname(setup_py))
 
-        # don't worry - the environments of functions called with
-        # subprocess.Process don't leak into each other
         os.environ.clear()
-        if env is not None:
-            os.environ.update(env)
+        os.environ.update(env)
 
         result = distutils.core.run_setup(
             str(setup_py), ('--dry-run',), stop_after='config')