Fix environment variables ignored in subparsers (#350)

configargparse.py

@@ -953,26 +953,41 @@ def __init__(self, *args, **kwargs):
     def _find_insertion_index(self, args):
         """Find the right index to insert config/env var args into the command line.
 
-        Handles three cases: if '--' separator exists, insert before it so
-        injected args don't end up in the positional-only region. If any
-        positional arg uses REMAINDER and there are no optional args on the
-        command line, prepend so REMAINDER doesn't swallow them. Otherwise
-        insert before the first optional arg, or append if none.
+        Inserts before the ``--`` separator if present, before a subparser
+        command so the parent parser sees injected args first, before the
+        first optional arg, or at position 0 when a REMAINDER positional
+        exists. Falls back to appending.
         """
         if "--" in args:
             return args.index("--")
+
+        # Find the first subcommand index, if any
+        subcmd_index = None
+        for action in self._actions:
+            if isinstance(action, argparse._SubParsersAction) and action.choices:
+                for i, arg in enumerate(args):
+                    if arg in action.choices:
+                        subcmd_index = i
+                        break
+                break
+
+        if subcmd_index is not None:
+            return subcmd_index
+
         first_opt = None
         for i, arg in enumerate(args):
             if arg.startswith(tuple(self.prefix_chars)):
                 first_opt = i
                 break
         if first_opt is not None:
             return first_opt
+
         # No optional args on command line
         if any(
             a.is_positional_arg and a.nargs == argparse.REMAINDER for a in self._actions
         ):
             return 0
+
         return len(args)
 
     def parse_args(

tests/test_configargparse.py

@@ -538,6 +538,35 @@ def testSubParsers(self):
         config_file1.close()
         config_file2.close()
 
+    def testSubParserEnvVar(self):
+        """Test that env vars work with subparsers (issue #350)."""
+        parser = configargparse.ArgumentParser(auto_env_var_prefix="")
+        parser.add_argument("--tenant", env_var="TENANT", required=True)
+        subparsers = parser.add_subparsers(dest="action")
+        appliance_parser = subparsers.add_parser("appliance")
+        appliance_parser.add_argument("--token", env_var="TOKEN", required=True)
+
+        # Test parent parser env var via env_vars param
+        ns = parser.parse_args(
+            args=["appliance", "--token", "test-token"],
+            env_vars={"TENANT": "test-tenant"},
+        )
+        self.assertEqual(ns.tenant, "test-tenant")
+        self.assertEqual(ns.token, "test-token")
+        self.assertEqual(ns.action, "appliance")
+
+        # Test both parent and subparser env vars via real os.environ
+        os.environ["TENANT"] = "test-tenant"
+        os.environ["TOKEN"] = "test-token"
+        try:
+            ns = parser.parse_args(args=["appliance"])
+            self.assertEqual(ns.tenant, "test-tenant")
+            self.assertEqual(ns.token, "test-token")
+            self.assertEqual(ns.action, "appliance")
+        finally:
+            del os.environ["TENANT"]
+            del os.environ["TOKEN"]
+
     def testAddArgsErrors(self):
         self.assertRaisesRegex(
             ValueError,