Fix environment variable parsing for store_true/store_false actions (#858)

Author: mauvilsa

CHANGELOG.rst

@@ -35,6 +35,9 @@ Fixed
 - ``--help`` no longer fails with ``IndexError`` for options without explicit
   help text while keeping ``argparse`` compatibility for ``help=None`` (`#854
   <https://github.com/omni-us/jsonargparse/pull/854>`__).
+- ``store_true`` and ``store_false`` arguments now parse boolean environment
+  variable values as ``true``/``false`` and raise a clear error for invalid
+  values (`#858 <https://github.com/omni-us/jsonargparse/pull/858>`__).
 
 Changed
 ^^^^^^^

jsonargparse/_core.py

@@ -531,7 +531,16 @@ def _load_env_vars(self, env: Union[dict[str, str], os._Environ], defaults: bool
             env_var = get_env_var(self, action)
             if env_var in env and not isinstance(action, (ActionConfigFile, _ActionSubCommands)):
                 env_val = env[env_var]
-                if _is_action_value_list(action):
+                if isinstance(action, (argparse._StoreTrueAction, argparse._StoreFalseAction)):
+                    if env_val == "true":
+                        env_val = True
+                    elif env_val == "false":
+                        env_val = False
+                    else:
+                        raise argparse.ArgumentError(
+                            action, f"Invalid boolean value for environment variable {env_var}: {env_val}"
+                        )
+                elif _is_action_value_list(action):
                     try:
                         list_env_val = load_value(env_val)
                         env_val = list_env_val if isinstance(list_env_val, list) else [env_val]

jsonargparse_tests/test_core.py

@@ -281,6 +281,22 @@ def test_parse_env_positional_nargs_plus(parser):
     assert parser.parse_env({"APP_REQ": '[""","""]'}).req == ['[""","""]']
 
 
+def test_parse_env_store_true_false(parser):
+    parser.env_prefix = "app"
+    parser.add_argument("--flag_true", action="store_true")
+    parser.add_argument("--flag_false", action="store_false")
+    assert parser.parse_args([]) == Namespace(flag_true=False, flag_false=True)
+    assert parser.get_defaults() == Namespace(flag_true=False, flag_false=True)
+    assert parser.parse_env({"APP_FLAG_TRUE": "true"}).flag_true is True
+    assert parser.parse_env({"APP_FLAG_TRUE": "false"}).flag_true is False
+    assert parser.parse_env({"APP_FLAG_FALSE": "false"}).flag_false is False
+    assert parser.parse_env({"APP_FLAG_FALSE": "true"}).flag_false is True
+    with pytest.raises(ArgumentError, match="Invalid boolean value for environment variable APP_FLAG_TRUE: not_bool"):
+        parser.parse_env({"APP_FLAG_TRUE": "not_bool"})
+    with pytest.raises(ArgumentError, match="Invalid boolean value for environment variable APP_FLAG_FALSE: not_bool"):
+        parser.parse_env({"APP_FLAG_FALSE": "not_bool"})
+
+
 def test_default_env_property():
     parser = ArgumentParser()
     assert False is parser.default_env