Revert make error when render mode is used without metadata render modes (#216)

gymnasium/envs/registration.py

@@ -624,8 +624,8 @@ def make(
             _kwargs["render_mode"] = mode[: -len("_list")]
             apply_render_collection = True
         else:
-            raise error.UnsupportedMode(
-                f"The environment is being initialised with render_mode={mode} "
+            logger.warn(
+                f"The environment is being initialised with render_mode={mode!r} "
                 f"that is not in the possible render_modes ({render_modes})."
             )
 

tests/envs/test_make.py

@@ -54,10 +54,16 @@ def register_make_testing_envs():
         entry_point="tests.envs.utils_envs:NoHumanNoRGB",
     )
 
+    gym.register(
+        id="test/NoRenderModesMetadata-v0",
+        entry_point="tests.envs.utils_envs:NoRenderModesMetadata",
+    )
+
     yield
 
     del gym.envs.registration.registry["RegisterDuringMakeEnv-v0"]
     del gym.envs.registration.registry["test.ArgumentEnv-v0"]
+    del gym.envs.registration.registry["test/NoRenderModesMetadata-v0"]
     del gym.envs.registration.registry["test/NoHuman-v0"]
     del gym.envs.registration.registry["test/NoHumanOldAPI-v0"]
     del gym.envs.registration.registry["test/NoHumanNoRGB-v0"]
@@ -304,6 +310,15 @@ def test_make_render_mode(register_make_testing_envs):
     ):
         gym.make("CarRacing-v2", render="human")
 
+    # This test checks that a user can create an environment without the metadata including the render mode
+    with pytest.warns(
+        UserWarning,
+        match=re.escape(
+            "\x1b[33mWARN: The environment is being initialised with render_mode='rgb_array' that is not in the possible render_modes ([]).\x1b[0m"
+        ),
+    ):
+        gym.make("test/NoRenderModesMetadata-v0", render_mode="rgb_array")
+
 
 def test_make_kwargs(register_make_testing_envs):
     env = gym.make(

tests/envs/utils_envs.py

@@ -47,3 +47,15 @@ class NoHumanNoRGB(gym.Env):
     def __init__(self, render_mode=None):
         assert render_mode in self.metadata["render_modes"]
         self.render_mode = render_mode
+
+
+class NoRenderModesMetadata(gym.Env):
+    """An environment that has rendering but has not updated the metadata."""
+
+    # metadata: dict[str, Any] = {"render_modes": []}
+
+    def __init__(self, render_mode):
+        self.render_mode = render_mode
+
+        self.observation_space = gym.spaces.Box(low=0, high=1)
+        self.action_space = gym.spaces.Box(low=0, high=1)