Add a compatibility layer for the new registration mechanism (#2818)

* Added some compat methods

* Some missing methods

* Update registration.py

* Style fix

gym/envs/registration.py

@@ -12,6 +12,7 @@ from dataclasses import dataclass, field
 from typing import (
     Any,
     Callable,
+    Iterable,
     Optional,
     Sequence,
     SupportsFloat,
@@ -337,8 +338,55 @@ def make(id: EnvSpec, **kwargs) -> Env: ...
 # fmt: on
 
 
+class EnvRegistry(dict):
+    """A glorified dictionary for compatibility reasons.
+    Turns out that some existing code directly used the old `EnvRegistry` code,
+    even though the intended API was just `register` and `make`. This reimplements some
+    of the old methods, so that e.g. pybullet environments will still work.
+    Ideally, nobody should ever use these methods, and they will be removed soon."""
+
+    # TODO: remove this at 1.0
+
+    def make(self, path: str, **kwargs) -> Env:
+        logger.warn(
+            "The `registry.make` method is deprecated. Please use `gym.make` instead."
+        )
+        return make(path, **kwargs)
+
+    def register(self, id: str, **kwargs) -> None:
+        logger.warn(
+            "The `registry.register` method is deprecated. Please use `gym.register` instead."
+        )
+        return register(id, **kwargs)
+
+    def all(self) -> Iterable[EnvSpec]:
+        logger.warn(
+            "The `registry.all` method is deprecated. Please use `registry.values` instead."
+        )
+        return self.values()
+
+    def spec(self, path: str) -> EnvSpec:
+        logger.warn(
+            "The `registry.spec` method is deprecated. Please use `gym.spec` instead."
+        )
+        return spec(path)
+
+    def namespace(self, ns: str):
+        logger.warn(
+            "The `registry.namespace` method is deprecated. Please use `gym.namespace` instead."
+        )
+        return namespace(ns)
+
+    @property
+    def env_specs(self):
+        logger.warn(
+            "The `registry.env_specs` property along with `EnvSpecTree` is deprecated. Please use `registry` directly as a dictionary instead."
+        )
+        return self
+
+
 # Global registry of environments. Meant to be accessed through `register` and `make`
-registry: dict[str, EnvSpec] = dict()
+registry: dict[str, EnvSpec] = EnvRegistry()
 current_namespace: Optional[str] = None