Deprecate the add_derived_space() API.

Issue #461.

compiler_gym/views/observation.py

@@ -4,6 +4,8 @@
 # LICENSE file in the root directory of this source tree.
 from typing import Callable, Dict, List
 
+from deprecated.sphinx import deprecated
+
 from compiler_gym.service.connection import ServiceError
 from compiler_gym.service.proto import ObservationSpace
 from compiler_gym.util.gym_type_hints import (
@@ -93,6 +95,13 @@ def _add_space(self, space: ObservationSpaceSpec):
         # env.observation.FooBar().
         setattr(self, space.id, lambda: self[space.id])
 
+    @deprecated(
+        version="0.2.1",
+        reason=(
+            "Use the derived_observation_spaces argument to CompilerEnv constructor. "
+            "See <https://github.com/facebookresearch/CompilerGym/issues/461>."
+        ),
+    )
     def add_derived_space(
         self,
         id: str,

tests/llvm/observation_spaces_test.py

@@ -1379,12 +1379,15 @@ def test_is_buildable_observation_space_not_buildable(env: LlvmEnv):
 
 def test_add_derived_space(env: LlvmEnv):
     env.reset()
-    env.observation.add_derived_space(
-        id="IrLen",
-        base_id="Ir",
-        space=Box(name="IrLen", low=0, high=float("inf"), shape=(1,), dtype=int),
-        translate=lambda base: [15],
-    )
+    with pytest.deprecated_call(
+        match="Use the derived_observation_spaces argument to CompilerEnv constructor."
+    ):
+        env.observation.add_derived_space(
+            id="IrLen",
+            base_id="Ir",
+            space=Box(name="IrLen", low=0, high=float("inf"), shape=(1,), dtype=int),
+            translate=lambda base: [15],
+        )
 
     value = env.observation["IrLen"]
     assert isinstance(value, list)