feat: addressing feedback on tests and key-presence

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: felipemontoya

docs/decisions/0001-service-entry-points.rst

@@ -88,7 +88,12 @@ workbench, third-party runtimes that don't override ``service()``) for a
 single small change, and gives a hard guarantee: *runtime-provided services
 always shadow plugin-provided ones*.  A pip package cannot replace or
 intercept ``user``, ``field-data``, ``i18n``, or any other service the host
-application provides deliberately.  Runtimes that override ``service()``
+application provides deliberately.  "Provided" is decided by key presence in
+``_services``, not truthiness: runtimes use an explicit ``None`` to mean
+"this service exists but is disabled here" — the Open edX LMS maps
+``completion`` to ``None`` for anonymous users, and this library's own test
+suite passes ``services={'i18n': None}`` — and a plugin must not resurrect a
+service the runtime switched off.  Runtimes that override ``service()``
 entirely keep that freedom — the fallback only exists in the default path
 they opt into by calling ``super().service()``.
 

docs/index.rst

@@ -22,5 +22,6 @@ in depth and guides developers through the process of creating an XBlock.
     plugins
     exceptions
     fragments
+    decisions/0001-service-entry-points
     xblock-tutorial/index
     xblock-utils/index

xblock/runtime.py

@@ -454,7 +454,9 @@ class under the ``xblock.service.v1`` entry-point group::
 
     Services that the runtime itself provides (via the ``services`` constructor
     argument or a ``service()`` override) always take precedence; entry points
-    are only consulted when the runtime does not offer the requested service.
+    are only consulted when the runtime has no entry for the requested name.
+    A runtime entry explicitly set to None counts as provided (it means the
+    runtime deliberately disabled the service) and is never overridden.
 
     The provider class is instantiated per service request as
     ``provider_class(runtime=runtime, xblock=block)``, mirroring
@@ -1132,8 +1134,9 @@ def service(self, block, service_name):
         declaration = block.service_declaration(service_name)
         if declaration is None:
             raise NoSuchServiceError(f"Service {service_name!r} was not requested.")
-        service = self._services.get(service_name)
-        if service is None:
+        if service_name in self._services:
+            service = self._services[service_name]
+        else:
             service = self._load_service_from_entry_point(block, service_name)
         if service is None and declaration == "need":
             raise NoSuchServiceError(f"Service {service_name!r} is not available.")

xblock/test/test_plugin_services.py

@@ -63,6 +63,22 @@ def test_runtime_service_shadows_plugin_service():
     assert block.runtime.service(block, 'ai_extensions') is sentinel
 
 
+@ServiceProvider.register_temp_plugin(
+    DummyAIService, identifier='ai_extensions', group='xblock.service.v1',
+)
+def test_runtime_none_service_disables_plugin_service():
+    wants_block = make_block(
+        WantsAIBlock, runtime=TestRuntime(services={'ai_extensions': None}),
+    )
+    assert wants_block.runtime.service(wants_block, 'ai_extensions') is None
+
+    needs_block = make_block(
+        NeedsAIBlock, runtime=TestRuntime(services={'ai_extensions': None}),
+    )
+    with pytest.raises(NoSuchServiceError):
+        needs_block.runtime.service(needs_block, 'ai_extensions')
+
+
 def test_missing_plugin_service_wanted_returns_none():
     block = make_block(WantsAIBlock)
     assert block.runtime.service(block, 'ai_extensions') is None