Fix scene context detection to return None by default

CHANGELOG.md

@@ -95,7 +95,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * Fixed error in `circle_to_compas` from Rhino.
 * Fixed Rhino to Rhino brep serialization.
 * Upated `compas.scene.Group.add()` to pass on group kwargs as default for child items.
-* Fixed bug in context detection, which wrongly defaults to `Viewer` instead of `None`.
+* Fixed `compas.scene.context.detect_current_context()` to return `None` by default instead of randomly selecting the first registered context, ensuring predictable behavior when creating scene objects without an explicit context.
 * Fixed bug in calculation of `compas.geometry.Polyhedron.edges` if geometry is computed using numpy.
 * Fixed bug in `Grpah.from_pointcloud` which uses degree parameter wrongly.
 

src/compas/scene/context.py

@@ -94,15 +94,15 @@ def register(item_type, sceneobject_type, context=None):
 
 def detect_current_context():
     """Chooses an appropriate context depending on available contexts and open instances. with the following priority:
-    1. Viewer
-    2. Plotter
-    3. Rhino / GH - checked explicitly since SceneObjects for both get registered when code is run from either.
-    4. Other
+    1. Rhino / GH - checked explicitly since SceneObjects for both get registered when code is run from either.
+    2. Blender
+    3. None (default) - returns the base scene object type
 
     Returns
     -------
-    str
-        Name of an available context, used as key in :attr:`SceneObject.ITEM_SCENEOBJECT`
+    str or None
+        Name of an available context, used as key in :attr:`SceneObject.ITEM_SCENEOBJECT`,
+        or None if no explicit context is detected.
 
     """
 
@@ -112,9 +112,6 @@ def detect_current_context():
         return "Rhino"
     if compas.is_blender():
         return "Blender"
-    # other_contexts = [v for v in ITEM_SCENEOBJECT.keys()]
-    # if other_contexts:
-    #     return other_contexts[0]
 
     return None
 

tests/compas/scene/test_scene.py

@@ -66,21 +66,47 @@ def test_get_sceneobject_cls_with_out_of_order_registration():
         sceneobject = SceneObject(item, context="fake")
         assert isinstance(sceneobject, FakeSubSceneObject)
 
-        def test_sceneobject_auto_context_discovery(mocker):
-            register_fake_context()
+    def test_sceneobject_requires_explicit_context_when_registered(mocker):
+        """Test that when a context is registered, it must be explicitly specified."""
+        register_fake_context()
 
-            item = FakeItem()
+        item = FakeItem()
+        # Without explicit context, should fail since context is None and FakeItem is not registered for None
+        with pytest.raises(SceneObjectNotRegisteredError):
             sceneobject = SceneObject(item)
 
-            assert isinstance(sceneobject, FakeSceneObject)
+        # With explicit context, should work
+        sceneobject = SceneObject(item, context="fake")
+        assert isinstance(sceneobject, FakeSceneObject)
+
+    def test_sceneobject_auto_context_discovery_no_context(mocker):
+        mocker.patch("compas.scene.context.compas.is_grasshopper", return_value=False)
+        mocker.patch("compas.scene.context.compas.is_rhino", return_value=False)
+        mocker.patch("compas.scene.context.compas.is_blender", return_value=False)
+
+        with pytest.raises(SceneObjectNotRegisteredError):
+            item = FakeSubItem()
+            _ = SceneObject(item)
 
-        def test_sceneobject_auto_context_discovery_no_context(mocker):
-            mocker.patch("compas.scene.context.compas.is_grasshopper", return_value=False)
-            mocker.patch("compas.scene.context.compas.is_rhino", return_value=False)
+    def test_detect_current_context_returns_none_by_default(mocker):
+        """Test that detect_current_context returns None when no explicit context is detected."""
+        from compas.scene.context import detect_current_context
 
-            with pytest.raises(SceneObjectNotRegisteredError):
-                item = FakeSubItem()
-                _ = SceneObject(item)
+        mocker.patch("compas.scene.context.compas.is_grasshopper", return_value=False)
+        mocker.patch("compas.scene.context.compas.is_rhino", return_value=False)
+        mocker.patch("compas.scene.context.compas.is_blender", return_value=False)
+
+        context = detect_current_context()
+        assert context is None
+
+    def test_scene_default_context_is_none(mocker):
+        """Test that Scene has context=None when no explicit context is detected."""
+        mocker.patch("compas.scene.context.compas.is_grasshopper", return_value=False)
+        mocker.patch("compas.scene.context.compas.is_rhino", return_value=False)
+        mocker.patch("compas.scene.context.compas.is_blender", return_value=False)
+
+        scene = Scene()
+        assert scene.context is None
 
     def test_sceneobject_transform():
         scene = Scene()