Fix KeyError in get_components() when the smallest set is found last

esper/__init__.py

@@ -493,6 +493,7 @@ def _get_components(*component_types: type[_C]) -> _Iterable[tuple[int, tuple[_C
     comp_db = _components
 
     min_set = None
+    min_type = None
     min_size = inf
     other_types = []
 
@@ -502,10 +503,11 @@ def _get_components(*component_types: type[_C]) -> _Iterable[tuple[int, tuple[_C
             return
         set_size = len(comp_set)
         if set_size < min_size:
-            if min_set is not None:
-                other_types.append(component_types[len(other_types)])
+            if min_type is not None:
+                other_types.append(min_type)
             min_size = set_size
             min_set = comp_set
+            min_type = ct
         else:
             other_types.append(ct)
 

tests/test_world.py

@@ -154,6 +154,32 @@ def test_get_three_components():
         assert isinstance(e, ComponentE)
 
 
+def test_get_components_smallest_set_missing_component():
+    # Regression test: _get_components scans for the smallest component set
+    # first. When a type is set aside before a new smallest set is found, the
+    # previously-smallest type must be the one moved aside. Component sizes are
+    # arranged so ComponentB is set aside, then ComponentC becomes the new
+    # smallest -- ComponentA (the prior smallest) must not be dropped, otherwise
+    # an entity that matches on the remaining types but lacks ComponentA raises
+    # a KeyError while building the result tuple.
+    esper.create_entity(ComponentB(), ComponentC())    # matches B and C, not A
+    esper.create_entity(ComponentA())
+    esper.create_entity(ComponentA())
+    esper.create_entity(ComponentB())
+    esper.create_entity(ComponentB())
+    entity_all = esper.create_entity(ComponentA(), ComponentB(), ComponentC())
+
+    # sizes: A=3, B=4, C=2 -> C is discovered as the smallest set last
+    result = esper.get_components(ComponentA, ComponentB, ComponentC)
+
+    assert len(result) == 1
+    ent, (a, b, c) = result[0]
+    assert ent == entity_all
+    assert isinstance(a, ComponentA)
+    assert isinstance(b, ComponentB)
+    assert isinstance(c, ComponentC)
+
+
 def test_try_component():
     entity1 = esper.create_entity(ComponentA(), ComponentB())