fix(annots): singleton-ness should be inerited

Author: kszucs

koerce/annots.py

@@ -723,7 +723,7 @@ def __new__(
         initable=None,
         hashable=None,
         immutable=None,
-        singleton=False,
+        singleton=None,
         allow_coercion=True,
         **kwargs,
     ):
@@ -747,6 +747,7 @@ def __new__(
             is_initable |= spec.initable
             is_hashable |= spec.hashable
             is_immutable |= spec.immutable
+            is_singleton |= spec.singleton
             signatures.append(spec.signature)
             attributes.update(spec.attributes)
 

koerce/tests/test_annots.py

@@ -2209,6 +2209,10 @@ class DataType(Annotable, singleton=True):
     nullable: bool = True
 
 
+class PrimitiveType(DataType):
+    pass
+
+
 def test_singleton_basics():
     one = OneAndOnly()
     only = OneAndOnly()
@@ -2219,6 +2223,15 @@ def test_singleton_basics():
     assert OneAndOnly.__instances__[key] is one
 
 
+def test_singleton_child_is_singleton():
+    prim1 = PrimitiveType()
+    prim2 = PrimitiveType()
+    assert prim1 is prim2
+    assert len(PrimitiveType.__instances__) == 1
+    assert PrimitiveType.__spec__.singleton is True
+    assert PrimitiveType.__instances__ is DataType.__instances__
+
+
 def test_singleton_lifetime() -> None:
     one = OneAndOnly()
     assert len(OneAndOnly.__instances__) == 1