Closes #221

Author: sobolevn

classes/contrib/mypy/validation/validate_associated_type.py

@@ -7,6 +7,7 @@
 _ASSOCIATED_TYPE_FULLNAME: Final = 'classes._typeclass.AssociatedType'
 
 # Messages:
+
 _WRONG_SUBCLASS_MSG: Final = (
     'Single direct subclass of "{0}" required; got "{1}"'
 )
@@ -20,6 +21,8 @@
     'generic instance declaration "{2}" with "{3}" type arguments'
 )
 
+_REDUNDANT_BODY_MSG: Final = 'Associated types must not have bodies'
+
 
 def check_type(
     associated_type: Instance,
@@ -35,9 +38,9 @@ def check_type(
     """
     return all([
         _check_base_class(associated_type, ctx),
+        _check_body(associated_type, ctx),
         _check_type_reuse(associated_type, typeclass, ctx),
         _check_generics(associated_type, typeclass, ctx),
-        # TODO: check_body
         # TODO: we also need to check type vars used on definition:
         # no values, no bounds (?)
     ])
@@ -63,6 +66,16 @@ def _check_base_class(
     return has_correct_base
 
 
+def _check_body(
+    associated_type: Instance,
+    ctx: MethodContext,
+) -> bool:
+    if associated_type.type.names:
+        ctx.api.fail(_REDUNDANT_BODY_MSG, ctx.context)
+        return False
+    return True
+
+
 def _check_type_reuse(
     associated_type: Instance,
     typeclass: Instance,

typesafety/test_associated_type/test_validation/test_bodies.yml

@@ -0,0 +1,29 @@
+- case: associated_type_with_method
+  disable_cache: false
+  main: |
+    from classes import AssociatedType, typeclass
+
+    class Compare(AssociatedType):
+        def some(self):
+            ...
+
+    @typeclass(Compare)
+    def compare(instance) -> int:
+        ...
+  out: |
+    main:7: error: Associated types must not have bodies
+
+
+- case: associated_type_with_attr
+  disable_cache: false
+  main: |
+    from classes import AssociatedType, typeclass
+
+    class Compare(AssociatedType):
+        x = 1
+
+    @typeclass(Compare)
+    def compare(instance) -> int:
+        ...
+  out: |
+    main:6: error: Associated types must not have bodies