Closes #224

Author: sobolevn

classes/contrib/mypy/validation/validate_associated_type.py

@@ -1,5 +1,5 @@
 from mypy.plugin import MethodContext
-from mypy.types import Instance
+from mypy.types import CallableType, Instance
 from typing_extensions import Final
 
 #: Fullname of the `AssociatedType` class.
@@ -14,6 +14,11 @@
     'AssociatedType "{0}" must not be reused, originally associated with "{1}"'
 )
 
+_GENERIC_MISSMATCH_MSG: Final = (
+    'Generic type "{0}" with "{1}" type arguments does not match ' +
+    'generic instance declaration "{2}" with "{3}" type arguments'
+)
+
 
 def check_type(
     associated_type: Instance,
@@ -30,8 +35,8 @@ def check_type(
     return all([
         _check_base_class(associated_type, ctx),
         _check_type_reuse(associated_type, typeclass, ctx),
+        _check_generics(associated_type, typeclass, ctx),
         # TODO: check_body
-        # TODO: check_generics_match_definition
         # TODO: we also need to check type vars used on definition:
         # no values, no bounds (?)
     ])
@@ -78,3 +83,27 @@ def _check_type_reuse(
 
     metadata['typeclass'] = fullname
     return has_reuse
+
+
+def _check_generics(
+    associated_type: Instance,
+    typeclass: Instance,
+    ctx: MethodContext,
+) -> bool:
+    assert isinstance(typeclass.args[1], CallableType)
+    instance_decl = typeclass.args[1].arg_types[0]
+    if not isinstance(instance_decl, Instance):
+        return True
+
+    if len(instance_decl.args) != len(associated_type.type.type_vars):
+        ctx.api.fail(
+            _GENERIC_MISSMATCH_MSG.format(
+                associated_type.type.fullname,
+                len(associated_type.type.type_vars),
+                instance_decl,
+                len(instance_decl.args),
+            ),
+            ctx.context,
+        )
+        return False
+    return True

typesafety/test_associated_type/test_validation/test_generic_missmatch.yml

@@ -0,0 +1,17 @@
+- case: typeclass_definied_by_wrong_type
+  disable_cache: false
+  main: |
+    from typing import List, TypeVar
+
+    from classes import AssociatedType, Supports, typeclass
+
+    X = TypeVar('X')
+
+    class Compare(AssociatedType):
+        ...
+
+    @typeclass(Compare)
+    def compare(instance: List[X]) -> X:
+        ...
+  out: |
+    main:10: error: Generic type "main.Compare" with "0" type arguments does not match generic instance declaration "builtins.list[X`-1]" with "1" type arguments