Also add support for generic types as converters

Author: chadrik

mypy/plugins/attrs.py

@@ -6,6 +6,7 @@
 from typing_extensions import Final, Literal
 
 import mypy.plugin  # To avoid circular imports.
+from mypy.applytype import apply_generic_arguments
 from mypy.checker import TypeChecker
 from mypy.errorcodes import LITERAL_REQ
 from mypy.expandtype import expand_type
@@ -24,6 +25,7 @@
     Decorator,
     Expression,
     FuncDef,
+    IndexExpr,
     JsonDict,
     LambdaExpr,
     ListExpr,
@@ -35,6 +37,7 @@
     SymbolTableNode,
     TempNode,
     TupleExpr,
+    TypeApplication,
     TypeInfo,
     TypeVarExpr,
     Var,
@@ -664,6 +667,26 @@ def _parse_converter(
             from mypy.checkmember import type_object_type  # To avoid import cycle.
 
             converter_type = type_object_type(converter_expr.node, ctx.api.named_type)
+    elif (
+        isinstance(converter_expr, IndexExpr)
+        and isinstance(converter_expr.analyzed, TypeApplication)
+        and isinstance(converter_expr.base, RefExpr)
+        and isinstance(converter_expr.base.node, TypeInfo)
+    ):
+        # The converter is a generic type.
+        from mypy.checkmember import type_object_type  # To avoid import cycle.
+
+        converter_type = type_object_type(converter_expr.base.node, ctx.api.named_type)
+        if isinstance(converter_type, CallableType):
+            converter_type = apply_generic_arguments(
+                converter_type,
+                converter_expr.analyzed.types,
+                ctx.api.msg.incompatible_typevar_value,
+                converter_type,
+            )
+        else:
+            converter_type = None
+
     if isinstance(converter_expr, LambdaExpr):
         # TODO: should we send a fail if converter_expr.min_args > 1?
         converter_info.init_type = AnyType(TypeOfAny.unannotated)

test-data/unit/check-attr.test

@@ -509,12 +509,9 @@ class Other(Generic[T]):
     def __init__(self, x: T) -> None:
         pass
 
-def other_converter(x: Callable[..., T]) -> Other[Callable[..., T]]:
-    return Other(x)
-
 @attr.s(auto_attribs=True)
 class B(Generic[T]):
-    x: Other[Callable[..., T]] = attr.ib(converter=other_converter)
+    x: Other[Callable[..., T]] = attr.ib(converter=Other[Callable[..., T]])
 
 b1 = B(get_int)
 reveal_type(b1)  # N: Revealed type is "__main__.B[builtins.int]"