Type-check class keyword in an __init_subclass__() call (#7452)

gantsevdenis · ilevkivskyi · commit 1f1153829805 · 2019-09-21T07:36:35.000-07:00
Fixes #7190
diff --git a/mypy/checker.py b/mypy/checker.py
@@ -26,7 +26,7 @@
     ARG_POS, ARG_STAR, LITERAL_TYPE, MDEF, GDEF,
     CONTRAVARIANT, COVARIANT, INVARIANT, TypeVarExpr, AssignmentExpr,
     is_final_node,
-)
+    ARG_NAMED)
 from mypy import nodes
 from mypy.literals import literal, literal_hash
 from mypy.typeanal import has_any_from_unimported_type, check_for_explicit_any
@@ -1675,6 +1675,7 @@ def visit_class_def(self, defn: ClassDef) -> None:
                 with self.scope.push_class(defn.info):
                     self.accept(defn.defs)
             self.binder = old_binder
+            self.check_init_subclass(defn)
             if not defn.has_incompatible_baseclass:
                 # Otherwise we've already found errors; more errors are not useful
                 self.check_multiple_inheritance(typ)
@@ -1704,6 +1705,50 @@ def visit_class_def(self, defn: ClassDef) -> None:
         if typ.is_protocol and typ.defn.type_vars:
             self.check_protocol_variance(defn)
 
+    def check_init_subclass(self, defn: ClassDef) -> None:
+        """Check that keywords in a class definition are valid arguments for __init_subclass__().
+
+        In this example:
+            1   class Base:
+            2       def __init_subclass__(cls, thing: int):
+            3           pass
+            4   class Child(Base, thing=5):
+            5       def __init_subclass__(cls):
+            6           pass
+            7   Child()
+
+        Base.__init_subclass__(thing=5) is called at line 4. This is what we simulate here.
+        Child.__init_subclass__ is never called.
+        """
+        # At runtime, only Base.__init_subclass__ will be called, so
+        # we skip the current class itself.
+        for base in defn.info.mro[1:]:
+            if '__init_subclass__' not in base.names:
+                continue
+            name_expr = NameExpr(defn.name)
+            name_expr.node = base
+            callee = MemberExpr(name_expr, '__init_subclass__')
+            args = list(defn.keywords.values())
+            arg_names = list(defn.keywords.keys())  # type: List[Optional[str]]
+            # 'metaclass' keyword is consumed by the rest of the type machinery,
+            # and is never passed to __init_subclass__ implementations
+            if 'metaclass' in arg_names:
+                idx = arg_names.index('metaclass')
+                arg_names.pop(idx)
+                args.pop(idx)
+            arg_kinds = [ARG_NAMED] * len(args)
+            call_expr = CallExpr(callee, args, arg_kinds, arg_names)
+            call_expr.line = defn.line
+            call_expr.column = defn.column
+            call_expr.end_line = defn.end_line
+            self.expr_checker.accept(call_expr,
+                                     allow_none_return=True,
+                                     always_allow_any=True)
+            # We are only interested in the first Base having __init_subclass__
+            # all other bases have already been checked.
+            break
+        return
+
     def check_protocol_variance(self, defn: ClassDef) -> None:
         """Check that protocol definition is compatible with declared
         variances of type variables.
diff --git a/test-data/unit/check-classes.test b/test-data/unit/check-classes.test
@@ -379,7 +379,7 @@ class B(A):
 [case testOverride__init_subclass__WithDifferentSignature]
 class A:
     def __init_subclass__(cls, x: int) -> None: pass
-class B(A):
+class B(A):  # E: Too few arguments for "__init_subclass__" of "A"
     def __init_subclass__(cls) -> None: pass
 
 [case testOverrideWithDecorator]
@@ -6164,6 +6164,102 @@ class C(B[int, T]):
         # TODO: error message could be better.
         self.x: Tuple[str, T]  # E: Incompatible types in assignment (expression has type "Tuple[str, T]", base class "A" defined the type as "Tuple[int, T]")
 
+[case testInitSubclassWrongType]
+class Base:
+    default_name: str
+
+    def __init_subclass__(cls, default_name: str):
+        super().__init_subclass__()
+        cls.default_name = default_name
+        return
+
+class Child(Base, default_name=5):  # E: Argument "default_name" to "__init_subclass__" of "Base" has incompatible type "int"; expected "str"
+    pass
+[builtins fixtures/object_with_init_subclass.pyi]
+
+[case testInitSubclassTooFewArgs]
+class Base:
+    default_name: str
+
+    def __init_subclass__(cls, default_name: str, **kwargs):
+        super().__init_subclass__()
+        cls.default_name = default_name
+        return
+
+class Child(Base):  # E: Too few arguments for "__init_subclass__" of "Base"
+    pass
+[builtins fixtures/object_with_init_subclass.pyi]
+
+[case testInitSubclassTooFewArgs2]
+class Base:
+    default_name: str
+
+    def __init_subclass__(cls, default_name: str, thing: int):
+        super().__init_subclass__()
+        cls.default_name = default_name
+        return
+# TODO implement this, so that no error is raised?
+d = {"default_name": "abc", "thing": 0}
+class Child(Base, **d):  # E: Too few arguments for "__init_subclass__" of "Base"
+    pass
+[builtins fixtures/object_with_init_subclass.pyi]
+
+[case testInitSubclassOK]
+class Base:
+    default_name: str
+    thing: int
+
+    def __init_subclass__(cls, default_name: str, thing:int, **kwargs):
+        super().__init_subclass__()
+        cls.default_name = default_name
+        return
+
+class Child(Base, thing=5, default_name=""):
+    pass
+[builtins fixtures/object_with_init_subclass.pyi]
+
+[case testInitSubclassWithMetaclassOK]
+class Base(type):
+    thing: int
+
+    def __init_subclass__(cls, thing: int):
+        cls.thing = thing
+
+class Child(Base, metaclass=Base, thing=0):
+    pass
+
+[case testTooManyArgsForObject]
+class A(thing=5):
+    pass
+[out]
+main:1: error: Unexpected keyword argument "thing" for "__init_subclass__" of "object"
+tmp/builtins.pyi:5: note: "__init_subclass__" of "object" defined here
+[builtins fixtures/object_with_init_subclass.pyi]
+
+[case testInitSubclassWithImports]
+from init_subclass.a import Base
+class Child(Base, thing=5):  # E: Missing positional arguments "default_name", "kwargs" in call to "__init_subclass__" of "Base"
+    pass
+[file init_subclass/a.py]
+class Base:
+    default_name: str
+    thing: int
+
+    def __init_subclass__(cls, default_name: str, thing:int, **kwargs):
+        pass
+[file init_subclass/__init__.py]
+[builtins fixtures/object_with_init_subclass.pyi]
+
+[case testInitSubclassWithImportsOK]
+from init_subclass.a import MidBase
+class Main(MidBase, test=True): pass
+[file init_subclass/a.py]
+class Base:
+    def __init_subclass__(cls, **kwargs) -> None: pass
+class MidBase(Base): pass
+[file init_subclass/__init__.py]
+[builtins fixtures/object_with_init_subclass.pyi]
+
 [case testOverrideGenericSelfClassMethod]
 from typing import Generic, TypeVar, Type, List
 
diff --git a/test-data/unit/fixtures/object_with_init_subclass.pyi b/test-data/unit/fixtures/object_with_init_subclass.pyi
@@ -0,0 +1,52 @@
+from typing import Sequence, Iterator, TypeVar, Mapping, Iterable, Optional, Union, overload, Tuple, Generic
+
+class object:
+    def __init__(self) -> None: ...
+    def __init_subclass__(cls) -> None: ...
+
+T = TypeVar('T')
+KT = TypeVar('KT')
+VT = TypeVar('VT')
+# copy pased from primitives.pyi
+class type:
+    def __init__(self, x) -> None: pass
+
+class int:
+    # Note: this is a simplification of the actual signature
+    def __init__(self, x: object = ..., base: int = ...) -> None: pass
+    def __add__(self, i: int) -> int: pass
+class float:
+    def __float__(self) -> float: pass
+class complex: pass
+class bool(int): pass
+class str(Sequence[str]):
+    def __add__(self, s: str) -> str: pass
+    def __iter__(self) -> Iterator[str]: pass
+    def __contains__(self, other: object) -> bool: pass
+    def __getitem__(self, item: int) -> str: pass
+    def format(self, *args) -> str: pass
+class bytes(Sequence[int]):
+    def __iter__(self) -> Iterator[int]: pass
+    def __contains__(self, other: object) -> bool: pass
+    def __getitem__(self, item: int) -> int: pass
+class bytearray: pass
+class tuple(Generic[T]): pass
+class function: pass
+class ellipsis: pass
+
+# copy-pasted from dict.pyi
+class dict(Mapping[KT, VT]):
+    @overload
+    def __init__(self, **kwargs: VT) -> None: pass
+    @overload
+    def __init__(self, arg: Iterable[Tuple[KT, VT]], **kwargs: VT) -> None: pass
+    def __getitem__(self, key: KT) -> VT: pass
+    def __setitem__(self, k: KT, v: VT) -> None: pass
+    def __iter__(self) -> Iterator[KT]: pass
+    def __contains__(self, item: object) -> int: pass
+    def update(self, a: Mapping[KT, VT]) -> None: pass
+    @overload
+    def get(self, k: KT) -> Optional[VT]: pass
+    @overload
+    def get(self, k: KT, default: Union[KT, T]) -> Union[VT, T]: pass
+    def __len__(self) -> int: ...
