Merge branch 'call-type-with-__new__'

Addresses much of #982.

mypy/checkmember.py

@@ -269,28 +269,41 @@ def add_class_tvars(t: Type, info: TypeInfo, is_classmethod: bool,
 def type_object_type(info: TypeInfo, builtin_type: Callable[[str], Instance]) -> Type:
     """Return the type of a type object.
 
-    For a generic type G with type variables T and S the type is of form
+    For a generic type G with type variables T and S the type is generally of form
 
-      def [T, S](...) -> G[T, S],
+      Callable[..., G[T, S]]
 
-    where ... are argument types for the __init__ method (without the self argument).
+    where ... are argument types for the __init__/__new__ method (without the self
+    argument). Also, the fallback type will be 'type' instead of 'function'.
     """
     init_method = info.get_method('__init__')
     if not init_method:
         # Must be an invalid class definition.
         return AnyType()
     else:
+        fallback = builtin_type('builtins.type')
+        if init_method.info.fullname() == 'builtins.object':
+            # No non-default __init__ -> look at __new__ instead.
+            new_method = info.get_method('__new__')
+            if new_method and new_method.info.fullname() != 'builtins.object':
+                # Found one! Get signature from __new__.
+                return type_object_type_from_function(new_method, info, fallback)
         # Construct callable type based on signature of __init__. Adjust
         # return type and insert type arguments.
-        init_type = method_type_with_fallback(init_method, builtin_type('builtins.function'))
-        if isinstance(init_type, CallableType):
-            return class_callable(init_type, info, builtin_type('builtins.type'))
-        else:
-            # Overloaded __init__.
-            items = []  # type: List[CallableType]
-            for it in cast(Overloaded, init_type).items():
-                items.append(class_callable(it, info, builtin_type('builtins.type')))
-            return Overloaded(items)
+        return type_object_type_from_function(init_method, info, fallback)
+
+
+def type_object_type_from_function(init_or_new: FuncBase, info: TypeInfo,
+                                   fallback: Instance) -> FunctionLike:
+    signature = method_type_with_fallback(init_or_new, fallback)
+    if isinstance(signature, CallableType):
+        return class_callable(signature, info, fallback)
+    else:
+        # Overloaded __init__/__new__.
+        items = []  # type: List[CallableType]
+        for item in cast(Overloaded, signature).items():
+            items.append(class_callable(item, info, fallback))
+        return Overloaded(items)
 
 
 def class_callable(init_type: CallableType, info: TypeInfo, type_type: Instance) -> CallableType:

mypy/semanal.py

@@ -1398,10 +1398,12 @@ def make_namedtuple_init(self, info: TypeInfo, items: List[str],
                                  NoneTyp(),
                                  self.named_type('__builtins__.function'),
                                  name=info.name())
-        return FuncDef('__init__',
+        func = FuncDef('__init__',
                        args,
                        Block([]),
                        typ=signature)
+        func.info = info
+        return func
 
     def analyze_types(self, items: List[Node]) -> List[Type]:
         result = []  # type: List[Type]

mypy/test/data/check-classes.test

@@ -1193,6 +1193,86 @@ class A:
 class B: pass
 
 
+-- __new__
+-- --------
+
+
+[case testConstructInstanceWith__new__]
+class C:
+    def __new__(cls, foo: int = None) -> 'C':
+        obj = object.__new__(cls)
+        return obj
+
+x = C(foo=12)
+x.a # E: "C" has no attribute "a"
+C(foo='') # E: Argument 1 to "C" has incompatible type "str"; expected "int"
+[builtins fixtures/__new__.py]
+
+[case testConstructInstanceWithDynamicallyTyped__new__]
+class C:
+    def __new__(cls, foo):
+        obj = object.__new__(cls)
+        return obj
+
+x = C(foo=12)
+x = C(foo='x')
+x.a # E: "C" has no attribute "a"
+C(bar='') # E: Unexpected keyword argument "bar" for "C"
+[builtins fixtures/__new__.py]
+
+[case testClassWith__new__AndCompatibilityWithType]
+class C:
+    def __new__(cls, foo: int = None) -> 'C':
+        obj = object.__new__(cls)
+        return obj
+def f(x: type) -> None: pass
+def g(x: int) -> None: pass
+f(C)
+g(C) # E: Argument 1 to "g" has incompatible type "C"; expected "int"
+[builtins fixtures/__new__.py]
+
+[case testClassWith__new__AndCompatibilityWithType2]
+class C:
+    def __new__(cls, foo):
+        obj = object.__new__(cls)
+        return obj
+def f(x: type) -> None: pass
+def g(x: int) -> None: pass
+f(C)
+g(C) # E: Argument 1 to "g" has incompatible type "C"; expected "int"
+[builtins fixtures/__new__.py]
+
+[case testGenericClassWith__new__]
+from typing import TypeVar, Generic
+T = TypeVar('T')
+class C(Generic[T]):
+    def __new__(cls, foo: T) -> 'C[T]':
+        obj = object.__new__(cls)
+        return obj
+    def set(self, x: T) -> None: pass
+c = C('')
+c.set('')
+c.set(1) # E: Argument 1 to "set" of "C" has incompatible type "int"; expected "str"
+[builtins fixtures/__new__.py]
+
+[case testOverloaded__new__]
+from typing import overload
+class C:
+    @overload
+    def __new__(cls, foo: int) -> 'C':
+        obj = object.__new__(cls)
+        return obj
+    @overload
+    def __new__(cls, x: str, y: str) -> 'C':
+        obj = object.__new__(cls)
+        return obj
+c = C(1)
+c.a # E: "C" has no attribute "a"
+C('', '')
+C('') # E: No overload variant of "C" matches argument types [builtins.str]
+[builtins fixtures/__new__.py]
+
+
 -- Special cases
 -- -------------
 

mypy/test/data/fixtures/__new__.py

@@ -0,0 +1,14 @@
+# builtins stub with object.__new__
+
+class object:
+    def __init__(self) -> None: pass
+
+    def __new__(cls): pass
+
+class type:
+    def __init__(self, x) -> None: pass
+
+class int: pass
+class bool: pass
+class str: pass
+class function: pass