Allow __init__ and __new__ to return NoReturn (#13480)

Co-authored-by: Bas van Beek <43369155+BvB93@users.noreply.github.com>

mypy/checker.py

@@ -1037,11 +1037,13 @@ def check_func_def(self, defn: FuncItem, typ: CallableType, name: str | None) ->
                 # precise type.
                 if isinstance(item, FuncDef):
                     fdef = item
-                    # Check if __init__ has an invalid, non-None return type.
+                    # Check if __init__ has an invalid return type.
                     if (
                         fdef.info
                         and fdef.name in ("__init__", "__init_subclass__")
-                        and not isinstance(get_proper_type(typ.ret_type), NoneType)
+                        and not isinstance(
+                            get_proper_type(typ.ret_type), (NoneType, UninhabitedType)
+                        )
                         and not self.dynamic_funcs[-1]
                     ):
                         self.fail(
@@ -1327,7 +1329,9 @@ def check___new___signature(self, fdef: FuncDef, typ: CallableType) -> None:
                 "returns",
                 "but must return a subtype of",
             )
-        elif not isinstance(get_proper_type(bound_type.ret_type), (AnyType, Instance, TupleType)):
+        elif not isinstance(
+            get_proper_type(bound_type.ret_type), (AnyType, Instance, TupleType, UninhabitedType)
+        ):
             self.fail(
                 message_registry.NON_INSTANCE_NEW_TYPE.format(format_type(bound_type.ret_type)),
                 fdef,

mypy/typeops.py

@@ -107,6 +107,15 @@ def tuple_fallback(typ: TupleType) -> Instance:
     return Instance(info, [join_type_list(items)])
 
 
+def get_self_type(func: CallableType, default_self: Instance | TupleType) -> Type | None:
+    if isinstance(get_proper_type(func.ret_type), UninhabitedType):
+        return func.ret_type
+    elif func.arg_types and func.arg_types[0] != default_self and func.arg_kinds[0] == ARG_POS:
+        return func.arg_types[0]
+    else:
+        return None
+
+
 def type_object_type_from_function(
     signature: FunctionLike, info: TypeInfo, def_info: TypeInfo, fallback: Instance, is_new: bool
 ) -> FunctionLike:
@@ -117,14 +126,7 @@ def type_object_type_from_function(
     # classes such as subprocess.Popen.
     default_self = fill_typevars(info)
     if not is_new and not info.is_newtype:
-        orig_self_types = [
-            (
-                it.arg_types[0]
-                if it.arg_types and it.arg_types[0] != default_self and it.arg_kinds[0] == ARG_POS
-                else None
-            )
-            for it in signature.items
-        ]
+        orig_self_types = [get_self_type(it, default_self) for it in signature.items]
     else:
         orig_self_types = [None] * len(signature.items)
 
@@ -177,7 +179,7 @@ def class_callable(
     default_ret_type = fill_typevars(info)
     explicit_type = init_ret_type if is_new else orig_self_type
     if (
-        isinstance(explicit_type, (Instance, TupleType))
+        isinstance(explicit_type, (Instance, TupleType, UninhabitedType))
         # We have to skip protocols, because it can be a subtype of a return type
         # by accident. Like `Hashable` is a subtype of `object`. See #11799
         and isinstance(default_ret_type, Instance)

mypy/types.py

@@ -1734,7 +1734,9 @@ def is_kw_arg(self) -> bool:
         return ARG_STAR2 in self.arg_kinds
 
     def is_type_obj(self) -> bool:
-        return self.fallback.type.is_metaclass()
+        return self.fallback.type.is_metaclass() and not isinstance(
+            get_proper_type(self.ret_type), UninhabitedType
+        )
 
     def type_object(self) -> mypy.nodes.TypeInfo:
         assert self.is_type_obj()

test-data/unit/check-classes.test

@@ -7296,6 +7296,74 @@ def meth1(self: Any, y: str) -> str: ...
 T = TypeVar("T")
 def meth2(self: Any, y: T) -> T: ...
 
+[case testNewAndInitNoReturn]
+from typing import NoReturn
+
+class A:
+    def __new__(cls) -> NoReturn: ...
+
+class B:
+    def __init__(self) -> NoReturn: ...
+
+class C:
+    def __new__(cls) -> "C": ...
+    def __init__(self) -> NoReturn: ...
+
+class D:
+    def __new__(cls) -> NoReturn: ...
+    def __init__(self) -> NoReturn: ...
+
+reveal_type(A())  # N: Revealed type is "<nothing>"
+reveal_type(B())  # N: Revealed type is "<nothing>"
+reveal_type(C())  # N: Revealed type is "<nothing>"
+reveal_type(D())  # N: Revealed type is "<nothing>"
+
+[case testOverloadedNewAndInitNoReturn]
+from typing import NoReturn, overload
+
+class A:
+    @overload
+    def __new__(cls) -> NoReturn: ...
+    @overload
+    def __new__(cls, a: int) -> "A": ...
+    def __new__(cls, a: int = ...) -> "A": ...
+
+class B:
+    @overload
+    def __init__(self) -> NoReturn: ...
+    @overload
+    def __init__(self, a: int) -> None: ...
+    def __init__(self, a: int = ...) -> None: ...
+
+class C:
+    def __new__(cls, a: int = ...) -> "C": ...
+    @overload
+    def __init__(self) -> NoReturn: ...
+    @overload
+    def __init__(self, a: int) -> None: ...
+    def __init__(self, a: int = ...) -> None: ...
+
+class D:
+    @overload
+    def __new__(cls) -> NoReturn: ...
+    @overload
+    def __new__(cls, a: int) -> "D": ...
+    def __new__(cls, a: int = ...) -> "D": ...
+    @overload
+    def __init__(self) -> NoReturn: ...
+    @overload
+    def __init__(self, a: int) -> None: ...
+    def __init__(self, a: int = ...) -> None: ...
+
+reveal_type(A())  # N: Revealed type is "<nothing>"
+reveal_type(A(1))  # N: Revealed type is "__main__.A"
+reveal_type(B())  # N: Revealed type is "<nothing>"
+reveal_type(B(1))  # N: Revealed type is "__main__.B"
+reveal_type(C())  # N: Revealed type is "<nothing>"
+reveal_type(C(1))  # N: Revealed type is "__main__.C"
+reveal_type(D())  # N: Revealed type is "<nothing>"
+reveal_type(D(1))  # N: Revealed type is "__main__.D"
+
 [case testClassScopeImportWithWrapperAndError]
 class Foo:
     from mod import foo # E: Unsupported class scoped import