implement @no_type_check for class defs

mypy/checkmember.py

@@ -162,6 +162,9 @@ def analyze_instance_member_access(name: str,
     if override_info:
         info = override_info
 
+    if info.is_no_type_check:
+        return AnyType(TypeOfAny.special_form)
+
     if (state.find_occurrences and
             info.name() == state.find_occurrences[0] and
             name == state.find_occurrences[1]):

mypy/nodes.py

@@ -2219,6 +2219,7 @@ class is generic then it will be a type constructor of higher kind.
     metaclass_type = None  # type: Optional[mypy.types.Instance]
 
     names = None  # type: SymbolTable      # Names defined directly in this type
+    is_no_type_check = False               # Was the class annotated with @no_type_check?
     is_abstract = False                    # Does the class have any abstract attributes?
     is_protocol = False                    # Is this a protocol class?
     runtime_protocol = False               # Does this protocol support isinstance checks?

mypy/semanal.py

@@ -487,6 +487,9 @@ def prepare_method_signature(self, func: FuncDef, info: TypeInfo) -> None:
         """Check basic signature validity and tweak annotation of self/cls argument."""
         # Only non-static methods are special.
         functype = func.type
+        if info.is_no_type_check:
+            func.type = AnyType(TypeOfAny.special_form)
+            return
         if not func.is_static:
             if not func.arguments:
                 self.fail('Method must have at least one argument', func)
@@ -807,6 +810,14 @@ def visit_class_def(self, defn: ClassDef) -> None:
                 self.analyze_class(defn)
 
     def analyze_class(self, defn: ClassDef) -> None:
+        if defn.decorators:
+            for decorator in reversed(defn.decorators):
+                if isinstance(decorator, NameExpr) and \
+                        decorator.name in ('no_type_check', 'typing.no_type_check'):
+                    defn.info.is_no_type_check = True
+                    defn.info.fallback_to_any = True
+                    return
+
         is_protocol = self.detect_protocol_base(defn)
         self.update_metaclass(defn)
         self.clean_up_bases_and_infer_type_variables(defn)

mypy/semanal_pass3.py

@@ -161,6 +161,8 @@ def visit_overloaded_func_def(self, fdef: OverloadedFuncDef) -> None:
             super().visit_overloaded_func_def(fdef)
 
     def visit_class_def(self, tdef: ClassDef) -> None:
+        if tdef.info.is_no_type_check:
+            return
         # NamedTuple base classes are validated in check_namedtuple_classdef; we don't have to
         # check them again here.
         self.scope.enter_class(tdef.info)