[clean strict optional] Use dummy TypeInfo instead of None in Instance.type (and few more fixes) (#3285)

Author: ilevkivskyi

mypy/checkmember.py

@@ -451,7 +451,7 @@ class B(A): pass
     info = itype.type  # type: TypeInfo
     if isinstance(t, CallableType):
         # TODO: Should we propagate type variable values?
-        tvars = [TypeVarDef(n, i + 1, None, builtin_type('builtins.object'), tv.variance)
+        tvars = [TypeVarDef(n, i + 1, [], builtin_type('builtins.object'), tv.variance)
                  for (i, n), tv in zip(enumerate(info.type_vars), info.defn.type_vars)]
         if is_classmethod:
             t = bind_self(t, original_type)

mypy/fixup.py

@@ -11,7 +11,7 @@
 from mypy.types import (
     CallableType, EllipsisType, Instance, Overloaded, TupleType, TypedDictType,
     TypeList, TypeVarType, UnboundType, UnionType, TypeVisitor,
-    TypeType
+    TypeType, NOT_READY
 )
 from mypy.visitor import NodeVisitor
 
@@ -156,7 +156,7 @@ def visit_instance(self, inst: Instance) -> None:
             # TODO: Is this needed or redundant?
             # Also fix up the bases, just in case.
             for base in inst.type.bases:
-                if base.type is None:
+                if base.type is NOT_READY:
                     base.accept(self)
         for a in inst.args:
             a.accept(self)
@@ -233,7 +233,7 @@ def visit_type_type(self, t: TypeType) -> None:
 
 
 def lookup_qualified(modules: Dict[str, MypyFile], name: str,
-                     quick_and_dirty: bool) -> SymbolNode:
+                     quick_and_dirty: bool) -> Optional[SymbolNode]:
     stnode = lookup_qualified_stnode(modules, name, quick_and_dirty)
     if stnode is None:
         return None

mypy/maptype.py

@@ -28,9 +28,7 @@ def map_instance_to_supertypes(instance: Instance,
     # FIX: Currently we should only have one supertype per interface, so no
     #      need to return an array
     result = []  # type: List[Instance]
-    typ = instance.type
-    assert typ is not None, 'Instance.type is not fixed after deserialization'
-    for path in class_derivation_paths(typ, supertype):
+    for path in class_derivation_paths(instance.type, supertype):
         types = [instance]
         for sup in path:
             a = []  # type: List[Instance]
@@ -60,7 +58,6 @@ def class_derivation_paths(typ: TypeInfo,
 
     for base in typ.bases:
         btype = base.type
-        assert btype is not None, 'Instance.type is not fixed after deserialization'
         if btype == supertype:
             result.append([btype])
         else:
@@ -75,7 +72,6 @@ def map_instance_to_direct_supertypes(instance: Instance,
                                       supertype: TypeInfo) -> List[Instance]:
     # FIX: There should only be one supertypes, always.
     typ = instance.type
-    assert typ is not None, 'Instance.type is not fixed after deserialization'
     result = []  # type: List[Instance]
 
     for b in typ.bases:
@@ -103,6 +99,4 @@ def instance_to_type_environment(instance: Instance) -> Dict[TypeVarId, Type]:
     arguments.  The type variables are mapped by their `id`.
 
     """
-    typ = instance.type
-    assert typ is not None, 'Instance.type is not fixed after deserialization'
-    return {binder.id: arg for binder, arg in zip(typ.defn.type_vars, instance.args)}
+    return {binder.id: arg for binder, arg in zip(instance.type.defn.type_vars, instance.args)}

mypy/nodes.py

@@ -2208,6 +2208,23 @@ def deserialize(cls, data: JsonDict) -> 'TypeInfo':
         return ti
 
 
+class FakeInfo(TypeInfo):
+    # types.py defines a single instance of this class, called types.NOT_READY.
+    # This instance is used as a temporary placeholder in the process of de-serialization
+    # of 'Instance' types. The de-serialization happens in two steps: In the first step,
+    # Instance.type is set to NOT_READY. In the second step (in fixup.py) it is replaced by
+    # an actual TypeInfo. If you see the assertion error below, then most probably something
+    # went wrong during the second step and an 'Instance' that raised this error was not fixed.
+    # Note:
+    # 'None' is not used as a dummy value for two reasons:
+    # 1. This will require around 80-100 asserts to make 'mypy --strict-optional mypy'
+    #    pass cleanly.
+    # 2. If NOT_READY value is accidentally used somewhere, it will be obvious where the value
+    #    is from, whereas a 'None' value could come from anywhere.
+    def __getattr__(self, attr: str) -> None:
+        raise AssertionError('De-serialization failure: TypeInfo not fixed')
+
+
 class SymbolTableNode:
     # Kind of node. Possible values:
     #  - LDEF: local definition (of any kind)

mypy/semanal.py

@@ -182,7 +182,7 @@ class SemanticAnalyzer(NodeVisitor):
     # Nested block depths of scopes
     block_depth = None  # type: List[int]
     # TypeInfo of directly enclosing class (or None)
-    type = None  # type: TypeInfo
+    type = None  # type: Optional[TypeInfo]
     # Stack of outer classes (the second tuple item contains tvars).
     type_stack = None  # type: List[TypeInfo]
     # Type variables that are bound by the directly enclosing class
@@ -1745,10 +1745,10 @@ def build_newtype_typeinfo(self, name: str, old_type: Type, base_type: Instance)
         info.is_newtype = True
 
         # Add __init__ method
-        args = [Argument(Var('cls'), NoneTyp(), None, ARG_POS),
+        args = [Argument(Var('self'), NoneTyp(), None, ARG_POS),
                 self.make_argument('item', old_type)]
         signature = CallableType(
-            arg_types=[cast(Type, None), old_type],
+            arg_types=[Instance(info, []), old_type],
             arg_kinds=[arg.kind for arg in args],
             arg_names=['self', 'item'],
             ret_type=old_type,

mypy/subtypes.py

@@ -323,9 +323,11 @@ def is_callable_subtype(left: CallableType, right: CallableType,
 
     if left.variables:
         # Apply generic type variables away in left via type inference.
-        left = unify_generic_callable(left, right, ignore_return=ignore_return)
-        if left is None:
+        unified = unify_generic_callable(left, right, ignore_return=ignore_return)
+        if unified is None:
             return False
+        else:
+            left = unified
 
     # Check return types.
     if not ignore_return and not is_compat(left.ret_type, right.ret_type):
@@ -493,7 +495,7 @@ def are_args_compatible(
 
 
 def unify_generic_callable(type: CallableType, target: CallableType,
-                           ignore_return: bool) -> CallableType:
+                           ignore_return: bool) -> Optional[CallableType]:
     """Try to unify a generic callable type with another callable type.
 
     Return unified CallableType if successful; otherwise, return None.

mypy/test/testtypes.py

@@ -75,18 +75,18 @@ def test_tuple_type(self) -> None:
         assert_equal(str(TupleType([self.x, AnyType()], None)), 'Tuple[X?, Any]')
 
     def test_type_variable_binding(self) -> None:
-        assert_equal(str(TypeVarDef('X', 1, None, self.fx.o)), 'X')
+        assert_equal(str(TypeVarDef('X', 1, [], self.fx.o)), 'X')
         assert_equal(str(TypeVarDef('X', 1, [self.x, self.y], self.fx.o)),
                      'X in (X?, Y?)')
 
     def test_generic_function_type(self) -> None:
         c = CallableType([self.x, self.y], [ARG_POS, ARG_POS], [None, None],
                      self.y, self.function, name=None,
-                     variables=[TypeVarDef('X', -1, None, self.fx.o)])
+                     variables=[TypeVarDef('X', -1, [], self.fx.o)])
         assert_equal(str(c), 'def [X] (X?, Y?) -> Y?')
 
-        v = [TypeVarDef('Y', -1, None, self.fx.o),
-             TypeVarDef('X', -2, None, self.fx.o)]
+        v = [TypeVarDef('Y', -1, [], self.fx.o),
+             TypeVarDef('X', -2, [], self.fx.o)]
         c2 = CallableType([], [], [], NoneTyp(), self.function, name=None, variables=v)
         assert_equal(str(c2), 'def [Y, X] ()')
 

mypy/typefixture.py

@@ -216,7 +216,7 @@ def make_type_info(self, name: str,
                     variance = variances[id - 1]
                 else:
                     variance = COVARIANT
-                v.append(TypeVarDef(n, id, None, self.o, variance=variance))
+                v.append(TypeVarDef(n, id, [], self.o, variance=variance))
             class_def.type_vars = v
 
         info = TypeInfo(SymbolTable(), class_def, module_name)