Fix type guard crashes (#11061)

Fixes #11007, fixes #10899, fixes #10647

Since the initial implementation of TypeGuard, there have been several fixes quickly applied to make mypy not crash on various TypeGuard things. This includes #10496, #10683 and #11015. We'll discuss how this PR relates to each of these three changes.

In particular, #10496 seems incorrect. As A5rocks discusses in #10899 , it introduces confusion between a type guarded variable and a TypeGuard[T]. This PR basically walks back that change entirely and renames TypeGuardType to TypeGuardedType to reduce that possible confusion.

Now, we still have the issue that TypeGuardedTypes are getting everywhere and causing unhappiness. I see two high level solutions to this:
a) Make TypeGuardedType a proper type, then delegate to the wrapped type in a bunch of type visitors and arbitrary amounts of other places where multiple types interact, and hope that we got all of them,
b) Make TypeGuardedType as an improper type (as it was in the original implementation)! Similar to TypeAliasType, it's just a wrapper for another type, so we unwrap it in get_proper_type. This is the approach this PR takes. This might feel controversial, but I think it could be the better option. It also means that if we type check we won't get type guard crashes.

#10683 is basically "remove call that leads to crash from the stacktrace". I think the join here (that ends up being with the wrapped type of the TypeGuardedType) is actually fine: if it's different, it tells us that the type changed, which is what we want to know. So seems fine to remove the special casing.

Finally, #11015. This is the other contentious part of this PR. I liked the idea of moving the core "type guard overrides narrowing" idea into meet.py, so I kept that. But my changes ended up regressing a reveal_type testTypeGuardNestedRestrictionAny test that was added. But it's not really clear to me how that worked or really, what it tested. I tried writing a simpler version of what I thought the test was meant to test (this is testTypeGuardMultipleCondition added in this PR), but that fails on master.

Anyway, this should at least fix the type guard crashes that have been coming up.

mypy/binder.py

@@ -5,7 +5,7 @@
 from typing_extensions import DefaultDict
 
 from mypy.types import (
-    Type, AnyType, PartialType, UnionType, TypeOfAny, NoneType, TypeGuardType, get_proper_type
+    Type, AnyType, PartialType, UnionType, TypeOfAny, NoneType, get_proper_type
 )
 from mypy.subtypes import is_subtype
 from mypy.join import join_simple
@@ -210,9 +210,7 @@ def update_from_options(self, frames: List[Frame]) -> bool:
             else:
                 for other in resulting_values[1:]:
                     assert other is not None
-                    # Ignore the error about using get_proper_type().
-                    if not contains_type_guard(other):
-                        type = join_simple(self.declarations[key], type, other)
+                    type = join_simple(self.declarations[key], type, other)
             if current_value is None or not is_same_type(type, current_value):
                 self._put(key, type)
                 changed = True
@@ -440,13 +438,3 @@ def get_declaration(expr: BindableExpression) -> Optional[Type]:
         if not isinstance(type, PartialType):
             return type
     return None
-
-
-def contains_type_guard(other: Type) -> bool:
-    # Ignore the error about using get_proper_type().
-    if isinstance(other, TypeGuardType):  # type: ignore[misc]
-        return True
-    other = get_proper_type(other)
-    if isinstance(other, UnionType):
-        return any(contains_type_guard(item) for item in other.relevant_items())
-    return False

mypy/checker.py

@@ -36,7 +36,7 @@
     UnionType, TypeVarId, TypeVarType, PartialType, DeletedType, UninhabitedType,
     is_named_instance, union_items, TypeQuery, LiteralType,
     is_optional, remove_optional, TypeTranslator, StarType, get_proper_type, ProperType,
-    get_proper_types, is_literal_type, TypeAliasType, TypeGuardType)
+    get_proper_types, is_literal_type, TypeAliasType, TypeGuardedType)
 from mypy.sametypes import is_same_type
 from mypy.messages import (
     MessageBuilder, make_inferred_type_note, append_invariance_notes, pretty_seq,
@@ -4265,7 +4265,7 @@ def find_isinstance_check_helper(self, node: Expression) -> Tuple[TypeMap, TypeM
                         # considered "always right" (i.e. even if the types are not overlapping).
                         # Also note that a care must be taken to unwrap this back at read places
                         # where we use this to narrow down declared type.
-                        return {expr: TypeGuardType(node.callee.type_guard)}, {}
+                        return {expr: TypeGuardedType(node.callee.type_guard)}, {}
         elif isinstance(node, ComparisonExpr):
             # Step 1: Obtain the types of each operand and whether or not we can
             # narrow their types. (For example, we shouldn't try narrowing the

mypy/constraints.py

@@ -7,7 +7,7 @@
     CallableType, Type, TypeVisitor, UnboundType, AnyType, NoneType, TypeVarType, Instance,
     TupleType, TypedDictType, UnionType, Overloaded, ErasedType, PartialType, DeletedType,
     UninhabitedType, TypeType, TypeVarId, TypeQuery, is_named_instance, TypeOfAny, LiteralType,
-    ProperType, get_proper_type, TypeAliasType, TypeGuardType
+    ProperType, get_proper_type, TypeAliasType
 )
 from mypy.maptype import map_instance_to_supertype
 import mypy.subtypes
@@ -544,9 +544,6 @@ def visit_union_type(self, template: UnionType) -> List[Constraint]:
     def visit_type_alias_type(self, template: TypeAliasType) -> List[Constraint]:
         assert False, "This should be never called, got {}".format(template)
 
-    def visit_type_guard_type(self, template: TypeGuardType) -> List[Constraint]:
-        assert False, "This should be never called, got {}".format(template)
-
     def infer_against_any(self, types: Iterable[Type], any_type: AnyType) -> List[Constraint]:
         res: List[Constraint] = []
         for t in types:

mypy/erasetype.py

@@ -4,7 +4,7 @@
     Type, TypeVisitor, UnboundType, AnyType, NoneType, TypeVarId, Instance, TypeVarType,
     CallableType, TupleType, TypedDictType, UnionType, Overloaded, ErasedType, PartialType,
     DeletedType, TypeTranslator, UninhabitedType, TypeType, TypeOfAny, LiteralType, ProperType,
-    get_proper_type, TypeAliasType, TypeGuardType
+    get_proper_type, TypeAliasType
 )
 from mypy.nodes import ARG_STAR, ARG_STAR2
 
@@ -90,9 +90,6 @@ def visit_union_type(self, t: UnionType) -> ProperType:
         from mypy.typeops import make_simplified_union
         return make_simplified_union(erased_items)
 
-    def visit_type_guard_type(self, t: TypeGuardType) -> ProperType:
-        return TypeGuardType(t.type_guard.accept(self))
-
     def visit_type_type(self, t: TypeType) -> ProperType:
         return TypeType.make_normalized(t.item.accept(self), line=t.line)
 

mypy/expandtype.py

@@ -1,7 +1,7 @@
 from typing import Dict, Iterable, List, TypeVar, Mapping, cast
 
 from mypy.types import (
-    Type, Instance, CallableType, TypeGuardType, TypeVisitor, UnboundType, AnyType,
+    Type, Instance, CallableType, TypeVisitor, UnboundType, AnyType,
     NoneType, TypeVarType, Overloaded, TupleType, TypedDictType, UnionType,
     ErasedType, PartialType, DeletedType, UninhabitedType, TypeType, TypeVarId,
     FunctionLike, TypeVarType, LiteralType, get_proper_type, ProperType,
@@ -129,9 +129,6 @@ def visit_union_type(self, t: UnionType) -> Type:
         from mypy.typeops import make_simplified_union  # asdf
         return make_simplified_union(self.expand_types(t.items), t.line, t.column)
 
-    def visit_type_guard_type(self, t: TypeGuardType) -> ProperType:
-        return TypeGuardType(t.type_guard.accept(self))
-
     def visit_partial_type(self, t: PartialType) -> Type:
         return t
 

mypy/fixup.py

@@ -9,7 +9,7 @@
     TypeVarExpr, ClassDef, Block, TypeAlias,
 )
 from mypy.types import (
-    CallableType, Instance, Overloaded, TupleType, TypeGuardType, TypedDictType,
+    CallableType, Instance, Overloaded, TupleType, TypedDictType,
     TypeVarType, UnboundType, UnionType, TypeVisitor, LiteralType,
     TypeType, NOT_READY, TypeAliasType, AnyType, TypeOfAny
 )
@@ -254,9 +254,6 @@ def visit_union_type(self, ut: UnionType) -> None:
             for it in ut.items:
                 it.accept(self)
 
-    def visit_type_guard_type(self, t: TypeGuardType) -> None:
-        t.type_guard.accept(self)
-
     def visit_void(self, o: Any) -> None:
         pass  # Nothing to descend into.
 

mypy/indirection.py

@@ -97,9 +97,6 @@ def visit_literal_type(self, t: types.LiteralType) -> Set[str]:
     def visit_union_type(self, t: types.UnionType) -> Set[str]:
         return self._visit(t.items)
 
-    def visit_type_guard_type(self, t: types.TypeGuardType) -> Set[str]:
-        return self._visit(t.type_guard)
-
     def visit_partial_type(self, t: types.PartialType) -> Set[str]:
         return set()
 

mypy/join.py

@@ -7,7 +7,7 @@
     Type, AnyType, NoneType, TypeVisitor, Instance, UnboundType, TypeVarType, CallableType,
     TupleType, TypedDictType, ErasedType, UnionType, FunctionLike, Overloaded, LiteralType,
     PartialType, DeletedType, UninhabitedType, TypeType, TypeOfAny, get_proper_type,
-    ProperType, get_proper_types, TypeAliasType, PlaceholderType, TypeGuardType
+    ProperType, get_proper_types, TypeAliasType, PlaceholderType
 )
 from mypy.maptype import map_instance_to_supertype
 from mypy.subtypes import (
@@ -432,9 +432,6 @@ def visit_type_type(self, t: TypeType) -> ProperType:
     def visit_type_alias_type(self, t: TypeAliasType) -> ProperType:
         assert False, "This should be never called, got {}".format(t)
 
-    def visit_type_guard_type(self, t: TypeGuardType) -> ProperType:
-        assert False, "This should be never called, got {}".format(t)
-
     def join(self, s: Type, t: Type) -> ProperType:
         return join_types(s, t)
 

mypy/meet.py

@@ -5,7 +5,7 @@
     Type, AnyType, TypeVisitor, UnboundType, NoneType, TypeVarType, Instance, CallableType,
     TupleType, TypedDictType, ErasedType, UnionType, PartialType, DeletedType,
     UninhabitedType, TypeType, TypeOfAny, Overloaded, FunctionLike, LiteralType,
-    ProperType, get_proper_type, get_proper_types, TypeAliasType, TypeGuardType
+    ProperType, get_proper_type, get_proper_types, TypeAliasType, TypeGuardedType
 )
 from mypy.subtypes import is_equivalent, is_subtype, is_callable_compatible, is_proper_subtype
 from mypy.erasetype import erase_type
@@ -51,16 +51,16 @@ def meet_types(s: Type, t: Type) -> ProperType:
 def narrow_declared_type(declared: Type, narrowed: Type) -> Type:
     """Return the declared type narrowed down to another type."""
     # TODO: check infinite recursion for aliases here.
+    if isinstance(narrowed, TypeGuardedType):  # type: ignore[misc]
+        # A type guard forces the new type even if it doesn't overlap the old.
+        return narrowed.type_guard
+
     declared = get_proper_type(declared)
     narrowed = get_proper_type(narrowed)
 
     if declared == narrowed:
         return declared
-    # Ignore the error about using get_proper_type().
-    if isinstance(narrowed, TypeGuardType):
-        # A type guard forces the new type even if it doesn't overlap the old.
-        return narrowed.type_guard
-    elif isinstance(declared, UnionType):
+    if isinstance(declared, UnionType):
         return make_simplified_union([narrow_declared_type(x, narrowed)
                                       for x in declared.relevant_items()])
     elif not is_overlapping_types(declared, narrowed,
@@ -146,6 +146,13 @@ def is_overlapping_types(left: Type,
     If 'prohibit_none_typevar_overlap' is True, we disallow None from overlapping with
     TypeVars (in both strict-optional and non-strict-optional mode).
     """
+    if (
+        isinstance(left, TypeGuardedType)  # type: ignore[misc]
+        or isinstance(right, TypeGuardedType)  # type: ignore[misc]
+    ):
+        # A type guard forces the new type even if it doesn't overlap the old.
+        return True
+
     left, right = get_proper_types((left, right))
 
     def _is_overlapping_types(left: Type, right: Type) -> bool:
@@ -161,11 +168,6 @@ def _is_overlapping_types(left: Type, right: Type) -> bool:
     if isinstance(left, PartialType) or isinstance(right, PartialType):
         assert False, "Unexpectedly encountered partial type"
 
-    # Ignore the error about using get_proper_type().
-    if isinstance(left, TypeGuardType) or isinstance(right, TypeGuardType):
-        # A type guard forces the new type even if it doesn't overlap the old.
-        return True
-
     # We should also never encounter these types, but it's possible a few
     # have snuck through due to unrelated bugs. For now, we handle these
     # in the same way we handle 'Any'.
@@ -657,9 +659,6 @@ def visit_type_type(self, t: TypeType) -> ProperType:
     def visit_type_alias_type(self, t: TypeAliasType) -> ProperType:
         assert False, "This should be never called, got {}".format(t)
 
-    def visit_type_guard_type(self, t: TypeGuardType) -> ProperType:
-        assert False, "This should be never called, got {}".format(t)
-
     def meet(self, s: Type, t: Type) -> ProperType:
         return meet_types(s, t)
 

mypy/sametypes.py

@@ -1,7 +1,7 @@
 from typing import Sequence
 
 from mypy.types import (
-    Type, TypeGuardType, UnboundType, AnyType, NoneType, TupleType, TypedDictType,
+    Type, UnboundType, AnyType, NoneType, TupleType, TypedDictType,
     UnionType, CallableType, TypeVarType, Instance, TypeVisitor, ErasedType,
     Overloaded, PartialType, DeletedType, UninhabitedType, TypeType, LiteralType,
     ProperType, get_proper_type, TypeAliasType)
@@ -151,12 +151,6 @@ def visit_union_type(self, left: UnionType) -> bool:
         else:
             return False
 
-    def visit_type_guard_type(self, left: TypeGuardType) -> bool:
-        if isinstance(self.right, TypeGuardType):
-            return is_same_type(left.type_guard, self.right.type_guard)
-        else:
-            return False
-
     def visit_overloaded(self, left: Overloaded) -> bool:
         if isinstance(self.right, Overloaded):
             return is_same_types(left.items, self.right.items)

mypy/server/astdiff.py

@@ -57,7 +57,7 @@ class level -- these are handled at attribute level (say, 'mod.Cls.method'
     FuncBase, OverloadedFuncDef, FuncItem, MypyFile, UNBOUND_IMPORTED
 )
 from mypy.types import (
-    Type, TypeGuardType, TypeVisitor, UnboundType, AnyType, NoneType, UninhabitedType,
+    Type, TypeVisitor, UnboundType, AnyType, NoneType, UninhabitedType,
     ErasedType, DeletedType, Instance, TypeVarType, CallableType, TupleType, TypedDictType,
     UnionType, Overloaded, PartialType, TypeType, LiteralType, TypeAliasType
 )
@@ -335,9 +335,6 @@ def visit_union_type(self, typ: UnionType) -> SnapshotItem:
         normalized = tuple(sorted(items))
         return ('UnionType', normalized)
 
-    def visit_type_guard_type(self, typ: TypeGuardType) -> SnapshotItem:
-        return ('TypeGuardType', snapshot_type(typ.type_guard))
-
     def visit_overloaded(self, typ: Overloaded) -> SnapshotItem:
         return ('Overloaded', snapshot_types(typ.items))
 

mypy/server/astmerge.py

@@ -59,7 +59,7 @@
     Type, SyntheticTypeVisitor, Instance, AnyType, NoneType, CallableType, ErasedType, DeletedType,
     TupleType, TypeType, TypeVarType, TypedDictType, UnboundType, UninhabitedType, UnionType,
     Overloaded, TypeVarType, TypeList, CallableArgument, EllipsisType, StarType, LiteralType,
-    RawExpressionType, PartialType, PlaceholderType, TypeAliasType, TypeGuardType
+    RawExpressionType, PartialType, PlaceholderType, TypeAliasType
 )
 from mypy.util import get_prefix, replace_object_state
 from mypy.typestate import TypeState
@@ -389,9 +389,6 @@ def visit_erased_type(self, t: ErasedType) -> None:
     def visit_deleted_type(self, typ: DeletedType) -> None:
         pass
 
-    def visit_type_guard_type(self, typ: TypeGuardType) -> None:
-        raise RuntimeError
-
     def visit_partial_type(self, typ: PartialType) -> None:
         raise RuntimeError
 

mypy/server/deps.py

@@ -99,7 +99,7 @@ class 'mod.Cls'. This can also refer to an attribute inherited from a
     Type, Instance, AnyType, NoneType, TypeVisitor, CallableType, DeletedType, PartialType,
     TupleType, TypeType, TypeVarType, TypedDictType, UnboundType, UninhabitedType, UnionType,
     FunctionLike, Overloaded, TypeOfAny, LiteralType, ErasedType, get_proper_type, ProperType,
-    TypeAliasType, TypeGuardType
+    TypeAliasType
 )
 from mypy.server.trigger import make_trigger, make_wildcard_trigger
 from mypy.util import correct_relative_import
@@ -967,9 +967,6 @@ def visit_unbound_type(self, typ: UnboundType) -> List[str]:
     def visit_uninhabited_type(self, typ: UninhabitedType) -> List[str]:
         return []
 
-    def visit_type_guard_type(self, typ: TypeGuardType) -> List[str]:
-        return typ.type_guard.accept(self)
-
     def visit_union_type(self, typ: UnionType) -> List[str]:
         triggers = []
         for item in typ.items:

mypy/subtypes.py

@@ -4,7 +4,7 @@
 from typing_extensions import Final
 
 from mypy.types import (
-    Type, AnyType, TypeGuardType, UnboundType, TypeVisitor, FormalArgument, NoneType,
+    Type, AnyType, UnboundType, TypeVisitor, FormalArgument, NoneType,
     Instance, TypeVarType, CallableType, TupleType, TypedDictType, UnionType, Overloaded,
     ErasedType, PartialType, DeletedType, UninhabitedType, TypeType, is_named_instance,
     FunctionLike, TypeOfAny, LiteralType, get_proper_type, TypeAliasType
@@ -475,9 +475,6 @@ def visit_overloaded(self, left: Overloaded) -> bool:
     def visit_union_type(self, left: UnionType) -> bool:
         return all(self._is_subtype(item, self.orig_right) for item in left.items)
 
-    def visit_type_guard_type(self, left: TypeGuardType) -> bool:
-        raise RuntimeError("TypeGuard should not appear here")
-
     def visit_partial_type(self, left: PartialType) -> bool:
         # This is indeterminate as we don't really know the complete type yet.
         raise RuntimeError
@@ -1377,14 +1374,6 @@ def visit_overloaded(self, left: Overloaded) -> bool:
     def visit_union_type(self, left: UnionType) -> bool:
         return all([self._is_proper_subtype(item, self.orig_right) for item in left.items])
 
-    def visit_type_guard_type(self, left: TypeGuardType) -> bool:
-        if isinstance(self.right, TypeGuardType):
-            # TypeGuard[bool] is a subtype of TypeGuard[int]
-            return self._is_proper_subtype(left.type_guard, self.right.type_guard)
-        else:
-            # TypeGuards aren't a subtype of anything else for now (but see #10489)
-            return False
-
     def visit_partial_type(self, left: PartialType) -> bool:
         # TODO: What's the right thing to do here?
         return False

mypy/type_visitor.py

@@ -19,7 +19,7 @@
 T = TypeVar('T')
 
 from mypy.types import (
-    Type, AnyType, CallableType, Overloaded, TupleType, TypeGuardType, TypedDictType, LiteralType,
+    Type, AnyType, CallableType, Overloaded, TupleType, TypedDictType, LiteralType,
     RawExpressionType, Instance, NoneType, TypeType,
     UnionType, TypeVarType, PartialType, DeletedType, UninhabitedType, TypeVarLikeType,
     UnboundType, ErasedType, StarType, EllipsisType, TypeList, CallableArgument,
@@ -103,10 +103,6 @@ def visit_type_type(self, t: TypeType) -> T:
     def visit_type_alias_type(self, t: TypeAliasType) -> T:
         pass
 
-    @abstractmethod
-    def visit_type_guard_type(self, t: TypeGuardType) -> T:
-        pass
-
 
 @trait
 @mypyc_attr(allow_interpreted_subclasses=True)
@@ -224,9 +220,6 @@ def visit_union_type(self, t: UnionType) -> Type:
     def translate_types(self, types: Iterable[Type]) -> List[Type]:
         return [t.accept(self) for t in types]
 
-    def visit_type_guard_type(self, t: TypeGuardType) -> Type:
-        return TypeGuardType(t.type_guard.accept(self))
-
     def translate_variables(self,
                             variables: Sequence[TypeVarLikeType]) -> Sequence[TypeVarLikeType]:
         return variables
@@ -326,9 +319,6 @@ def visit_star_type(self, t: StarType) -> T:
     def visit_union_type(self, t: UnionType) -> T:
         return self.query_types(t.items)
 
-    def visit_type_guard_type(self, t: TypeGuardType) -> T:
-        return t.type_guard.accept(self)
-
     def visit_overloaded(self, t: Overloaded) -> T:
         return self.query_types(t.items)
 

mypy/typeanal.py

@@ -14,7 +14,7 @@
 from mypy.types import (
     Type, UnboundType, TypeVarType, TupleType, TypedDictType, UnionType, Instance, AnyType,
     CallableType, NoneType, ErasedType, DeletedType, TypeList, TypeVarType, SyntheticTypeVisitor,
-    StarType, PartialType, EllipsisType, UninhabitedType, TypeType, TypeGuardType, TypeVarLikeType,
+    StarType, PartialType, EllipsisType, UninhabitedType, TypeType, TypeVarLikeType,
     CallableArgument, TypeQuery, union_items, TypeOfAny, LiteralType, RawExpressionType,
     PlaceholderType, Overloaded, get_proper_type, TypeAliasType, TypeVarLikeType, ParamSpecType
 )
@@ -547,9 +547,6 @@ def visit_callable_type(self, t: CallableType, nested: bool = True) -> Type:
                                   )
         return ret
 
-    def visit_type_guard_type(self, t: TypeGuardType) -> Type:
-        return t
-
     def anal_type_guard(self, t: Type) -> Optional[Type]:
         if isinstance(t, UnboundType):
             sym = self.lookup_qualified(t.name, t)