A sketchy hack to fix TypeGuard crash in logical expressions (#11015)

Support or expressions involving type guard checks.

Co-authored-by: Ivan Levkivskyi <ilevkivskyi@dropbox.com>

Author: ilevkivskyi

mypy/binder.py

@@ -203,7 +203,7 @@ def update_from_options(self, frames: List[Frame]) -> bool:
                 for other in resulting_values[1:]:
                     assert other is not None
                     # Ignore the error about using get_proper_type().
-                    if not isinstance(other, TypeGuardType):  # type: ignore[misc]
+                    if not contains_type_guard(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)
@@ -431,3 +431,13 @@ 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

@@ -4167,6 +4167,11 @@ def find_isinstance_check_helper(self, node: Expression) -> Tuple[TypeMap, TypeM
                         self.fail("Type guard requires positional argument", node)
                         return {}, {}
                     if literal(expr) == LITERAL_TYPE:
+                        # Note: we wrap the target type, so that we can special case later.
+                        # Namely, for isinstance() we use a normal meet, while TypeGuard is
+                        # 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)}, {}
         elif isinstance(node, ComparisonExpr):
             # Step 1: Obtain the types of each operand and whether or not we can

mypy/checkexpr.py

@@ -4179,10 +4179,6 @@ def narrow_type_from_binder(self, expr: Expression, known_type: Type,
         """
         if literal(expr) >= LITERAL_TYPE:
             restriction = self.chk.binder.get(expr)
-            # Ignore the error about using get_proper_type().
-            if isinstance(restriction, TypeGuardType):  # type: ignore[misc]
-                # A type guard forces the new type even if it doesn't overlap the old.
-                return restriction.type_guard
             # If the current node is deferred, some variables may get Any types that they
             # otherwise wouldn't have. We don't want to narrow down these since it may
             # produce invalid inferred Optional[Any] types, at least.

mypy/meet.py

@@ -56,7 +56,11 @@ def narrow_declared_type(declared: Type, narrowed: Type) -> Type:
 
     if declared == narrowed:
         return declared
-    if isinstance(declared, UnionType):
+    # Ignore the error about using get_proper_type().
+    if isinstance(narrowed, TypeGuardType):  # type: ignore[misc]
+        # A type guard forces the new type even if it doesn't overlap the old.
+        return narrowed.type_guard
+    elif 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,
@@ -157,6 +161,11 @@ 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):  # type: ignore[misc]
+        # 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'.

test-data/unit/check-typeguard.test

@@ -370,3 +370,47 @@ if guard(a):
     reveal_type(a)  # N: Revealed type is "__main__.A"
 reveal_type(a)  # N: Revealed type is "__main__.A"
 [builtins fixtures/tuple.pyi]
+
+[case testTypeGuardNestedRestrictionAny]
+from typing_extensions import TypeGuard
+from typing import Any
+
+class A: ...
+def f(x: object) -> TypeGuard[A]: ...
+def g(x: object) -> None: ...
+
+def test(x: Any) -> None:
+    if not(f(x) or x):
+        return
+    g(reveal_type(x))  # N: Revealed type is "Union[__main__.A, Any]"
+[builtins fixtures/tuple.pyi]
+
+[case testTypeGuardNestedRestrictionUnionOther]
+from typing_extensions import TypeGuard
+from typing import Any
+
+class A: ...
+class B: ...
+def f(x: object) -> TypeGuard[A]: ...
+def f2(x: object) -> TypeGuard[B]: ...
+def g(x: object) -> None: ...
+
+def test(x: object) -> None:
+    if not(f(x) or f2(x)):
+        return
+    g(reveal_type(x))  # N: Revealed type is "Union[__main__.A, __main__.B]"
+[builtins fixtures/tuple.pyi]
+
+[case testTypeGuardNestedRestrictionUnionIsInstance]
+from typing_extensions import TypeGuard
+from typing import Any, List
+
+class A: ...
+def f(x: List[object]) -> TypeGuard[List[str]]: ...
+def g(x: object) -> None: ...
+
+def test(x: List[object]) -> None:
+    if not(f(x) or isinstance(x, A)):
+        return
+    g(reveal_type(x))  # N: Revealed type is "Union[builtins.list[builtins.str], __main__.<subclass of "list" and "A">]"
+[builtins fixtures/tuple.pyi]