Fix some higher-order behavior of TypeGuard and TypeIs

docs/changelog.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+- Fix some higher-order behavior of `TypeGuard` and `TypeIs` (#719)
 - Add support for `TypeIs` from PEP 742 (#718)
 - More PEP 695 support: generic classes and functions. Scoping rules
   are not yet fully implemented. (#703)

pyanalyze/name_check_visitor.py

@@ -1986,6 +1986,11 @@ def visit_FunctionDef(self, node: FunctionDefNode) -> Value:
                 expected_return = info.return_annotation | KnownValue(NotImplemented)
             else:
                 expected_return = info.return_annotation
+            if isinstance(expected_return, AnnotatedValue):
+                expected_return, _ = unannotate_value(expected_return, TypeIsExtension)
+                expected_return, _ = unannotate_value(
+                    expected_return, TypeGuardExtension
+                )
 
             with self.asynq_checker.set_func_name(
                 node.name,

pyanalyze/test_typeis.py

@@ -126,10 +126,8 @@ def main(a: int):
 
     @assert_passes()
     def testTypeIsHigherOrder(self):
-        import collections.abc
         from typing import Callable, TypeVar, Iterable, List
-        from typing_extensions import TypeIs
-        from pyanalyze.value import assert_is_value, GenericValue, AnyValue, AnySource
+        from typing_extensions import TypeIs, assert_type
 
         T = TypeVar("T")
         R = TypeVar("R")
@@ -143,13 +141,7 @@ def is_float(a: object) -> TypeIs[float]:
         def capybara() -> None:
             a: List[object] = ["a", 0, 0.0]
             b = filter(is_float, a)
-            # TODO should be Iterable[float]
-            assert_is_value(
-                b,
-                GenericValue(
-                    collections.abc.Iterable, [AnyValue(AnySource.generic_argument)]
-                ),
-            )
+            assert_type(b, Iterable[float])
 
     @assert_passes()
     def testTypeIsMethod(self):
@@ -277,10 +269,8 @@ def main1(a: object) -> None:
 
     @assert_passes()
     def testTypeIsOverload(self):
-        import collections.abc
         from typing import Callable, Iterable, Iterator, List, Optional, TypeVar
-        from typing_extensions import TypeIs, overload
-        from pyanalyze.value import assert_is_value, GenericValue, AnyValue, AnySource
+        from typing_extensions import TypeIs, overload, assert_type
 
         T = TypeVar("T")
         R = TypeVar("R")
@@ -302,21 +292,13 @@ def is_int_typeguard(a: object) -> TypeIs[int]:
         def is_int_bool(a: object) -> bool:
             return False
 
-        iter_any = GenericValue(
-            collections.abc.Iterator, [AnyValue(AnySource.generic_argument)]
-        )
-
         def main(a: List[Optional[int]]) -> None:
             bb = filter(lambda x: x is not None, a)
-            # TODO Iterator[Optional[int]]
-            assert_is_value(bb, iter_any)
-            # Also, if you replace 'bool' with 'Any' in the second overload, bb is Iterator[Any]
+            assert_type(bb, Iterator[Optional[int]])
             cc = filter(is_int_typeguard, a)
-            # TODO Iterator[int]
-            assert_is_value(cc, iter_any)
+            assert_type(cc, Iterator[int])
             dd = filter(is_int_bool, a)
-            # TODO Iterator[Optional[int]]
-            assert_is_value(dd, iter_any)
+            assert_type(dd, Iterator[Optional[int]])
 
     @assert_passes()
     def testTypeIsDecorated(self):
@@ -345,7 +327,7 @@ def is_float(self, a: object) -> TypeIs[float]:
                 return False
 
         class D(C):
-            def is_float(self, a: object) -> bool:  # TODO: incompatible_override
+            def is_float(self, a: object) -> bool:  # E: incompatible_override
                 return False
 
     @assert_passes()
@@ -576,10 +558,10 @@ def with_bool(o: object) -> bool:
             return False
 
         accepts_typeguard(with_typeguard)
-        accepts_typeguard(with_bool)  # TODO error
+        accepts_typeguard(with_bool)  # E: incompatible_argument
 
-        different_typeguard(with_typeguard)  # TODO error
-        different_typeguard(with_bool)  # TODO error
+        different_typeguard(with_typeguard)  # E: incompatible_argument
+        different_typeguard(with_bool)  # E: incompatible_argument
 
     @assert_passes()
     def testTypeIsAsGenericFunctionArg(self):
@@ -602,7 +584,7 @@ def with_bool(o: object) -> bool:
 
         accepts_typeguard(with_bool_typeguard)
         accepts_typeguard(with_str_typeguard)
-        accepts_typeguard(with_bool)  # TODO error
+        accepts_typeguard(with_bool)  # E: incompatible_argument
 
     @assert_passes()
     def testTypeIsAsOverloadedFunctionArg(self):
@@ -662,9 +644,9 @@ def with_typeguard_b(o: object) -> TypeIs[B]:
         def with_typeguard_c(o: object) -> TypeIs[C]:
             return False
 
-        accepts_typeguard(with_typeguard_a)  # TODO error
+        accepts_typeguard(with_typeguard_a)  # E: incompatible_argument
         accepts_typeguard(with_typeguard_b)
-        accepts_typeguard(with_typeguard_c)  # TODO error
+        accepts_typeguard(with_typeguard_c)  # E: incompatible_argument
 
     @assert_passes()
     def testTypeIsWithIdentityGeneric(self):
@@ -786,7 +768,7 @@ def typeguard(x: object, y: str) -> TypeIs[str]: ...
         @overload
         def typeguard(x: object, y: int) -> TypeIs[int]: ...
 
-        def typeguard(x: object, y: Union[int, str]) -> Union[TypeIs[int], TypeIs[str]]:
+        def typeguard(x: object, y: Union[int, str]) -> bool:
             return False
 
         def capybara(x: object) -> None:
@@ -805,7 +787,7 @@ def capybara(x: object) -> None:
     @assert_passes()
     def testGenericAliasWithTypeIs(self):
         from typing import Callable, List, TypeVar
-        from typing_extensions import TypeIs
+        from typing_extensions import TypeIs, assert_type
 
         T = TypeVar("T")
         A = Callable[[object], TypeIs[List[T]]]
@@ -817,8 +799,7 @@ def test(f: A[T]) -> T:
             raise NotImplementedError
 
         def capybara() -> None:
-            pass
-            # TODO: assert_type(test(foo), List[str])
+            assert_type(test(foo), str)
 
     @assert_passes()
     def testNoCrashOnDunderCallTypeIs(self):

pyanalyze/value.py

@@ -1853,6 +1853,12 @@ def substitute_typevars(self, typevars: TypeVarMap) -> "Extension":
     def walk_values(self) -> Iterable[Value]:
         return []
 
+    def can_assign(self, value: Value, ctx: CanAssignContext) -> CanAssign:
+        return {}
+
+    def can_be_assigned(self, value: Value, ctx: CanAssignContext) -> CanAssign:
+        return {}
+
 
 @dataclass(frozen=True)
 class CustomCheckExtension(Extension):
@@ -1868,6 +1874,12 @@ def substitute_typevars(self, typevars: TypeVarMap) -> "Extension":
     def walk_values(self) -> Iterable[Value]:
         yield from self.custom_check.walk_values()
 
+    def can_assign(self, value: Value, ctx: CanAssignContext) -> CanAssign:
+        return self.custom_check.can_assign(value, ctx)
+
+    def can_be_assigned(self, value: Value, ctx: CanAssignContext) -> CanAssign:
+        return self.custom_check.can_be_assigned(value, ctx)
+
 
 @dataclass(frozen=True)
 class ParameterTypeGuardExtension(Extension):
@@ -1928,6 +1940,26 @@ def substitute_typevars(self, typevars: TypeVarMap) -> Extension:
     def walk_values(self) -> Iterable[Value]:
         yield from self.guarded_type.walk_values()
 
+    def can_assign(self, value: Value, ctx: CanAssignContext) -> CanAssign:
+        can_assign_maps = []
+        if isinstance(value, AnnotatedValue):
+            for ext in value.get_metadata_of_type(Extension):
+                if isinstance(ext, TypeIsExtension):
+                    return CanAssignError("TypeGuard is not compatible with TypeIs")
+                elif isinstance(ext, TypeGuardExtension):
+                    # TypeGuard is covariant
+                    left_can_assign = self.guarded_type.can_assign(
+                        ext.guarded_type, ctx
+                    )
+                    if isinstance(left_can_assign, CanAssignError):
+                        return CanAssignError(
+                            "Incompatible types in TypeIs", children=[left_can_assign]
+                        )
+                    can_assign_maps.append(left_can_assign)
+        if not can_assign_maps:
+            return CanAssignError(f"{value} is not a TypeGuard")
+        return unify_bounds_maps(can_assign_maps)
+
 
 @dataclass(frozen=True)
 class TypeIsExtension(Extension):
@@ -1947,6 +1979,33 @@ def substitute_typevars(self, typevars: TypeVarMap) -> Extension:
     def walk_values(self) -> Iterable[Value]:
         yield from self.guarded_type.walk_values()
 
+    def can_assign(self, value: Value, ctx: CanAssignContext) -> CanAssign:
+        can_assign_maps = []
+        if isinstance(value, AnnotatedValue):
+            for ext in value.get_metadata_of_type(Extension):
+                if isinstance(ext, TypeGuardExtension):
+                    return CanAssignError("TypeGuard is not compatible with TypeIs")
+                elif isinstance(ext, TypeIsExtension):
+                    # TypeIs is invariant
+                    left_can_assign = self.guarded_type.can_assign(
+                        ext.guarded_type, ctx
+                    )
+                    if isinstance(left_can_assign, CanAssignError):
+                        return CanAssignError(
+                            "Incompatible types in TypeIs", children=[left_can_assign]
+                        )
+                    right_can_assign = ext.guarded_type.can_assign(
+                        self.guarded_type, ctx
+                    )
+                    if isinstance(right_can_assign, CanAssignError):
+                        return CanAssignError(
+                            "Incompatible types in TypeIs", children=[right_can_assign]
+                        )
+                    can_assign_maps += [left_can_assign, right_can_assign]
+        if not can_assign_maps:
+            return CanAssignError(f"{value} is not a TypeIs")
+        return unify_bounds_maps(can_assign_maps)
+
 
 @dataclass(frozen=True)
 class HasAttrGuardExtension(Extension):
@@ -2120,8 +2179,8 @@ def can_assign(self, other: Value, ctx: CanAssignContext) -> CanAssign:
         if isinstance(can_assign, CanAssignError):
             return can_assign
         bounds_maps = [can_assign]
-        for custom_check in self.get_metadata_of_type(CustomCheckExtension):
-            custom_can_assign = custom_check.custom_check.can_assign(other, ctx)
+        for ext in self.get_metadata_of_type(Extension):
+            custom_can_assign = ext.can_assign(other, ctx)
             if isinstance(custom_can_assign, CanAssignError):
                 return custom_can_assign
             bounds_maps.append(custom_can_assign)
@@ -2132,8 +2191,8 @@ def can_be_assigned(self, other: Value, ctx: CanAssignContext) -> CanAssign:
         if isinstance(can_assign, CanAssignError):
             return can_assign
         bounds_maps = [can_assign]
-        for custom_check in self.get_metadata_of_type(CustomCheckExtension):
-            custom_can_assign = custom_check.custom_check.can_be_assigned(other, ctx)
+        for ext in self.get_metadata_of_type(Extension):
+            custom_can_assign = ext.can_be_assigned(other, ctx)
             if isinstance(custom_can_assign, CanAssignError):
                 return custom_can_assign
             bounds_maps.append(custom_can_assign)