[ty] Respect the gradual guarantee when narrowing using isinstance() and issubclass()

crates/ty_python_semantic/resources/mdtest/narrow/isinstance.md

@@ -211,3 +211,100 @@ def f(
     else:
         reveal_type(d)  # revealed: P & ~AlwaysFalsy
 ```
+
+## Narrowing if an object of type `Any` or `Unknown` is used as the second argument
+
+In order to preserve the gradual guarantee, we intersect with the type of the second argument if the
+type of the second argument is a dynamic type:
+
+```py
+from typing import Any
+from something_unresolvable import SomethingUnknown  # error: [unresolved-import]
+
+class Foo: ...
+
+def f(a: Foo, b: Any):
+    if isinstance(a, SomethingUnknown):
+        reveal_type(a)  # revealed: Foo & Unknown
+
+    if isinstance(a, b):
+        reveal_type(a)  # revealed: Foo & Any
+```
+
+## Narrowing if an object with an intersection/union/TypeVar type is used as the second argument
+
+If an intersection with only positive members is used as the second argument, and all positive
+members of the intersection are valid arguments for the second argument to `isinstance()`, we
+intersect with each positive member of the intersection:
+
+```toml
+[environment]
+python-version = "3.12"
+```
+
+```py
+from typing import Any
+from ty_extensions import Intersection
+
+class Foo: ...
+
+class Bar:
+    attribute: int
+
+class Baz:
+    attribute: str
+
+def f(x: Foo, y: Intersection[type[Bar], type[Baz]], z: type[Any]):
+    if isinstance(x, y):
+        reveal_type(x)  # revealed: Foo & Bar & Baz
+
+    if isinstance(x, z):
+        reveal_type(x)  # revealed: Foo & Any
+```
+
+The same if a union type is used:
+
+```py
+def g(x: Foo, y: type[Bar | Baz]):
+    if isinstance(x, y):
+        reveal_type(x)  # revealed: (Foo & Bar) | (Foo & Baz)
+```
+
+And even if a `TypeVar` is used, providing it has valid upper bounds/constraints:
+
+```py
+from typing import TypeVar
+
+T = TypeVar("T", bound=type[Bar])
+
+def h_old_syntax(x: Foo, y: T) -> T:
+    if isinstance(x, y):
+        reveal_type(x)  # revealed: Foo & Bar
+        reveal_type(x.attribute)  # revealed: int
+
+    return y
+
+def h[U: type[Bar | Baz]](x: Foo, y: U) -> U:
+    if isinstance(x, y):
+        reveal_type(x)  # revealed: (Foo & Bar) | (Foo & Baz)
+        reveal_type(x.attribute)  # revealed: int | str
+
+    return y
+```
+
+Or even a tuple of tuple of typevars that have intersection bounds...
+
+```py
+from ty_extensions import Intersection
+
+class Spam: ...
+class Eggs: ...
+class Ham: ...
+class Mushrooms: ...
+
+def i[T: Intersection[type[Bar], type[Baz | Spam]], U: (type[Eggs], type[Ham])](x: Foo, y: T, z: U) -> tuple[T, U]:
+    if isinstance(x, (y, (z, Mushrooms))):
+        reveal_type(x)  # revealed: (Foo & Bar & Baz) | (Foo & Bar & Spam) | (Foo & Eggs) | (Foo & Ham) | (Foo & Mushrooms)
+
+    return (y, z)
+```

crates/ty_python_semantic/resources/mdtest/narrow/issubclass.md

@@ -278,3 +278,82 @@ def _(x: type[UsesMeta1], y: type[UsesMeta2]):
     else:
         reveal_type(y)  # revealed: type[UsesMeta2]
 ```
+
+## Narrowing if an object with an intersection/union/TypeVar type is used as the second argument
+
+If an intersection with only positive members is used as the second argument, and all positive
+members of the intersection are valid arguments for the second argument to `isinstance()`, we
+intersect with each positive member of the intersection:
+
+```toml
+[environment]
+python-version = "3.12"
+```
+
+```py
+from typing import Any, ClassVar
+from ty_extensions import Intersection
+
+class Foo: ...
+
+class Bar:
+    attribute: ClassVar[int]
+
+class Baz:
+    attribute: ClassVar[str]
+
+def f(x: type[Foo], y: Intersection[type[Bar], type[Baz]], z: type[Any]):
+    if issubclass(x, y):
+        reveal_type(x)  # revealed: type[Foo] & type[Bar] & type[Baz]
+
+    if issubclass(x, z):
+        reveal_type(x)  # revealed: type[Foo] & Any
+```
+
+The same if a union type is used:
+
+```py
+def g(x: type[Foo], y: type[Bar | Baz]):
+    if issubclass(x, y):
+        reveal_type(x)  # revealed: (type[Foo] & type[Bar]) | (type[Foo] & type[Baz])
+```
+
+And even if a `TypeVar` is used, providing it has valid upper bounds/constraints:
+
+```py
+from typing import TypeVar
+
+T = TypeVar("T", bound=type[Bar])
+
+def h_old_syntax(x: type[Foo], y: T) -> T:
+    if issubclass(x, y):
+        reveal_type(x)  # revealed: type[Foo] & type[Bar]
+        reveal_type(x.attribute)  # revealed: int
+
+    return y
+
+def h[U: type[Bar | Baz]](x: type[Foo], y: U) -> U:
+    if issubclass(x, y):
+        reveal_type(x)  # revealed: (type[Foo] & type[Bar]) | (type[Foo] & type[Baz])
+        reveal_type(x.attribute)  # revealed: int | str
+
+    return y
+```
+
+Or even a tuple of tuple of typevars that have intersection bounds...
+
+```py
+from ty_extensions import Intersection
+
+class Spam: ...
+class Eggs: ...
+class Ham: ...
+class Mushrooms: ...
+
+def i[T: Intersection[type[Bar], type[Baz | Spam]], U: (type[Eggs], type[Ham])](x: type[Foo], y: T, z: U) -> tuple[T, U]:
+    if issubclass(x, (y, (z, Mushrooms))):
+        # revealed: (type[Foo] & type[Bar] & type[Baz]) | (type[Foo] & type[Bar] & type[Spam]) | (type[Foo] & type[Eggs]) | (type[Foo] & type[Ham]) | (type[Foo] & type[Mushrooms])
+        reveal_type(x)
+
+    return (y, z)
+```

crates/ty_python_semantic/src/types/narrow.rs

@@ -9,8 +9,8 @@ use crate::semantic_index::predicate::{
 use crate::types::function::KnownFunction;
 use crate::types::infer::infer_same_file_expression_type;
 use crate::types::{
-    IntersectionBuilder, KnownClass, SubclassOfType, Truthiness, Type, UnionBuilder,
-    infer_expression_types,
+    ClassLiteral, ClassType, IntersectionBuilder, KnownClass, SubclassOfInner, SubclassOfType,
+    Truthiness, Type, TypeVarBoundOrConstraints, UnionBuilder, infer_expression_types,
 };
 
 use ruff_db::parsed::{ParsedModuleRef, parsed_module};
@@ -167,9 +167,13 @@ impl ClassInfoConstraintFunction {
     /// The `classinfo` argument can be a class literal, a tuple of (tuples of) class literals. PEP 604
     /// union types are not yet supported. Returns `None` if the `classinfo` argument has a wrong type.
     fn generate_constraint<'db>(self, db: &'db dyn Db, classinfo: Type<'db>) -> Option<Type<'db>> {
-        let constraint_fn = |class| match self {
-            ClassInfoConstraintFunction::IsInstance => Type::instance(db, class),
-            ClassInfoConstraintFunction::IsSubclass => SubclassOfType::from(db, class),
+        let constraint_fn = |class: ClassLiteral<'db>| match self {
+            ClassInfoConstraintFunction::IsInstance => {
+                Type::instance(db, class.default_specialization(db))
+            }
+            ClassInfoConstraintFunction::IsSubclass => {
+                SubclassOfType::from(db, class.default_specialization(db))
+            }
         };
 
         match classinfo {
@@ -186,13 +190,70 @@ impl ClassInfoConstraintFunction {
                 if class_literal.is_known(db, KnownClass::Any) {
                     None
                 } else {
-                    Some(constraint_fn(class_literal.default_specialization(db)))
+                    Some(constraint_fn(class_literal))
+                }
+            }
+            Type::SubclassOf(subclass_of_ty) => match subclass_of_ty.subclass_of() {
+                SubclassOfInner::Class(ClassType::NonGeneric(class)) => Some(constraint_fn(class)),
+                // It's not valid to use a generic alias as the second argument to `isinstance()` or `issubclass()`,
+                // e.g. `isinstance(x, list[int])` fails at runtime.
+                SubclassOfInner::Class(ClassType::Generic(_)) => None,
+                SubclassOfInner::Dynamic(dynamic) => Some(Type::Dynamic(dynamic)),
+            },
+            Type::Dynamic(_) => Some(classinfo),
+            Type::Intersection(intersection) => {
+                if intersection.negative(db).is_empty() {
+                    let mut builder = IntersectionBuilder::new(db);
+                    for element in intersection.positive(db) {
+                        builder = builder.add_positive(self.generate_constraint(db, *element)?);
+                    }
+                    Some(builder.build())
+                } else {
+                    // TODO: can we do better here?
+                    None
                 }
             }
-            Type::SubclassOf(subclass_of_ty) => {
-                subclass_of_ty.subclass_of().into_class().map(constraint_fn)
+            Type::Union(union) => {
+                let mut builder = UnionBuilder::new(db);
+                for element in union.elements(db) {
+                    builder = builder.add(self.generate_constraint(db, *element)?);
+                }
+                Some(builder.build())
             }
-            _ => None,
+            Type::TypeVar(type_var) => match type_var.bound_or_constraints(db)? {
+                TypeVarBoundOrConstraints::UpperBound(bound) => self.generate_constraint(db, bound),
+                TypeVarBoundOrConstraints::Constraints(constraints) => {
+                    self.generate_constraint(db, Type::Union(constraints))
+                }
+            },
+
+            // It's not valid to use a generic alias as the second argument to `isinstance()` or `issubclass()`,
+            // e.g. `isinstance(x, list[int])` fails at runtime.
+            Type::GenericAlias(_) => None,
+
+            Type::AlwaysFalsy
+            | Type::AlwaysTruthy
+            | Type::BooleanLiteral(_)
+            | Type::BoundMethod(_)
+            | Type::BoundSuper(_)
+            | Type::BytesLiteral(_)
+            | Type::Callable(_)
+            | Type::DataclassDecorator(_)
+            | Type::Never
+            | Type::MethodWrapper(_)
+            | Type::ModuleLiteral(_)
+            | Type::FunctionLiteral(_)
+            | Type::ProtocolInstance(_)
+            | Type::PropertyInstance(_)
+            | Type::SpecialForm(_)
+            | Type::NominalInstance(_)
+            | Type::LiteralString
+            | Type::StringLiteral(_)
+            | Type::IntLiteral(_)
+            | Type::KnownInstance(_)
+            | Type::TypeIs(_)
+            | Type::WrapperDescriptor(_)
+            | Type::DataclassTransformer(_) => None,
         }
     }
 }