[ty] Ensure Literal types are considered assignable to anything their Instance supertypes are assignable to

crates/ty_python_semantic/resources/mdtest/type_properties/is_assignable_to.md

@@ -97,12 +97,19 @@ turn a subtype of `str`:
 ```py
 from ty_extensions import static_assert, is_assignable_to
 from typing_extensions import Literal, LiteralString
+from typing import Sequence, Any
 
 static_assert(is_assignable_to(Literal["foo"], Literal["foo"]))
 static_assert(is_assignable_to(Literal["foo"], LiteralString))
 static_assert(is_assignable_to(Literal["foo"], str))
+static_assert(is_assignable_to(Literal["foo"], Sequence))
+static_assert(is_assignable_to(Literal["foo"], Sequence[str]))
+static_assert(is_assignable_to(Literal["foo"], Sequence[Any]))
 
 static_assert(is_assignable_to(LiteralString, str))
+static_assert(is_assignable_to(LiteralString, Sequence))
+static_assert(is_assignable_to(LiteralString, Sequence[str]))
+static_assert(is_assignable_to(LiteralString, Sequence[Any]))
 
 static_assert(not is_assignable_to(Literal["foo"], Literal["bar"]))
 static_assert(not is_assignable_to(str, Literal["foo"]))

crates/ty_python_semantic/src/types.rs

@@ -1655,6 +1655,13 @@ impl<'db> Type<'db> {
                 }
             }
 
+            _ if self
+                .literal_fallback_instance(db)
+                .is_some_and(|instance| instance.is_assignable_to(db, target)) =>
+            {
+                true
+            }
+
             (Type::ClassLiteral(class_literal), Type::Callable(_)) => {
                 if let Some(callable) = class_literal.into_callable(db) {
                     return callable.is_assignable_to(db, target);