[ty] Fix normalization of unions containing instances parameterized with unions (#18112)

Author: AlexWaygood

crates/ty_python_semantic/resources/mdtest/directives/cast.md

@@ -73,5 +73,8 @@ def f(x: Any, y: Unknown, z: Any | str | int):
     c = cast(Unknown, y)
     reveal_type(c)  # revealed: Unknown
 
-    d = cast(str | int | Any, z)  # error: [redundant-cast]
+    d = cast(Unknown, x)
+    reveal_type(d)  # revealed: Unknown
+
+    e = cast(str | int | Any, z)  # error: [redundant-cast]
 ```

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

@@ -118,6 +118,23 @@ class R: ...
 static_assert(is_equivalent_to(Intersection[tuple[P | Q], R], Intersection[tuple[Q | P], R]))
 ```
 
+## Unions containing generic instances parameterized by unions
+
+```toml
+[environment]
+python-version = "3.12"
+```
+
+```py
+from ty_extensions import is_equivalent_to, static_assert
+
+class A: ...
+class B: ...
+class Foo[T]: ...
+
+static_assert(is_equivalent_to(A | Foo[A | B], Foo[B | A] | A))
+```
+
 ## Callable
 
 ### Equivalent

crates/ty_python_semantic/src/types.rs

@@ -985,15 +985,15 @@ impl<'db> Type<'db> {
             Type::Tuple(tuple) => Type::Tuple(tuple.normalized(db)),
             Type::Callable(callable) => Type::Callable(callable.normalized(db)),
             Type::ProtocolInstance(protocol) => protocol.normalized(db),
+            Type::NominalInstance(instance) => Type::NominalInstance(instance.normalized(db)),
+            Type::Dynamic(_) => Type::any(),
             Type::LiteralString
-            | Type::NominalInstance(_)
             | Type::PropertyInstance(_)
             | Type::AlwaysFalsy
             | Type::AlwaysTruthy
             | Type::BooleanLiteral(_)
             | Type::BytesLiteral(_)
             | Type::StringLiteral(_)
-            | Type::Dynamic(_)
             | Type::Never
             | Type::FunctionLiteral(_)
             | Type::MethodWrapper(_)
@@ -1007,10 +1007,7 @@ impl<'db> Type<'db> {
             | Type::IntLiteral(_)
             | Type::BoundSuper(_)
             | Type::SubclassOf(_) => self,
-            Type::GenericAlias(generic) => {
-                let specialization = generic.specialization(db).normalized(db);
-                Type::GenericAlias(GenericAlias::new(db, generic.origin(db), specialization))
-            }
+            Type::GenericAlias(generic) => Type::GenericAlias(generic.normalized(db)),
             Type::TypeVar(typevar) => match typevar.bound_or_constraints(db) {
                 Some(TypeVarBoundOrConstraints::UpperBound(bound)) => {
                     Type::TypeVar(TypeVarInstance::new(

crates/ty_python_semantic/src/types/class.rs

@@ -164,6 +164,10 @@ pub struct GenericAlias<'db> {
 }
 
 impl<'db> GenericAlias<'db> {
+    pub(super) fn normalized(self, db: &'db dyn Db) -> Self {
+        Self::new(db, self.origin(db), self.specialization(db).normalized(db))
+    }
+
     pub(crate) fn definition(self, db: &'db dyn Db) -> Definition<'db> {
         self.origin(db).definition(db)
     }
@@ -207,6 +211,13 @@ pub enum ClassType<'db> {
 
 #[salsa::tracked]
 impl<'db> ClassType<'db> {
+    pub(super) fn normalized(self, db: &'db dyn Db) -> Self {
+        match self {
+            Self::NonGeneric(_) => self,
+            Self::Generic(generic) => Self::Generic(generic.normalized(db)),
+        }
+    }
+
     /// Returns the class literal and specialization for this class. For a non-generic class, this
     /// is the class itself. For a generic alias, this is the alias's origin.
     pub(crate) fn class_literal(

crates/ty_python_semantic/src/types/infer.rs

@@ -5048,16 +5048,16 @@ impl<'db> TypeInferenceBuilder<'db> {
                                             overload.parameter_types()
                                         {
                                             let db = self.db();
-                                            if (source_type.is_equivalent_to(db, *casted_type)
-                                                || source_type.normalized(db)
-                                                    == casted_type.normalized(db))
-                                                && !source_type.any_over_type(db, &|ty| {
-                                                    matches!(
-                                                        ty,
-                                                        Type::Dynamic(dynamic)
-                                                            if dynamic != DynamicType::Any
-                                                    )
-                                                })
+                                            let contains_unknown_or_todo = |ty| matches!(ty, Type::Dynamic(dynamic) if dynamic != DynamicType::Any);
+                                            if source_type.is_equivalent_to(db, *casted_type)
+                                                || (source_type.normalized(db)
+                                                    == casted_type.normalized(db)
+                                                    && !casted_type.any_over_type(db, &|ty| {
+                                                        contains_unknown_or_todo(ty)
+                                                    })
+                                                    && !source_type.any_over_type(db, &|ty| {
+                                                        contains_unknown_or_todo(ty)
+                                                    }))
                                             {
                                                 if let Some(builder) = self
                                                     .context

crates/ty_python_semantic/src/types/instance.rs

@@ -75,6 +75,10 @@ impl<'db> NominalInstanceType<'db> {
         }
     }
 
+    pub(super) fn normalized(self, db: &'db dyn Db) -> Self {
+        Self::from_class(self.class.normalized(db))
+    }
+
     pub(super) fn is_subtype_of(self, db: &'db dyn Db, other: Self) -> bool {
         // N.B. The subclass relation is fully static
         self.class.is_subclass_of(db, other.class)