[ty] Improve the Display for generic type[] types (#19667)

Author: AlexWaygood

crates/ty_python_semantic/resources/mdtest/type_of/basic.md

@@ -151,6 +151,28 @@ class Foo(type[int]): ...
 reveal_type(Foo.__mro__)  # revealed: tuple[<class 'Foo'>, @Todo(GenericAlias instance), <class 'object'>]
 ```
 
+## Display of generic `type[]` types
+
+```toml
+[environment]
+python-version = "3.12"
+```
+
+```py
+from typing import Generic, TypeVar
+
+class Foo[T]: ...
+
+S = TypeVar("S")
+
+class Bar(Generic[S]): ...
+
+def _(x: Foo[int], y: Bar[str], z: list[bytes]):
+    reveal_type(type(x))  # revealed: type[Foo[int]]
+    reveal_type(type(y))  # revealed: type[Bar[str]]
+    reveal_type(type(z))  # revealed: type[list[bytes]]
+```
+
 ## `@final` classes
 
 `type[]` types are eagerly converted to class-literal types if a class decorated with `@final` is

crates/ty_python_semantic/src/types/display.rs

@@ -109,9 +109,12 @@ impl Display for DisplayRepresentation<'_> {
             }
             Type::GenericAlias(generic) => write!(f, "<class '{}'>", generic.display(self.db)),
             Type::SubclassOf(subclass_of_ty) => match subclass_of_ty.subclass_of() {
-                // Only show the bare class name here; ClassBase::display would render this as
-                // type[<class 'Foo'>] instead of type[Foo].
-                SubclassOfInner::Class(class) => write!(f, "type[{}]", class.name(self.db)),
+                SubclassOfInner::Class(ClassType::NonGeneric(class)) => {
+                    write!(f, "type[{}]", class.name(self.db))
+                }
+                SubclassOfInner::Class(ClassType::Generic(alias)) => {
+                    write!(f, "type[{}]", alias.display(self.db))
+                }
                 SubclassOfInner::Dynamic(dynamic) => write!(f, "type[{dynamic}]"),
             },
             Type::SpecialForm(special_form) => special_form.fmt(f),