NewType doesn't work with tuples

[zsol]

Describe the Bug

Foo = NewType("Foo", tuple[int, int])

complains that the second argument to NewType is invalid.

(I actually expected type Foo = NewType(...) to work, but that doesn't seem to work in any other type checker either.

Sandbox Link

https://pyrefly.org/sandbox/?code=GYJw9gtgBALgngBwJYDsDmUkQWEMoBUAUEQGJhhQC8UAcgKYDuAKovQBQBE5YnANLACuCADb0A2qhgCpAXQCUJIA

(Only applicable for extension issues) IDE Information

No response

[yangdanny97]

The spec says:

NewType accepts exactly two arguments: a name for the new unique type, and a base class. The latter should be a proper class (i.e., not a type construct like Union, etc.), or another unique type created by calling NewType.

So NewType("Foo", ...) would be invalid.

I think we're tripping up because tuples have 2 different representations internally due to the special behaviors it requires, so Pyrefly doesn't consider it to be a "proper" class. We could convert it to a class, but I think right now the conversion is lossy since the class representation is equivalent to an unbounded tuple.

[yangdanny97]

Filed #278 which is a separate/underlying issue

[zsol]

So NewType("Foo", ...) would be invalid.

Sorry I meant

type Foo = NewType("Foo", tuple[int, int])