Type_length_limit attribute behavior

[Wiktor]

What reference says about the attribute:

The type_length_limit attribute limits the maximum number of type substitutions made when constructing a concrete type during monomorphization. It is applied at the crate level, and uses the MetaNameValueStr syntax to set the limit based on the number of type substitutions.

#![type_length_limit = "4"]

fn f<T>(x: T) {}

// This fails to compile because monomorphizing to
// `f::<((((i32,), i32), i32), i32)>` requires more than 4 type elements.
f(((((1,), 2), 3), 4));

My question:
Is this code example correct? In my mind, there's only one instance of the function after monomorphization (f::<((((i32,), i32), i32), i32)>) and it fails to compile because the limit is too low to even compile empty main function.

[drewtato]

It's not how many functions can be produced from one generic function, it's how deeply nested generics can be.

T 
-> (A, B)
-> ((C, D), i32)
-> (((E, F), i32), i32)
-> ((((G,), i32), i32), i32)
-> ((((i32,), i32), i32), i32)

These are the 5 substitutions.

I've never seen anyone even mention this attribute, probably because 1 million is an incredibly high limit, and the type solver usually recognizes infinite types as being infinite.