Make Rust type rules standalone functions

[joaotgouveia]

Changes the format of the Rust side of type rules to:

fn t<digit>() -> TYPE {
    return DEFAULT-INITIALIZER;
}

Actual changes to rules:

• The initializer for the unsafe rules t1, t2, and t3 in fstream was changed from ::std::fs::File::open("")? to ::std::fs::File::open("").unwrap(). This change was made because the ? operator requires the function to return a value of type Result or Option. Additionally, other rules for file-related types already use ::std::fs::File::open("").unwrap() as an initializer (for example, rule t1 in iostream).

• Added a missing generic parameter to the refcount rules f10 and f11 in unique_ptr. These rules were relying on the struct defined at the top of the type.

[lucic71]

Looks good!

[lucic71]

I think we should add an assert or change init to only accept { X }, not { return X; } or other type of expressions.

[joaotgouveia]

Aren't these two alternatives equivalent in practice? I opted to accept both options because I thought the added flexibility might be useful in the future, particularly when generating these rules automatically. Even if that doesn't turn out to be the case, what would be the disadvantages of allowing both forms?

[lucic71]

Even if that doesn't turn out to be the case, what would be the disadvantages of allowing both forms?

None, { X } just feels more natural

[joaotgouveia]

Should I change it to only allow that form then?

[lucic71]

Yes, please. And also make sure that we only support:

fn t<digit>() -> TYPE {
    DEFAULT-INITIALIZER
}

not

fn t<digit>() -> TYPE {
    expr1;
    expr2;
    ...
    DEFAULT-INITIALIZER
}