Use a proper error for unnecessary priv usage in struct fields.

[flaper87]

This code throws a reserved keyword error instead of warning about the unnecessary visibility.

struct Test {
   priv a: int
}

fn main(){}

test.rs:2:4: 2:8 error: `priv` is a reserved keyword
test.rs:2    priv a: int
             ^~~~

I think we should handle this case and print a proper error message.

[huonw]

priv is no longer a visibility at all, i.e. writing this is similar to writing struct Test { do a: int } as far as the compiler can tell. (It's now just a historical thing that priv ever meant anything.)

However, it seems like an ok idea to explicitly check for the priv reserved word for a little while (just to help people upgrade their code).

[aochagavia]

I would like to do this, but I really don't know where to begin... I don't know anything about the parser, but I know that it is possible to make lints. Would that be useful for this case? Can anybody mentor?

[nrc]

@aochagavia I think there is nothing to do here since it is not a bug, sorry. If you find another similar bug you would like to have a go at, please ping me and I can mentor you (or maybe recommend someone else if its outside my area).

[flaper87]

FWIW, I think it's worth providing a better error in this case since things like struct Test { pub t: int } are allowed. I know pirv is gone but still a nicer upgrade path for users would be nice. Not big deal, I guess.