zeroize_derive: Build fails on latest nightly

[devashishdxt]

If you have following tuple struct:

#[derive(Zeroize, ZeroizeOnDrop)]
struct MyNum(u8);

The build fails with the following error:

#[derive(Zeroize, ZeroizeOnDrop)]
         ^^^^^^^ invalid suffix `usize`

This may be because the generated implementation looks like this:

impl Zeroize for MyNum {
    fn zeroize(&mut self) {
        self.0usize.zeroize()
    }
}

Possible reasons:
Recently, this pull request was merged: rust-lang/rust#59421 which introduced this regression: rust-lang/rust#59553

Playground: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=1fdfb92bcacca661092abdce42cf8810

[tarcieri]

It seems I should've used synstructure to walk the fields of the struct. Not sure if that'd address this in particular, but I'd hope it would at least make it not-my-problem.

[tarcieri]

This should hopefully be fixed by the move to synstructure