Support versionize on packed structs

[rbradford]

Signed-off-by: Rob Bradford [email protected]

[acatangiu]

Changes look good to me.

Could you add a unit-test to exercise this?

[sandreim]

@acatangiu The tests should be added in the versionize crate, it won't work to use the proc macro in the same crate.

@rbradford I'm getting the following error when trying to build the versionize tests using your derive changes, probably something is missing from this PR?

   Compiling versionize_derive v0.1.4 (/home/ANT.AMAZON.COM/sandreim/versionize_derive)
error[E0277]: the trait bound `proc_macro2::TokenTree: syn::token::CustomToken` is not satisfied
   --> /home/ANT.AMAZON.COM/sandreim/versionize_derive/src/lib.rs:223:47
    |
223 |                 while let Some(token) = input.parse()? {
    |                                               ^^^^^ the trait `syn::token::CustomToken` is not implemented for `proc_macro2::TokenTree`
    |
    = note: required because of the requirements on the impl of `syn::token::Token` for `proc_macro2::TokenTree`
    = note: required because of the requirements on the impl of `syn::parse::Parse` for `std::option::Option<proc_macro2::TokenTree>`

error: aborting due to previous error

[acatangiu]

@rbradford do you still need this? Is it building for you?

[rbradford]

@acatangiu Yup, works grand. We use it in production in Cloud Hypervisor.