WIP: Codegen option to create module hierarchy

[kriswuollett]

Work-in-progress PR for generating protobufs in a module hierarchy

• resolves How to import proto file in different packages with same name? #260
• resolves Codegen option to create module hierarchy #438
• resolves Reused names in different protobuf packages #644
• prerequisite gRPC service code generation for tonic #687,

TODO:

• add tests
• code generate the mod.rs files I'm currently writing by hand when testing in a another repo which uses a build.rs snippet like:

let manifest_dir = PathBuf::from(env::var("CARGO_MANIFEST_DIR")?);
let out_dir = manifest_dir.join("src").join("test_pb");
codegen.out_dir(out_dir);
codegen.customize(
    Customize::default()
        .gen_mod_rs_hierarchy_out_dir_mod_name("test_pb".to_owned())
        .gen_mod_rs(false),
);

Need guidance on:

• intended usage of idents, components in RustPath-like structures

[kriswuollett]

Testing output in a tonic::Codec PR that I'll probably move to tonic repo once ready: appbiotic/code#21. I'll be checking in the generated tree of mod.rs files temporarily to show progress. The proto tree seems to compile OK but haven't done comprehensive tests yet.

[stepancheg]

Sorry the project is low support.

If you have some specific question, I'll try to answer.

[kriswuollett]

No worries, the project really helped me get started with ffi this past year, both as user and reading the code. Thanks for checking in on me.

Wanted to do something that made includes like a monorepo. Just switched over to cbindgen this week so I could do a header file per crate and being able to specify adding things like the dependencies includes. Doesn't have all the nice types like safer-ffi, but I only need return and free raw mut ptr structs so works ok at the moment.