Maintain a manifest of generated files

[jparise]

This is signifiant rewrite of the compiler task to support manifests,
making us a better mix citizen and adding support for mix clean-based
file cleanup.

Our manifest is written as a binary-encoded Erlang term to give us the
most forward-compatible file format. At the moment, we only store a
manifest version number and the list of generated files, but we may
expand this in the future to include additional dependency information
such as the "version" of the code that was used to generate these files.
See #138 for a more detailed discussion.

[dantswain]

Why add @specs to private functions? It doesn't actively hurt anything but it is a maintenance burden... just curious.

[jparise]

Ironically, I added these when I played with moving some logic into another module, where these functions were public. I continued to find them useful as a way to document the internal arguments.

[dantswain]

lol I started digging around the mix source to see how they handle this and notice you've also been doing your homework @jparise ;)

It really seems like there should be a Mix.CompileTask behaviour or something... I'm still not clear which parts of this hook in to the compiler chain automatically... I assume if one calls mix clean then mix iterates over the compiler tasks and calls clean on each?

The only other feedback I have, and it's a take-it-or-leave-it kind of thing, would be to create a module that encapsulates dealing with the manifest. Might be overkill.

[jparise]

Yeah, I spent a lot of time reading through mix to best understand how tasks like this should work.

• mix clean calls all available clean functions on the modules listed in Mix.compilers.
• mix compile calls all available manifests functions on all compile.* tasks.

Also, I added @recursive true to our compile task, which makes it run recursively when called as part of an umbrella project.

I ultimately decided not to introduce another module because the manifest bits are specific to this task and don't need to be part of our Thrift.Generator code. And reading the updated task end-to-end isn't too complicated, even with these changes.

[sourcelevel-bot]

Ebert has finished reviewing this Pull Request and has found:

• 2 fixed issues! 🎉

But beware that this branch is 14 commits behind the pinterest:thrift_tng branch, and a review of an up to date branch would produce more accurate results.

You can see more details about this review at https://ebertapp.io/github/pinterest/elixir-thrift/pulls/234.