Prototype: Add annotations command

[Morriar]

Motivation

Provide a way to share shims across projects:

$ tapioca annotations

This is feature is similar to the sorbet-typed command of srb.

Implementation

This command follows these steps:

1. Gather the central repository index.json (see below)
2. List all the gems from the project Gemfile.lock
3. Delete all files in sorbet/rbi/annotations that do not match the gems inside Gemfile.lock
4. For each gem in Gemfile.lock, if the gem is listed in index.json, download it and store it in sorbet/rbi/annotations/

The structure of the repo must be as follows:

index.json
rbi/
    annotations/
        gem1.rbi
        gem2.rbi

For now, the structure of the index.json is the following:

{
  "gem1": {},
  "gem2": {},
}

Where gem1 and gem2 are the names of gems we can find in the repo under /rbi/annotations/. The {} hash will be used to store options later. We use a hash rather than an array to avoid duplicated entries.

There are a lot of TODOs remaining:

• Handle multiple repos
• Handle private repos
• Handle gem versioning
• Merge conflicts between repos

But I think this is enough to get us started.

An example of repository can be found at https://github.com/Shopify/rbi-central.

Tests

See automated tests.

Special thanks to @KaanOzkan who has been instrumental on making all of this working internally and ready to open-source.

[paracycle]

I have a few nitpicks but LGTM. We can iterate on this later, once we see people using it.