Import ruby/ruby-signature

[soutaro]

This PR is to move source code from ruby/ruby-signature to ruby/ruby. Waiting for any suggestion to finish the transition. 🙏

The expected workflow is the following:

1. ruby-signature gem is under development for Ruby 2.7.
2. The gem will release for Ruby 2.7 as an opt-in gem.
3. The gem will ship with Ruby 2.8/3.0. (No need to gem install with those versions.)
4. ruby/ruby will be the upstream for the library once this PR get merged.

Questions I have:

• How can I run tests?
• How can I run racc for parser.
• How can I write .gemspec for ruby/ruby repository.

[hsbt]

I have the some concerns.

1. How use test/signature instead of test/ruby-signature? Because the test files for lib/foo are test/foo or test/test_foo.rb in the current structure.
2. How move sig/test to test/sig?

[k0kubun]

Just curious: Is there any motivation to make this default gems instead of bundled gems?

Default gems are double-master development and hard to sync. Because of the maintenance cost, in general I insist that we should not use default gems unless we need to workaround load issues (rubygems, bundler, and its dependencies).

[soutaro]

I'm sorry for the late reply. (It was 1.5 months ago. 😱)

@hsbt Sounds reasonable. I'll try to move the files.

@k0kubun I don't have strong opinion, and it seems like making RBS a bundled gem makes sense to me. What I don't want is having double-master. I strongly want to have one upstream in ruby repository.

[soutaro]

We had talked about this and concluded that ruby-signature repo won't be merged for now. The gem will be ship with Ruby3 as a bundled gem, but the development will continue on ruby/ruby-signature repository.