feat: Add support for RBS inline type annotations

[pcasaretto]

Summary

This PR adds support for recognizing RBS (Ruby Signature) inline type annotation comments in Ruby code. This enables better editor support for Ruby's type annotations by distinguishing them from regular comments in the AST.

Motivation

RBS is Ruby's official type signature language, and increasingly Ruby developers are using inline RBS comments to annotate their code with type information:

#: (Integer) -> String
def to_hex(num)
  num.to_s(16)
end

x = 42 #: Integer

Currently, tree-sitter-ruby treats these as regular comments, making it impossible for editors to provide enhanced support for type annotations (different highlighting, hover information, etc.).

Implementation

This implementation takes a minimal approach - it recognizes RBS comment patterns without parsing the type syntax itself:

• #: comments are recognized as rbs_type_comment tokens
• #| comments (multi-line continuations) are recognized as rbs_continuation_comment tokens
• Regular # comments remain unchanged

Why not parse the full RBS syntax?

1. Separation of concerns: RBS is effectively a different language. Tools that need to understand RBS types can extract the comment content and parse it with a dedicated RBS parser.
2. Simplicity: Full RBS syntax would require 200+ additional grammar rules
3. Maintenance: Keeping them separate means each parser can evolve independently

Changes

• grammar.js: Added rbs_type_comment and rbs_continuation_comment token rules
• queries/highlights.scm: Added highlighting as @type.annotation (vs @comment for regular comments)
• test/corpus/rbs_annotations.txt: Added comprehensive test coverage with 11 test cases

Testing

All tests pass (301 total, including 11 new RBS tests):

• ✅ Method signatures
• ✅ Variable annotations
• ✅ Type assertions
• ✅ Multi-line signatures
• ✅ Complex types (unions, generics, optionals)
• ✅ Mixed regular and RBS comments

Impact

• Non-breaking: Existing Ruby parsing is completely unchanged
• Editor-friendly: Provides foundation for enhanced type annotation support
• Future-proof: Can be extended if needed without breaking changes

Related Work

• tree-sitter-rbs - Standalone parser for .rbs files
• RBS documentation
• Sorbet RBS support

[Morriar]

Could you add a test showing the behavior if the #: is found inside a string:

puts "#: Hello, World"

[pcasaretto]

Done!

[pcasaretto]

Added some more edge cases involving strings.

[Morriar]

This is a cool change, how do we get someone from the team to review/merge it? @amaanq I see you've been active in this repo recently 🙏