Sorbet RBI Generation Skill

Generate Sorbet type signatures in separate

.rbi

files. RBI files are used when you cannot or should not modify the original Ruby source - such as for gems, generated code, or legacy codebases.

Instructions

When generating Sorbet RBI signatures, always follow these steps.

Copy this checklist and track your progress:

Sorbet RBI Generation Progress:
- [ ] Step 1: Analyze the Ruby source
- [ ] Step 2: Generate RBI files
- [ ] Step 3: Eliminate `T.untyped` in signatures
- [ ] Step 4: Review and refine signatures
- [ ] Step 5: Validate signatures with Sorbet

Rules

• You MUST NOT run Ruby code of the project.
• You MUST NOT use

  T.untyped

  . Infer the proper type instead.
• You MUST NOT use

  T.unsafe

  - it bypasses type checking entirely.
• You MUST NOT use

  T.cast

  - it forces types without verification.
• You MUST ask the user to provide more details if something is not clear.
• You MUST prepend any command with

  bundle exec

  if the project has Gemfile.
• You MUST use

  sig { }

  block syntax for method signatures.
• You MUST add

  extend T::Sig

  to classes/modules before using

  sig

  .
• You MUST NOT add method bodies in RBI files - only signatures and empty method definitions.
• You MUST place RBI files in

  ./rbi

  directory.

1. Analyze the Ruby Source

Always perform this step.

Read and understand the Ruby source file:

• Identify all classes, modules, methods, constants and instance variables.
• Note inheritance, module inclusion and definitions based on metaprogramming.
• Note visibility modifiers -

  public

  ,

  private

  ,

  protected

  .
• Note type parameters for generic classes.

2. Generate RBI Files

Always perform this step.

1. Determine the correct RBI directory:

   Place RBI files in

   ./rbi

   directory. Sorbet reads all

   .rbi

   files from this location.

   RBI files are needed to describe code Sorbet cannot understand statically:

   • Gem definitions
   • Methods created with

     define_method

     or

     method_missing

   • Constants from

     const_get

     /

     const_set

   • Dynamic ancestors added via

     extend

   • DSL-generated methods (Rails, ActiveRecord, etc.)

2. Create the RBI file with typed sigil:

   # typed: strict
   

3. Add

   extend T::Sig

   to each class/module:

   class MyClass
     extend T::Sig
   end
   

4. Add method stubs with signatures (no method bodies):

Example - Ruby Source:

class User
  attr_reader :name, :age

  def initialize(name, age)
    @name = name
    @age = age
  end

  def greet(greeting)
    "#{greeting}, #{@name}!"
  end
end

Example - RBI File (

rbi/user.rbi

):

# typed: strict

class User
  extend T::Sig

  sig { returns(String) }
  attr_reader :name

  sig { returns(Integer) }
  attr_reader :age

  sig { params(name: String, age: Integer).void }
  def initialize(name, age); end

  sig { params(greeting: String).returns(String) }
  def greet(greeting); end
end

• RBI files mirror structure but contain only signatures and empty method stubs
• See syntax.md for the full Sorbet RBI syntax guide

3. Eliminate

T.untyped

in Signatures

Always perform this step.

• Review all signatures and replace

  T.untyped

  with proper types.
• Use code context, method calls, and tests to infer types.
• Use

  T.untyped

  only as a last resort when type cannot be determined.

4. Review and Refine Signatures

Always perform this step.

• Verify signatures are correct, coherent, and complete.
• Remove unnecessary

  T.untyped

  types.
• Ensure all methods and attributes have signatures.
• Verify class hierarchy and module inclusions match the source.
• Fix any errors and repeat until signatures are correct.

5. Validate Signatures with Sorbet

Always perform this step.

Run Sorbet type checker to validate signatures:

srb tc

Or with bundle:

bundle exec srb tc

This checks:

• Signature syntax correctness
• Type consistency
• Method parameter/return type matching
• Class/module structure matching source

Fix any errors reported and repeat until validation passes.

References

• syntax.md - Sorbet RBI syntax guide
• references/ - Real-world RBI examples from stripe-ruby
• Sorbet RBI documentation - Official RBI docs