midudev Sorbet RBI Generation Skill
Generate or update Sorbet type signatures in separate .rbi files. Supports both full generation from scratch and partial updates for individual changed 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 execif the project has Gemfile. - You MUST use
sig { }block syntax for method signatures. - You MUST add
extend T::Sigto classes/modules before usingsig. - You MUST NOT add method bodies in RBI files - only signatures and empty method definitions.
- You MUST place RBI files in
./rbidirectory. - You MUST use the tracking file when processing multiple files to ensure no files are missed.
Multi-File Processing
When processing multiple Ruby files, create a tracking file to ensure all files are covered:
Create tracking file
.sorbet-rbi-generation-todo.tmp:[ ] app/models/user.rb [ ] app/models/post.rb [ ] app/services/auth_service.rbProcess files one by one:
- Take the next pending
[ ]entry - Complete all steps (1-5) for that file
- Mark as processed
[x] - Save the tracking file
- Continue to next pending entry
- Take the next pending
Cleanup: Remove the tracking file after all files are processed:
rm .sorbet-rbi-generation-todo.tmp
If interrupted, the tracking file allows resuming from where you left off.
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.
Determine the correct RBI directory:
Place RBI files in
./rbidirectory. Sorbet reads all.rbifiles from this location.RBI files are needed to describe code Sorbet cannot understand statically:
- Gem definitions
- Methods created with
define_methodormethod_missing - Constants from
const_get/const_set - Dynamic ancestors added via
extend - DSL-generated methods (Rails, ActiveRecord, etc.)
Create the RBI file with typed sigil:
# typed: strictAdd
extend T::Sigto each class/module:class MyClass extend T::Sig endAdd 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.untypedwith proper types. - Use code context, method calls, and tests to infer types.
- Use
T.untypedonly 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.untypedtypes. - 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