TypeGuessr

Warning: This project is under active development. Breaking changes may occur without notice.

A heuristic type inference CLI for Ruby. Detects potential NoMethodError sites by analyzing method call patterns — no type annotations needed.

TypeGuessr uses duck-type inference: if a variable calls methods foo, bar, and baz, it finds all classes that define ALL three methods. If no class matches (zero candidates), that's a potential NoMethodError.

The method index is built at runtime via ObjectSpace, so it includes all loaded classes, mixins, and inherited methods — no static analysis gaps.

Add to your project's Gemfile:

group :development do
  gem 'type-guessr', require: false
end

Then run:

bundle install

# Check current project
bundle exec type-guessr check

# Check a specific project
bundle exec type-guessr check --path=/path/to/project

# Rails project (loads full environment)
bundle exec type-guessr check --boot=config/environment.rb

# JSON output for CI/tooling
bundle exec type-guessr check --json

Found 3 zero-candidate node(s) in 42 project files:

app/services/order_processor.rb:
  L15  ParamNode  payment  [charge, refund, status]

app/models/report.rb:
  L42  LocalVariable  data  [transform, validate, export_csv]
  L78  ParamNode  formatter  [header, body, footer, finalize]

Each finding shows a variable/parameter where no class defines ALL the methods called on it.

type-guessr check
       │
       ├── Prism AST walker (static call extraction)
       │     Finds: which methods are called on each variable/parameter
       │
       └── Runtime server (subprocess)
             Boots project via Bundler
             Scans ObjectSpace for all loaded modules
             Builds method index: method_name → Set[class_name]
             Serves queries over stdin/stdout JSON IPC

After checking out the repo, run bin/setup to install dependencies. Then, run bundle exec rspec to run the tests.

Bug reports and pull requests are welcome on GitHub at https://github.com/riseshia/type-guessr.