Steep - Gradual Typing for Ruby

Installation

Install via RubyGems.

$ gem install steep --pre

Note that Steep is not released yet (pre-released). Add --pre for gem install.

Requirements

Steep requires Ruby 2.4.

Usage

Steep does not infer types from Ruby programs, but requires declaring types and writing annotations. You have to go on the following three steps.

1. Declare Signatures

Declare signatures in .rbi files.

interface _Foo {
  def do_something: (String) -> any
}

module Fooable : _Foo {
  def foo: (Array<String>) { (String) -> String } -> any
}

class SuperFoo {
  include Fooable

  def name: -> String
  def do_something: (String) -> any
  def bar: (?Symbol, size: Integer) -> Symbol
}

2. Annotate Ruby Code

Write annotations to your Ruby code.

class Foo
  # @implements SuperFoo
  # @type const Helper: FooHelper

  # @dynamic name
  attr_reader :name

  def do_something(string)
    # ...
  end

  def bar(symbol = :default, size:)
    Helper.run_bar(symbol, size: size)
  end
end

3. Type Check

Run steep check command to type check.

$ steep check lib/foo.rb
foo.rb:41:18: NoMethodError: type=FooHelper, method=run_bar
foo.rb:42:24: NoMethodError: type=String, method==~

Commandline

steep check is the command to run type checking.

Signature Directory

Use -I option to specify signature file or signature directory.

$ steep check -I my-types.rbi test.rb

If you don't specify -I option, it assumes sig directory.

Detecting Fallback

When Steep finds a node which cannot be typed, it assumes the type of the node is any. any type does not raise any type error so that fallback to any may hide some type errors.

Using --fallback-any-is-error option prints the fallbacks.

$ steep check --fallback-any-is-error test.rb

Dump All Types

When you are debugging, printing all types of all node in the source code may help.

Use --dump-all-types for that.

$ steep check --dump-all-types test.rb

Examples

You can find examples in smoke directory.

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/soutaro/steep.