Overloading bug (Crystal issue #4775)

test.cr

# Using crystal 0.23.1
# See https://github.com/crystal-lang/crystal/issues/4775
# Run `crystal spec test.cr` to test

# PART 0: Definitions

module Abstract
  abstract class Dog
    def initialize(@color : String)
    end

    abstract def bark
  end

  # Cats are here to show that when the special dog is barking after the special cat's meowing it's still awaited to compile
  abstract class Cat
    def initialize(@color : String)
    end

    abstract def meow
  end

  abstract class Zoo
    def make_some_noise
      color = case rand(2)
              when 0 then "Black"
              else        "White"
              end

      animal = select_animal
      if animal.is_a?(Abstract::Dog.class)
        animal.new(color).bark
      elsif animal.is_a?(Abstract::Cat.class)
        animal.new(color).meow
      end
    end

    private abstract def select_animal : Abstract::Dog.class | Abstract::Cat.class | Nil
  end
end

module MyDogs
  class Special < Abstract::Dog
    # This dog is unusual, it has size
    def initialize(color : String, @size : Int32)
      super(color)
    end

    def bark
      p "Specical #{@color} dog with a size of #{@size} inches barks"
    end
  end

  class B < Abstract::Dog
    def bark
      p "#{@color} dog B barks"
    end
  end

  class C < Abstract::Dog
    def bark
      p "#{@color} dog C barks"
    end
  end

  class D < Abstract::Dog
    def bark
      p "#{@color} dog D barks"
    end
  end
end

module MyCats
  # This Cat utilizes unusual Dog!
  class Special < Abstract::Cat
    def meow
      p "Special #{@color} cat meows to a same big special dog, and it answers: "
      MyDogs::Special.new(@color, 42).bark
    end
  end

  class B < Abstract::Cat
    def meow
      p "#{@color} cat B meows"
    end
  end
end

# PART 1: Successfully compiled

require "spec"

class MyZoo1 < Abstract::Zoo
  def select_animal
    MyDogs::B
  end
end

class MyZoo2 < Abstract::Zoo
  def select_animal
    MyCats::Special # It's here, initializing special dog with an additional argument
  end
end

class MyZoo3 < Abstract::Zoo
  def select_animal
    case rand(3)
    when 0
      MyCats::Special # Also here, but #make_some_noise still doesn't have to initialize Special Dog explicitly
    else
      MyDogs::B
    end
  end
end

class MyZoo4 < Abstract::Zoo
  def select_animal
    case rand(2)
    when 0
      MyDogs::B
    else
      MyDogs::B
    end
  end
end

class MyZoo5 < Abstract::Zoo
  def select_animal
    case rand(2)
    when 0
      MyDogs::C
    else
      MyDogs::C
    end
  end
end

class MyZoo6 < Abstract::Zoo
  def select_animal
    case rand(2)
    when 0
      MyDogs::D
    when 1
      MyDogs::D
    end
  end
end

class MyZoo7 < Abstract::Zoo
  def select_animal
    case rand(3)
    when 0
      MyCats::Special
    when 1
      MyCats::B
    else
      MyDogs::B
    end
  end
end

describe Abstract::Zoo do
  {% for value in (1..7) %}
    it "MyZoo{{value.id}} compiles" do
      MyZoo{{value.id}}.new.make_some_noise
      true.should be_truthy
    end
  {% end %}
end

# PART 2: Failing to compile

class MyZooWhichCantCompile < Abstract::Zoo
  def select_animal
    # Uncomment an expression to see it in action

    # Fails as expected with `wrong number of arguments for 'MyDogs::Special.new' (given 1, expected 2)`

    # MyDogs::Special

    # These fail with `wrong number of arguments for 'MyDogs::Special#initialize' (given 1, expected 2)`

    # case rand(2)
    # when 0
    #   MyDogs::B
    # else
    #   MyDogs::C
    # end

    # case rand(2)
    # when 0
    #   MyDogs::B
    # when 1
    #   MyDogs::C
    # end

    # case rand(3)
    # when 0
    #   MyCats::Special
    # when 1
    #   MyDogs::B
    # when 2
    #   MyDogs::C
    # end

    # case rand(3)
    # when 0
    #   MyCats::Special
    # when 1
    #   MyDogs::B
    # else
    #   MyDogs::C
    # end

    # case rand(4)
    # when 0
    #   MyCats::Special
    # when 1
    #   MyDogs::B
    # when 2
    #   MyDogs::C
    # end

    # case rand(4)
    # when 0
    #   MyCats::Special
    # when 1
    #   MyDogs::B
    # else
    #   MyDogs::C
    # end

    # case rand(4)
    # when 0
    #   MyCats::Special
    # when 1
    #   MyCats::B
    # when 2
    #   MyDogs::C
    # else
    #   MyDogs::D
    # end

    # case rand(4)
    # when 0
    #   MyCats::Special
    # when 1
    #   MyDogs::B
    # when 2
    #   MyDogs::C
    # when 3
    #   MyDogs::D
    # end
  end
end

MyZooWhichCantCompile.new.make_some_noise