Allow inheriting mocks matchers

[nepalez]

With reference to #1055

Allows rspec matchers inherited from RSpec::Mocks::Matchers::* to be used
both in mocks and expectations:

  class ReceiveFoo < RSpec::Mocks::Matchers::Receive
    def initialize
      super :foo, nil
    end
  end

  describe "receiving foo" do
    it "works" do
      object = double

      allow(object).to receive_foo
      expect(object).to receive_foo

      object.foo
    end
  end

[myronmarston]

Suggestion: instead of doing a linear search over all the ancestors and implicitly using the matcher class name, what do you think of creating an explicit "tag" module that you can check instead? I'm thinking of something like this:

module RSpec
  module Mocks
    module Matchers
      # exists just so we can "tag" all rspec-mocks matchers to make detection of them easier.
      module Matcher; end

      # now include the module in each of our matcher classes...
      class HaveReceived
        include Matcher
      end

      class Receive
        include Matcher
      end

      class ReceiveMessages
        include Matcher
      end

      class ReceiveMessageChain
        include Matcher
      end

      # ...and then we can detect rspec-mocks matchers with a simple `===` check:
      def matcher_allowed?(matcher)
        RSpec::Mocks::Matchers::Matcher === matcher
      end
    end
  end
end

[nepalez]

Amazing technics :)

It seems offhand, that if we go this way, it can lead us to extraction of the "essential/mockable" part of the matcher to the module. For now this is just a speculation, I need time to play with the idea.

[JonRowe]

It seems offhand, that if we go this way, it can lead us to extraction of the "essential/mockable" part of the matcher to the module. For now this is just a speculation, I need time to play with the idea.

No. Delegation is more useful than inheritance in this fashion. We don't want to encourage more inheritance of our private APIs only support reasonable use cases like this. This module should only be used to improve the detection of inherited matchers from our own.

[soulcutter]

https://en.wikipedia.org/wiki/Marker_interface_pattern 👍

[JonRowe]

Thanks! :)