[Discussion] Allow arity -1 in ROP to improve testability

MR: Allow arity -1 in ROP to improve testability (!151574 - closed)

Description

In the Remote-Development codebase where we implement a Railway-Oriented-Programming style, should we update validate_lambda_or_singleton_method to allow functions with arity -1 https://apidock.com/ruby/Method/arity to support directly mocking collaborators (see Context for example)?

Context

The following discussion from !147718 (merged) should be addressed:

• @pslaughter started a discussion: (+3 comments)

  suggestion: There's a lot of mocking indirection here (e.g. the need to mock :method). I'd expect to be able to do just something like:

  allow(RemoteDevelopment::Workspaces::Create::PersonalAccessTokenCreator).to receive(:create).with(value) do
    create(:personal_access_token)
    Result.ok(value)
  end

  which actually works if I update this check in result.rb

  diff --git a/lib/result.rb b/lib/result.rb
  index 5e72b3f13cb3..289f4393a34d 100644
  --- a/lib/result.rb
  +++ b/lib/result.rb
  @@ -198,7 +198,7 @@ def validate_lambda_or_singleton_method(lambda_or_singleton_method)
   
       arity = lambda_or_singleton_method.arity
   
  -    return if arity == 1
  +    return if arity == 1 || arity == -1
   
       err_msg = "'Result##{__method__}' expects a lambda or singleton method object with a single argument " \
                 "(arity of 1), but instead received '#{lambda_or_singleton_method.inspect}' with an arity of #{arity}."
  

  An arity of -1 means it takes a variable number of arguments which means we can interact with it as if it just included a single argument and it won't break the pipeline. It's weird that rspec changes the arity of this when you start stubbing things, but allowing -1 seems reasonable (and more preferable than all the mocking indirection at the moment).

  The issue with the mocking indirection on :method is that we actually miss that we're trying to include the :create method. The tests still pass with a bug like this:

  diff --git a/ee/lib/remote_development/workspaces/create/creator.rb b/ee/lib/remote_development/workspaces/create/creator.rb
  index 12b6e484b2fa..7385ad613a84 100644
  --- a/ee/lib/remote_development/workspaces/create/creator.rb
  +++ b/ee/lib/remote_development/workspaces/create/creator.rb
  @@ -30,7 +30,7 @@ def self.create(value)
   
               result =
                 initial_result
  -                .and_then(PersonalAccessTokenCreator.method(:create))
  +                .and_then(PersonalAccessTokenCreator.method(:foo))
                   .and_then(WorkspaceCreator.method(:create))
                   .and_then(WorkspaceVariablesCreator.method(:create))
   
  

  WDYT? Are you up for updating our result.rb check to allow arity of -1 here? Is there a better way we can make sure we're testing things a bit more integrated?