Implement If() macro

[richardboehme]

This commit adds an If() macro to conditionally execute steps in an operation. It's implementation is based on the implementation of the Wrap() macro to execute the nested sub-activity.

Right know if one needed a step to execute only if a specific condition is true we used early returns:

class Operation < Trailblazer::Operation
  step :conditional_step

  def conditional_step(_, model:, **)
    return true unless model.condition?
   
    # do something...
  end
end

With this macro we can transform that into:

class Operation < Trailblazer::Operation
  step If(->(_, model:, **) { model.condition? }) { 
    step :conditional_step
  }

  def conditional_step(_, model:, **)
    # do something...
  end
end

If you have any ideas on how to further improve this, let us know.

[richardboehme]

Just noticed there is another PR for an If macro already (#43). From my point of view our implementation feels a bit more like trailblazer and has some better test coverage.

[apotonick]

Should we allow two signatures here, one without ctx so the "immutable" environment becomes more obvious, or is this more confusing? @yogeshjain999

[yogeshjain999]

Yeah, I think we should!

BTW, does conditional_step show up in the trace ? I think we would have apply similar logic of defining activity as we do in Each macro, yeah ?

[apotonick]

Okay @richardboehme and I agreed that introducing a new signature without ctx as first positional argument is more work, inconsistent since Each/dataset also allows mutating, and harder to remember.

[apotonick]

After pondering over this PR for ... half a year, I'm wondering, couldn't we reuse Nested()'s mechanics here? We should use a taskWrap "decider" instead of calling the conditional step ourselves! Here's some insight

trailblazer-macro/lib/trailblazer/macro/nested.rb

Line 29 in e76d090

[Nested::Decider.new(callable), id: "Nested.compute_nested_activity", prepend: "task_wrap.call_task"],

[richardboehme]

@apotonick We tried to reuse Nested::Decider and improve the implementation. What do you think?

[apotonick]

Is ctx[:"result.condition.#{name}"] important to keep?