draft: core(exec): Add attribute to check for idempotency attributes

[tuxmea]

fixes #13

[tuxmea]

I would like to present this change to the Language Steering Committee.
We can use this PR as discussion basis.

[binford2k]

what about idempotency_alert = [ :none, :warn, :error ] with :warn being default?

That would make it less of a breaking change, but would start warning people when they have the exec that never ends. In the uncommon case in which the user wants to run the exec every time, they could set it to :none.

Alternatively, we could default to :none and make the breaking change totally opt-in.

In a future release, we could have strict mode set this to :error

[trefzer]

I see noo additional value to check this on every puppet run. For me this is a typical lint check to warn the developer of his 'fault' but at the end it's his decision. There is not additional added value to warn on every puppet run (I know you can supress...) since the running exec is marked as a changing resource anyway. I think we should invest the compute power for this check better.

Additional remark about the implementation:
It would probably less resource consuming, if you implement the check on the provider side (executed on any change). So it does not run on every puppet run if idempotency is fullfilled. If idempotency is not given, it warns on every run.

[tuxmea]

Many thanks for the feedback.
Would it make sense to have a short discussion on this during next Vox Pupuli monthly?
Then we can decide if we want to implement a solution like this or if we want to close this.
I am happy with both decisions.