[FEATURE REQUEST] alwaysunless and alwaysif requisites

[maminson]

Is your feature request related to a problem? Please describe.
Requisites that guarantee that a state will run under certain conditions don't exist, in particular with use of the onchanges and prereq requisites.

Describe the solution you'd like
The implementation of alwaysunless and alwaysif requisites, mutually exclusive with unless and onlyif:

• alwaysunless: specifies that a state will always run when any of the specified commands return False, operating as NAND.
• alwaysif: specifies that if each command listed in alwaysif returns True, then the state is always run. If any of the specified commands return False, the state is not guaranteed to run.

For further clarification, here's a truth table, the left side describing the scenario and the right side showing if a state with the given requisite will run:

onchanges/prereq is True	Requisite Command is True		unless	onlyif	alwaysunless	alwaysif
❌	❌		❌	❌	✅	❌
✅	❌		✅	❌	✅	✅
❌	✅		❌	❌	❌	✅
✅	✅		❌	✅	✅	✅

If implemented, these requisites could be used like so:

/path/to/isofiles:
  file.recurse:
    - source: salt://isofiles

mkisofs -rJo /path/to/iso /path/to/isofiles:
  cmd.run:
    - alwaysunless:
      - fun: file.file_exists
        path: /path/to/iso
    - onchanges:
      - /path/to/isofiles

Describe alternatives you've considered
An existing workaround is the use of additional states:

/path/to/isofiles:
  file.recurse:
    - source: salt://isofiles

iso created:
  file.managed:
    - name: /path/to/iso
  cmd.run:
    - name: mkisofs -rJo /path/to/iso /path/to/isofiles
    - onchanges:
      - /path/to/isofiles
      - file: iso created

While this could be an argument against the alwaysunless and alwaysif requisites, similar alternatives exist for unless and onlyif as well, so their existence suggests that alwaysunless and alwaysif should exist too.

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[OrangeDog]

It's not clear what you want your example to do. If you want the ISO to always exist and have the latest contents, and not re-create if it hasn't changed:

/path/to/isofiles:
  file.recurse:
    - source: salt://isofiles

mkisofs -rJo /path/to/iso /path/to/isofiles:
  cmd.run:
    - creates: /path/to/iso
    - watch:
      - /path/to/isofiles

I'm not sure where the requisite returning False comes into it, but onfail is what handles that.

Wanting to always run the next thing even if a requisite fails is very unlikely, and probably means there shouldn't be a requisite in the first place. You could use order if an ordering is still needed in that case, or e.g. suppress the failure of a cmd.run with success_retcodes etc.

In any case, such semantics are entirely separate from unless/onlyif. If a feature really is missing, it should not be added in this form.