Add checks for "idle" links

There are cases where linkage won't work. We should chack for all of them:

• Branching after time interpolator (already checked)
• Multiple time interpolators chained
• Time interpolator after pull-based component
• Push-based component after pull-based component

added coupling usability labels

mentioned in merge request !102 (merged)

mentioned in issue #3 (closed)

Maybe inputs, outputs and adapters could have a property that indicates push and pull abilities?

Trial 1: needs_push

Failed!

Maybe, just needs_push would be sufficient?

• Input: false
• Output: true
• CallbackInput: true
• CallbackOutput: false
• Adapter: false
• TimeAdapter (interp etc.): true

Examples:

• WORKS: Output >> Input - true >> false
• WORKS: Output >> Adapter >> Input - true >> false >> false
• WORKS: CallbackOutput >> Input - false >> false
• WORKS: Output >> CallbackInput - true >> true
• ERROR: CallbackOutput >> CallbackInput - false >> true - Can't work!
• ERROR: CallbackOutput >> Adapter >> CallbackInput - false >> false >> true - Can't work!
• ERROR: CallbackOutput >> TimeAdapter >> Input - false >> true >> false
• WARNING: Output >> TimeAdapter >> CallbackInput - true >> true >> true
• WORKS: Output >> Adapter >> CallbackInput - true >> false >> true

Criterion: if true comes after false, it won't work.

The last example works, but would be detected as not working.

Would two properties help? needs_push and needs_pull?

Trial 2: needs_pull and needs_push

Push left, pull right:

• Input: -/+
• Output: +/-
• CallbackInput: +/-
• CallbackOutput: -/+
• Adapter: -/-
• TimeAdapter (interp etc.): +/-

Examples:

• WORKS: Output >> Input - +/- >> -/+
• WORKS: Output >> Adapter >> Input - +/- >> -/- >> -/+
• WORKS: CallbackOutput >> Input - -/+ >> -/+
• WORKS: Output >> CallbackInput - +/- >> +/-
• ERROR: CallbackOutput >> CallbackInput - -/+ >> +/-
• ERROR: CallbackOutput >> Adapter >> CallbackInput - -/+ >> -/- >> +/-
• ERROR: CallbackOutput >> TimeAdapter >> Input - -/+ >> +/- >> -/+
• WARNING: Output >> TimeAdapter >> CallbackInput - +/- >> +/- >> +/-
• WORKS: Output >> Adapter >> CallbackInput - +/- >> -/- >> +/-

Criterion: Over each link, no two pairs are allowed to be two facing +. I.e. not only check adjacent, but also with each combination of adapters skipped.

So the algorithm could be:

1. go from lef to right through the link
2. if there is a + on the right side, note it
3. if there has been a + on the right, a + on the left is a fail
4. do the same backwards, left/right swapped

mentioned in merge request !112 (merged)

added in-progress label

assigned to @mlange

changed milestone to %metadata-rework

mentioned in commit 59b89708

closed with merge request !112 (merged)