Grouping layers

[anton-kotik]

For projects with huge number of layers, it would be useful to allow group layers. Something like this:

deptrac:
  layers:
    - {name: AAA, collectors: ...}
    - {name: ABB, collectors: ...}
    - {name: CBB, collectors: ...}
    - {name: BBB, collectors: ...}
    - {name: XAX, collectors: ...}
    - {name: CCX, collectors: ...}
  groups:
    GroupA: [AAA, ABB, XAX]
    GroupB: [ABB, CBB, BBB]
    GroupC: [CBB, CXX]
    GroupX: [XAX, CCX]
    GroupAB: [GroupA, GroupB]
    GroupCX: [GroupC, GroupX]
    GroupAX: [GroupA, GroupX]
  ruleset:
    CBB: [GroupAX]         # CBB can use AAA, ABB, XAX, CCX
    GroupA: [GroupAB, CCX] # [AAA, ABB, XAX] can use AAA, XAX, ABB, CBB, BBB, CXX
    GroupX: [GroupA, BBB]  # [XAX, CCX] can use AAA, ABB, XAX, BBB

Notes:

• Any layer can be included in several groups. For example, layer CBB is included into GroupB, GroupC, GroupAB, GroupCX groups.
• Ruleset for groups should be merged. For example, XAX can use all allowed dependencies from both rules GroupA: [GroupAB, CCX] and GroupX: [GroupA, BBB], because XAX is included into both GroupA and GroupX.

---

Real example, one of many actually: we have dozens separated APIs. Each concrete API is a separate layer, so dependencies between them are forbidden. And we have common dependencies we would like to allow for all these API layers, now we have to write a massive ruleset:

deptrac:
  layers:
    - {name: Api1, collectors: ...}
    - {name: Api2, collectors: ...}
    - {name: Api3, collectors: ...}
    - ...
    - {name: Common1, collectors: ...}
    - {name: Common2, collectors: ...}
    - {name: Common3, collectors: ...}
    - ...
  ruleset:
    Api1: [Common1, Common2, Common2, ...]
    Api2: [Common1, Common2, Common2, ...]
    Api3: [Common1, Common2, Common2, ...]
    ...

More clear version could be:

deptrac:
  layers:
    - {name: Api1, collectors: ...}
    - {name: Api2, collectors: ...}
    - {name: Api3, collectors: ...}
    - ...
    - {name: Common1, collectors: ...}
    - {name: Common2, collectors: ...}
    - {name: Common3, collectors: ...}
    - ...
  groups:
    API: [Api1, Api2, Api3, ...]
    Common: [Common1, Common2, Common3...]
  ruleset:
    API: [CommonGroup]

[patrickkusebauch]

This could be done fairly easily once #1002 is merged.

[patrickkusebauch]

Closing as #1002 is now merged.