Centralise general id delimiter

[dwsutherland]

This PR:

• Centralises the ID delimiter.
• Fixes bug in ID generated in prerequisites dump.
• Imports to functional tests

Sibling PR: cylc/cylc-uiserver#140
(needs to be merge after this one)

The centralisation/put-at-lower-level is needed due to:

• A circular import error occurred while trying to fix the prerequisite dump. (ID_DELIM defined in data_store_mgr, but prerequisites is imported to data_store_mgr indirectly)
• Future proofing.

Justification for cylc/flow/__init__.py location:

• Not only used by tasks (i.e. shouldn't go in cylc/flow/task_id.py), used for workflow/jobs/families ...etc.
• Used by multiple modules (i.e. tasks/jobs/data-store/..etc) and UIS, but also as we become more event driven (i.e. the change in state might create a data element with only fields changed which gets merged locally and sent).
• If we decide on a delimiter for external use that jumps through the def/datetime/shell CLI/Cylc constraints then it can be used internally too (which means more reliance on centralized ID_DELIM). See Universal suite/task/cycle delimiter (universal identifier) #3592

Could be it's own module.. But, as a one-liner and used by UIS, cylc.flow seems appropriate.

Requirements check-list

• I have read CONTRIBUTING.md and added my name as a Code Contributor.
• Contains logically grouped changes (else tidy your branch by rebase).
• Does not contain off-topic changes (use other PRs for other changes).
• Already covered by existing tests.
• No change log entry required (why? e.g. invisible to users).
• No documentation update required.

[dwsutherland]

The bug was the conditions using a false ID for their taskProxy, so now works:

query {
  workflows(ids: ["sutherlander|baz"]) {
    taskProxies (ids: ["*|bar"]) {
      id
      state
      prerequisites {
        expression
        satisfied
        conditions {
          reqState
          exprAlias
          taskProxy {
            id
          }
        }
      }
    }
  }
}

{
  "data": {
    "workflows": [
      {
        "taskProxies": [
          {
            "id": "sutherlander|baz|20170101T0000+12|bar",
            "state": "waiting",
            "prerequisites": [
              {
                "expression": "c0 | c1",
                "satisfied": false,
                "conditions": [
                  {
                    "reqState": "succeeded",
                    "exprAlias": "c0",
                    "taskProxy": {
                      "id": "sutherlander|baz|20170101T0000+12|foo"
                    }
                  },
                  {
                    "reqState": "succeeded",
                    "exprAlias": "c1",
                    "taskProxy": {
                      "id": "sutherlander|baz|20170101T0000+12|qux"
                    }
                  }
                ]
              }
            ]
          }
        ]
      }
    ]
  }
}

[hjoliver]

Doesn't matter that this was a different delimiter here? (/ vs |)

[hjoliver]

(Or was that the bug? it's used in PbConditions)

[dwsutherland]

Yes, this was the bug that needed fixed. But can't import from cylc.flow.data_store_mgr.