Universal suite/task/cycle delimiter (universal identifier)

[hjoliver]

specification: cylc/cylc-admin#115

For suite/task IDs, the new hierarchical ID chosen by @dwsutherland for use in the back-end has nice properties but can't be used on the command line because the delimiter is the shell pipe character.

Supersedes #3542 - please refer to the discussion there. The general solution to this problem should support the original use case of that issue (allow dots in task names).

[dwsutherland]

As mentioned in the superseded ticket; We may need to use a two character delimiter to satisfy
all constraints of shell/Cylc-Conf/datetime ...

[oliver-sanders]

Proposal:

• Use / as the separator (as originally intended) but use // to separate the flow from the cycle.
• Support :<arg> as a state selector (e.g. the current cylc trigger flow *:failed).

# regular form (e.g. element ids in GraphQL schema)
[~user[/]]flow//cycle/task/job

# expanded form with selectors (e.g. CLI querying)
[~user[/]]flow[:state]//cycle[:state]/task[:state]/job[:state]

Examples (equivalent GraphQL arguments under current scheme)

# flow under account user (wid="user|flow")
~user/flow

# the task foo at all cycles in flow (wid="flow|*|foo")
flow//*/foo

# all running tasks in foo (wid="flow|*|*" state="running")
flow//*/*:running

# all running workflows (wid="*" state="running")
*:running

cylc-admin proposal PR: cylc/cylc-admin#115

[oliver-sanders]

Assigning myself, initially for phase 1 i.e. permitting the new syntax on the CLI.