parameterization: make parameters avaliable to other suite.rc sections

[ColemanTom]

If possible, I think it could be useful to extend the parameterizing mechanism for task names to be usable for custom messages for triggering purposes.

e.g.

graph = """
foo:out_1 => bar_1
foo:out_2 => bar_2
foo:out_3 => bar_3
"""

Could simplify to:

graph = "foo:out<n> => bar<n>"

Similarly

[[some_polling_task]]]
    [[[output]]]
        out_1 = "message_1"
        out_2 = "message_2"
        out_3 = "message_3"

Becomes:

[[some_polling_task]]]
    [[[output]]]
         out<n> = "message<n>"

NOTE: I'm relatively inexperienced with Cylc, so these may not be the most Cylc-y way of doing things. If there are better approaches to take I would welcome them.

Regards,
Tom

[oliver-sanders]

Updating the title of this issue to reflect the broader issue of parameters not being available throughout most of the cylc configuration. Parameterizations, currently, can only be used in the graph, inherit and script (via an environment variable) items.

[hjoliver]

Expanding on Oliver's point a bit - current use reflects the fact that suite parameters are exclusively for parameterizing task names, not a general parameterization mechanism. However I think @ColemanTom's suggestion on this issue is a very natural extension. And then #2456 takes it even further...

[hjoliver]

A related thread on the mail list: https://groups.google.com/forum/#!topic/cylc/NIl0yWTGq-M

[hjoliver]

@trwhitcomb has posted another suggestion on Discourse: it would be useful to have parameterised external triggers. https://cylc.discourse.group/t/parameterized-clock-triggers/114

[oliver-sanders]

Likely the best solution is to supersede this with #1962

[hjoliver]

ditto #3229 (comment)
(however, if we do get a chance it might be worth reopening this one - for outputs and xtriggers - in suite.rc parameters)