Separation of functionality in cylc.config

[oliver-sanders]

At present cylc.config.SuiteConfig performs multiple duties:

• Parsing
  • Parsec (edited by @matthewrmshin also consider other file formats e.g. YAML, TOML, etc)
  • (edited by @matthewrmshin) Use formal grammar - https://github.com/cylc/cylc/pull/3003#issuecomment-474169711
• Processing / Transformation
  • e.g: Non-cycling suite becomes integer cycling suite with single cycle (edited by @matthewrmshin see #2905)
• Validation
  • Passive validation/verification done in the passing and processing steps
  • Special checks only run for cylc validate e.g. cyclic dependency check
  • (edited by @matthewrmshin see also #2425)
• Construction of runtime objects
  • e.g: TaskDef, TaskTrigger, ...)

These functionalities could do with being prised apart. Doing so should yield an efficiency bonus (e.g. TaskDef objects are currently constructed for cylc validate, cylc graph, cylc get-config, ... calls despite not being needed).

[hjoliver]

Note: https://github.com/cylc/cylc/blob/master/tests/param_expand/01-basic.t#L392 - inconsistence between graph and runtime handling of space and parameter expansion (e.g. in the graph, we remove all whitespace up front so subsequent regexes can ignore it; however, that might have been a bad call: https://github.com/cylc/cylc/issues/2534#issuecomment-356245200

[oliver-sanders]

Likely a desirable prerequisite to #1962

@matthewrmshin I don't think this is going to fit in with cylc-8, should this bump to cylc-9 and the config refactoring work required to the Python API?

[hjoliver]

@oliver-sanders - agreed, this is more Cylc-9-y (at least, not really needed for Cylc-8).