Handle parentheses on RHS of trigger expression

[MetRonnie]

Description

Fix a bug where using parentheses on the right hand side of a graph trigger would cause traceback.

Reproduction

R1 = a => (b & c)

$ cylc validate

Traceback

Traceback (most recent call last):
  File "~/.conda/envs/cylc8/bin/cylc", line 8, in <module>
    sys.exit(main())
  File "~/cylc-flow/cylc/flow/scripts/cylc.py", line 660, in main
    execute_cmd(command, *cmd_args)
  File "~/cylc-flow/cylc/flow/scripts/cylc.py", line 286, in execute_cmd
    entry_point.resolve()(*args)
  File "~/cylc-flow/cylc/flow/terminal.py", line 232, in wrapper
    wrapped_function(*wrapped_args, **wrapped_kwargs)
  File "~/cylc-flow/cylc/flow/scripts/validate.py", line 133, in main
    _main(parser, options, workflow_id)
  File "~/cylc-flow/cylc/flow/scripts/validate.py", line 137, in _main
    asyncio.run(wrapped_main(parser, options, workflow_id))
  File "~/.conda/envs/cylc8/lib/python3.10/asyncio/runners.py", line 44, in run
    return loop.run_until_complete(main)
  File "~/.conda/envs/cylc8/lib/python3.10/asyncio/base_events.py", line 646, in run_until_complete
    return future.result()
  File "~/cylc-flow/cylc/flow/scripts/validate.py", line 155, in wrapped_main
    cfg = WorkflowConfig(
  File "~/cylc-flow/cylc/flow/config.py", line 518, in __init__
    self.load_graph()
  File "~/cylc-flow/cylc/flow/config.py", line 2123, in load_graph
    parser.parse_graph(graph)
  File "~/cylc-flow/cylc/flow/graph_parser.py", line 465, in parse_graph
    self._proc_dep_pair(pair)
  File "~/cylc-flow/cylc/flow/graph_parser.py", line 627, in _proc_dep_pair
    self._families_all_to_all(expr, rights, info, family_trig_map)
  File "~/cylc-flow/cylc/flow/graph_parser.py", line 671, in _families_all_to_all
    self._compute_triggers(expr, rights, n_expr, n_info)
  File "~/cylc-flow/cylc/flow/graph_parser.py", line 852, in _compute_triggers
    suicide_char, name, output, opt_char = m.groups()  # type: ignore
AttributeError: 'NoneType' object has no attribute 'groups'

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).
• No dependency changes
• Tests are included
• Changelog entry included
• No docs update needed
• If this is a bug fix, PR should be raised against the relevant ?.?.x branch.

[hjoliver]

LGTM, and fixes the bug. One general question though:

Given that parentheses are actually meaningless on the right (because OR is not allowed) - which you're handling by stripping them out 👍 - maybe we should just disallow them, and then not have to check for mismatch?

[MetRonnie]

Don't mind too much but IMO this feels like it would be less annoying to users

[wxtim]

I'm outputting the entire thing might be helpful.

Suggested change

	mismatch_msg = 'Mismatched parentheses in: "{}"'
	if left and left.count("(") != left.count(")"):
	raise GraphParseError(mismatch_msg.format(left))
	if right.count("(") != right.count(")"):
	raise GraphParseError(mismatch_msg.format(right))
	mismatch_msg = 'Mismatched parentheses in: "{} => {}"'
	if left and left.count("(") != left.count(")"):
	raise GraphParseError(mismatch_msg.format(left, right))
	if right.count("(") != right.count(")"):
	raise GraphParseError(mismatch_msg.format(left, right))

[MetRonnie]

Sometimes there will be no arrow involved, however

[wxtim]

Legit - I've made a suggestion. Take it or leave it (it will break some of your new tests if you take it).