Stop searching platform groups after first match.

[wxtim]

Platform selection from a platform group was missing a break in the for loop, leading to the possibility of the wrong platform being selected.

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).
• Applied any dependency changes to both setup.cfg (and conda-environment.yml if present).
• Tests are included (or explain why tests are not needed).
• CHANGES.md entry included if this is a change that can affect users
• Cylc-Doc pull request opened if required at cylc/cylc-doc/pull/XXXX.
• If this is a bug fix, PR should be raised against the relevant ?.?.x branch.

[MetRonnie]

Kicking tests

[MetRonnie]

This aleph platform group is a little confusing to me

[wxtim]

Without the break the loop runs for .*_letters, aleph and hebrew_letters in that order.

When it runs over .*_letters it matches to hebrew_letters (the platform_name we inputted into the function. It then sets platform_name = aleph from .*letters list of platforms.

If we put the break in the iteration then stops. But without it the loop runs for aleph and sets platform_name=alpha.

Finally on the third iteration platform_name = alpha which does not match hebrew letters (this is OK behaviour).

The break is only needed if a platform_name set by an earlier platform group matches a later platform group. Otherwise it's just inefficient, because it keeps searching.

(The original test is checking that despite the name hebrew_letters matches .*_letters and not hebrew_letters)

[MetRonnie]

Ah, wrong base branch. Need to rebase onto 8.1.x

[MetRonnie]

I have suggested a comment in light of your explanation, to clarify the test

Can you add a description of the bug to the PR body?

[wxtim]

Yes. That's a good idea, this test is wierd and non obvious
Feel free to add the following if you like.

Suggested change

	[[aleph]]
	# Group with same name as platform to try and
	# trip up the platform selection logic after it
	# has processed [[.*_letters]] below
	[[aleph]]
	# Group with same name as platform to try and
	# trip up the platform selection logic after it
	# has processed [[.*_letters]] below
	# https://github.com/cylc/cylc-flow/pull/5398#discussion_r1130692633

or

Suggested change

	[[aleph]]
	# Group with same name as platform to try and
	# trip up the platform selection logic after it
	# has processed [[.*_letters]] below
	[[aleph]]
	# Group with same name as platform to try and
	# trip up the platform selection logic after it
	# has processed [[.*_letters]] below
	# https://github.com/cylc/cylc-flow/pull/5398

[hjoliver]

👍