Sniffs not loaded when one-standard directories are being registered in installed_paths

[jrfnl]

If any external standard or a custom ruleset refers to a complete standard and this standard is registered in the installed_paths config as a one-standard directory, a Reference sniff ... does not exist error will be thrown and no sniffs will be run.

Bug introduced in #1450 (by me, sorry!).

The reason for this is that the getInstalledStandardPath() method expects a string, but will in actual fact receive a SimpleXMLElement object when a complete standard is included by another standard. This was previously not documented in the function doc block as a possibility.

While in the original code, the $standards name was only used as a concatenated string - which triggered the SimpleXML.toString() method -, the fix in #1450 introduced a strict comparison without the toString() conversion, causing the bug.

Installed_paths	string $standards	SimpleXMLElement $standards
"Standards" directory	✅	✅
one-standard directory	✅	❌ <= This is what this fixes.

While debugging this, I also noticed that this method is called for every single ref in the ruleset and would go through the whole loop before returning null, while for refs which refer to a custom xml ruleset or to a sniff or sniff category, null can be returned a lot earlier and for paths which don't resolve to a ruleset, part of the loop can be skipped.

---

Testing the fix:

Using the WordPress Coding Standards as an example to demonstrate what I mean, set installed_paths like so:
phpcs --config-set installed_paths /path/to/WordPressCS/WordPress,/path/to/WordPressCS/WordPress-Core,/path/to/WordPressCS/WordPress-Docs,/path/to/WordPressCS/WordPress-Extra,/path/to/WordPressCS/WordPress-VIP

Custom ruleset test.xml:

<?xml version="1.0"?>
<ruleset name="Test">
	<rule ref="WordPress-Core"/>
</ruleset>

Then run PHPCS against any file:
phpcs ./test-file.php --standard=test.xml

[jrfnl]

@gsherwood Is there anything I can do or clarify about this PR to move this forward ?

[gsherwood]

Is there anything I can do or clarify about this PR to move this forward ?

No, it's just my time. I'm trying to find a little time to work on PHPCS each day, but it's not working out so well. But I'll get through the backlog.

[jrfnl]

@gsherwood ❤️

[gsherwood]

I looked into where this was coming from and I don't think there is any problem with your previous fix. I think the source of this problem was actually from a call to expandRulesetReference where I thought I was passing in a string but I was really passing into a SimpleXML object. It was being implicitly cast to a string in many places, so I just made it explicit before I made the call.

I'll take a look at the performance bit of the PR now.

[gsherwood]

Those performance changes looked good, thanks. I removed the string casts and param comment change now that the method should only accept strings.

[jrfnl]

Excellent. Thanks!