fix(utils): match_regex_list crashes on an empty-string pattern

[devteamaegis]

What's broken

match_regex_list checks item_matcher[-1] != "$" to decide whether to anchor each pattern. With the default substring_matching=False, an empty-string element makes ""[-1] raise:

>>> from sentry_sdk.utils import match_regex_list
>>> match_regex_list("anything", [""])
IndexError: string index out of range

exclude_beat_tasks in the Celery integration flows straight into this with the default mode, so an empty string in that user-supplied list crashes the beat instrumentation.

Why it happens

Indexing item_matcher[-1] on an empty string is out of range.

Fix

Short-circuit on empty: (not item_matcher or item_matcher[-1] != "$"). An empty matcher then becomes "$", which matches end-of-string — a sane result instead of a crash.

Test

Added a case asserting match_regex_list("anything", [""]) returns without raising; existing anchored/substring behavior is unchanged.

Fixes #6504

[ericapisani]

Thanks for opening the issue and pull request to address this.

There's a couple of things we'll need to address before this gets merged - let me know if you have any questions about what I've mentioned below.

[ericapisani]

Rather than have this be a standalone test, this case can be incorporated into the test above (test_match_regex_list) as one of the parameterized test cases. You'll just need to add the expected outcome as the last element in the array.

This means that last 2 assertions around foo/foobar can also be removed since we already have test cases that check similar behaviour within the array (lines 553 and 554 above)

[ericapisani]

While this fixes the index error, the result that's returned from this change means match_regex_list("anything", [""]) will return True.

An empty string likely represents a typo/mistake on the developers part, and so we should treat this as if [] was passed in.

This would mean that this conditional should look like the following instead:

    for item_matcher in regex_list:
        if not item_matcher:
            return False

        if not substring_matching and item_matcher[-1] != "$":
            item_matcher += "$"