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GeezerVison is showing github.com — fix(utils): match_regex_list crashes on an empty-string pattern by devteamaegis · Pull Request #6505 · getsentry/sentry-python

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devteamaegis commented Jun 4, 2026

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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

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          fix(utils): handle empty string in match_regex_list

d42a94a

devteamaegis requested a review from a team as a code owner

June 4, 2026 18:03

ericapisani requested changes

Jun 4, 2026

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ericapisani left a comment

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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.

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tests/test_utils.py Outdated


		def test_match_regex_list_empty_string_pattern():
		# An empty-string pattern must not raise IndexError (regression test).
		result = match_regex_list("anything", [""])

ericapisani Jun 4, 2026

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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)

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sentry_sdk/utils.py Outdated


		for item_matcher in regex_list:
		if not substring_matching and item_matcher[-1] != "$":
		if not substring_matching and (not item_matcher or item_matcher[-1] != "$"):

ericapisani Jun 4, 2026

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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] != "$":
            item_matcher += "$"

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sentrivana added the Waiting for: Community label

Jun 8, 2026

devteamaegis force-pushed the fix/match-regex-list-empty-string branch from 4043b13 to d42a94a Compare

June 11, 2026 19:44

cursor Bot reviewed

Jun 11, 2026

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Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{❌ Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, enable autofix in the Cursor dashboard.}

^{Reviewed by Cursor Bugbot for commit d42a94a. Configure here.}

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sentry_sdk/utils.py Resolved

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sentry Bot reviewed

Jun 11, 2026

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sentry_sdk/utils.py Outdated

Comment on lines 1743 to 1744

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

sentry Bot Jun 11, 2026

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Bug: An empty string "" in regex_list causes match_regex_list to always return True. The fix item_matcher += "$" is incorrect as re.search("$", ...) always matches.
_{Severity: HIGH}

Suggested Fix

Instead of converting an empty item_matcher to "$", the function should explicitly handle an empty string in regex_list to mean "match nothing". This could be done by returning False immediately if item_matcher is empty after processing, or by ensuring the regex pattern for an empty string does not match everything.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent. Verify if this is a real issue. If it is, propose a fix; if not, explain why it's
not valid.

Location: sentry_sdk/utils.py#L1743-L1744

Potential issue: The function `match_regex_list` incorrectly handles an empty string
`""` in `regex_list`. The proposed fix converts an empty `item_matcher` to `"$"` before
performing a regex search. However, `re.search("$", item)` always returns a match
because the `$` metacharacter matches the end-of-string position, which is present in
every string. As a result, if any `regex_list` contains an empty string, the function
will incorrectly return `True` for all items. For example, setting `exclude_beat_tasks =
[""]` in the Celery integration would silently exclude all beat tasks from
instrumentation.

Also affects:

sentry_sdk/integrations/celery/beat.py:130

_{Did we get this right? 👍 / 👎 to inform future reviews.}

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          fix(utils): treat empty-string pattern like empty list in match_regex…

27447a4

…_list

Address review feedback: an empty string in regex_list represents a
typo/mistake and should be treated as if [] was passed, returning False
rather than matching every item. Fold the regression case into the
parameterized test_match_regex_list cases and drop the redundant
standalone test.

getsantry Bot commented Jul 3, 2026

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This issue has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you remove the label Waiting for: Community, I will leave it alone ... forever!

"A weed is but an unloved flower." ― Ella Wheeler Wilcox 🥀

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getsantry Bot added the Stale label

Jul 3, 2026

getsantry Bot commented Jul 25, 2026

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This issue has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you remove the label Waiting for: Community, I will leave it alone ... forever!

"A weed is but an unloved flower." ― Ella Wheeler Wilcox 🥀

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devteamaegis commented Jul 26, 2026

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Thanks for the review @ericapisani — both points addressed.

Empty-pattern handling: adopted your suggested conditional, so an empty item_matcher now hits return False before the anchoring logic. match_regex_list("anything", [""]) returns False (treated like []) instead of matching everything, which also resolves the Bugbot finding about re.search("$", ...) always matching and the exclude_beat_tasks fallout.
Test: folded the case into the parameterized test_match_regex_list as ["some-string", [""], False] and removed the standalone test plus the redundant foo/foobar assertions already covered by existing cases.

Verified the empty-string list now returns False while normal patterns still match. Let me know if you'd like anything else.

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alexander-alderman-webb commented Jul 28, 2026

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Closing in favor of #6896

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alexander-alderman-webb closed this

Jul 28, 2026

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match_regex_list raises IndexError when a pattern list contains an empty string

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