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GeezerVison is showing github.com — fix: Avoid `IndexError` in `match_regex_list()` by alexander-alderman-webb · Pull Request #6896 · getsentry/sentry-python

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alexander-alderman-webb commented Jul 28, 2026 •

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Description

This approach still allows matching empty strings.

Issues

Closes #6504

Reminders

Please add tests to validate your changes, and lint your code using uv run ruff.
Add GH Issue ID & Linear ID (if applicable)
PR title should use conventional commit style (feat:, fix:, ref:, meta:)
For external contributors: CONTRIBUTING.md, Sentry SDK development docs, Discord community

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          fix: Avoid IndexError in match_regex_list()

a01cef7

This was referenced Jul 28, 2026

fix: skip empty patterns in match_regex_list to prevent IndexError #6842

Closed

fix(utils): match_regex_list crashes on an empty-string pattern #6505

Closed

fix(match_regex_list): handle empty string patterns without IndexError #6802

Closed

alexander-alderman-webb marked this pull request as ready for review

July 28, 2026 07:45

alexander-alderman-webb requested a review from a team as a code owner

July 28, 2026 07:45

sentry Bot reviewed

Jul 28, 2026

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sentry_sdk/utils.py

Comment on lines +1739 to 1740

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

sentry Bot Jul 28, 2026

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Bug: The fix for an IndexError causes an empty string in regex_list to be treated as a pattern that matches everything, leading to unintended consequences.
_{Severity: HIGH}

Suggested Fix

The function match_regex_list should handle empty strings in regex_list explicitly. Instead of converting "" to "$", it should either skip empty strings (possibly with a warning) or only match them against empty input strings. This will prevent the unintended "match-all" behavior.

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#L1739-L1740

Potential issue: The change in `match_regex_list` prevents an `IndexError` when an item
in `regex_list` is an empty string. However, it introduces a new issue. An empty string
pattern `""` is converted to `"$"` which, when used with `re.search`, matches the end of
any string. Consequently, if a configuration list like `trace_propagation_targets` or
`exclude_beat_tasks` contains an empty string, `match_regex_list` will return `True` for
every input. This could lead to all HTTP requests having trace propagation enabled, or
all Celery beat tasks being excluded from monitoring, failing silently instead of
crashing.

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

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alexander-alderman-webb Jul 28, 2026

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that's what I would expect with an empty regex

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alexander-alderman-webb mentioned this pull request

Jul 28, 2026

fix: handle empty string in match_regex_list to prevent IndexError #6509

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github-actions Bot commented Jul 28, 2026

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Codecov Results 📊

📊 Comparison with Base Branch

Metric	Change
Total Tests	📈 +52
Passed Tests	📈 +51
Failed Tests	📈 +1
Skipped Tests	—

➕ New Tests (2)

View new tests

test_cache_spans_get_span_name[True-get-args4-kwargs4-]
- File: tests.integrations.django.test_cache_module
- Status: ❌ Failing
test_cache_spans_get_span_name[False-get-args4-kwargs4-]
- File: tests.integrations.django.test_cache_module
- Status: ❌ Failing

➖ Removed Tests (1)

View removed tests

test_continuous_profiler_auto_start_and_stop_sampled[experiment-thread]
- File: tests.profiler.test_continuous_profiler

❌ Failed Tests

`test_cache_spans_get_span_name[True-get-args4-kwargs4-]`

File: tests.integrations.django.test_cache_module
Suite: py3.12-django-v6.0.6
Error: AssertionError: assert 'U\x1bvB8yI궖4Th\x02%t' == '' + U#x1BvB8yI궖4Th#x02%t

Stack Trace

tests/integrations/django/test_cache_module.py:578: in test_cache_spans_get_span_name
    assert _get_span_description(method_name, args, kwargs) == expected_name
E   AssertionError: assert 'U\x1bvB8yI궖4Th\x02%t' == ''
E     
E     + U#x1BvB8yI궖4Th#x02%t

`test_cache_spans_get_span_name[False-get-args4-kwargs4-]`

File: tests.integrations.django.test_cache_module
Suite: py3.12-django-v6.0.6
Error: AssertionError: assert 'U\x1bvB8yI궖4Th\x02%t' == '' + U#x1BvB8yI궖4Th#x02%t

Stack Trace

tests/integrations/django/test_cache_module.py:578: in test_cache_spans_get_span_name
    assert _get_span_description(method_name, args, kwargs) == expected_name
E   AssertionError: assert 'U\x1bvB8yI궖4Th\x02%t' == ''
E     
E     + U#x1BvB8yI궖4Th#x02%t

✅ Patch coverage is 100.00%. Project has 2558 uncovered lines.
✅ Project coverage is 89.57%. Comparing base (base) to head (head).

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
+ Coverage    89.56%    89.57%    +0.01%
==========================================
  Files          193       193         —
  Lines        24531     24531         —
  Branches      8678      8678         —
==========================================
+ Hits         21971     21973        +2
- Misses        2560      2558        -2
- Partials      1400      1398        -2

Generated by Codecov Action

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Chenghao999 reviewed

Aug 6, 2026

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Good minimal fix for the crash. One semantic point to consider: with this change an empty matcher becomes "$", and re.search("$", item) matches every string — so if regex_list ever contains an empty pattern, match_regex_list will now return True for any item instead of crashing. If an empty pattern should be ignored rather than match everything, an explicit if not item_matcher: continue would express that intent.

I also checked the substring_matching path: it only appends/reads the tail, no equivalent item_matcher[0] access, so this is the only crash site. LGTM otherwise.

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match_regex_list raises IndexError when a pattern list contains an empty string

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alexander-alderman-webb commented Jul 28, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Description

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github-actions Bot commented Jul 28, 2026

Codecov Results 📊

📊 Comparison with Base Branch

➕ New Tests (2)

➖ Removed Tests (1)

❌ Failed Tests

test_cache_spans_get_span_name[True-get-args4-kwargs4-]

test_cache_spans_get_span_name[False-get-args4-kwargs4-]

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alexander-alderman-webb commented Jul 28, 2026 •

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`test_cache_spans_get_span_name[True-get-args4-kwargs4-]`

`test_cache_spans_get_span_name[False-get-args4-kwargs4-]`