Finish round 3 singletons: S8519, S112, ratings S3776 (Sonar)

[mzeier]

Round 3 remainder for thunderbird/addons-server#419, as listed in the coordinator's status note: S8519, the two S112s, and the ratings S3776 still over 15 after #535.

Changes, each with its no-behavior-change argument

1. python:S8519 src/olympia/amo/search.py ES.__getitem__ (AaEh92RwMSBE_HpBvXx8 (line 104)). return list(new)[0] becomes return _first_item(new). This is the _first_item() pattern from P1-11: Sonar fixes in activity (S8512, S8519, S7496, S5806, S1192, S2638, S1172, S1940) #473: next(iter(...)), re-raising IndexError('list index out of range') on an empty result, the same type and message list(...)[0] raised.
   • Query count is unchanged. list(new) called ES.__len__ and then ES.__iter__. Both go through _do_search(), which caches _results_cache, so that was one ES query. next(iter(new)) calls __iter__ -> _do_search() once: still one ES query.
   • For object results, the original len() evaluated the type.objects.filter(id__in=...) queryset, and ObjectSearchResults.__iter__ then reused its cache. Now __iter__ evaluates it, still exactly once. That generator builds its dict eagerly, so taking only the first element skips no work.
2. python:S112 src/olympia/amo/utils.py resize_image (AaEh92NnMSBE_HpBvXxT (line 668)): Exception becomes ValueError, with the same message. Callers:
   • devhub/tasks.py (icon/preview resizing) and users/tasks.py wrap it in except Exception, which still catches ValueError.
   • versions/tasks.py and the other devhub calls don't catch it, so it propagates as before.
   • amo/tests/test_amo_utils.py::test_resize_image uses pytest.raises(Exception, match=...), which still passes.
3. python:S112 src/olympia/lib/settings_base.py read_only_mode (AaEh92ixMSBE_HpBvX1X (line 1451)): Exception becomes RuntimeError, with the same message. No caller catches it: it runs at settings import (or amo/tests/test_readonly.py's fixture with a valid env). I used a built-in so the settings module doesn't gain a Django import.
4. python:S3776 src/olympia/ratings/views.py RatingViewSet.filter_queryset (AaEh92f7MSBE_HpBvX0l (line 373)): the whole if self.action == 'list': body moves verbatim into _filter_list_queryset(qs), which returns qs. The same parameters are read and parsed in the same order, with the same ParseError messages and the same self.pagination_class assignment. filter_queryset still calls super().filter_queryset(qs) last.

Decorators checked: the AST comparison of every pre-existing function's decorator list between stage-eks and this branch shows 0 changes. RatingViewSet.filter_queryset and ES.__getitem__ carry no decorators, before or after; _first_item and _filter_list_queryset are new and undecorated.

Tests

flake8 is clean on changed lines. CI pytest covers amo/tests/test_search.py, amo/tests/test_amo_utils.py, amo/tests/test_readonly.py and ratings/tests/test_views.py. Local Greptile review skipped: org quota.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

Python Test Results

5 763 tests  +5 763   5 709 ✅ +5 709   6m 42s ⏱️ + 6m 42s
    1 suites +    1      54 💤 +   54 
    1 files   +    1       0 ❌ ±    0 

Results for commit c0a63ac. ± Comparison against base commit 1039ee9.