Skip fixture-discovery scan for fixture-less plugins - #15086
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FixtureManager.parsefactories() walked dir() and validated every attribute of every registered plugin on each Config build, even though most builtin plugins define no fixtures. Holders can now declare this with the __pytest_no_fixtures__ marker, in which case the scan is skipped entirely. The marker is applied to all fixture-less builtin plugin modules, the TerminalReporter, and the Config / PytestPluginManager objects (22 holders per session build). Attribute introspections per session build drop from 2258 to 1052 (-53%) with an identical registered fixture set. A meta test guards the marker: it fails if any marked holder actually defines a fixture, so a fixture can never be silently dropped. Closes pytest-dev#14877.
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Problem
FixtureManager.parsefactories()walksdir(plugin)and validates everyattribute of every registered plugin on every
Configbuild, even thoughmost builtin plugins define zero fixtures. Per the profiling in #14877 this
is pure overhead, paid repeatedly by anything that builds many configs
(
pytester-based suites first of all — i.e. pytest's own test suite).Approach
Holders can now declare that they define no fixtures with the
__pytest_no_fixtures__marker;parsefactoriesreturns early for them(the lookup uses
safe_getattr, so arbitrary user objects are unaffected).The marker is applied to:
mark,main,runner,helpconfig,python,terminal,debugging,unittest,skipping,legacypath,pastebin,assertion,setuponly,setupplan,stepwise,unraisableexception,threadexception,warnings,reports,faulthandler)TerminalReporter(registered as an instance)ConfigandPytestPluginManagerobjects22 holders skipped per session build in total. Modules that do define
fixtures (
fixtures— including thepytestconfigfixture,capture,tmpdir,monkeypatch,recwarn,junitxml,doctest,cacheprovider,logging,subtests) are untouched and scanned exactly as before.To address the failure mode noted in the issue (a fixture added to a marked
holder would be silently dropped),
testing/test_meta.py::test_no_fixtures_opt_out_holders_define_no_fixtureswalks every marked holder and fails if any of them actually defines a
fixture.
Measured
Per session build + collect-only run (default plugin set):
dir()names scanned)_check_for_wrapped_fixturevalidationstesting/test_config.py(-n 8, pytester-heavy, single runs each):31.67s → 29.80s.
--fixturesoutput verified identical (modulo shiftedline numbers from the added marker lines).
Tests
test_no_fixtures_opt_out_holders_define_no_fixtures: passestesting/test_meta.py,testing/test_pluginmanager.py: 108 passed, 1 skippedtesting/python/fixtures.py: 242 passed, 3 xfailedtesting/test_config.py: 290 passed, 1 xfailedtesting/test_doctest.py,testing/test_conftest.py: 202 passed, 1 skipped, 1 xfailedChangelog entry added (
changelog/14877.improvement.rst).Note on the design
The issue leans toward push-based discovery or per-holder caching over a
manual flag. This PR takes the flag direction because it is the minimal,
reviewable change that captures the measured win with zero behavior change
for fixture-defining plugins, and the new meta test removes the flag's
silent-drop failure mode. Happy to rework toward caching if maintainers
prefer.
Closes #14877.