Skip fixture-discovery scan for fixture-less plugins

changelog/14877.improvement.rst

@@ -0,0 +1,9 @@
+Reduced per-session startup overhead in fixture discovery: plugins which declare
+they define no fixtures via the new internal ``__pytest_no_fixtures__`` marker
+(all fixture-less builtin plugins, the terminal reporter, and the config
+objects) are no longer scanned attribute-by-attribute by
+``FixtureManager.parsefactories`` on every ``Config`` build. This roughly
+halves the number of attribute introspections during plugin registration
+(e.g. 2258 to 1052 in a default session) and speeds up anything which builds
+many configs, such as :fixture:`pytester`-based test suites. A meta test
+guards that no holder carrying the marker actually defines a fixture.

src/_pytest/assertion/__init__.py

@@ -3,6 +3,11 @@
 
 from __future__ import annotations
 
+
+# This plugin defines no fixtures: opt out of the fixture-discovery scan in
+# FixtureManager.parsefactories (#14877).
+__pytest_no_fixtures__ = True
+
 from collections.abc import Generator
 import sys
 from typing import Any

src/_pytest/config/__init__.py

@@ -497,6 +497,10 @@ class PytestPluginManager(PluginManager):
     * ``conftest.py`` loading during start-up.
     """
 
+    # This plugin defines no fixtures: opt out of the fixture-discovery scan
+    # in FixtureManager.parsefactories (#14877).
+    __pytest_no_fixtures__ = True
+
     def __init__(self) -> None:
         from _pytest.assertion import DummyRewriteHook
         from _pytest.assertion import RewriteHook
@@ -1118,6 +1122,10 @@ class Config:
         invocation.
     """
 
+    # This object defines no fixtures: opt out of the fixture-discovery scan
+    # in FixtureManager.parsefactories (#14877).
+    __pytest_no_fixtures__ = True
+
     @final
     @dataclasses.dataclass(frozen=True)
     class InvocationParams:

src/_pytest/debugging.py

@@ -4,6 +4,11 @@
 
 from __future__ import annotations
 
+
+# This plugin defines no fixtures: opt out of the fixture-discovery scan in
+# FixtureManager.parsefactories (#14877).
+__pytest_no_fixtures__ = True
+
 import argparse
 from collections.abc import Callable
 from collections.abc import Generator

src/_pytest/faulthandler.py

@@ -1,5 +1,10 @@
 from __future__ import annotations
 
+
+# This plugin defines no fixtures: opt out of the fixture-discovery scan in
+# FixtureManager.parsefactories (#14877).
+__pytest_no_fixtures__ = True
+
 from collections.abc import Generator
 import os
 import sys

src/_pytest/fixtures.py

@@ -2296,6 +2296,14 @@ def parsefactories(
         else:
             holderobj_tp = cast("type | types.ModuleType", holderobj)
 
+        # Skip the scan entirely for holders which declare that they define
+        # no fixtures. Walking dir() and validating every attribute of every
+        # registered plugin on each Config build is pure overhead for
+        # fixture-less plugins (#14877). The lookup is done safely, like the
+        # loop below, because the holder may be an arbitrary user object.
+        if safe_getattr(holderobj, "__pytest_no_fixtures__", False):
+            return
+
         for name in dir(holderobj):
             # Read the raw __dict__ entry first so staticmethod/classmethod
             # wrappers are not hidden by descriptor binding.

src/_pytest/helpconfig.py

@@ -3,6 +3,11 @@
 
 from __future__ import annotations
 
+
+# This plugin defines no fixtures: opt out of the fixture-discovery scan in
+# FixtureManager.parsefactories (#14877).
+__pytest_no_fixtures__ = True
+
 import argparse
 from collections.abc import Generator
 from collections.abc import Sequence

src/_pytest/legacypath.py

@@ -3,6 +3,11 @@
 
 from __future__ import annotations
 
+
+# This plugin defines no fixtures: opt out of the fixture-discovery scan in
+# FixtureManager.parsefactories (#14877).
+__pytest_no_fixtures__ = True
+
 import dataclasses
 from pathlib import Path
 import shlex

src/_pytest/main.py

@@ -2,6 +2,11 @@
 
 from __future__ import annotations
 
+
+# This plugin defines no fixtures: opt out of the fixture-discovery scan in
+# FixtureManager.parsefactories (#14877).
+__pytest_no_fixtures__ = True
+
 import argparse
 from collections.abc import Callable
 from collections.abc import Iterable

src/_pytest/mark/__init__.py

@@ -2,6 +2,11 @@
 
 from __future__ import annotations
 
+
+# This plugin defines no fixtures: opt out of the fixture-discovery scan in
+# FixtureManager.parsefactories (#14877).
+__pytest_no_fixtures__ = True
+
 import collections
 from collections.abc import Collection
 from collections.abc import Iterable

src/_pytest/pastebin.py

@@ -3,6 +3,11 @@
 
 from __future__ import annotations
 
+
+# This plugin defines no fixtures: opt out of the fixture-discovery scan in
+# FixtureManager.parsefactories (#14877).
+__pytest_no_fixtures__ = True
+
 from io import StringIO
 import tempfile
 from typing import IO

src/_pytest/python.py

@@ -3,6 +3,11 @@
 
 from __future__ import annotations
 
+
+# This plugin defines no fixtures: opt out of the fixture-discovery scan in
+# FixtureManager.parsefactories (#14877).
+__pytest_no_fixtures__ = True
+
 import abc
 from collections import Counter
 from collections import defaultdict

src/_pytest/reports.py

@@ -1,6 +1,11 @@
 # mypy: allow-untyped-defs
 from __future__ import annotations
 
+
+# This plugin defines no fixtures: opt out of the fixture-discovery scan in
+# FixtureManager.parsefactories (#14877).
+__pytest_no_fixtures__ = True
+
 from collections.abc import Iterable
 from collections.abc import Iterator
 from collections.abc import Mapping

src/_pytest/runner.py

@@ -3,6 +3,11 @@
 
 from __future__ import annotations
 
+
+# This plugin defines no fixtures: opt out of the fixture-discovery scan in
+# FixtureManager.parsefactories (#14877).
+__pytest_no_fixtures__ = True
+
 import bdb
 from collections.abc import Callable
 import dataclasses

src/_pytest/setuponly.py

@@ -1,5 +1,10 @@
 from __future__ import annotations
 
+
+# This plugin defines no fixtures: opt out of the fixture-discovery scan in
+# FixtureManager.parsefactories (#14877).
+__pytest_no_fixtures__ = True
+
 from collections.abc import Generator
 
 from _pytest._io.saferepr import saferepr

src/_pytest/setupplan.py

@@ -1,5 +1,10 @@
 from __future__ import annotations
 
+
+# This plugin defines no fixtures: opt out of the fixture-discovery scan in
+# FixtureManager.parsefactories (#14877).
+__pytest_no_fixtures__ = True
+
 from _pytest.config import Config
 from _pytest.config import ExitCode
 from _pytest.config.argparsing import Parser

src/_pytest/skipping.py

@@ -3,6 +3,11 @@
 
 from __future__ import annotations
 
+
+# This plugin defines no fixtures: opt out of the fixture-discovery scan in
+# FixtureManager.parsefactories (#14877).
+__pytest_no_fixtures__ = True
+
 from collections.abc import Generator
 from collections.abc import Mapping
 import dataclasses

src/_pytest/stepwise.py

@@ -1,5 +1,10 @@
 from __future__ import annotations
 
+
+# This plugin defines no fixtures: opt out of the fixture-discovery scan in
+# FixtureManager.parsefactories (#14877).
+__pytest_no_fixtures__ = True
+
 import dataclasses
 from datetime import datetime
 from datetime import timedelta

src/_pytest/terminal.py

@@ -6,6 +6,11 @@
 
 from __future__ import annotations
 
+
+# This plugin defines no fixtures: opt out of the fixture-discovery scan in
+# FixtureManager.parsefactories (#14877).
+__pytest_no_fixtures__ = True
+
 import argparse
 from collections import Counter
 from collections.abc import Callable
@@ -385,6 +390,10 @@ def get_location(self, config: Config) -> str | None:
 
 @final
 class TerminalReporter:
+    # This plugin defines no fixtures: opt out of the fixture-discovery scan
+    # in FixtureManager.parsefactories (#14877).
+    __pytest_no_fixtures__ = True
+
     def __init__(self, config: Config, file: TextIO | None = None) -> None:
         import _pytest.config
 

src/_pytest/threadexception.py

@@ -1,5 +1,10 @@
 from __future__ import annotations
 
+
+# This plugin defines no fixtures: opt out of the fixture-discovery scan in
+# FixtureManager.parsefactories (#14877).
+__pytest_no_fixtures__ = True
+
 import collections
 from collections.abc import Callable
 import functools

src/_pytest/unittest.py

@@ -3,6 +3,11 @@
 
 from __future__ import annotations
 
+
+# This plugin defines no fixtures: opt out of the fixture-discovery scan in
+# FixtureManager.parsefactories (#14877).
+__pytest_no_fixtures__ = True
+
 from collections.abc import Callable
 from collections.abc import Generator
 from collections.abc import Iterable

src/_pytest/unraisableexception.py

@@ -1,5 +1,10 @@
 from __future__ import annotations
 
+
+# This plugin defines no fixtures: opt out of the fixture-discovery scan in
+# FixtureManager.parsefactories (#14877).
+__pytest_no_fixtures__ = True
+
 import collections
 from collections.abc import Callable
 import functools

src/_pytest/warnings.py

@@ -1,6 +1,11 @@
 # mypy: allow-untyped-defs
 from __future__ import annotations
 
+
+# This plugin defines no fixtures: opt out of the fixture-discovery scan in
+# FixtureManager.parsefactories (#14877).
+__pytest_no_fixtures__ = True
+
 from collections.abc import Generator
 from contextlib import contextmanager
 from typing import Literal

testing/test_meta.py

@@ -6,11 +6,19 @@
 
 from __future__ import annotations
 
+import importlib
 import pkgutil
 import subprocess
 import sys
+import types
 
 import _pytest
+from _pytest.compat import safe_getattr
+from _pytest.compat import safe_isclass
+from _pytest.config import Config
+from _pytest.config import PytestPluginManager
+from _pytest.fixtures import FixtureFunctionDefinition
+from _pytest.terminal import TerminalReporter
 import pytest
 
 
@@ -32,3 +40,59 @@ def test_no_warnings(module: str) -> None:
         "-c", f"__import__({module!r})",
     ))
     # fmt: on
+
+
+def _opted_out_holders() -> list[object]:
+    """All holders carrying the ``__pytest_no_fixtures__`` opt-out marker."""
+    holders: list[object] = [Config, PytestPluginManager, TerminalReporter]
+    for _, name, _ in pkgutil.walk_packages(
+        _pytest.__path__, prefix=_pytest.__name__ + "."
+    ):
+        module = importlib.import_module(name)
+        if safe_getattr(module, "__pytest_no_fixtures__", False):
+            holders.append(module)
+    return holders
+
+
+def _discoverable_fixture_names(holder: object) -> list[str]:
+    """Names which ``FixtureManager.parsefactories`` would register as
+    fixtures on ``holder``.
+
+    Mirrors the detection in ``parsefactories``: fixtures are looked up on the
+    module itself, or on the class for instance holders.
+    """
+    if not safe_isclass(holder) and not isinstance(holder, types.ModuleType):
+        holder = type(holder)
+    return [
+        name
+        for name in dir(holder)
+        if type(safe_getattr(holder, name, None)) is FixtureFunctionDefinition
+    ]
+
+
+def test_no_fixtures_opt_out_holders_define_no_fixtures() -> None:
+    """Guard for the ``__pytest_no_fixtures__`` opt-out (see #14877).
+
+    ``FixtureManager.parsefactories`` skips fixture discovery entirely for
+    holders carrying the marker, so any fixture defined on such a holder
+    would silently never be collected. Fail here if that ever happens.
+    """
+    holders = _opted_out_holders()
+    assert holders, "expected some holders to carry __pytest_no_fixtures__"
+    offenders = {
+        getattr(holder, "__name__", repr(holder)): _discoverable_fixture_names(holder)
+        for holder in holders
+    }
+    offenders = {name: found for name, found in offenders.items() if found}
+    assert not offenders, (
+        "holders marked __pytest_no_fixtures__ define fixtures which "
+        f"parsefactories would silently skip: {offenders}"
+    )
+
+
+def test_discoverable_fixture_names_supports_instance_holders() -> None:
+    """Instance holders resolve to their class, mirroring parsefactories."""
+    holder_cls = type("Plugin", (), {"my_fixture": pytest.fixture(lambda: 1)})
+
+    assert _discoverable_fixture_names(holder_cls()) == ["my_fixture"]
+    assert _discoverable_fixture_names(holder_cls) == ["my_fixture"]