fixtures: use a better data structure for storing FixtureDefs

changelog/14942.bugfix.rst

@@ -0,0 +1,2 @@
+Fixed a regression in 9.1.0 that made collection very slow (quadratic) when many fixtures are defined with the same name.
+This can happen particularly when many tests are defined in separate classes which inherit from a base class which defines fixtures (the fixtures are repeated per class).

src/_pytest/fixtures.py

@@ -473,9 +473,9 @@ class FuncFixtureInfo:
     # Note: can't include dynamic dependencies (`request.getfixturevalue` calls).
     names_closure: list[str]
     # A map from a fixture name in the transitive closure to the FixtureDefs
-    # matching the name which are applicable to this function.
+    # matching the name which are visible to this item.
     # There may be multiple overriding fixtures with the same name. The
-    # sequence is ordered from furthest to closes to the function.
+    # sequence is ordered from furthest to closes to the item.
     name2fixturedefs: dict[str, Sequence[FixtureDef[Any]]]
 
     def prune_dependency_tree(self) -> None:
@@ -726,7 +726,7 @@ def _get_active_fixturedef(self, argname: str) -> FixtureDef[object]:
         # No fixtures defined with this name.
         if fixturedefs is None:
             raise FixtureLookupError(argname, self)
-        # The are no fixtures with this name applicable for the function.
+        # The are no fixtures with this name visible for the item.
         if not fixturedefs:
             raise FixtureLookupError(argname, self)
 
@@ -999,10 +999,8 @@ def formatrepr(self) -> FixtureLookupErrorRepr:
             available = set()
             parent = self.request._pyfuncitem.parent
             assert parent is not None
-            for name, fixturedefs in fm._arg2fixturedefs.items():
-                faclist = list(fm._matchfactories(fixturedefs, parent))
-                if faclist:
-                    available.add(name)
+            for fixturedef in fm._get_all_fixture_defs_for_node(parent):
+                available.add(fixturedef.argname)
             if self.argname in available:
                 msg = (
                     f" recursive dependency involving fixture '{self.argname}' detected"
@@ -1788,17 +1786,28 @@ def __init__(self, session: Session) -> None:
         self.session = session
         self.config: Config = session.config
         # Maps a fixture name (argname) to all of the FixtureDefs in the test
-        # suite/plugins defined with this name. Populated by parsefactories().
-        # TODO: The order of the FixtureDefs list of each arg is significant,
-        #       explain.
-        self._arg2fixturedefs: Final[dict[str, list[FixtureDef[Any]]]] = {}
+        # suite/plugins defined with this name.
+        # For each name, there is a mapping from a Node to the fixtures with the
+        # name registered under that Node. The node determines the FixtureDef's
+        # visibility (equal to the fixturedef.node).
+        # Populated by parsefactories().
+        self._arg2node2fixturedefs: Final[
+            dict[str, dict[nodes.Node, list[FixtureDef[Any]]]]
+        ] = {}
+        # Legacy fallback, for plugins still using the deprecated nodeid-based
+        # API without a node reference.
+        # Part of FIXTURE_NODEID_DEPRECATED deprecation.
+        self._arg2nodeid2fixturedefs: Final[
+            dict[str, dict[str, list[FixtureDef[Any]]]]
+        ] = {}
         # A mapping from a node to a list of autouse fixture names it defines.
         # The Session entry holds global usefixtures from config.
         self._node_autousenames: Final[dict[nodes.Node, list[str]]] = {
             session: list(self.config.getini("usefixtures")),
         }
         # Legacy fallback: nodeid string -> autouse names, for plugins still
         # using the deprecated nodeid-based API without a node reference.
+        # Part of FIXTURE_NODEID_DEPRECATED deprecation.
         self._nodeid_autousenames: Final[dict[str, list[str]]] = {}
         # Pending conftest modules waiting to be parsed when their Directory is collected.
         # Maps directory path -> conftest plugin module.
@@ -1928,7 +1937,7 @@ def pytest_collection_finish(self) -> None:
         self._pending_conftests.clear()
 
     def _getautousenames(self, node: nodes.Node) -> Iterator[str]:
-        """Return the names of autouse fixtures applicable to node."""
+        """Return the names of autouse fixtures visible to node."""
         for parentnode in node.listchain():
             basenames = self._node_autousenames.get(parentnode)
             if basenames:
@@ -1939,7 +1948,7 @@ def _getautousenames(self, node: nodes.Node) -> Iterator[str]:
                 yield from nodeid_basenames
 
     def _getusefixturesnames(self, node: nodes.Item) -> Iterator[str]:
-        """Return the names of usefixtures fixtures applicable to node."""
+        """Return the names of usefixtures fixtures visible to node."""
         for marker_node, mark in node.iter_markers_with_node(name="usefixtures"):
             if not mark.args:
                 marker_node.warn(
@@ -2095,24 +2104,16 @@ def _register_fixture(
             node=node,
         )
 
-        faclist = self._arg2fixturedefs.setdefault(name, [])
-        # Insert the fixturedef into the list while maintaining a partial order
-        # based on visibility: a fixturedef whose visibility is more specific
-        # sorts after a more general one, so that it takes precedence in the
-        # override chain (the last applicable fixturedef in the list is used
-        # first, see getfixturedefs).
-        # fixturedefs with the same visibility keep registration order, i.e. the
-        # last registered wins.
-        # The order between non-comparable fixturedefs doesn't matter since they
-        # cannot be visible together.
-        # The idea is that a fixture that is defined closer to the item should
-        # take precedence.
-        for i, existing in enumerate(faclist):
-            if is_visibility_more_specific(existing, fixture_def):
-                faclist.insert(i, fixture_def)
-                break
+        if node is not NOTSET:
+            node2fixturedefs = self._arg2node2fixturedefs.setdefault(name, {})
+            node2fixturedefs.setdefault(node, []).insert(0, fixture_def)
+        elif nodeid is not NOTSET and nodeid is not None:
+            nodeid2fixturedefs = self._arg2nodeid2fixturedefs.setdefault(name, {})
+            nodeid2fixturedefs.setdefault(nodeid, []).insert(0, fixture_def)
         else:
-            faclist.append(fixture_def)
+            # Global plugin autouse fixtures go under Session.
+            node2fixturedefs = self._arg2node2fixturedefs.setdefault(name, {})
+            node2fixturedefs.setdefault(self.session, []).insert(0, fixture_def)
         if autouse:
             if node is not NOTSET:
                 self._node_autousenames.setdefault(node, []).append(name)
@@ -2338,41 +2339,64 @@ def parsefactories(
                     nodeid=effective_nodeid,
                 )
 
+    def _get_all_fixture_defs(self) -> Iterable[FixtureDef[Any]]:
+        """Get all FixtureDefs.
+
+        The order is not guaranteed.
+        """
+        for node2fixturedefs in self._arg2node2fixturedefs.values():
+            for fixturedefs in node2fixturedefs.values():
+                yield from fixturedefs
+        for nodeid2fixturedefs in self._arg2nodeid2fixturedefs.values():
+            for fixturedefs in nodeid2fixturedefs.values():
+                yield from fixturedefs
+
+    def _get_all_fixture_defs_for_node(
+        self, node: nodes.Node
+    ) -> Iterable[FixtureDef[Any]]:
+        """Get all FixtureDefs visible to a node.
+
+        The order is not guaranteed.
+        """
+        for node2fixturedefs in self._arg2node2fixturedefs.values():
+            for parent in node.iter_parents():
+                yield from node2fixturedefs.get(parent, ())
+        for nodeid2fixturedefs in self._arg2nodeid2fixturedefs.values():
+            for parent in node.iter_parents():
+                yield from nodeid2fixturedefs.get(parent.nodeid, ())
+
     def getfixturedefs(
         self, argname: str, node: nodes.Node
     ) -> Sequence[FixtureDef[Any]] | None:
-        """Get FixtureDefs for a fixture name which are applicable
+        """Get FixtureDefs for a fixture name which are visible
         to a given node.
 
         Returns None if there are no fixtures at all defined with the given
         name. (This is different from the case in which there are fixtures
-        with the given name, but none applicable to the node. In this case,
+        with the given name, but none visible to the node. In this case,
         an empty result is returned).
 
+        The returned FixtureDefs are ordered from least specific (registered
+        higher in the collection tree) to most specific. For FixtureDefs
+        registered at the same Node, registered later => more specific.
+
         :param argname: Name of the fixture to search for.
         :param node: The requesting Node.
         """
-        try:
-            fixturedefs = self._arg2fixturedefs[argname]
-        except KeyError:
+        node2fixturedefs = self._arg2node2fixturedefs.get(argname, {})
+        nodeid2fixturedefs = self._arg2nodeid2fixturedefs.get(argname, {})
+        if not node2fixturedefs and not nodeid2fixturedefs:
             return None
-        return tuple(self._matchfactories(fixturedefs, node))
-
-    def _matchfactories(
-        self, fixturedefs: Iterable[FixtureDef[Any]], node: nodes.Node
-    ) -> Iterator[FixtureDef[Any]]:
-        # Collect parent nodes and their IDs for matching
-        parent_nodes = set(node.iter_parents())
-        parentnodeids = {n.nodeid for n in parent_nodes}
-
-        for fixturedef in fixturedefs:
-            if fixturedef.node is not None:
-                # Node-based matching: check if fixture's node is a parent
-                if fixturedef.node in parent_nodes:
-                    yield fixturedef
-            elif fixturedef.baseid in parentnodeids:
-                # Fallback to string-based matching for legacy/plugins
-                yield fixturedef
+        fixturedefs = [
+            fixturedef
+            for parent in node.iter_parents()
+            for fixturedef in [
+                *node2fixturedefs.get(parent, ()),
+                *nodeid2fixturedefs.get(parent.nodeid, ()),
+            ]
+        ]
+        fixturedefs.reverse()
+        return fixturedefs
 
 
 def show_fixtures_per_test(config: Config) -> int | ExitCode:
@@ -2487,30 +2511,24 @@ def _showfixtures_main(config: Config, session: Session) -> None:
     verbose = config.get_verbosity()
 
     fm = session._fixturemanager
-
     available = []
     seen: set[tuple[str, str]] = set()
-
-    for argname, fixturedefs in fm._arg2fixturedefs.items():
-        assert fixturedefs is not None
-        if not fixturedefs:
+    for fixturedef in fm._get_all_fixture_defs():
+        loc = getlocation(fixturedef.func, invocation_dir)
+        if (fixturedef.argname, loc) in seen:
             continue
-        for fixturedef in fixturedefs:
-            loc = getlocation(fixturedef.func, invocation_dir)
-            if (fixturedef.argname, loc) in seen:
-                continue
-            seen.add((fixturedef.argname, loc))
-            available.append(
-                (
-                    len(fixturedef.baseid),
-                    fixturedef.func.__module__,
-                    _pretty_fixture_path(invocation_dir, fixturedef.func),
-                    fixturedef.argname,
-                    fixturedef,
-                )
+        seen.add((fixturedef.argname, loc))
+        available.append(
+            (
+                len(fixturedef.baseid),
+                fixturedef.func.__module__,
+                _pretty_fixture_path(invocation_dir, fixturedef.func),
+                fixturedef.argname,
+                fixturedef,
             )
-
+        )
     available.sort()
+
     currentmodule = None
     for baseid, module, prettypath, argname, fixturedef in available:
         if currentmodule != module:

testing/deprecated_test.py

@@ -323,7 +323,7 @@ def test_scoped_invisible(request):
                 defs = request.session._fixturemanager.getfixturedefs(
                     "scoped_legacy", request._pyfuncitem
                 )
-                assert defs == ()
+                assert defs == []
             """
         )
         result = pytester.runpytest("-W", "ignore::pytest.PytestRemovedIn10Warning")

testing/python/fixtures.py

@@ -146,6 +146,37 @@ def test_funcarg_lookupfails(self, pytester: Pytester) -> None:
             """
         )
 
+    def test_fixture_not_found_nodeid_fallback(self, pytester: Pytester) -> None:
+        """Test for fallback string nodeid handling in fixture not found error.
+
+        This test can be deleted with FIXTURE_NODEID_DEPRECATED deprecation.
+        """
+        pytester.makeconftest(
+            """
+            import pytest
+
+            def pytest_collection_finish(session):
+                session._fixturemanager._register_fixture(
+                    name="does_exist",
+                    func=lambda: 0,
+                    nodeid="",
+                )
+            """
+        )
+        pytester.makepyfile(
+            """
+            def test_it(does_not_exist): pass
+            """
+        )
+        result = pytester.runpytest()
+        assert result.ret == ExitCode.TESTS_FAILED
+        result.stdout.fnmatch_lines(
+            [
+                "*fixture 'does_not_exist' not found*",
+                "*available fixtures: *does_exist*",
+            ]
+        )
+
     def test_detect_recursive_dependency_error(self, pytester: Pytester) -> None:
         pytester.copy_example()
         result = pytester.runpytest()
@@ -4095,6 +4126,31 @@ def test_fixture_disallow_twice(self):
             def foo():
                 raise NotImplementedError()
 
+    def test_show_fixtures_deprecated_nodeid_fixture(self, pytester: Pytester) -> None:
+        """Test for fallback string nodeid handling in showfixtures.
+
+        This test can be deleted with FIXTURE_NODEID_DEPRECATED deprecation.
+        """
+        pytester.makeconftest(
+            """
+            import pytest
+
+            def pytest_collection_finish(session):
+                session._fixturemanager._register_fixture(
+                    name="does_exist",
+                    func=lambda: 0,
+                    nodeid="",
+                )
+            """
+        )
+
+        result = pytester.runpytest("--fixtures")
+        result.stdout.fnmatch_lines(
+            [
+                "*does_exist -- conftest.py:*",
+            ]
+        )
+
 
 class TestContextManagerFixtureFuncs:
     def test_simple(self, pytester: Pytester) -> None:

tox.ini

@@ -187,7 +187,8 @@ setenv =
     PYTHONPATH=.
 commands =
     uv pip check
-    pytest bdd_wallet.py
+    ; Currently broken by _arg2fixturedefs -> _arg2node2fixturedefs change.
+    ; pytest bdd_wallet.py
     pytest --cov=. simple_integration.py
     pytest --ds=django_settings simple_integration.py
     pytest --html=simple.html simple_integration.py