Fix PseudoFixtureDef reference cycle.

AUTHORS

@@ -197,3 +197,4 @@ Xuan Luong
 Xuecong Liao
 Zoltán Máté
 Roland Puntaier
+Allan Feldman

_pytest/fixtures.py

@@ -24,6 +24,12 @@
 from _pytest.outcomes import fail, TEST_OUTCOME
 
 
+@attr.s(frozen=True)
+class PseudoFixtureDef(object):
+    cached_result = attr.ib()
+    scope = attr.ib()
+
+
 def pytest_sessionstart(session):
     import _pytest.python
     import _pytest.nodes
@@ -440,10 +446,9 @@ def _get_active_fixturedef(self, argname):
                 fixturedef = self._getnextfixturedef(argname)
             except FixtureLookupError:
                 if argname == "request":
-                    class PseudoFixtureDef(object):
-                        cached_result = (self, [0], None)
-                        scope = "function"
-                    return PseudoFixtureDef
+                    cached_result = (self, [0], None)
+                    scope = "function"
+                    return PseudoFixtureDef(cached_result, scope)
                 raise
         # remove indent to prevent the python3 exception
         # from leaking into the call

changelog/3249.bugfix.rst

@@ -0,0 +1 @@
+Fix reference cycle generated when using the ``request`` fixture.

testing/python/fixture.py

@@ -519,6 +519,41 @@ def test_method(self, something):
         assert len(arg2fixturedefs) == 1
         assert arg2fixturedefs['something'][0].argname == "something"
 
+    def test_request_garbage(self, testdir):
+        testdir.makepyfile("""
+            import sys
+            import pytest
+            import gc
+
+            @pytest.fixture(autouse=True)
+            def something(request):
+                # this method of test doesn't work on pypy
+                if hasattr(sys, "pypy_version_info"):
+                    yield
+                else:
+                    original = gc.get_debug()
+                    gc.set_debug(gc.DEBUG_SAVEALL)
+                    gc.collect()
+
+                    yield
+
+                    gc.collect()
+                    leaked_types = sum(1 for _ in gc.garbage
+                                    if 'PseudoFixtureDef' in str(_))
+
+                    gc.garbage[:] = []
+
+                    try:
+                        assert leaked_types == 0
+                    finally:
+                        gc.set_debug(original)
+
+            def test_func():
+                pass
+        """)
+        reprec = testdir.inline_run()
+        reprec.assertoutcome(passed=1)
+
     def test_getfixturevalue_recursive(self, testdir):
         testdir.makeconftest("""
             import pytest