fix: improve caching of parameterized fixtures

The fix for Issue pytest-dev#6541 caused regression where cache hits became
cache misses, unexpectedly.  Attempt to restore the previous behavior,
while also retaining the fix for the bug.

Fixes: Issue pytest-dev#6962

AUTHORS

@@ -306,6 +306,7 @@ Nicholas Devenish
 Nicholas Murphy
 Niclas Olofsson
 Nicolas Delaby
+Nicolas Simonds
 Nico Vidal
 Nikolay Kondratyev
 Nipunn Koorapati

changelog/6962.bugfix.rst

@@ -0,0 +1 @@
+Fixed bug where parametrized fixtures were not being cached correctly, being recreated every time.

src/_pytest/fixtures.py

@@ -1056,9 +1056,16 @@ def execute(self, request: SubRequest) -> FixtureValue:
         my_cache_key = self.cache_key(request)
         if self.cached_result is not None:
             cache_key = self.cached_result[1]
-            # note: comparison with `==` can fail (or be expensive) for e.g.
-            # numpy arrays (#6497).
-            if my_cache_key is cache_key:
+
+            # note: `__eq__` is not required to return a bool, and sometimes
+            # doesn't, e.g., numpy arrays (#6497).  Coerce the comparison
+            # into a bool, and if that fails, fall back to an identity check.
+            try:
+                cache_hit = bool(my_cache_key == cache_key)
+            except (ValueError, RuntimeError):
+                cache_hit = my_cache_key is cache_key
+
+            if cache_hit:
                 if self.cached_result[2] is not None:
                     exc, exc_tb = self.cached_result[2]
                     raise exc.with_traceback(exc_tb)

testing/python/fixtures.py

@@ -1557,6 +1557,37 @@ def test_printer_2(self):
         result = pytester.runpytest()
         result.stdout.fnmatch_lines(["* 2 passed in *"])
 
+    def test_parameterized_fixture_caching(self, pytester: Pytester) -> None:
+        pytester.makepyfile(
+            """
+            import pytest
+            from itertools import count
+
+            CACHE_HITS = count(0)
+
+            def pytest_generate_tests(metafunc):
+                if "my_fixture" in metafunc.fixturenames:
+                    param = "d%s" % "1"
+                    print("param id=%d" % id(param), flush=True)
+                    metafunc.parametrize("my_fixture", [param, "d2"], indirect=True)
+
+            @pytest.fixture(scope='session')
+            def my_fixture(request):
+                next(CACHE_HITS)
+
+            def test1(my_fixture):
+                pass
+
+            def test2(my_fixture):
+                pass
+
+            def teardown_module():
+                assert next(CACHE_HITS) == 2
+            """
+        )
+        result = pytester.runpytest()
+        result.stdout.no_fnmatch_line("* ERROR at teardown *")
+
 
 class TestFixtureManagerParseFactories:
     @pytest.fixture