Allow ovewriting a parametrized fixture while reusing the parent fixt…

…ure's value

Fix pytest-dev#1953

changelog/1953.bugfix.rst

@@ -0,0 +1,20 @@
+Fix error when overwriting a fixture, reusing the original fixture value, when the overwritten fixture is parameterized:
+
+.. code-block:: python
+
+    # conftest.py
+    import pytest
+
+
+    @pytest.fixture(params=[1, 2])
+    def foo(request):
+        return request.param
+
+
+    # test_foo.py
+    import pytest
+
+
+    @pytest.fixture
+    def foo(foo):
+        return foo * 2

src/_pytest/fixtures.py

@@ -1530,9 +1530,8 @@ def sort_by_scope(arg_name: str) -> int:
 
     def pytest_generate_tests(self, metafunc: "Metafunc") -> None:
         for argname in metafunc.fixturenames:
-            faclist = metafunc._arg2fixturedefs.get(argname)
-            if faclist:
-                fixturedef = faclist[-1]
+            fixture_defs = metafunc._arg2fixturedefs.get(argname, ())
+            for fixturedef in reversed(fixture_defs):
                 if fixturedef.params is not None:
                     markers = list(metafunc.definition.iter_markers("parametrize"))
                     for parametrize_mark in markers:
@@ -1555,8 +1554,10 @@ def pytest_generate_tests(self, metafunc: "Metafunc") -> None:
                             scope=fixturedef.scope,
                             ids=fixturedef.ids,
                         )
-            else:
-                continue  # Will raise FixtureLookupError at setup time.
+                # stop if the current fixturedef doesn't also depend on its own
+                # argname, in case it is being overwritten (#1953)
+                if argname not in fixturedef.argnames:
+                    break
 
     def pytest_collection_modifyitems(self, items: "List[nodes.Item]") -> None:
         # Separate parametrized setups.

testing/python/fixtures.py

@@ -396,6 +396,34 @@ def test_spam(spam):
         result = testdir.runpytest(testfile)
         result.stdout.fnmatch_lines(["*3 passed*"])
 
+    def test_override_fixture_reusing_with_params(self, testdir):
+        """Override a fixture at a lower level, reusing the higher-level fixture that
+        is parametrized (#1953).
+        """
+        testdir.makeconftest(
+            """
+            import pytest
+
+            @pytest.fixture(params=[1, 2])
+            def foo(request):
+                return request.param
+            """
+        )
+        testdir.makepyfile(
+            """
+            import pytest
+
+            @pytest.fixture
+            def foo(foo):
+                return foo * 2
+
+            def test_spam(foo):
+                assert foo in (2, 4)
+            """
+        )
+        result = testdir.runpytest()
+        result.stdout.fnmatch_lines(["*2 passed*"])
+
     def test_autouse_fixture_plugin(self, testdir):
         # A fixture from a plugin has no baseid set, which screwed up
         # the autouse fixture handling.