Show deprecation warning for cached_setup

changelog/3616.deprecation.rst

@@ -6,3 +6,6 @@ The following accesses have been documented as deprecated for years, but are now
         usage of Function.Module is deprecated, please use pytest.Module instead
 
   Users should just ``import pytest`` and access those objects using the ``pytest`` module.
+
+* ``request.cached_setup``, this was the precursor of the setup/teardown mechanism available to fixtures. You can
+  consult `funcarg comparision section in the docs <https://docs.pytest.org/en/latest/funcarg_compare.html>`_.

src/_pytest/fixtures.py

@@ -479,6 +479,11 @@ class FixtureRequest(FuncargnamesCompatAttr):
             or ``session`` indicating the caching lifecycle of the resource.
         :arg extrakey: added to internal caching key of (funcargname, scope).
         """
+        msg = (
+            "cached_setup is deprecated and will be removed in a future release. "
+            "Use standard fixture functions instead."
+        )
+        warnings.warn(RemovedInPytest4Warning(msg), stacklevel=2)
         if not hasattr(self.config, "_setupcache"):
             self.config._setupcache = {}  # XXX weakref?
         cachekey = (self.fixturename, self._getscopeitem(scope), extrakey)

testing/deprecated_test.py

@@ -47,6 +47,27 @@ def test_compat_properties_deprecation(testdir):
     )
 
 
+def test_cached_setup_deprecation(testdir):
+    testdir.makepyfile(
+        """
+        import pytest
+        @pytest.fixture
+        def fix(request):
+            return request.cached_setup(lambda: 1)
+
+        def test_foo(fix):
+            assert fix == 1
+    """
+    )
+    result = testdir.runpytest()
+    result.stdout.fnmatch_lines(
+        [
+            "*test_cached_setup_deprecation.py:4:*cached_setup is deprecated*",
+            "*1 passed, 1 warnings in*",
+        ]
+    )
+
+
 @pytest.mark.filterwarnings("default")
 def test_funcarg_prefix_deprecation(testdir):
     testdir.makepyfile(

testing/python/fixture.py

@@ -977,6 +977,7 @@ class TestRequestCachedSetup(object):
         )
         reprec.assertoutcome(passed=4)
 
+    @pytest.mark.filterwarnings("ignore:cached_setup is deprecated")
     def test_request_cachedsetup_extrakey(self, testdir):
         item1 = testdir.getitem("def test_func(): pass")
         req1 = fixtures.FixtureRequest(item1)
@@ -994,6 +995,7 @@ class TestRequestCachedSetup(object):
         assert ret1 == ret1b
         assert ret2 == ret2b
 
+    @pytest.mark.filterwarnings("ignore:cached_setup is deprecated")
     def test_request_cachedsetup_cache_deletion(self, testdir):
         item1 = testdir.getitem("def test_func(): pass")
         req1 = fixtures.FixtureRequest(item1)