Warn when implementations exist for pytest_namespace hook

This hook has been deprecated and will be removed in the future.

Fix #2639

changelog/2639.removal.rst

@@ -0,0 +1,3 @@
+``pytest_namespace`` has been deprecated.
+
+Plugins who need this feature are suggested to import ``pytest`` and set attributes explicitly during ``pytest_configure``.

setup.py

@@ -69,7 +69,7 @@ def main():
     # if _PYTEST_SETUP_SKIP_PLUGGY_DEP is set, skip installing pluggy;
     # used by tox.ini to test with pluggy master
     if "_PYTEST_SETUP_SKIP_PLUGGY_DEP" not in os.environ:
-        install_requires.append("pluggy>=0.5,<0.8")
+        install_requires.append("pluggy>=0.7")
     environment_marker_support_level = get_environment_marker_support_level()
     if environment_marker_support_level >= 2:
         install_requires.append('funcsigs;python_version<"3.0"')

src/_pytest/hookspec.py

@@ -1,6 +1,7 @@
 """ hook specifications for pytest plugins, invoked from main.py and builtin plugins.  """
 
 from pluggy import HookspecMarker
+from .deprecated import RemovedInPytest4Warning
 
 hookspec = HookspecMarker("pytest")
 
@@ -22,17 +23,27 @@ def pytest_addhooks(pluginmanager):
     """
 
 
-@hookspec(historic=True)
+@hookspec(
+    historic=True,
+    warn_on_impl=RemovedInPytest4Warning(
+        "pytest_namespace is deprecated and will be removed soon"
+    ),
+)
 def pytest_namespace():
     """
-    (**Deprecated**) this hook causes direct monkeypatching on pytest, its use is strongly discouraged
     return dict of name->object to be made globally available in
     the pytest namespace.
 
     This hook is called at plugin registration time.
 
     .. note::
         This hook is incompatible with ``hookwrapper=True``.
+
+    .. warning::
+        This hook has been **deprecated** and will be removed in pytest 4.0.
+
+        Plugins who need this feature are suggested
+        to import ``pytest`` and set attributes explicitly during ``pytest_configure``.
     """