[WIP] Introduce deprecations page

fix #3996

CHANGELOG.rst

@@ -24,19 +24,9 @@ pytest 3.8.0 (2018-09-05)
 Deprecations and Removals
 -------------------------
 
-- `#2452 <https://github.com/pytest-dev/pytest/issues/2452>`_: ``Config.warn`` has been deprecated, it should be replaced by calls to the standard ``warnings.warn``.
+- `#2452 <https://github.com/pytest-dev/pytest/issues/2452>`_: ``Config.warn`` and ``Node.warn`` have been
-
+  deprecated, see `<https://docs.pytest.org/en/latest/deprecations.html#config-warn-and-node-warn>`_ for rationale and
-  ``Node.warn`` now supports two signatures:
+  examples.
-
-  * ``node.warn(PytestWarning("some message"))``: is now the recommended way to call this function. The warning
-    instance must be a ``PytestWarning`` or subclass  instance.
-
-  * ``node.warn("CI", "some message")``: this code/message form is now deprecated and should be converted to
-    the warning instance form above.
-
-  ``RemovedInPytest4Warning`` and ``PytestExperimentalApiWarning`` are now part of the public API and should be accessed
-  using ``pytest.RemovedInPytest4Warning`` and ``pytest.PytestExperimentalApiWarning``.
-
 
 - `#3936 <https://github.com/pytest-dev/pytest/issues/3936>`_: ``@pytest.mark.filterwarnings`` second parameter is no longer regex-escaped,
   making it possible to actually use regular expressions to check the warning message.
@@ -253,15 +243,10 @@ pytest 3.7.0 (2018-07-30)
 Deprecations and Removals
 -------------------------
 
-- `#2639 <https://github.com/pytest-dev/pytest/issues/2639>`_: ``pytest_namespace`` has been deprecated.
+- `#2639 <https://github.com/pytest-dev/pytest/issues/2639>`_: ``pytest_namespace`` has been `deprecated <https://docs.pytest.org/en/latest/deprecations.html#pytest-namespace>`_.
-
-  See the documentation for ``pytest_namespace`` hook for suggestions on how to deal
-  with this in plugins which use this functionality.
 
 
-- `#3661 <https://github.com/pytest-dev/pytest/issues/3661>`_: Calling a fixture function directly, as opposed to request them in a test function, now issues a ``RemovedInPytest4Warning``. It will be changed into an error in pytest ``4.0``.
+- `#3661 <https://github.com/pytest-dev/pytest/issues/3661>`_: Calling a fixture function directly, as opposed to request them in a test function, now issues a ``RemovedInPytest4Warning``. See `the documentation for rationale and examples <https://docs.pytest.org/en/latest/deprecations.html#calling-fixtures-directly>`_.
-
-  This is a great source of confusion to new users, which will often call the fixture functions and request them from test functions interchangeably, which breaks the fixture resolution model.
 
 
 
@@ -623,7 +608,7 @@ Deprecations and Removals
   <https://github.com/pytest-dev/pytest/issues/2770>`_)
 
 - Defining ``pytest_plugins`` is now deprecated in non-top-level conftest.py
-  files, because they "leak" to the entire directory tree. (`#3084
+  files, because they "leak" to the entire directory tree. `See the docs <https://docs.pytest.org/en/latest/deprecations.html#pytest-plugins-in-non-top-level-conftest-files>`_ for the rationale behind this decision (`#3084
   <https://github.com/pytest-dev/pytest/issues/3084>`_)
 
 

doc/en/backwards-compatibility.rst

@@ -17,4 +17,6 @@ When the deprecation expires (e.g. 4.0 is released), we won't remove the depreca
 Deprecation Roadmap
 -------------------
 
-We track deprecation and removal of features using milestones and the `deprecation <https://github.com/pytest-dev/pytest/issues?q=label%3A%22type%3A+deprecation%22>`_ and `removal <https://github.com/pytest-dev/pytest/labels/type%3A%20removal>`_ labels on GitHub.
+Features currently deprecated and removed in previous releases can be found in :ref:`deprecations`.
+
+We track future deprecation and removal of features using milestones and the `deprecation <https://github.com/pytest-dev/pytest/issues?q=label%3A%22type%3A+deprecation%22>`_ and `removal <https://github.com/pytest-dev/pytest/labels/type%3A%20removal>`_ labels on GitHub.

doc/en/contents.rst

@@ -39,6 +39,7 @@ Full pytest documentation
    bash-completion
 
    backwards-compatibility
+   deprecations
    historical-notes
    license
    contributing

doc/en/deprecations.rst

@@ -0,0 +1,176 @@
+.. _deprecations:
+
+Deprecations and Removals
+=========================
+
+This page lists all pytest features that are currently deprecated or have been removed in previous major releases.
+The objective is to give users a clear rationale why a certain feature has been removed, and what alternatives can be
+used instead.
+
+Deprecated Features
+-------------------
+
+
+``Config.warn`` and ``Node.warn``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. deprecated:: 3.8
+
+Those methods were part of the internal pytest warnings system, but since ``3.8`` pytest is using the builtin warning
+system for its own warnings, so those two functions are now deprecated.
+
+``Config.warn`` should be replaced by calls to the standard ``warnings.warn``.
+
+``Node.warn`` now supports two signatures:
+
+* ``node.warn(PytestWarning("some message"))``: is now the recommended way to call this function.
+  The warning instance must be a PytestWarning or subclass.
+
+* ``node.warn("CI", "some message")``: this code/message form is now deprecated and should be converted to the warning instance form above.
+
+
+``pytest_namespace``
+~~~~~~~~~~~~~~~~~~~~
+
+.. deprecated:: 3.7
+
+This hook is deprecated because it greatly complicates the pytest internals regarding configuration and initialization, making some
+bug fixes and refactorings impossible.
+
+Example of usage:
+
+.. code-block:: python
+
+    class MySymbol:
+        ...
+
+
+    def pytest_namespace():
+        return {"my_symbol": MySymbol()}
+
+
+Plugin authors relying on this hook should instead require that users now import the plugin modules directly (with an appropriate public API).
+
+As a stopgap measure, plugin authors may still inject their names into pytest's namespace, usually during ``pytest_configure``:
+
+.. code-block:: python
+
+    import pytest
+
+
+    def pytest_configure():
+        pytest.my_symbol = MySymbol()
+
+
+
+Calling fixtures directly
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. deprecated:: 3.7
+
+Calling a fixture function directly, as opposed to request them in a test function, is deprecated.
+
+For example:
+
+.. code-block:: python
+
+    @pytest.fixture
+    def cell():
+        return ...
+
+
+    @pytest.fixture
+    def full_cell():
+        cell = cell()
+        cell.make_full()
+        return cell
+
+This is a great source of confusion to new users, which will often call the fixture functions and request them from test functions interchangeably, which breaks the fixture resolution model.
+
+In those cases just request the function directly in the dependent fixture:
+
+.. code-block:: python
+
+    @pytest.fixture
+    def cell():
+        return ...
+
+
+    @pytest.fixture
+    def full_cell(cell):
+        cell.make_full()
+        return cell
+
+
+record_xml_property
+~~~~~~~~~~~~~~~~~~~
+
+.. deprecated:: 3.5
+
+The ``record_xml_property`` fixture is now deprecated in favor of the more generic ``record_property``, which
+can be used by other consumers (for example ``pytest-html``) to obtain custom information about the test run.
+
+This is just a matter of renaming the fixture as the API is the same:
+
+.. code-block:: python
+
+    def test_foo(record_xml_property):
+        ...
+
+Change to:
+
+.. code-block:: python
+
+    def test_foo(record_property):
+        ...
+
+pytest_plugins in non-top-level conftest files
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. deprecated:: 3.5
+
+Defining ``pytest_plugins`` is now deprecated in non-top-level conftest.py
+files because they will activate referenced plugins *globally*, which is surprising because for all other pytest
+features ``conftest.py`` files are only *active* for tests at or below it.
+
+
+Removed Features
+----------------
+
+As stated in our :ref:`backwards-compatibility` policy, deprecated features are removed only in major releases after
+an appropriate period of deprecation has passed.
+
+
+Reinterpretation mode (``--assert=reinterp``)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+*Removed in version 3.0.*
+
+Reinterpretation mode has now been removed and only plain and rewrite
+mode are available, consequently the ``--assert=reinterp`` option is
+no longer available.  This also means files imported from plugins or
+``conftest.py`` will not benefit from improved assertions by
+default, you should use ``pytest.register_assert_rewrite()`` to
+explicitly turn on assertion rewriting for those files.
+
+Removed command-line options
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+*Removed in version 3.0.*
+
+The following deprecated commandline options were removed:
+
+* ``--genscript``: no longer supported;
+* ``--no-assert``: use ``--assert=plain`` instead;
+* ``--nomagic``: use ``--assert=plain`` instead;
+* ``--report``: use ``-r`` instead;
+
+py.test-X* entry points
+~~~~~~~~~~~~~~~~~~~~~~~
+
+*Removed in version 3.0.*
+
+Removed all ``py.test-X*`` entry points. The versioned, suffixed entry points
+were never documented and a leftover from a pre-virtualenv era. These entry
+points also created broken entry points in wheels, so removing them also
+removes a source of confusion for users.