Introduce deprecations page

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``.
-
-  ``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  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``.
-
+- `#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
+  examples.
 
 - `#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.
-
-  See the documentation for ``pytest_namespace`` hook for suggestions on how to deal
-  with this in plugins which use this functionality.
-
+- `#2639 <https://github.com/pytest-dev/pytest/issues/2639>`_: ``pytest_namespace`` has been `deprecated <https://docs.pytest.org/en/latest/deprecations.html#pytest-namespace>`_.
 
-- `#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``.
 
-  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.
+- `#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>`_.
 
 
 
@@ -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>`_)
 
 

changelog/3996.doc.rst

@@ -0,0 +1,3 @@
+New `Deprecations and Removals <https://docs.pytest.org/en/latest/deprecations.html>`_ page shows all currently
+deprecated features, the rationale to do so, and alternatives to update your code. It also list features removed
+from pytest in past major releases to help those with ancient pytest versions to upgrade.

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 +1,315 @@
+.. _deprecations:
+
+Deprecations and Removals
+=========================
+
+This page lists all pytest features that are currently deprecated or have been removed in past major releases.
+The objective is to give users a clear rationale why a certain feature has been removed, and what alternatives
+should be used instead.
+
+Deprecated Features
+-------------------
+
+Below is a complete list of all pytest features which are considered deprecated. Using those features will issue
+:class:`_pytest.warning_types.PytestWarning` or subclasses, which can be filtered using
+:ref:`standard warning filters <warnings>`.
+
+``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
+
+``Node.get_marker``
+~~~~~~~~~~~~~~~~~~~
+
+.. deprecated:: 3.6
+
+As part of a large :ref:`marker-revamp`, :meth:`_pytest.nodes.Node.get_marker` is deprecated. See
+:ref:`the documentation <update marker code>` on tips on how to update your code.
+
+
+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.
+
+Metafunc.addcall
+~~~~~~~~~~~~~~~~
+
+.. deprecated:: 3.3
+
+:meth:`_pytest.python.Metafunc.addcall` was a precursor to the current parametrized mechanism. Users should use
+:meth:`_pytest.python.Metafunc.parametrize` instead.
+
+marks in ``pytest.mark.parametrize``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. deprecated:: 3.2
+
+Applying marks to values of a ``pytest.mark.parametrize`` call is now deprecated. For example:
+
+.. code-block:: python
+
+    @pytest.mark.parametrize(
+        "a, b", [(3, 9), pytest.mark.xfail(reason="flaky")(6, 36), (10, 100)]
+    )
+    def test_foo(a, b):
+        ...
+
+This code applies the ``pytest.mark.xfail(reason="flaky")`` mark to the ``(6, 36)`` value of the above parametrization
+call.
+
+This was considered hard to read and understand, and also its implementation presented problems to the code preventing
+further internal improvements in the marks architecture.
+
+To update the code, use ``pytest.param``:
+
+.. code-block:: python
+
+    @pytest.mark.parametrize(
+        "a, b",
+        [(3, 9), pytest.param((6, 36), marks=pytest.mark.xfail(reason="flaky")), (10, 100)],
+    )
+    def test_foo(a, b):
+        ...
+
+
+
+Passing command-line string to ``pytest.main()``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. deprecated:: 3.0
+
+Passing a command-line string to ``pytest.main()`` is deprecated:
+
+.. code-block:: python
+
+    pytest.main("-v -s")
+
+Pass a list instead:
+
+.. code-block:: python
+
+    pytest.main(["-v", "-s"])
+
+
+By passing a string, users expect that pytest will interpret that command-line using the shell rules they are working
+on (for example ``bash`` or ``Powershell``), but this is very hard/impossible to do in a portable way.
+
+
+``yield`` tests
+~~~~~~~~~~~~~~~
+
+.. deprecated:: 3.0
+
+pytest supports ``yield``-style tests, where a test function actually ``yield`` functions and values
+that are then turned into proper test methods. Example:
+
+.. code-block:: python
+
+    def check(x, y):
+        assert x ** x == y
+
+
+    def test_squared():
+        yield check, 2, 4
+        yield check, 3, 9
+
+This would result into two actual test functions being generated.
+
+This form of test function doesn't support fixtures properly, and users should switch to ``pytest.mark.parametrize``:
+
+.. code-block:: python
+
+    @pytest.mark.parametrize("x, y", [(2, 4), (3, 9)])
+    def test_squared():
+        assert x ** x == y
+
+
+``pytest_funcarg__`` prefix
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. deprecated:: 3.0
+
+In very early pytest versions fixtures could be defined using the ``pytest_funcarg__`` prefix:
+
+.. code-block:: python
+
+    def pytest_funcarg__data():
+        return SomeData()
+
+Switch over to the ``@pytest.fixture`` decorator:
+
+.. code-block:: python
+
+    @pytest.fixture
+    def data():
+        return SomeData()
+
+[pytest] section in setup.cfg files
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. deprecated:: 3.0
+
+``[pytest]`` sections in ``setup.cfg`` files should now be named ``[tool:pytest]``
+to avoid conflicts with other distutils commands.
+
+Result log (``--result-log``)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. deprecated:: 3.0
+
+The ``--resultlog`` command line option has been deprecated: it is little used
+and there are more modern and better alternatives, for example `pytest-tap <https://tappy.readthedocs.io/en/latest/>`_.
+
+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.

doc/en/mark.rst

@@ -52,6 +52,8 @@ should add ``--strict`` to ``addopts``:
         serial
 
 
+.. _marker-revamp:
+
 Marker revamp and iteration
 ---------------------------