Release 4.0.0a3

Signed-off-by: Bernát Gábor <[email protected]>

Author: gaborbernat

docs/changelog.rst

@@ -5,6 +5,52 @@ Release History
 
 .. towncrier release notes start
 
+v4.0.0a3 (2021-01-13)
+---------------------
+
+Features - 4.0.0a3
+~~~~~~~~~~~~~~~~~~
+- Raise exception when set env enters into a circular reference - by :user:`gaborbernat`. (`#1779 <https://github.com/tox-dev/tox/issues/1779>`_)
+- - Raise exception when variable substitution enters into a circle.
+  - Add ``{/}`` as substitution for os specific path separator.
+  - Add ``{env_bin_dir}`` constant substitution.
+  - Implement support for ``--discover`` flag - by :user:`gaborbernat`. (`#1784 <https://github.com/tox-dev/tox/issues/1784>`_)
+
+Bugfixes - 4.0.0a3
+~~~~~~~~~~~~~~~~~~
+- Entries in the ``set_env`` does not reference environments from ``set_env`` - by :user:`gaborbernat`. (`#1776 <https://github.com/tox-dev/tox/issues/1776>`_)
+- ``env`` substitution does not uses values from ``set_env`` - by :user:`gaborbernat`. (`#1779 <https://github.com/tox-dev/tox/issues/1779>`_)
+- Adopt tox 3 base pass env list, by adding:
+
+  - on all platforms: ``LANG``, ``LANGUAGE``, ``CURL_CA_BUNDLE``, ``SSL_CERT_FILE`` , ``LD_LIBRARY_PATH`` and ``REQUESTS_CA_BUNLDE``,
+  - on Windows: ``SYSTEMDRIVE`` - by :user:`gaborbernat`. (`#1780 <https://github.com/tox-dev/tox/issues/1780>`_)
+- Fixed a bug that crashed tox where calling tox with the recreate flag and when multiple environments were reusing the
+  same package - by :user:`gaborbernat`. (`#1782 <https://github.com/tox-dev/tox/issues/1782>`_)
+- - Python version markers are stripped in package dependencies (after wrongfully being detected as an extra marker).
+  - In packaging APIs do not set ``PYTHONPATH`` (to empty string) if ``backend-path`` is empty.
+  - Fix commands parsing on Windows (do not auto-escape ``\`` - instead users should use the new ``{\}``, and on parsed
+    arguments strip both ``'`` and ``"`` quoted outcomes).
+  - Allow windows paths in substitution set/default (the ``:`` character used to separate substitution arguments may
+    also be present in paths on Windows - do not support single capital letter values as substitution arguments) -
+    by :user:`gaborbernat`. (`#1784 <https://github.com/tox-dev/tox/issues/1784>`_)
+- Rework how we handle python packaging environments:
+
+  - the base packaging environment changed from ``.package`` to ``.pkg``,
+  - merged the ``sdist``, ``wheel`` and ``dev`` separate packaging implementations into one, and internally dynamically
+    pick the one that's needed,
+  - the base packaging environment always uses the same python environment as tox is installed into,
+  - the base packaging environment is used to get the metadata of the project (via PEP-517) and to build ``sdist`` and
+    ``dev`` packages,
+  - for building wheels introduced a new per env configurable option ``wheel_build_env``, if the target python major/minor
+    and implementation for the run tox environment and the base package tox environment matches set this to ``.pkg``,
+    otherwise this is ``.pkg-{implementation}{major}{minor}``,
+  - internally now packaging environments can create further packaging environments they are responsible of managing,
+  - updated ``depends`` to use the packaging logic,
+  - add support skip missing interpreters for depends and show config,
+
+  by :user:`gaborbernat`. (`#1804 <https://github.com/tox-dev/tox/issues/1804>`_)
+
+
 v4.0.0a2 (2021-01-09)
 ---------------------