Clarify 4.0 changes

Author: jacobtylerwalls

doc/whatsnew/4/4.0/index.rst

@@ -12,10 +12,64 @@
 Summary -- Release highlights
 =============================
 
-Pylint now supports Python 3.14.
+- Pylint now supports Python 3.14.
+
+- Pylint's inference engine (``astroid``) is now much more precise,
+  understanding implicit booleanness and ternary expressions. (Thanks @zenlyj!)
+
+Consider this example:
+
+.. code-block:: python
+
+    class Result:
+        errors: dict | None = None
+
+    result = Result()
+    if result.errors:
+        result.errors[field_key]
+        # inference engine understands result.errors cannot be None
+        # pylint no longer raises unsubscriptable-object
 
 The required ``astroid`` version is now 4.0.0. See the
 `astroid changelog <https://pylint.readthedocs.io/projects/astroid/en/latest/changelog.html#what-s-new-in-astroid-4-0-0>`_
 for additional fixes, features, and performance improvements applicable to pylint.
 
+- Handling of ``invalid-name`` at the module level was patchy. Now,
+  module-level constants that are reassigned are treated as variables and checked
+  against ``--variable-rgx`` rather than ``--const-rgx``. Module-level lists,
+  sets, and objects can pass against either regex.
+
+Here, ``LIMIT`` is reassigned, so pylint only uses ``--variable-rgx``:
+
+.. code-block:: python
+
+    LIMIT = 500  # [invalid-name]
+    if sometimes:
+        LIMIT = 1  # [invalid-name]
+
+If this is undesired, refactor using *exclusive* assignment so that it is
+evident that this assignment happens only once:
+
+.. code-block:: python
+
+    if sometimes:
+        LIMIT = 1
+    else:
+        LIMIT = 500  # exclusive assignment: uses const regex, no warning
+
+Lists, sets, and objects still pass against either ``const-rgx`` or ``variable-rgx``
+even if reassigned, but are no longer completely skipped:
+
+.. code-block:: python
+
+    MY_LIST = []
+    my_list = []
+    My_List = []  # [invalid-name]
+
+Remember to adjust the
+`regexes <https://pylint.readthedocs.io/en/latest/user_guide/messages/convention/invalid-name.html>`_
+and
+`allow lists <https://pylint.readthedocs.io/en/latest/user_guide/configuration/all-options.html#good-names>`_
+to your liking.
+
 .. towncrier release notes start