DOCS: Add ruff section to the dev guide docs (#5701)

* added ruff section to the dev guide docs.

* added whatsnew

* Update docs/src/developers_guide/contributing_ci_tests.rst

Co-authored-by: Bill Little <bill.little@metoffice.gov.uk>

* Update docs/src/developers_guide/contributing_ci_tests.rst

Co-authored-by: Bill Little <bill.little@metoffice.gov.uk>

* Update docs/src/developers_guide/contributing_ci_tests.rst

Co-authored-by: Bill Little <bill.little@metoffice.gov.uk>

* Update docs/src/developers_guide/contributing_ci_tests.rst

Co-authored-by: Bill Little <bill.little@metoffice.gov.uk>

---------

Co-authored-by: Bill Little <bill.little@metoffice.gov.uk>

docs/src/developers_guide/contributing_ci_tests.rst

@@ -1,7 +1,7 @@
-.. _developer_testing_ci:
-
 .. include:: ../common_links.inc
 
+.. _developer_testing_ci:
+
 Continuous Integration (CI) Testing
 ===================================
 
@@ -119,5 +119,32 @@ See the `pre-commit.ci dashboard`_ for details of recent past and active Iris jo
   Append to the ``ignore-words-list`` option any **valid words** that are
   considered **not** a typo and should **not** be corrected by `codespell`_.
 
+ruff
+----
+As of **Iris 3.8** `ruff`_ has been adopted to ensure our codebase is using best
+practice.  `ruff`_ is configured in the `Iris`_ GitHub repository using  
+`.pre-commit-config.yaml`_.  
+
+You can install and run `ruff`_ in your development **iris-dev** conda environment
+via::
+
+   conda activate iris-dev
+   pip install ruff
+   cd iris
+   ruff .
+
+.. note::
+
+  The `ruff`_ ``pre-commit`` hook checks for compliance of the whole codebase.
+  This hook is configured in the ``[tool.ruff]`` section
+  of the ``pyproject.toml`` file.
+
+  Edit the ``.ruff.toml`` file to include any *temporary* rules to be ignored. Edit the ``pyproject.toml`` to include any *permanent* rules to be ignored. We
+  aim to be fully `ruff`_ compliant as possible.
+
+For more information on how to use `ruff`_ please see the `ruff documentation`_.
+
+
 .. _.pre-commit-config.yaml: https://github.com/SciTools/iris/blob/main/.pre-commit-config.yaml
 .. _pre-commit.ci dashboard: https://results.pre-commit.ci/repo/github/5312648
+.. _ruff documentation: https://docs.astral.sh/ruff/tutorial/

docs/src/whatsnew/latest.rst

@@ -169,6 +169,9 @@ This document explains the changes made to Iris for this release
    :class:`~iris.cube.Cube` standard names in
    :func:`iris.analysis.calculus.curl`. (:pull:`5680`)
 
+#. `@tkknight`_ added ruff documentation in the :ref:`developer_testing_ci` of the
+   :ref:`developers_guide`. (:pull:`5701`)
+
 
 💼 Internal
 ===========