Add Reference Implementation section

Signed-off-by: Fridolin Pokorny <fridolin.pokorny@datadoghq.com>
python · dstufft · Apr 3, 2023 · Mar 27, 2023 · Mar 27, 2023 · Mar 28, 2023
commit 28d93a07082620dbad3c8325d6c6610dd09b68b5
@@ -287,12 +287,23 @@ a ``direct_url.json`` file:
 * ``pip install app --no-index --find-links "https://example.com/"``
 
 This behaviour can be tested using changes to pip implemented in the PR
-`fridex/pip#1`_.
+`pypa/pip#11865`_.
 
 Reference Implementation
 ========================
 
-[Link to any existing implementation and details about its state, e.g. proof-of-concept.]
+A proof-of-concept for creating the ``provenance_url.json`` metadata file when
+installing a Python distribution is available in the PR to pip
+`pypa/pip#11865`_. It reuses the already available implementation for the
+`direct URL data structure <direct_url_data_>`_ to provide
+``provenance_url.json`` metadata file for cases when ``direct_url.json`` is not
+created.
+
+A prototype called `pip-preserve <pip_preserve>`_ was developed to
+demonstrate creation of ``requirements.txt`` file considering ``direct_url.json``
+and ``provenance_url.json`` metadata files.  This tool mimics the ``pip
+freeze`` functionality, but the listing of installed packages includes also
+hashes of Python distributions.
 
 Rejected Ideas
 ==============
@@ -376,10 +387,13 @@ maintainers of these installers is valuable to possibly enrich the
 References
 ==========
 
-.. _fridex/pip#1: https://github.com/fridex/pip/pull/1/
+.. _pypa/pip#11865: https://github.com/pypa/pip/pull/11865
 
 .. _fridex/pip#2: https://github.com/fridex/pip/pull/2/
 
+.. _direct_url_data: https://packaging.python.org/en/latest/specifications/direct-url-data-structure/
+
+.. _pip_preserve: https://pypi.org/project/pip-preserve/
 
 Acknowledgements
 ================