PEP 499: Delegate to Nick Coghlan (#946)

Also updates the PEP with links to the reference implementation,
and adds an Open Questions section to highlight known areas of
compatibility risk.

pep-0499.txt

@@ -3,6 +3,7 @@ Title: ``python -m foo`` should bind ``sys.modules['foo']`` in addition to ``sys
 Version: $Revision$
 Last-Modified: $Date$
 Author: Cameron Simpson <cs@cskk.id.au>, Chris Angelico <rosuav@gmail.com>, Joseph Jevnik <joejev@gmail.com>
+BDFL-Delegate: Nick Coghlan
 Status: Draft
 Type: Standards Track
 Content-Type: text/x-rst
@@ -152,6 +153,51 @@ where ``__name__`` is expected to be "__main__".
 This PEP explicitly preserves that semantic.
 
 
+Reference Implementation
+========================
+
+`BPO 36375 <https://bugs.python.org/issue36375>`_ is the issue tracker entry
+for the PEP's reference implementation, with the current draft PR being
+available `on GitHub <https://github.com/python/cpython/pull/12490>`_.
+
+
+Open Questions
+==============
+
+This proposal does raise some backwards compatibility concerns, and these will
+need to be well understood, and either a deprecation process designed, or clear
+porting guidelines provided.
+
+Pickle compatibility
+--------------------
+
+If no changes are made to the pickle module, then pickles that were previously
+being written with the correct module name (due to a dual import) may start
+being written with `__main__` as their module name instead, and hence fail to be
+loaded correctly by other projects.
+
+Scenarios to be checked:
+
+* `python script.py` writing, `python -m script` reading
+* `python -m script` writing, `python script.py` reading
+* `python -m script` writing, `python some_other_app.py` reading
+* `old_python -m script` writing, `new_python -m script` reading
+* `new_python -m script` writing, `old_python -m script` reading
+
+
+Projects that special-case `__main__`
+-------------------------------------
+
+In order to get the regression test suite to pass, the current reference
+implementation had to patch `pdb` to avoid destroying its own global namespace.
+
+This suggests there may be a broader compatibility issue where some scripts are
+relying on direct execution and import giving different namespaces (just as
+package execution keeps the two separate by executing the `__main__` submodule
+in the `__main__` namespace, while the package name references the `__init__`
+file as usual.
+
+
 Background
 ==========