PEP 763: add an appendix comparing ecosystems (#4091)

Signed-off-by: William Woodruff <william@yossarian.net>
Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

peps/pep-0763.rst

@@ -106,8 +106,13 @@ The Python ecosystem is continuing to grow,
 meaning that future deletions of projects can be reasonably assumed to
 be *just, as if not more,* disruptive than the deletions sampled above.
 
-Given the above, this PEP concludes that deletions now present a greater risk
+Given all of the above, this PEP concludes that deletions now present a greater
-and detriment to the Python ecosystem than a benefit.
+risk and detriment to the Python ecosystem than a benefit.
+
+In addition to these technical arguments, there is also precedent
+from other packaging ecosystems for limiting the ability of users to delete
+projects and their constituent releases. This precedent is documented in
+:ref:`Appendix A <pep763-appendix-a>`.
 
 Specification
 =============
@@ -264,6 +269,115 @@ usage, this PEP identifies several limitations to this approach:
    PyPI is not straightforward, and there is limited possibility to gather a
    project's download statistics from mirrors or other distributions systems.
 
+.. _pep763-appendix-a:
+
+Appendix A: Precedent in other ecosystems
+=========================================
+
+The following is a table of support for deletion in different packaging
+ecosystems. An ecosystem is considered to **not** support deletion
+if it restrict's a user's ability to perform deletions in a manner similar
+to this PEP.
+
+An earlier version of this table, showing only deletion, was
+compiled by Donald Stufft and others on the Python discussion forum in
+`July 2022 <https://discuss.python.org/t/17227/59>`__.
+
+.. list-table::
+  :header-rows: 1
+
+  * - Ecosystem (Index)
+    - Deletion
+    - Yanking
+    - Notes
+  * - Python (PyPI)
+    - ✅ [#f1]_
+    - ✅ [#f2]_
+    - Deletion currently completely unrestricted.
+  * - Rust (crates.io)
+    - ❌
+    - ✅ [#f3]_
+    - Deletion by users not allowed at all.
+  * - JavaScript (npm)
+    - ❌ [#f4]_
+    - ✅ [#f5]_
+    - Deletion is limited by criteria similar to this PEP.
+  * - Ruby (RubyGems)
+    - ✅ [#f6]_
+    - ❌
+    - RubyGems calls deletion "yanking." Yanking in PyPI's terms is not supported at all.
+  * - Java (Maven Central)
+    - ❌ [#f7]_
+    - ❌
+    - Deletion by users not allowed at all.
+  * - PHP (Packagist)
+    - ❌
+    - ❌
+    - Deletion restricted after an undocumented number of installs [#f8]_.
+  * - .NET (NuGet)
+    - ❌ [#f9]_
+    - ✅ [#f10]_
+    - NuGet calls yanking "unlisting."
+  * - Elixir (Hex)
+    - ❌ [#f11]_
+    - ✅ [#f11]_
+    - Hex calls yanking "retiring."
+  * - R (CRAN)
+    - ❌ [#f12]_
+    - ✅ [#f12]_
+    - Deletion is limited to within 24 hours of initial release or
+      60 minutes for subsequent versions. CRAN calls yanking "archiving."
+  * - Perl (CPAN)
+    - ✅
+    - ❌
+    - Yanking is not supported at all. Deletion seemingly encouraged,
+      at least as of 2021 [#f13]_.
+  * - Lua (LuaRocks)
+    - ✅ [#f14]_
+    - ✅ [#f14]_
+    - LuaRocks calls yanking "archiving."
+
+The following trends are present:
+
+* A strong majority of indices **do not** support deletion (7 vs. 4)
+* A strong majority of indices **do** support yanking (7 vs. 4)
+* The overwhelming majority of indices support one or the other or neither,
+  but **not** both (13 vs. 2)
+
+  * PyPI and LuaRocks are notable outliers in supporting **both** deletion and
+    yanking.
+
+Footnotes
+=========
+
+.. [#f1] https://pypi.org/help/#deletion
+
+.. [#f2] https://pypi.org/help/#yanked
+
+.. [#f3] https://doc.rust-lang.org/cargo/commands/cargo-yank.html
+
+.. [#f4] https://docs.npmjs.com/unpublishing-packages-from-the-registry
+
+.. [#f5] https://docs.npmjs.com/deprecating-and-undeprecating-packages-or-package-versions
+
+.. [#f6] https://guides.rubygems.org/removing-a-published-gem/
+
+.. [#f7] https://central.sonatype.org/faq/can-i-change-a-component/
+
+.. [#f8] https://github.com/composer/packagist/issues/875
+
+.. [#f9] https://learn.microsoft.com/en-us/nuget/nuget-org/policies/deleting-packages
+
+.. [#f10] https://learn.microsoft.com/en-us/nuget/nuget-org/policies/deleting-packages#unlisting-a-package
+
+.. [#f11] https://hex.pm/docs/faq#can-packages-be-removed-from-the-repository
+
+.. [#f12] https://cran.r-project.org/web/packages/policies.html
+
+.. [#f13] https://neilb.org/2021/05/10/delete-your-old-releases.html
+
+.. [#f14] https://luarocks.org/changes
+
 Copyright
 =========