From d2e9be2b076699b1a8e8d6b6f9ea4bebbd6956f9 Mon Sep 17 00:00:00 2001
From: Martin Weinelt <hexa@darmstadt.ccc.de>
Date: Wed, 2 Jul 2025 04:19:06 +0200
Subject: [PATCH] buildPython*: throw on empty format

This is the ratchet that disallows introducing new python packages that
do not define a package format.
---
 doc/release-notes/rl-2511.section.md                       | 4 ++++
 .../interpreters/python/mk-python-derivation.nix           | 7 ++++---
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/doc/release-notes/rl-2511.section.md b/doc/release-notes/rl-2511.section.md
index 2a90ec5891e5..2c5eb1492217 100644
--- a/doc/release-notes/rl-2511.section.md
+++ b/doc/release-notes/rl-2511.section.md
@@ -61,6 +61,10 @@
 - `reaction` has been updated to version 2, which includes some breaking changes.
   For more information, [check the release article](https://blog.ppom.me/en-reaction-v2).
 
+- The `buildPythonPackage` and `buildPythonApplication` functions now require
+  an explicit `format` attribute. Previously the default format used setuptools
+  and called `setup.py` from the source tree, which is deprecated.
+  The modern alternative is to configure `pyproject = true` with `build-system = [ setuptools ]`.
 
 ### Deprecations {#sec-nixpkgs-release-25.11-lib-deprecations}
 
diff --git a/pkgs/development/interpreters/python/mk-python-derivation.nix b/pkgs/development/interpreters/python/mk-python-derivation.nix
index f4c86aa91112..4c1ac3664af4 100644
--- a/pkgs/development/interpreters/python/mk-python-derivation.nix
+++ b/pkgs/development/interpreters/python/mk-python-derivation.nix
@@ -211,7 +211,7 @@ let
         else if format != null then
           format
         else
-          "setuptools";
+          throw "${name} does not configure a `format`. To build with setuptools as before, set `pyproject = true` and `build-system = [ setuptools ]`.`";
 
       withDistOutput = withDistOutput' format';
 
@@ -268,11 +268,12 @@ let
 
       isSetuptoolsDependency = isSetuptoolsDependency' (attrs.pname or null);
 
+      name = namePrefix + attrs.name or "${finalAttrs.pname}-${finalAttrs.version}";
+
     in
     (cleanAttrs attrs)
     // {
-
-      name = namePrefix + attrs.name or "${finalAttrs.pname}-${finalAttrs.version}";
+      inherit name;
 
       inherit catchConflicts;