From d5a9a624062d065e0328c13cae42fa05bc2b2d1e Mon Sep 17 00:00:00 2001
From: Gaetan Lepage <gaetan@glepage.com>
Date: Tue, 24 Jun 2025 18:59:33 +0200
Subject: [PATCH] python3Packages.mmcv: fix on python 3.13

---
 pkgs/development/python-modules/mmcv/default.nix | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/pkgs/development/python-modules/mmcv/default.nix b/pkgs/development/python-modules/mmcv/default.nix
index 3f7b5f9f4ce9..cc9efa952bf3 100644
--- a/pkgs/development/python-modules/mmcv/default.nix
+++ b/pkgs/development/python-modules/mmcv/default.nix
@@ -48,10 +48,17 @@ buildPythonPackage rec {
     hash = "sha256-NNF9sLJWV1q6uBE73LUW4UWwYm4TBMTBJjJkFArBmsc=";
   };
 
-  postPatch = ''
-    substituteInPlace setup.py \
-      --replace-fail "cpu_use = 4" "cpu_use = $NIX_BUILD_CORES"
-  '';
+  postPatch =
+    # Fails in python >= 3.13
+    # exec(compile(f.read(), version_file, "exec")) does not populate the locals() namesp
+    # In python 3.13, the locals() dictionary in a function does not automatically update with
+    # changes made by exec().
+    # https://peps.python.org/pep-0558/
+    ''
+      substituteInPlace setup.py \
+        --replace-fail "cpu_use = 4" "cpu_use = $NIX_BUILD_CORES" \
+        --replace-fail "return locals()['__version__']" "return '${version}'"
+    '';
 
   nativeBuildInputs = [
     ninja