curv: downgrade eigen

pkgs/by-name/cu/curv/package.nix

@@ -2,6 +2,8 @@
   lib,
   stdenv,
   fetchFromGitea,
+  fetchFromGitLab,
+  fetchpatch,
   cmake,
   git,
   pkg-config,
@@ -41,7 +43,33 @@ stdenv.mkDerivation rec {
   buildInputs =
     [
       boost
-      eigen
+      # https://codeberg.org/doug-moen/curv/issues/228
+      # reverts 'eigen: 3.4.0 -> 3.4.0-unstable-2022-05-19'
+      # https://github.com/nixos/nixpkgs/commit/d298f046edabc84b56bd788e11eaf7ed72f8171c
+      (eigen.overrideAttrs (old: rec {
+        version = "3.4.0";
+        src = fetchFromGitLab {
+          owner = "libeigen";
+          repo = "eigen";
+          rev = version;
+          hash = "sha256-1/4xMetKMDOgZgzz3WMxfHUEpmdAm52RqZvz6i0mLEw=";
+        };
+        patches = (old.patches or [ ]) ++ [
+          # Fixes e.g. onnxruntime on aarch64-darwin:
+          # https://hydra.nixos.org/build/248915128/nixlog/1,
+          # originally suggested in https://github.com/NixOS/nixpkgs/pull/258392.
+          #
+          # The patch is from
+          # ["Fix vectorized reductions for Eigen::half"](https://gitlab.com/libeigen/eigen/-/merge_requests/699)
+          # which is two years old,
+          # but Eigen hasn't had a release in two years either:
+          # https://gitlab.com/libeigen/eigen/-/issues/2699.
+          (fetchpatch {
+            url = "https://gitlab.com/libeigen/eigen/-/commit/d0e3791b1a0e2db9edd5f1d1befdb2ac5a40efe0.patch";
+            hash = "sha256-8qiNpuYehnoiGiqy0c3Mcb45pwrmc6W4rzCxoLDSvj0=";
+          })
+        ];
+      }))
       glm
       libGL
       libpng