From 9a61e64ccfd2144353d114c79db578bd1f2cec42 Mon Sep 17 00:00:00 2001
From: Daniel <sanchez.quiros.daniel@gmail.com>
Date: Tue, 24 Feb 2026 15:27:39 +0100
Subject: [PATCH] Fix nix build

---
 flake.nix | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/flake.nix b/flake.nix
index ad2bc918..a9751f5a 100644
--- a/flake.nix
+++ b/flake.nix
@@ -91,11 +91,22 @@
               pkgs.pkg-config
               pkgs.clang
               pkgs.llvmPackages.libclang.lib
+              pkgs.gnutar  # Required for crane's archive operations (macOS tar lacks --sort)
             ];
             LIBCLANG_PATH = "${pkgs.llvmPackages.libclang.lib}/lib";
             # Point the risc0-circuit-recursion build script to the pre-fetched zip
             # so it doesn't try to download it inside the sandbox.
             RECURSION_SRC_PATH = "${recursionZkr}";
+            # Provide a writable HOME so risc0-build-kernel can use its cache directory
+            # (needed on macOS for Metal kernel compilation cache).
+            # On macOS, append /usr/bin to PATH so xcrun (Metal compiler) can be found,
+            # while keeping Nix tools (like gnutar) first in PATH.
+            # This requires running with --option sandbox false for Metal GPU support.
+            preBuild = ''
+              export HOME=$(mktemp -d)
+            '' + pkgs.lib.optionalString pkgs.stdenv.isDarwin ''
+              export PATH="$PATH:/usr/bin"
+            '';
           };
 
           walletFfiPackage = craneLib.buildPackage (