fix(sccache): enable on darwin using /tmp for temporary files

Author: yvan-sraka

nix/cargo-pgrx/buildPgrxExtension.nix

@@ -168,20 +168,25 @@ let
       echo "Platform: ${stdenv.system}"
       echo "isDarwin: ${lib.boolToString stdenv.isDarwin}"
 
-      # sccache doesn't work in Nix Darwin sandbox due to temporary directory restrictions
-      if [[ "${lib.boolToString stdenv.isDarwin}" != "true" && -d "/nix/var/cache/sccache" && -w "/nix/var/cache/sccache" ]]; then
-        # Test if sccache can actually write to the directory (sandbox check)
+      # Configure sccache based on platform
+      if [[ -d "/nix/var/cache/sccache" && -w "/nix/var/cache/sccache" ]]; then
         if touch "/nix/var/cache/sccache/.test" 2>/dev/null && rm -f "/nix/var/cache/sccache/.test" 2>/dev/null; then
-          echo "sccache: cache directory available and writable in sandbox, enabling"
+          ${lib.optionalString stdenv.isDarwin ''
+            echo "sccache: Darwin detected, configuring with /tmp for temporary files"
+            export TMPDIR=/tmp
+          ''}
+          ${lib.optionalString (!stdenv.isDarwin) ''
+            echo "sccache: Linux detected, cache directory available and writable in sandbox, enabling"
+          ''}
           export RUSTC_WRAPPER="${sccache}/bin/sccache"
           export SCCACHE_DIR="/nix/var/cache/sccache"
           export SCCACHE_CACHE_SIZE="50G"
           export SCCACHE_LOG=debug
         else
-          echo "sccache: cache directory not accessible in sandbox (needs extra-sandbox-paths configuration), skipping"
+          echo "sccache: cache directory not accessible in sandbox, skipping"
         fi
       else
-        echo "sccache: not available or running on Darwin, skipping"
+        echo "sccache: cache directory not available, skipping"
       fi
 
       echo "Executing cargo-pgrx buildPhase"