fix(sccache): use NIX_BUILD_TOP for temp files on darwin with __noChroot

Author: yvan-sraka

nix/cargo-pgrx/buildPgrxExtension.nix

@@ -176,11 +176,12 @@ let
         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, enabling"
           ${lib.optionalString stdenv.isDarwin ''
-            # Darwin: use /tmp for temp files (allowed by sandbox-defaults.sb)
-            export TMPDIR=/tmp
-            export TEMP=/tmp
-            export TEMPDIR=/tmp
-            export TMP=/tmp
+            # Darwin: use build directory for temp files (nixbld user owns it with __noChroot)
+            export TMPDIR="$NIX_BUILD_TOP/sccache-tmp"
+            export TEMP="$NIX_BUILD_TOP/sccache-tmp"
+            export TEMPDIR="$NIX_BUILD_TOP/sccache-tmp"
+            export TMP="$NIX_BUILD_TOP/sccache-tmp"
+            mkdir -p "$TMPDIR"
           ''}
           export RUSTC_WRAPPER="${sccache}/bin/sccache"
           export SCCACHE_DIR="/nix/var/cache/sccache"