Don't set $PARALLEL with eval-cores

Author: edolstra

.github/workflows/build.yml

@@ -144,21 +144,29 @@ jobs:
           path: flake-regressions/tests
       - uses: DeterminateSystems/determinate-nix-action@main
       - uses: DeterminateSystems/flakehub-cache-action@main
-      - env:
-          PARALLEL: "-P 50%"
+      - name: Run flake regression tests
+        env:
+          PARALLEL: ${{ !contains(matrix.nix_config, 'eval-cores') && '-P 50%' || '-P 1' }}
           FLAKE_REGRESSION_GLOB: ${{ matrix.glob }}
           NIX_CONFIG: ${{ matrix.nix_config }}
           PREFETCH: "1"
           GC_INITIAL_HEAP_SIZE: "32G"
         run: |
           set -x
+          echo "PARALLEL: $PARALLEL"
+          echo "NIX_CONFIG: $NIX_CONFIG"
           if [ ! -z "${NSC_CACHE_PATH:-}" ]; then
             mkdir -p "${NSC_CACHE_PATH}/nix/xdg-cache"
             export XDG_CACHE_HOME="${NSC_CACHE_PATH}/nix/xdg-cache"
           fi
           nix build -L --out-link ./new-nix
           export PATH=$(pwd)/new-nix/bin:$PATH
 
+          nix config show lazy-trees
+          nix config show eval-cores
+          lscpu
+          nproc
+
           if ! flake-regressions/eval-all.sh; then
             echo "Some failed, trying again"
             printf "\n\n\n\n\n\n\n\n"