Check that nix-env output doesn't depend on the Nixpkgs location

pkgs/top-level/nixpkgs-basic-release-checks.nix

@@ -19,15 +19,8 @@ pkgs.runCommand "nixpkgs-release-checks" { src = nixpkgs; buildInputs = [nix]; }
         exit 1
     fi
 
-    # Make sure that derivation paths do not depend on the Nixpkgs path.
-    mkdir $TMPDIR/foo
-    ln -s $(readlink -f $src) $TMPDIR/foo/bar
-    p1=$(nix-instantiate $src --dry-run -A firefox --show-trace)
-    p2=$(nix-instantiate $TMPDIR/foo/bar --dry-run -A firefox --show-trace)
-    if [ "$p1" != "$p2" ]; then
-        echo "Nixpkgs evaluation depends on Nixpkgs path ($p1 vs $p2)!"
-        exit 1
-    fi
+    src2=$TMPDIR/foo
+    cp -rd $src $src2
 
     # Check that all-packages.nix evaluates on a number of platforms without any warnings.
     for platform in ${pkgs.lib.concatStringsSep " " supportedSystems}; do
@@ -42,7 +35,25 @@ pkgs.runCommand "nixpkgs-release-checks" { src = nixpkgs; buildInputs = [nix]; }
             --arg config '{ allowAliases = false; }' \
             --option experimental-features 'no-url-literals' \
             -qa --drv-path --system-filter \* --system \
-            "''${opts[@]}" 2>&1 >/dev/null | tee eval-warnings.log
+            "''${opts[@]}" 2> eval-warnings.log > packages1
+
+        s1=$(sha1sum packages1 | cut -c1-40)
+        echo $s1
+
+        nix-env -f $src2 \
+            --show-trace --argstr system "$platform" \
+            --arg config '{ allowAliases = false; }' \
+            --option experimental-features 'no-url-literals' \
+            -qa --drv-path --system-filter \* --system \
+            "''${opts[@]}" > packages2
+
+        s2=$(sha1sum packages2 | cut -c1-40)
+
+        if [[ $s1 != $s2 ]]; then
+            echo "Nixpkgs evaluation depends on Nixpkgs path"
+            diff packages1 packages2
+            exit 1
+        fi
 
         # Catch any trace calls not caught by NIX_ABORT_ON_WARN (lib.warn)
         if [ -s eval-warnings.log ]; then