nix-support/binary-tarball.nix: Pass through root paths

Passing through root paths allows external programs to see
which nix and cacert are in a binary tarball,
e.g. to recreate it from substituters

Change-Id: I27431134df53bbc6623484f8a0822004b51f7c87

nix-support/binary-tarball.nix

@@ -5,29 +5,33 @@
   system,
 }:
 let
-  installerClosureInfo = buildPackages.closureInfo {
-    rootPaths = [
-      nix
-      cacert
-    ];
-  };
+  rootPaths = [
+    nix
+    cacert
+  ];
+  installerClosureInfo = buildPackages.closureInfo { inherit rootPaths; };
 
   meta.description = "Distribution-independent Lix bootstrap binaries for ${system}";
 in
-buildPackages.runCommand "lix-binary-tarball-${nix.version}" { inherit meta; } ''
-  cp ${installerClosureInfo}/registration $TMPDIR/reginfo
+buildPackages.runCommand "lix-binary-tarball-${nix.version}"
+  {
+    inherit meta;
+    passthru.rootPaths = rootPaths;
+  }
+  ''
+    cp ${installerClosureInfo}/registration $TMPDIR/reginfo
 
-  dir=lix-${nix.version}-${system}
-  fn=$out/$dir.tar.xz
-  mkdir -p $out/nix-support
-  echo "file binary-dist $fn" >> $out/nix-support/hydra-build-products
-  tar cvfJ $fn \
-    --owner=0 --group=0 --mode=u+rw,uga+r \
-    --mtime='1970-01-01' \
-    --absolute-names \
-    --hard-dereference \
-    --transform "s,$TMPDIR/reginfo,$dir/.reginfo," \
-    --transform "s,$NIX_STORE,$dir/store,S" \
-    $TMPDIR/reginfo \
-    $(cat ${installerClosureInfo}/store-paths)
-''
+    dir=lix-${nix.version}-${system}
+    fn=$out/$dir.tar.xz
+    mkdir -p $out/nix-support
+    echo "file binary-dist $fn" >> $out/nix-support/hydra-build-products
+    tar cvfJ $fn \
+      --owner=0 --group=0 --mode=u+rw,uga+r \
+      --mtime='1970-01-01' \
+      --absolute-names \
+      --hard-dereference \
+      --transform "s,$TMPDIR/reginfo,$dir/.reginfo," \
+      --transform "s,$NIX_STORE,$dir/store,S" \
+      $TMPDIR/reginfo \
+      $(cat ${installerClosureInfo}/store-paths)
+  ''