make s6-rc-database a package

pkgs/s6-rc-database/default.nix

@@ -0,0 +1,31 @@
+# generate s6-rc database,  by generating closure of all
+# config.services and calling s6-rc-compile on them
+
+{
+  stdenvNoCC
+, buildPackages
+, closureInfo
+, writeText
+, services ? []
+}:
+let closure-info = closureInfo { rootPaths = services; };
+in stdenvNoCC.mkDerivation  {
+  name = "s6-rc-database";
+  nativeBuildInputs = [buildPackages.s6-rc];
+  builder = writeText "find-s6-services" ''
+    source $stdenv/setup
+    mkdir -p $out
+    srcs=""
+    shopt -s nullglob
+    for i in $(cat  ${closure-info}/store-paths ); do
+      if test -d $i; then
+        for j in $i/* ; do
+          if test -f $j/type ; then
+            srcs="$srcs $i"
+          fi
+        done
+      fi
+    done
+    s6-rc-compile $out/compiled $srcs
+    '';
+  }