wip: rewrite s6-rc-up-tree in an actual procgramming language

and write some tests for it, too

pkgs/s6-rc-up-tree/default.nix

@@ -1,4 +1,54 @@
 {
-  writeAshScriptBin
+  lualinux,
+  writeFennel,
+  anoia,
+  fennel,
+  stdenv,
+  fennelrepl,
 }:
-writeAshScriptBin "s6-rc-up-tree" {} (builtins.readFile ./s6-rc-up-tree.sh)
+stdenv.mkDerivation {
+  name = "s6-rc-up-tree";
+  src = ./.;
+  nativeBuildInputs = [ fennelrepl ];
+  # propagatedBuildInputs = [ s6-rc-up-tree ];
+  installPhase = ''
+    mkdir -p $out/bin
+    cp -p ${writeFennel "s6-rc-up-tree" {
+      packages = [fennel
+                  # anoia nellie
+                  lualinux ] ;
+      mainFunction = "run";
+    } ./s6-rc-up-tree.fnl } $out/bin/s6-rc-up-tree
+  '';
+  postBuild = ''
+    export PATH=./scripts:$PATH
+    patchShebangs ./scripts
+    export TEST_LOG=./log
+    fail(){ cat $TEST_LOG | od -c; exit 1; }
+    expect(){
+      test "$(echo $(cat $TEST_LOG))" = "$@" || fail;
+    }
+    # given a service with no rdepends, starts only that service
+    fennelrepl ./test.fnl ${./test-services} turmeric
+    expect "turmeric"
+
+    # given a controlled service with no rdepends, starts only that service
+    fennelrepl ./test.fnl ${./test-services} wombat
+    expect "wombat"
+
+    # uncontrolled rdepends start
+    fennelrepl ./test.fnl ${./test-services} thyme
+    expect "thyme rosemary"
+
+    # stopped controlled rdepends don't start
+    fennelrepl ./test.fnl ${./test-services} enables-wan
+    expect "enables-wan" # not wattle, even though it depends
+
+    # started controlled rdepends are running, so starting them is harmless
+
+    # descendants which depend on a _different_ controlled service, which is down, don't start
+
+    # descendants which depend on a _different_ controlled service, which is up, do start
+
+  '';
+}