oops, add the flattenTree.nix file

flattenTree.nix

@@ -0,0 +1,35 @@
+tree:
+let
+  op = sum: path: val:
+    let
+      pathStr = builtins.concatStringsSep "_" path;
+    in
+    if (builtins.typeOf val) != "set" then
+    # ignore that value
+    # builtins.trace "${pathStr} is not of type set"
+      sum
+    else if val ? type && val.type == "derivation" then
+    # builtins.trace "${pathStr} is a derivation"
+    # we used to use the derivation outPath as the key, but that crashes Nix
+    # so fallback on constructing a static key
+      (sum // {
+        "${pathStr}" = val;
+      })
+    else if val ? recurseForDerivations && val.recurseForDerivations == true then
+    # builtins.trace "${pathStr} is a recursive"
+    # recurse into that attribute set
+      (recurse sum path val)
+    else
+    # ignore that value
+    # builtins.trace "${pathStr} is something else"
+      sum
+  ;
+
+  recurse = sum: path: val:
+    builtins.foldl'
+      (sum: key: op sum (path ++ [ key ]) val.${key})
+      sum
+      (builtins.attrNames val)
+  ;
+in
+recurse { } [ ] tree