Add record support to lib.generators.toPreserves

flake.nix

@@ -12,7 +12,7 @@
 
       overlay = final: prev:
         with final; {
-          lib = lib.extend libOverlay;
+          lib = prev.lib.extend libOverlay;
           syndicate-rs = callPackage ./syndicate-rs {
             rust = rust-bin.nightly.latest.default;
           };

lib.nix

@@ -4,20 +4,32 @@ in with lib; {
 
   generators = with final.generators;
     prev.generators // {
+
+      # Generates Preserves from an arbitrary value.
+      # Records are generated for functions that take
+      # a single formal argument `toRecord` and return
+      # a list of values.
       toPreserves = { }@args:
-        v:
-        let concatItems = lib.strings.concatStringsSep " ";
-        in if isAttrs v then
+        let
+          toPreserves' = toPreserves args;
+          concatItems = toString;
+        in v:
+        if isAttrs v then
           "{ ${
             concatItems (lib.attrsets.mapAttrsToList
-              (key: val: "${key}: ${toPreserves args val}") v)
+              (key: val: "${key}: ${toPreserves' val}") v)
           } }"
         else if isList v then
-          "[ ${concatItems (map (toPreserves args) v)} ]"
+          "[ ${concatItems (map toPreserves' v)} ]"
         else if isBool v then
           (if v then "#t" else "#f")
         else if isFunction v then
-          abort "generators.toPreserves: cannot convert a function to Preserves"
+          (if (lib.functionArgs v) == { toRecord = false; } then
+            let items = v { toRecord = null; };
+            in "<${head items} ${toString (map toPreserves' (tail items))}>"
+          else
+            abort
+            "generators.toPreserves: cannot convert a function to Preserves")
         else if isNull v then
           "null"
         else