formats.ini: Introduce `listToValue` argument (#121613)

Allows coercing lists to values. E.g.

  formats.ini { listToValue = lib.concatMapStringsSep ", " (lib.generators.mkValueStringDefault {}); }

1 files changed, 24 insertions, 2 deletions

diff --git a/pkgs/pkgs-lib/formats.nix b/pkgs/pkgs-lib/formats.nix
index 14589f8ecdc3a..4b6982f387d08 100644
--- a/pkgs/pkgs-lib/formats.nix
+++ b/pkgs/pkgs-lib/formats.nix
@@ -56,7 +56,16 @@ rec {
       };
     };
 
-  ini = { listsAsDuplicateKeys ? false, ... }@args: {
+  ini = {
+    # Represents lists as duplicate keys
+    listsAsDuplicateKeys ? false,
+    # Alternative to listsAsDuplicateKeys, converts list to non-list
+    # listToValue :: [IniAtom] -> IniAtom
+    listToValue ? null,
+    ...
+    }@args:
+    assert !listsAsDuplicateKeys || listToValue == null;
+    {
 
     type = with lib.types; let
 
@@ -74,12 +83,25 @@ rec {
           coercedTo singleIniAtom lib.singleton (listOf singleIniAtom) // {
             description = singleIniAtom.description + " or a list of them for duplicate keys";
           }
+        else if listToValue != null then
+          coercedTo singleIniAtom lib.singleton (nonEmptyListOf singleIniAtom) // {
+            description = singleIniAtom.description + " or a non-empty list of them";
+          }
         else
           singleIniAtom;
 
     in attrsOf (attrsOf iniAtom);
 
-    generate = name: value: pkgs.writeText name (lib.generators.toINI args value);
+    generate = name: value:
+      let
+        transformedValue =
+          if listToValue != null
+          then
+            lib.mapAttrs (section: lib.mapAttrs (key: val:
+              if lib.isList val then listToValue val else val
+            )) value
+          else value;
+      in pkgs.writeText name (lib.generators.toINI (removeAttrs args ["listToValue"]) transformedValue);
 
   };