lib: change default flagSeparator from " " to null

The " " default was confusing: it didn't join with a space but produced
separate argv entries. Change the default to null which clearly means
"separate argv entries", while " " now actually joins with a space
(single arg). This makes the semantics consistent with "=".

null  → ["--flag" "value"]  (separate args, default)
"="   → ["--flag=value"]    (joined)
" "   → ["--flag value"]    (joined with space)

Author: Lassulus

checks/flags-empty-list.nix

@@ -13,7 +13,6 @@ let
       "--empty" = [ ];
       "--output" = "file.txt";
     };
-    flagSeparator = " ";
   };
 
 in

checks/flags-false.nix

@@ -15,7 +15,6 @@ let
       "--empty" = [ ];
       "--output" = "file.txt";
     };
-    flagSeparator = " ";
   };
 
 in

checks/flags-list.nix

@@ -15,7 +15,6 @@ let
       ];
       "--verbose" = true;
     };
-    flagSeparator = " ";
   };
 
   wrappedWithEqualsSep = self.lib.wrapPackage {

checks/flags-space-separator.nix

@@ -11,7 +11,6 @@ let
       "--greeting" = "hi";
       "--verbose" = true;
     };
-    flagSeparator = " ";
   };
 
 in

lib/default.nix

@@ -2,14 +2,18 @@
 let
   /**
     flagToArgs {
-      flagSeparator: str,
+      flagSeparator: null | str,
       name: str,
       flag: bool | str | [ str | [ str ] ]
-    } -> [ str
+    } -> [ str ]
+
+    flagSeparator = null  -> ["--flag" "value"]  (separate argv entries, default)
+    flagSeparator = "="   -> ["--flag=value"]     (joined with separator)
+    flagSeparator = " "   -> ["--flag value"]     (joined with space, single arg)
   */
   flagToArgs =
     {
-      flagSeparator ? " ",
+      flagSeparator ? null,
       name,
       flag,
     }:
@@ -18,7 +22,7 @@ let
     else if flag == true then
       [ name ]
     else if builtins.isString flag then
-      if flagSeparator == " " then
+      if flagSeparator == null then
         [
           name
           flag
@@ -30,7 +34,7 @@ let
       lib.concatMap (
         v:
         if builtins.isString v then
-          if flagSeparator == " " then
+          if flagSeparator == null then
             [
               name
               v
@@ -379,7 +383,7 @@ let
     - `runtimeInputs`: List of packages to add to PATH (optional)
     - `env`: Attribute set of environment variables to export (optional)
     - `flags`: Attribute set of command-line flags to add (optional)
-    - `flagSeparator`: Separator between flag names and values when generating args from flags (optional, defaults to " ")
+    - `flagSeparator`: Separator between flag names and values when generating args from flags (optional, defaults to null for separate argv entries, use "=" for joined)
     - `args`: List of command-line arguments like argv in execve (optional, auto-generated from flags if not provided)
     - `preHook`: Shell script to run before executing the command (optional)
     - `postHook`: Shell script to run after executing the command, removes the `exec` call. use with care (optional)
@@ -445,8 +449,8 @@ let
       runtimeInputs ? [ ],
       env ? { },
       flags ? { },
-      flagSeparator ? " ",
-      # " " for "--flag value" or "=" for "--flag=value"
+      flagSeparator ? null,
+      # null for "--flag" "value" (separate args) or "=" for "--flag=value"
       args ? generateArgsFromFlags flags flagSeparator,
       preHook ? "",
       postHook ? "",

lib/modules/flags.nix

@@ -56,11 +56,12 @@ in
   };
 
   options.flagSeparator = lib.mkOption {
-    type = lib.types.str;
-    default = " ";
+    type = lib.types.nullOr lib.types.str;
+    default = null;
     description = ''
       Separator between flag names and values when generating args from flags.
-      " " for "--flag value" or "=" for "--flag=value"
+      null (default) for separate argv entries: "--flag" "value"
+      "=" for joined: "--flag=value"
     '';
   };