nixos/git: allow lists for config to keep things in order

nixos/modules/programs/git.nix

···
       };
 
       config = mkOption {
-        type = with types; attrsOf (attrsOf anything);
-        default = { };
+        type =
+          with types;
+          let
+            gitini = attrsOf (attrsOf anything);
+          in
+          either gitini (listOf gitini) // {
+            merge = loc: defs:
+              let
+                config = foldl'
+                  (acc: { value, ... }@x: acc // (if isList value then {
+                    ordered = acc.ordered ++ value;
+                  } else {
+                    unordered = acc.unordered ++ [ x ];
+                  }))
+                  {
+                    ordered = [ ];
+                    unordered = [ ];
+                  }
+                  defs;
+              in
+              [ (gitini.merge loc config.unordered) ] ++ config.ordered;
+          };
+        default = [ ];
         example = {
           init.defaultBranch = "main";
           url."https://github.com/".insteadOf = [ "gh:" "github:" ];
         };
         description = lib.mdDoc ''
-          Configuration to write to /etc/gitconfig. See the CONFIGURATION FILE
-          section of git-config(1) for more information.
+          Configuration to write to /etc/gitconfig. A list can also be
+          specified to keep the configuration in order. For example, setting
+          `config` to `[ { foo.x = 42; } { bar.y = 42; }]` will put the `foo`
+          section before the `bar` section unlike the default alphabetical
+          order, which can be helpful for sections such as `include` and
+          `includeIf`. See the CONFIGURATION FILE section of git-config(1) for
+          more information.
         '';
       };
 
···
   config = mkMerge [
     (mkIf cfg.enable {
       environment.systemPackages = [ cfg.package ];
-      environment.etc.gitconfig = mkIf (cfg.config != {}) {
-        text = generators.toGitINI cfg.config;
+      environment.etc.gitconfig = mkIf (cfg.config != [ ]) {
+        text = concatMapStringsSep "\n" generators.toGitINI cfg.config;
       };
     })
     (mkIf (cfg.enable && cfg.lfs.enable) {