thunderbird: add native host support

modules/programs/thunderbird.nix

@@ -136,6 +136,24 @@ let
     '') prefs)}
     ${extraPrefs}
   '';
+
+  nativeMessagingHostsPath = if isDarwin then
+    "${cfg.vendorPath}/NativeMessagingHosts"
+  else
+    "${cfg.vendorPath}/native-messaging-hosts";
+
+  nativeMessagingHostsJoined = pkgs.symlinkJoin {
+    name = "th_native-messaging-hosts";
+    paths = [
+      # Link a .keep file to keep the directory around
+      (pkgs.writeTextDir "lib/mozilla/native-messaging-hosts/.keep" "")
+      # Link package configured native messaging hosts (entire mail app actually)
+      cfg.package
+    ]
+    # Link user configured native messaging hosts
+      ++ cfg.nativeMessagingHosts;
+  };
+
 in {
   meta.maintainers = with hm.maintainers; [ d-dervishi jkarlson ];
 
@@ -158,6 +176,29 @@ in {
         description = "profile version, set null for nix-darwin";
       };
 
+      vendorPath = mkOption {
+        internal = true;
+        type = with types; nullOr str;
+        # Thunderbird doesn't look in `Application Support` on macOS for user
+        # config (in contrast to global settings that are the same for Firefox
+        # and Thunderbird):
+        # https://developer.thunderbird.net/add-ons/mailextensions/supported-webextension-api
+        default = if isDarwin then "Library/Mozilla" else ".mozilla";
+        example = ".mozilla";
+        description =
+          "Directory containing the native messaging hosts directory.";
+      };
+
+      nativeMessagingHosts = optionalAttrs (cfg.vendorPath != null) (mkOption {
+        visible = true;
+        type = types.listOf types.package;
+        default = [ ];
+        description = ''
+          Additional packages containing native messaging hosts that should be
+          made available to Thunderbird extensions.
+        '';
+      });
+
       profiles = mkOption {
         type = with types;
           attrsOf (submodule ({ config, name, ... }: {
@@ -403,7 +444,13 @@ in {
     home.file = mkMerge ([{
       "${thunderbirdConfigPath}/profiles.ini" =
         mkIf (cfg.profiles != { }) { text = generators.toINI { } profilesIni; };
-    }] ++ flip mapAttrsToList cfg.profiles (name: profile: {
+    }] ++ optional (cfg.vendorPath != null) {
+      "${nativeMessagingHostsPath}" = {
+        source =
+          "${nativeMessagingHostsJoined}/lib/mozilla/native-messaging-hosts";
+        recursive = true;
+      };
+    } ++ flip mapAttrsToList cfg.profiles (name: profile: {
       "${thunderbirdProfilesPath}/${name}/chrome/userChrome.css" =
         mkIf (profile.userChrome != "") { text = profile.userChrome; };