cpack: add CPACK_DMG_FILESYSTEM

Allow users to configure the filesystem format of the generated `.dmg`
via the `CPACK_DMG_FILESYSTEM` option.

Fixes: #21874

Help/cpack_gen/dmg.rst

@@ -103,6 +103,12 @@ on macOS:
 
  - Default: ``CPACK_PACKAGE_FILE_NAME-<component>``
 
+.. variable:: CPACK_DMG_FILESYSTEM
+
+ The filesystem format. Common values are ``APFS`` and ``HFS+``.
+ See ``man hdiutil`` for a full list of supported formats.
+ Defaults to ``HFS+``.
+
 .. variable:: CPACK_COMMAND_HDIUTIL
 
  Path to the ``hdiutil(1)`` command used to operate on disk image files on

Help/release/dev/cpack-dmg-filesystem.rst

@@ -0,0 +1,5 @@
+cpack-dmg-filesystem
+--------------------
+
+* The :cpack_gen:`CPack DragNDrop Generator` gained option
+  :variable:`CPACK_DMG_FILESYSTEM` to control the ``.dmg`` filesystem.

Source/CPack/cmCPackDragNDropGenerator.cxx

@@ -273,6 +273,11 @@ int cmCPackDragNDropGenerator::CreateDMG(const std::string& src_dir,
     ? this->GetOption("CPACK_DMG_FORMAT")
     : "UDZO";
 
+  const std::string cpack_dmg_filesystem =
+    this->GetOption("CPACK_DMG_FILESYSTEM")
+    ? this->GetOption("CPACK_DMG_FILESYSTEM")
+    : "HFS+";
+
   // Get optional arguments ...
   std::string cpack_license_file =
     this->GetOption("CPACK_RESOURCE_FILE_LICENSE")
@@ -418,7 +423,7 @@ int cmCPackDragNDropGenerator::CreateDMG(const std::string& src_dir,
   temp_image_command << " -ov";
   temp_image_command << " -srcfolder \"" << staging.str() << "\"";
   temp_image_command << " -volname \"" << cpack_dmg_volume_name << "\"";
-  temp_image_command << " -fs HFS+";
+  temp_image_command << " -fs \"" << cpack_dmg_filesystem << "\"";
   temp_image_command << " -format " << temp_image_format;
   temp_image_command << " \"" << temp_image << "\"";