This patch adds a new attribute called format_dynamic_key_arg. It's intended to be used instead of format_arg for methods/functions that load the formatting string from some external source based on the given key value. The attribute tells Clang that it has to avoid -Wformat warnings when key strings have no formatting specifiers. Otherwise it tells Clang that it can assume that the key strings use the same formatting layout as the external formatting string values (i.e. Clang can perform the normal -Wformat related checks).
This attribute is useful for certain Objective-C methods like NSBundle.localizedStringForKey that load the values dynamically based on a specified key value.