I'd like to add an extension to Clang's format string checking, as well as extend the format string attributes to add UTF-16 (u) and UTF-32 (U) length modifiers to the c, C, s, and S type specifiers.
I've chosen lower case and upper case u to match the C and C++ standards for string literal specifiers, u"" and U"" telling the compiler to create a UTF-16 and UTF-32 string literals respectively.
as for the function attributes, my plan is to create uprintf and Uprintf arguments to the gcc style attributes e.g. __attribute__(__format__(uprintf)) and __attribute__(__format__(Uprintf))
I've chosen uprintf and Uprintf to match C and C++'s string type indicators as well, though it might be a better idea to go with u16printf and u32printf to match C++'s u16string and u32string types?