[clang] [libcxx] [llvm] [Clang] Add warnings when mixing different charN_t types (PR #138708)

[Dimitrij Mijoski via cfe-commits]

================
@@ -484,7 +484,7 @@ template <class InternT, class ExternT>
 void utf8_to_utf16_in_ok(const std::codecvt<InternT, ExternT, mbstate_t>& cvt) {
   // UTF-8 string of 1-byte CP, 2-byte CP, 3-byte CP and 4-byte CP
   const unsigned char input[] = "b\u0448\uAAAA\U0010AAAA";
-  const char16_t expected[]   = {'b', 0x0448, 0xAAAA, 0xDBEA, 0xDEAA, 0};
+  const InternT expected[]    = {0x62, 0x0448, 0xAAAA, 0xDBEA, 0xDEAA, 0};
   static_assert(array_size(input) == 11, "");
   static_assert(array_size(expected) == 6, "");
 
----------------
dimztimz wrote:

Initially these test were written in c++11 and the variable `expected` was Unicode string literal. The variable `exp` is there to get the type i want. I use the same trick for the input data, see variables `input` and `in`. But later I ported this test to be c++98 because appreantly libc++ supports these codecvts in that mode too, and i had to drop the usage of Unicode string literals.

https://github.com/llvm/llvm-project/pull/138708