The old code used a char32_t to temporarily store a UTF-16 code point. Upon finding it to be a surrogate, it then had to narrow it back to char16_t for the call to QChar::surrogateToUcs4(). It also invoked QChar(uint), a ctor which should have never existed to begin with. Rewrite the functions to keep the UTF-16 code point in a char16_t variable until it's inspected to be either safe for promotion to char32_t or else has been decoded (or decoding failed). This requires to write 'uc = c' twice instead of once, but allows us to add a comment on the failed-decoding path to guide the reader of the code, improving readability. Specifically declare `uc` as uninit'ed to provoke compiler warnings when code is changed to forget to assign to `uc`. Found by Clang 21's -Wcharacter-conversion. Amends the start of the public history. Pick-to: 6.10 6.8 6.5 Change-Id: I8d43b4c0e0b3852ddf730f349886bd6943b94f17 Reviewed-by: Ahmad Samir <a.samirh78@gmail.com>