QChar: remove confusing foldCase(ch, ch&) overload

For years, I've been confused by the various foldCase() overloads,
until Clang 21 -Wcharacter-conversion now forced me down the rabbit
hole.

Turns out that there's just one user of the ch,ch& overload and it's
readily ported to the ch*,ch* overload, so do that and remove the
now-unused overload.

Amends the start of the public history.

Pick-to: 6.10 6.8 6.5
Change-Id: I8ddd22b08423540f58c1a5fe0ef36c93c8b337f1
Reviewed-by: Ahmad Samir <[email protected]>
Reviewed-by: Thiago Macieira <[email protected]>

2 files changed, 1 insertions, 12 deletions

diff --git a/src/corelib/text/qchar.cpp b/src/corelib/text/qchar.cpp
index f2bc22c421a..4b89f67d276 100644
--- a/src/corelib/text/qchar.cpp
+++ b/src/corelib/text/qchar.cpp
@@ -1688,15 +1688,6 @@ static inline char32_t foldCase(const char16_t *cur, const char16_t *start)
     return convertCase_helper(ucs4, QUnicodeTables::CaseFold);
 }
 
-static inline char32_t foldCase(char16_t ch, char16_t &last) noexcept
-{
-    char32_t ucs4 = ch;
-    if (QChar::isLowSurrogate(ch) && QChar::isHighSurrogate(last))
-        ucs4 = QChar::surrogateToUcs4(last, ch);
-    last = ch;
-    return convertCase_helper(ucs4, QUnicodeTables::CaseFold);
-}
-
 static inline char16_t foldCase(char16_t ch) noexcept
 {
     return convertCase_helper(ch, QUnicodeTables::CaseFold);
diff --git a/src/corelib/text/qstring.cpp b/src/corelib/text/qstring.cpp
index 615cf3e6752..46c01bf232a 100644
--- a/src/corelib/text/qstring.cpp
+++ b/src/corelib/text/qstring.cpp
@@ -1197,15 +1197,13 @@ Q_NEVER_INLINE static int ucstricmp(qsizetype alen, const char16_t *a, qsizetype
     if (a == b)
         return qt_lencmp(alen, blen);
 
-    char16_t alast = 0;
-    char16_t blast = 0;
     qsizetype l = qMin(alen, blen);
     qsizetype i;
     for (i = 0; i < l; ++i) {
 //         qDebug() << Qt::hex << alast << blast;
 //         qDebug() << Qt::hex << "*a=" << *a << "alast=" << alast << "folded=" << foldCase (*a, alast);
 //         qDebug() << Qt::hex << "*b=" << *b << "blast=" << blast << "folded=" << foldCase (*b, blast);
-        int diff = foldCase(a[i], alast) - foldCase(b[i], blast);
+        int diff = foldCase(a + i, a) - foldCase(b + i, b);
         if ((diff))
             return diff;
     }