QChar: avoid char{32→16}_t narrowing in normalizationQuickCheckHelper()

Same pattern as in the previous few patches: the old code used a
char32_t to temporarily store a UTF-16 code point, narrowing it back
to char16_t in a call to QChar::surrogateToUcs4(), triggering Clang 21
-Wcharacter-conversion.

Solution is also the same: keep the UTF-16 code unit in a separate
variable, until we have determined whether it needs surrogate decoding
or merely promotion to char32_t.

Amends 2e0a4b13addf1f56112bac38448be96fb02f650d.

Pick-to: 6.10 6.8 6.5
Change-Id: I291871c73b26a1766c30f0c1c6858e09d9693678
Reviewed-by: Ahmad Samir <[email protected]>

1 files changed, 6 insertions, 3 deletions

diff --git a/src/corelib/text/qchar.cpp b/src/corelib/text/qchar.cpp
index 4b89f67d276..d3011c34538 100644
--- a/src/corelib/text/qchar.cpp
+++ b/src/corelib/text/qchar.cpp
@@ -2092,7 +2092,7 @@ static bool normalizationQuickCheckHelper(QString *str, QString::NormalizationFo
     uchar lastCombining = 0;
     for (qsizetype i = from; i < length; ++i) {
         qsizetype pos = i;
-        char32_t uc = string[i];
+        const char16_t uc = string[i];
         if (uc < 0x80) {
             // ASCII characters are stable code points
             lastCombining = 0;
@@ -2100,6 +2100,7 @@ static bool normalizationQuickCheckHelper(QString *str, QString::NormalizationFo
             continue;
         }
 
+        char32_t ucs4;
         if (QChar::isHighSurrogate(uc)) {
             ushort low = string[i + 1];
             if (!QChar::isLowSurrogate(low)) {
@@ -2109,10 +2110,12 @@ static bool normalizationQuickCheckHelper(QString *str, QString::NormalizationFo
                 continue;
             }
             ++i;
-            uc = QChar::surrogateToUcs4(uc, low);
+            ucs4 = QChar::surrogateToUcs4(uc, low);
+        } else {
+            ucs4 = uc;
         }
 
-        const QUnicodeTables::Properties *p = qGetProp(uc);
+        const QUnicodeTables::Properties *p = qGetProp(ucs4);
 
         if (p->combiningClass < lastCombining && p->combiningClass > 0)
             return false;