QString: add {setUtf16,setUnicode}(const char16_t*) overloads

This is a first step for adding QT_NO_INTEGRAL_STRINGS in the next
commit.

Mark setUtf16(const ushort *) as obsolete.

Use the weak overload workaround, so that the call isn't ambiguous if
it's called on a nullptr.

[ChangeLog][QtCore][QString] Added setUtf16(const char16_t *) and
setUnicode(const char16_t *) overloads.

Task-number: QTBUG-125871
Change-Id: I25d12c19876466c235c0d9928aae6fd332836bf5
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit be3bf632e1cf80b16475f8353e4753b38317626b)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/text/qstring.cpp

@@ -6143,7 +6143,16 @@ QString& QString::setUnicode(const QChar *unicode, qsizetype size)
 }
 
 /*!
-    \fn QString &QString::setUtf16(const ushort *unicode, qsizetype size)
+    \fn QString::setUnicode(const char16_t *unicode, qsizetype size)
+    \overload
+    \since 6.9
+
+    \sa unicode(), setUtf16()
+*/
+
+/*!
+    \fn QString::setUtf16(const char16_t *unicode, qsizetype size)
+    \since 6.9
 
     Resizes the string to \a size characters and copies \a unicode
     into the string.
@@ -6157,6 +6166,11 @@ QString& QString::setUnicode(const QChar *unicode, qsizetype size)
     \sa utf16(), setUnicode()
 */
 
+/*!
+    \fn QString &QString::setUtf16(const ushort *unicode, qsizetype size)
+    \obsolete Use the \c char16_t overload instead.
+*/
+
 /*!
     \fn QString QString::simplified() const
 
@@ -7586,8 +7600,8 @@ QString QString::vasprintf(const char *cformat, va_list ap)
             }
             case 's': {
                 if (length_mod == lm_l) {
-                    const ushort *buff = va_arg(ap, const ushort*);
+                    const char16_t *buff = va_arg(ap, const char16_t*);
-                    const ushort *ch = buff;
+                    const auto *ch = buff;
                     while (precision != 0 && *ch != 0) {
                         ++ch;
                         --precision;

src/corelib/text/qstring.h

@@ -768,7 +768,17 @@ public:
 
     QString &setRawData(const QChar *unicode, qsizetype size);
     QString &setUnicode(const QChar *unicode, qsizetype size);
-    inline QString &setUtf16(const ushort *utf16, qsizetype size); // ### Qt 7 char16_t
+    Q_WEAK_OVERLOAD
+    QString &setUnicode(const char16_t *utf16, qsizetype size)
+    { return setUnicode(reinterpret_cast<const QChar *>(utf16), size); }
+    QString &setUtf16(const char16_t *utf16, qsizetype size)
+    { return setUnicode(reinterpret_cast<const QChar *>(utf16), size); }
+
+#if !QT_CORE_REMOVED_SINCE(6, 9)
+    Q_WEAK_OVERLOAD
+#endif
+    QString &setUtf16(const ushort *autf16, qsizetype asize)
+    { return setUnicode(reinterpret_cast<const QChar *>(autf16), asize); }
 
     int compare(const QString &s, Qt::CaseSensitivity cs = Qt::CaseSensitive) const noexcept;
     int compare(QLatin1StringView other, Qt::CaseSensitivity cs = Qt::CaseSensitive) const noexcept;
@@ -1417,8 +1427,6 @@ void QString::squeeze()
         d.clearFlag(Data::CapacityReserved);
 }
 
-QString &QString::setUtf16(const ushort *autf16, qsizetype asize)
-{ return setUnicode(reinterpret_cast<const QChar *>(autf16), asize); }
 QChar &QString::operator[](qsizetype i)
 { verify(i, 1); return data()[i]; }
 QChar &QString::front() { return operator[](0); }

tests/auto/corelib/text/qstring/tst_qstring.cpp

@@ -5937,14 +5937,15 @@ void tst_QString::setRawData()
 void tst_QString::setUnicode()
 {
     const QChar ptr[] = { u'ሴ', QChar(0x0000) };
+    const char16_t utf16[] = { u'ሴ', 0x0000 };
 
     QTest::ThrowOnFailEnabler throwOnFail;
 
     auto doTest = [](const auto ptr, QString &str) mutable {
-        // make sure that the data is copied
+        // make sure that the data was copied
-        QVERIFY(str.constData() != ptr);
+        QCOMPARE_NE(str.constData(), reinterpret_cast<const QChar *>(ptr));
         QVERIFY(str.isDetached());
-        QCOMPARE(str, QString(ptr, 1));
+        QCOMPARE(str, QString(reinterpret_cast<const QChar *>(ptr), 1));
 
         // make sure that the string is resized, even if the data is nullptr
         str = u"test"_s;
@@ -5959,6 +5960,23 @@ void tst_QString::setUnicode()
         QVERIFY(!str.isDetached());
         str.setUnicode(ptr, 1);
         doTest(ptr, str);
+        str.setUnicode(nullptr, 0);
+    }
+
+    {
+        QString str;
+        QVERIFY(!str.isDetached());
+        str.setUnicode(utf16, 1);
+        doTest(utf16, str);
+        str.setUnicode(nullptr, 0);
+    }
+
+    {
+        QString str;
+        QVERIFY(!str.isDetached());
+        str.setUtf16(utf16, 1);
+        doTest(utf16, str);
+        str.setUtf16(nullptr, 0);
     }
 }