QString: remove op+=(char) and op+=(QChar::SpecialCharacter)

The former messes in bad ways with the overload set (it, fatally,
attracts char16_t, e.g.). The latter was probably added in response to
ambiguities between (char) and (QChar). While it's harmless now,
remove it, since it no longer pulls its weight.

The no-ascii warning is now coming from QChar(char), so the protection
isn't lost.

[ChangeLog][QtCore][QString] The += operators taking char and
QChar::SpecialCharacter have been removed as they cause adding a
char16_t to QString to call the char overload, losing information. The
append() function was not affected.

Change-Id: I57116314bcc71c0d9476159513c0c10048239db3
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

src/corelib/text/qstring.cpp

@@ -5931,22 +5931,6 @@ QString& QString::fill(QChar ch, int size)
     Appends the string view \a str to this string.
 */
 
-/*! \fn QString &QString::operator+=(char ch)
-
-    \overload operator+=()
-
-    Appends the character \a ch to this string. Note that the character is
-    converted to Unicode using the fromLatin1() function, unlike other 8-bit
-    functions that operate on UTF-8 data.
-
-    You can disable this function by defining \c QT_NO_CAST_FROM_ASCII
-    when you compile your applications. This can be useful if you want
-    to ensure that all user-visible strings go through QObject::tr(),
-    for example.
-
-    \sa QT_NO_CAST_FROM_ASCII
-*/
-
 /*! \fn QString &QString::operator+=(QChar ch)
 
     \overload operator+=()
@@ -5954,13 +5938,6 @@ QString& QString::fill(QChar ch, int size)
     Appends the character \a ch to the string.
 */
 
-/*! \fn QString &QString::operator+=(QChar::SpecialCharacter c)
-
-    \overload operator+=()
-
-    \internal
-*/
-
 /*!
     \fn bool operator==(const char *s1, const QString &s2)
 

src/corelib/text/qstring.h

@@ -570,7 +570,6 @@ public:
         return *this;
     }
 
-    inline QString &operator+=(QChar::SpecialCharacter c) { return append(QChar(c)); }
 #if QT_STRINGVIEW_LEVEL < 2
     inline QString &operator+=(const QString &s) { return append(s); }
     inline QString &operator+=(const QStringRef &s) { return append(s); }
@@ -859,8 +858,6 @@ public:
     { return append(QString::fromUtf8(s)); }
     inline QT_ASCII_CAST_WARN QString &operator+=(const QByteArray &s)
     { return append(QString::fromUtf8(s)); }
-    inline QT_ASCII_CAST_WARN QString &operator+=(char c)
-    { return append(QChar::fromLatin1(c)); }
 
     inline QT_ASCII_CAST_WARN bool operator==(const char *s) const;
     inline QT_ASCII_CAST_WARN bool operator!=(const char *s) const;

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

@@ -447,10 +447,9 @@ private slots:
     void operator_pluseq_qchar_data()         { operator_pluseq_data(true); }
     void operator_pluseq_qbytearray()         { operator_pluseq_impl<QByteArray>(); }
     void operator_pluseq_qbytearray_data()    { operator_pluseq_data(); }
-    void operator_pluseq_char()               { operator_pluseq_impl<char, QString &(QString::*)(char)>(); }
-    void operator_pluseq_char_data()          { operator_pluseq_data(true); }
     void operator_pluseq_charstar()           { operator_pluseq_impl<const char *, QString &(QString::*)(const char *)>(); }
     void operator_pluseq_charstar_data()      { operator_pluseq_data(); }
+    void operator_pluseq_special_cases();
     void operator_pluseq_bytearray_special_cases_data();
     void operator_pluseq_bytearray_special_cases();
 
@@ -2703,6 +2702,17 @@ void tst_QString::append_bytearray_special_cases()
     }
 }
 
+void tst_QString::operator_pluseq_special_cases()
+{
+    {
+        QString a;
+        a += QChar::CarriageReturn;
+        a += '\r';
+        a += u'\x1111';
+        QCOMPARE(a, QStringView(u"\r\r\x1111"));
+    }
+}
+
 void tst_QString::operator_pluseq_data(bool emptyIsNoop)
 {
     append_data(emptyIsNoop);