QChar: make construction from integral explicit

QChar should not be convertible from any integral type except from
char16_t, short and possibly char (since it's a direct superset).

David provided the perfect example:

  if (str == 123) { ~~~ }

compiles, with 123 implicitly converted to QChar (str == "123"
was meant instead). But similarly one can construct other
scenarios where QString(123) gets accidentally used (instead of
QString::number(123)), like QString s; s += 123;.

Add a macro to revert to the implicit constructors, for backwards
compatibility.

The breaks are mostly in tests that "abuse" of integers (arithmetic,
etc.). Maybe it's time for user-defined literals for QChar/QString,
but that is left for another commit.

[ChangeLog][Potentially Source-Incompatible Changes][QChar] QChar
constructors from integral types are now by default explicit.
It is recommended to use explicit conversions, QLatin1Char,
QChar::fromUcs4 instead of implicit conversions. The old behavior
can be restored by defining the QT_IMPLICIT_QCHAR_CONSTRUCTION
macro.

Change-Id: I6175f6ab9bcf1956f6f97ab0c9d9d5aaf777296d
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

2 files changed, 2 insertions, 2 deletions

diff --git a/src/gui/text/windows/qwindowsfontdatabase.cpp b/src/gui/text/windows/qwindowsfontdatabase.cpp
index 9ee1c5aba6..79ea08f9b6 100644
--- a/src/gui/text/windows/qwindowsfontdatabase.cpp
+++ b/src/gui/text/windows/qwindowsfontdatabase.cpp
@@ -485,7 +485,7 @@ static QChar *createFontFile(const QString &faceName)
         const int nameLength = qMin(faceName.length(), LF_FACESIZE - 1);
         faceNamePtr = new QChar[nameLength + 1];
         memcpy(static_cast<void *>(faceNamePtr), faceName.utf16(), sizeof(wchar_t) * nameLength);
-        faceNamePtr[nameLength] = 0;
+        faceNamePtr[nameLength] = u'\0';
     }
     return faceNamePtr;
 }
diff --git a/src/gui/text/windows/qwindowsfontengine.cpp b/src/gui/text/windows/qwindowsfontengine.cpp
index 46774fa304..b2855d19dd 100644
--- a/src/gui/text/windows/qwindowsfontengine.cpp
+++ b/src/gui/text/windows/qwindowsfontengine.cpp
@@ -376,7 +376,7 @@ void QWindowsFontEngine::recalcAdvances(QGlyphLayout *glyphs, QFontEngine::Shape
                     oldFont = SelectObject(hdc, hfont);
 
                 if (!ttf) {
-                    QChar ch[2] = { ushort(glyph), 0 };
+                    QChar ch[2] = { ushort(glyph), u'\0' };
                     int chrLen = 1;
                     if (QChar::requiresSurrogates(glyph)) {
                         ch[0] = QChar::highSurrogate(glyph);