Fix mime type parsing with Qt 5

The behavior of QStringView::mid is slightly different between Qt 5 and
Qt 6, so use Utils::midView which was created exactly to cover that.

Change-Id: Ia084e93c36fb152ac725f1b8eaa38a07dfb939e1
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: Christian Stenger <christian.stenger@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/libs/utils/mimetypes2/mimemagicrule.cpp

@@ -40,8 +40,11 @@
 #include "mimemagicrule_p.h"
 
 #include "mimetypeparser_p.h"
-#include <QtCore/QList>
+
+#include "porting.h"
+
 #include <QtCore/QDebug>
+#include <QtCore/QList>
 #include <qendian.h>
 
 namespace Utils {
@@ -260,8 +263,11 @@ MimeMagicRule::MimeMagicRule(const QString &type,
 
     // Parse for offset as "1" or "1:10"
     const int colonIndex = offsets.indexOf(QLatin1Char(':'));
-    const QStringView startPosStr = QStringView{offsets}.mid(0, colonIndex); // \ These decay to returning 'offsets'
-    const QStringView endPosStr   = QStringView{offsets}.mid(colonIndex + 1);// / unchanged when colonIndex == -1
+    const QStringView startPosStr
+        = Utils::midView(offsets, 0, colonIndex); // \ These decay to returning 'offsets'
+    const QStringView endPosStr = Utils::midView(offsets,
+                                                 colonIndex
+                                                     + 1); // / unchanged when colonIndex == -1
     if (Q_UNLIKELY(!MimeTypeParserBase::parseNumber(startPosStr, &m_startPos, errorString)) ||
         Q_UNLIKELY(!MimeTypeParserBase::parseNumber(endPosStr, &m_endPos, errorString))) {
         m_type = Invalid;

src/libs/utils/porting.h

@@ -65,7 +65,7 @@ inline StringView make_stringview(const QString &s)
 }
 
 // QStringView::mid in Qt5 does not do bounds checking, in Qt6 it does
-inline QStringView midView(const QString &s, int offset, int length)
+inline QStringView midView(const QString &s, int offset, int length = -1)
 {
 #if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
     const int size = s.size();
@@ -77,7 +77,7 @@ inline QStringView midView(const QString &s, int offset, int length)
         if (length + offset <= 0)
             return {};
         return QStringView(s).left(length + offset);
-    } else if (length > size - offset)
+    } else if (length < 0 || length > size - offset)
         return QStringView(s).mid(offset);
     return QStringView(s).mid(offset, length);
 #else