Unify all mid() functions in QtBase.

Up to now, Qt had at least 3 different implementations of the mid().
Only QString::mid implementation was not crashing on edge cases and
was protected against overflows, therefore I picked that one as the
base implementation, even if it has weird semantics for an invalid
input.

As a side effect QVector::mid was slightly optimized to not detach in
all cases (which follows current QList behavior). Documentation of
QVector::mid and QList::mid was updated to not mention "copy of data"
which could suggest that the mid() result is detached.

QStringRef::mid was fixed and now it follows general Qt behavior, by
returning a null value for a null input.

Change-Id: Ie9ff5d98372bd193d66508e6dd92b6ed1180ad9b
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 13 insertions, 10 deletions

diff --git a/src/corelib/tools/qbytearray.cpp b/src/corelib/tools/qbytearray.cpp
index 9c2a242e8e..6fed3ae5c9 100644
--- a/src/corelib/tools/qbytearray.cpp
+++ b/src/corelib/tools/qbytearray.cpp
@@ -2677,19 +2677,22 @@ QByteArray QByteArray::right(int len) const
 
 QByteArray QByteArray::mid(int pos, int len) const
 {
-    if ((d->size == 0 && d->ref.isStatic()) || pos > d->size)
+    using namespace QtPrivate;
+    switch (QContainerImplHelper::mid(size(), &pos, &len)) {
+    case QContainerImplHelper::Null:
         return QByteArray();
-    if (len < 0)
-        len = d->size - pos;
-    if (pos < 0) {
-        len += pos;
-        pos = 0;
+    case QContainerImplHelper::Empty:
+    {
+        QByteArrayDataPtr empty = { Data::allocate(0) };
+        return QByteArray(empty);
     }
-    if (len + pos > d->size)
-        len = d->size - pos;
-    if (pos == 0 && len == d->size)
+    case QContainerImplHelper::Full:
         return *this;
-    return QByteArray(d->data() + pos, len);
+    case QContainerImplHelper::Subset:
+        return QByteArray(d->data() + pos, len);
+    }
+    Q_UNREACHABLE();
+    return QByteArray();
 }
 
 /*!