Ensure left/right/mid behave in a compatible way

QString and QStringRef did bounds checking for left/right/mid, whereas
QStringView was asserting on out of bounds.

Relax the behavior for QStringView and do bounds checking on pos/n
as well. This removes a source of potentially hidden errors when porting
from QStringRef (or QString) to QStringView.

Unfortunately, one difference remains, where QByteArray::left/right()
behaves differently (and somewhat more sane) than QString and
QStringRef. We're keeping the difference here, as it has been around
for many years.

Mark left/right/mid as obsolete and to be replaced with the new
first/last/slice methods.

Change-Id: I18c203799ba78c928a4610a6038089f27696c22e
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

1 files changed, 31 insertions, 1 deletions

diff --git a/src/corelib/tools/qarraydata.h b/src/corelib/tools/qarraydata.h
index b6fc05e108..de52713348 100644
--- a/src/corelib/tools/qarraydata.h
+++ b/src/corelib/tools/qarraydata.h
@@ -306,7 +306,37 @@ namespace QtPrivate {
 struct Q_CORE_EXPORT QContainerImplHelper
 {
     enum CutResult { Null, Empty, Full, Subset };
-    static CutResult mid(int originalLength, int *position, int *length);
+    static constexpr CutResult mid(qsizetype originalLength, qsizetype *_position, qsizetype *_length)
+    {
+        qsizetype &position = *_position;
+        qsizetype &length = *_length;
+        if (position > originalLength) {
+            position = 0;
+            length = 0;
+            return Null;
+        }
+
+        if (position < 0) {
+            if (length < 0 || length + position >= originalLength) {
+                position = 0;
+                length = originalLength;
+                return Full;
+            }
+            if (length + position <= 0) {
+                position = length = 0;
+                return Null;
+            }
+            length += position;
+            position = 0;
+        } else if (size_t(length) > size_t(originalLength - position)) {
+            length = originalLength - position;
+        }
+
+        if (position == 0 && length == originalLength)
+            return Full;
+
+        return length > 0 ? Subset : Empty;
+    }
 };
 }