Loosen the API contract for QStringView::left() and friends

Remove the assertions in QStringView::left() and friends and
turn them into runtime bounds checking instead. This changes
the behavior to be compatible with what we do in Qt 6 (see
change d2833a3ce5af725d66ef9338f2a61b766dd3cb2d) and simplifies
porting from QStringRef to QStringView.

Task-number: QTBUG-86516
Change-Id: I28e3beb4f42c7b9dfc52813cbcfa322a3df5685a
Reviewed-by: Sona Kurazyan <sona.kurazyan@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

2 files changed, 22 insertions, 9 deletions

diff --git a/src/corelib/text/qstringview.cpp b/src/corelib/text/qstringview.cpp
index 9df656dc59..93febceb19 100644
--- a/src/corelib/text/qstringview.cpp
+++ b/src/corelib/text/qstringview.cpp
@@ -604,7 +604,9 @@ QT_BEGIN_NAMESPACE
     Returns the substring starting at position \a start in this object,
     and extending to the end of the string.
 
-    \note The behavior is undefined when \a start < 0 or \a start > size().
+    \note Until 5.15.1, the behavior was undefined when \a start < 0 or
+    \a start > size(). Since 5.15.2, the behavior is compatible with
+    QString::mid().
 
     \sa left(), right(), chopped(), chop(), truncate()
 */
@@ -616,8 +618,9 @@ QT_BEGIN_NAMESPACE
     Returns the substring of length \a length starting at position
     \a start in this object.
 
-    \note The behavior is undefined when \a start < 0, \a length < 0,
-    or \a start + \a length > size().
+    \note Until 5.15.1, the behavior was undefined when \a start < 0, \a length < 0,
+    or \a start + \a length > size(). Since 5.15.2, the behavior is compatible with
+    QString::mid().
 
     \sa left(), right(), chopped(), chop(), truncate()
 */
@@ -628,7 +631,8 @@ QT_BEGIN_NAMESPACE
     Returns the substring of length \a length starting at position
     0 in this object.
 
-    \note The behavior is undefined when \a length < 0 or \a length > size().
+    \note Until 5.15.1, the behavior was undefined when \a length < 0 or \a length > size().
+    Since 5.15.2, the behavior is compatible with QString::left().
 
     \sa mid(), right(), chopped(), chop(), truncate()
 */
@@ -639,7 +643,8 @@ QT_BEGIN_NAMESPACE
     Returns the substring of length \a length starting at position
     size() - \a length in this object.
 
-    \note The behavior is undefined when \a length < 0 or \a length > size().
+    \note Until 5.15.1, the behavior was undefined when \a length < 0 or \a length > size().
+    Since 5.15.2, the behavior is compatible with QString::right().
 
     \sa mid(), left(), chopped(), chop(), truncate()
 */
diff --git a/src/corelib/text/qstringview.h b/src/corelib/text/qstringview.h
index 9b85dcffa5..72ddd91968 100644
--- a/src/corelib/text/qstringview.h
+++ b/src/corelib/text/qstringview.h
@@ -238,13 +238,21 @@ public:
     Q_REQUIRED_RESULT Q_DECL_CONSTEXPR QChar at(qsizetype n) const { return (*this)[n]; }
 
     Q_REQUIRED_RESULT Q_DECL_CONSTEXPR QStringView mid(qsizetype pos) const
-    { return Q_ASSERT(pos >= 0), Q_ASSERT(pos <= size()), QStringView(m_data + pos, m_size - pos); }
+    {
+        return QStringView(m_data + qBound(qsizetype(0), pos, m_size), m_size - qBound(qsizetype(0), pos, m_size));
+    }
     Q_REQUIRED_RESULT Q_DECL_CONSTEXPR QStringView mid(qsizetype pos, qsizetype n) const
-    { return Q_ASSERT(pos >= 0), Q_ASSERT(n >= 0), Q_ASSERT(pos + n <= size()), QStringView(m_data + pos, n); }
+    {
+        return QStringView(m_data + qBound(qsizetype(0), pos, m_size), qBound(qsizetype(0), pos + n, m_size) - qBound(qsizetype(0), pos, m_size));
+    }
     Q_REQUIRED_RESULT Q_DECL_CONSTEXPR QStringView left(qsizetype n) const
-    { return Q_ASSERT(n >= 0), Q_ASSERT(n <= size()), QStringView(m_data, n); }
+    {
+        return QStringView(m_data, (size_t(n) > size_t(m_size) ? m_size : n));
+    }
     Q_REQUIRED_RESULT Q_DECL_CONSTEXPR QStringView right(qsizetype n) const
-    { return Q_ASSERT(n >= 0), Q_ASSERT(n <= size()), QStringView(m_data + m_size - n, n); }
+    {
+        return QStringView(m_data + m_size - (size_t(n) > size_t(m_size) ? m_size : n), (size_t(n) > size_t(m_size) ? m_size : n));
+    }
     Q_REQUIRED_RESULT Q_DECL_CONSTEXPR QStringView chopped(qsizetype n) const
     { return Q_ASSERT(n >= 0), Q_ASSERT(n <= size()), QStringView(m_data, m_size - n); }