Deprecate Q(Persistent)ModelIndex::child

Due to how invalid model indices are handled in Qt, child() is unsuitable
for general purpose usage. In particular you can never get a top level
item in the model because the root model index by definition hasn't got
a pointer to the model it belongs.

That makes child() useless for anything but tree models (and even there
you'd need to special case your code anyhow).

[ChangeLog][QtCore][QModelIndex] QModelIndex::child has
been deprecated due to its lack of generality.
Use model->index(row, column, index) instead.

[ChangeLog][QtCore][QPersistentModelIndex] QPersistentModelIndex::child has
been deprecated due to its lack of generality.
Use model->index(row, column, index) instead.

Change-Id: Ice73c17133aaf71355fa2af1eacfe64da01bd456
Reviewed-by: Thorbjørn Lund Martsum <[email protected]>
Reviewed-by: David Faure <[email protected]>

src/corelib/itemmodels/qabstractitemmodel.cpp

@@ -364,7 +364,7 @@ quintptr QPersistentModelIndex::internalId() const
  Returns the parent QModelIndex for this persistent index, or an invalid
  QModelIndex if it has no parent.
 
- \sa child(), sibling(), model()
+ \sa sibling(), model()
 */
 QModelIndex QPersistentModelIndex::parent() const
 {
@@ -377,7 +377,7 @@ QModelIndex QPersistentModelIndex::parent() const
  Returns the sibling at \a row and \a column or an invalid QModelIndex if
  there is no sibling at this position.
 
- \sa parent(), child()
+ \sa parent()
 */
 
 QModelIndex QPersistentModelIndex::sibling(int row, int column) const
@@ -387,7 +387,12 @@ QModelIndex QPersistentModelIndex::sibling(int row, int column) const
  return QModelIndex();
 }
 
+#if QT_DEPRECATED_SINCE(5, 8)
 /*!
+ \obsolete
+
+ Use QAbstractItemModel::index() instead.
+
  Returns the child of the model index that is stored in the given \a row
  and \a column.
 
@@ -397,9 +402,10 @@ QModelIndex QPersistentModelIndex::sibling(int row, int column) const
 QModelIndex QPersistentModelIndex::child(int row, int column) const
 {
  if (d)
- return d->index.child(row, column);
+ return d->index.model()->index(row, column, d->index);
  return QModelIndex();
 }
+#endif
 
 /*!
  Returns the data for the given \a role for the item referred to by the
@@ -1099,12 +1105,16 @@ void QAbstractItemModel::resetInternalData()
  Returns the sibling at \a row and \a column. If there is no sibling at this
  position, an invalid QModelIndex is returned.
 
- \sa parent(), child()
+ \sa parent()
 */
 
 /*!
  \fn QModelIndex QModelIndex::child(int row, int column) const
 
+ \obsolete
+
+ Use QAbstractItemModel::index() instead.
+
  Returns the child of the model index that is stored in the given \a row and
  \a column.
 
@@ -1153,7 +1163,7 @@ void QAbstractItemModel::resetInternalData()
  Returns the parent of the model index, or QModelIndex() if it has no
  parent.
 
- \sa child(), sibling(), model()
+ \sa sibling(), model()
 */
 
 /*!

src/corelib/itemmodels/qabstractitemmodel.h

@@ -63,7 +63,9 @@ class Q_CORE_EXPORT QModelIndex
  inline void *internalPointer() const Q_DECL_NOTHROW { return reinterpret_cast<void*>(i); }
  inline QModelIndex parent() const;
  inline QModelIndex sibling(int row, int column) const;
- inline QModelIndex child(int row, int column) const;
+#if QT_DEPRECATED_SINCE(5, 8)
+ QT_DEPRECATED_X("Use QAbstractItemModel::index") inline QModelIndex child(int row, int column) const;
+#endif
  inline QVariant data(int role = Qt::DisplayRole) const;
  inline Qt::ItemFlags flags() const;
  Q_DECL_CONSTEXPR inline const QAbstractItemModel *model() const Q_DECL_NOTHROW { return m; }
@@ -128,7 +130,9 @@ class Q_CORE_EXPORT QPersistentModelIndex
  quintptr internalId() const;
  QModelIndex parent() const;
  QModelIndex sibling(int row, int column) const;
- QModelIndex child(int row, int column) const;
+#if QT_DEPRECATED_SINCE(5, 8)
+ QT_DEPRECATED_X("Use QAbstractItemModel::index") QModelIndex child(int row, int column) const;
+#endif
  QVariant data(int role = Qt::DisplayRole) const;
  Qt::ItemFlags flags() const;
  const QAbstractItemModel *model() const;
@@ -419,8 +423,10 @@ inline QModelIndex QModelIndex::parent() const
 inline QModelIndex QModelIndex::sibling(int arow, int acolumn) const
 { return m ? (r == arow && c == acolumn) ? *this : m->sibling(arow, acolumn, *this) : QModelIndex(); }
 
+#if QT_DEPRECATED_SINCE(5, 8)
 inline QModelIndex QModelIndex::child(int arow, int acolumn) const
 { return m ? m->index(arow, acolumn, *this) : QModelIndex(); }
+#endif
 
 inline QVariant QModelIndex::data(int arole) const
 { return m ? m->data(*this, arole) : QVariant(); }