Editor: multi cursor support

Adding a way to create multiple cursors that can insert/remove text at
arbitrary positions in the document. Adding cursors is done by pressing
alt + up/down or by clicking into the editor while holding the alt key.

Fixes: QTCREATORBUG-16013
Change-Id: I495d27d95a3d277220946616ef30efc241da0120
Reviewed-by: Christian Stenger <christian.stenger@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Artem Sokolovskii <artem.sokolovskii@qt.io>
Reviewed-by: David Schulz <david.schulz@qt.io>

src/libs/utils/multitextcursor.h

@@ -0,0 +1,106 @@
+/****************************************************************************
+**
+** Copyright (C) 2021 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#pragma once
+
+#include "utils_global.h"
+
+#include <QTextCursor>
+
+QT_BEGIN_NAMESPACE
+class QKeyEvent;
+class QPlainTextEdit;
+QT_END_NAMESPACE
+
+namespace Utils {
+
+class QTCREATOR_UTILS_EXPORT MultiTextCursor
+{
+public:
+    MultiTextCursor();
+    explicit MultiTextCursor(const QList<QTextCursor> &cursors);
+
+    /// replace all cursors with \param cursors and the last one will be the new main cursors
+    void setCursors(const QList<QTextCursor> &cursors);
+    const QList<QTextCursor> cursors() const;
+
+    /// \returns whether this multi cursor contains any cursor
+    bool isNull() const;
+    /// \returns whether this multi cursor contains more than one cursor
+    bool hasMultipleCursors() const;
+    /// \returns the number of cursors handled by this cursor
+    int cursorCount() const;
+
+    /// the \param cursor that is appended by added by \brief addCursor
+    /// will be interpreted as the new main cursor
+    void addCursor(const QTextCursor &cursor);
+    /// convenience function that removes the old main cursor and appends
+    /// \param cursor as the new main cursor
+    void replaceMainCursor(const QTextCursor &cursor);
+    /// \returns the main cursor
+    QTextCursor mainCursor() const;
+    /// \returns the main cursor and removes it from this multi cursor
+    QTextCursor takeMainCursor();
+
+    void beginEditBlock();
+    void endEditBlock();
+    /// merges overlapping cursors together
+    void mergeCursors();
+
+    /// applies the move key event \param e to all cursors in this multi cursor
+    bool handleMoveKeyEvent(QKeyEvent *e, QPlainTextEdit *edit, bool camelCaseNavigationEnabled);
+    /// applies the move \param operation to all cursors in this multi cursor \param n times
+    /// with the move \param mode
+    void movePosition(QTextCursor::MoveOperation operation, QTextCursor::MoveMode mode, int n = 1);
+
+    /// \returns whether any cursor has a selection
+    bool hasSelection() const;
+    /// \returns the selected text of all cursors that have a selection separated by
+    /// a newline character
+    QString selectedText() const;
+    /// removes the selected text of all cursors that have a selection from the document
+    void removeSelectedText();
+
+    /// inserts \param text into all cursors, potentially removing correctly selected text
+    void insertText(const QString &text, bool selectNewText = false);
+
+    bool operator==(const MultiTextCursor &other) const;
+    bool operator!=(const MultiTextCursor &other) const;
+
+    using iterator = QList<QTextCursor>::iterator;
+    using const_iterator = QList<QTextCursor>::const_iterator;
+
+    iterator begin() { return m_cursors.begin(); }
+    iterator end() { return m_cursors.end(); }
+    const_iterator begin() const { return m_cursors.begin(); }
+    const_iterator end() const { return m_cursors.end(); }
+    const_iterator constBegin() const { return m_cursors.constBegin(); }
+    const_iterator constEnd() const { return m_cursors.constEnd(); }
+
+private:
+    QList<QTextCursor> m_cursors;
+};
+
+} // namespace Utils