Clang: Provide tooltips

This includes also the query data for the help system (F1) for an
identifier under cursor.

Regressions (libclang changes necessary):
 - Function signatures do not contain default values.
 - Aliases are not resolved for/at:
   - template types
   - qualified name of a type

Fixes/Improvements:
 - Resolve "auto"
 - On a template type, show also the template parameter.
 - For a typedef like
     typedef long long superlong;
   the tooltip was "long long superlong", which was confusing.
   Now, "long long" is shown.

New:
 - Show first or \brief paragraph of a documentation comment.
 - Show size of a class at definition.
 - Show size of a field member in class definition.

Task-number: QTCREATORBUG-11259
Change-Id: Ie1a07930d0e882015d07dc43e35bb81a685cdeb8
Reviewed-by: Marco Bubke <marco.bubke@qt.io>

src/plugins/clangcodemodel/clanghoverhandler.h

@@ -0,0 +1,60 @@
+/****************************************************************************
+**
+** Copyright (C) 2018 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 <cpptools/baseeditordocumentprocessor.h>
+#include <cpptools/cpphoverhandler.h>
+#include <texteditor/basehoverhandler.h>
+
+namespace ClangCodeModel {
+namespace Internal {
+
+class ClangHoverHandler : public TextEditor::BaseHoverHandler
+{
+    Q_DECLARE_TR_FUNCTIONS(ClangHoverHandler)
+
+public:
+    ClangHoverHandler();
+    ~ClangHoverHandler() override;
+
+    void identifyMatchAsync(TextEditor::TextEditorWidget *editorWidget,
+                            int pos,
+                            ReportPriority report) override;
+    void decorateToolTip() override;
+    void operateTooltip(TextEditor::TextEditorWidget *editorWidget, const QPoint &point) override;
+
+private:
+    void cancelAsyncCheck() override;
+    void processToolTipInfo(const CppTools::ToolTipInfo &info);
+
+private:
+    int m_cursorPosition = -1;
+    QScopedPointer<QFutureWatcher<CppTools::ToolTipInfo>> m_futureWatcher;
+    ReportPriority m_reportPriority;
+};
+
+} // namespace Internal
+} // namespace ClangCodeModel