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/clangbackendreceiver.cpp

@@ -128,6 +128,18 @@ QFuture<CppTools::SymbolInfo> BackendReceiver::addExpectedRequestFollowSymbolMes
     return futureInterface.future();
 }
 
+QFuture<CppTools::ToolTipInfo> BackendReceiver::addExpectedToolTipMessage(quint64 ticket)
+{
+    QTC_CHECK(!m_toolTipsTable.contains(ticket));
+
+    QFutureInterface<CppTools::ToolTipInfo> futureInterface;
+    futureInterface.reportStarted();
+
+    m_toolTipsTable.insert(ticket, futureInterface);
+
+    return futureInterface.future();
+}
+
 bool BackendReceiver::isExpectingCodeCompletedMessage() const
 {
     return !m_assistProcessorsTable.isEmpty();
@@ -272,6 +284,72 @@ void BackendReceiver::references(const ReferencesMessage &message)
     futureInterface.reportFinished();
 }
 
+static TextEditor::HelpItem::Category toHelpItemCategory(ToolTipInfo::QdocCategory category)
+{
+    switch (category) {
+    case ToolTipInfo::Unknown:
+        return TextEditor::HelpItem::Unknown;
+    case ToolTipInfo::ClassOrNamespace:
+        return TextEditor::HelpItem::ClassOrNamespace;
+    case ToolTipInfo::Enum:
+        return TextEditor::HelpItem::Enum;
+    case ToolTipInfo::Typedef:
+        return TextEditor::HelpItem::Typedef;
+    case ToolTipInfo::Macro:
+        return TextEditor::HelpItem::Macro;
+    case ToolTipInfo::Brief:
+        return TextEditor::HelpItem::Brief;
+    case ToolTipInfo::Function:
+        return TextEditor::HelpItem::Function;
+    }
+
+    return TextEditor::HelpItem::Unknown;
+}
+
+static QStringList toStringList(const Utf8StringVector &utf8StringVector)
+{
+    QStringList list;
+    list.reserve(utf8StringVector.size());
+
+    for (const Utf8String &utf8String : utf8StringVector)
+        list << utf8String.toString();
+
+    return list;
+}
+
+static CppTools::ToolTipInfo toToolTipInfo(const ToolTipMessage &message)
+{
+    CppTools::ToolTipInfo info;
+
+    const ToolTipInfo backendInfo = message.toolTipInfo();
+
+    info.text = backendInfo.text();
+    info.briefComment = backendInfo.briefComment();
+
+    info.qDocIdCandidates = toStringList(backendInfo.qdocIdCandidates());
+    info.qDocMark = backendInfo.qdocMark();
+    info.qDocCategory = toHelpItemCategory(backendInfo.qdocCategory());
+
+    info.sizeInBytes = backendInfo.sizeInBytes();
+
+    return info;
+}
+
+void BackendReceiver::tooltip(const ToolTipMessage &message)
+{
+    qCDebugIpc() << "ToolTipMessage" << message.toolTipInfo().text();
+
+    const quint64 ticket = message.ticketNumber();
+    QFutureInterface<CppTools::ToolTipInfo> futureInterface = m_toolTipsTable.take(ticket);
+    QTC_CHECK(futureInterface != QFutureInterface<CppTools::ToolTipInfo>());
+
+    if (futureInterface.isCanceled())
+        return; // A new request was issued making this one outdated.
+
+    futureInterface.reportResult(toToolTipInfo(message));
+    futureInterface.reportFinished();
+}
+
 void BackendReceiver::followSymbol(const ClangBackEnd::FollowSymbolMessage &message)
 {
     qCDebugIpc() << "FollowSymbolMessage with"