LSP: Allow users to see timing data

It's often interesting to know how long it takes for a reply to a
request to come in. While that data is in principle already available
from the inspector, a dedicated logging category gives much quicker
results.

Change-Id: Idd43c6e69422140863a7adaa33a7bc17dd8e6492
Reviewed-by: David Schulz <david.schulz@qt.io>

src/libs/languageserverprotocol/jsonrpcmessages.cpp

@@ -37,6 +37,7 @@
 #include <QTextCodec>
 
 namespace LanguageServerProtocol {
+Q_LOGGING_CATEGORY(timingLog, "qtc.languageserverprotocol.timing", QtWarningMsg)
 
 constexpr const char CancelRequest::methodName[];
 
@@ -148,4 +149,10 @@ CancelRequest::CancelRequest(const CancelParameter &params)
     : Notification(methodName, params)
 { }
 
+void logElapsedTime(const QString &method, const QElapsedTimer &t)
+{
+    qCDebug(timingLog) << "received server reply to" << method
+                       << "after" << t.elapsed() << "ms";
+}
+
 } // namespace LanguageServerProtocol

src/libs/languageserverprotocol/jsonrpcmessages.h

@@ -34,6 +34,7 @@
 #include <utils/variant.h>
 
 #include <QDebug>
+#include <QElapsedTimer>
 #include <QHash>
 #include <QJsonObject>
 #include <QJsonValue>
@@ -294,6 +295,8 @@ public:
     { return JsonRpcMessage::isValid(errorMessage) && id().isValid(); }
 };
 
+void LANGUAGESERVERPROTOCOL_EXPORT logElapsedTime(const QString &method, const QElapsedTimer &t);
+
 template <typename Result, typename ErrorDataType, typename Params>
 class Request : public Notification<Params>
 {
@@ -316,9 +319,13 @@ public:
 
     Utils::optional<ResponseHandler> responseHandler() const final
     {
-        auto callback = [callback = m_callBack](const QByteArray &content, QTextCodec *codec) {
+        QElapsedTimer timer;
+        timer.start();
+        auto callback = [callback = m_callBack, method = this->method(), t = std::move(timer)]
+                (const QByteArray &content, QTextCodec *codec) {
             if (!callback)
                 return;
+            logElapsedTime(method, t);
             QString parseError;
             const QJsonObject &object = JsonRpcMessageHandler::toJsonObject(content,
                                                                             codec,