Qml Debugger: Support "evaluate" while engine is running

Newer versions of Qt can evaluate expressions without pausing the
QML engine. We can take advantage of that. At the same time we can
remove the crutch of using QQmlEngineDebugService for this. The
latter produces inconsistent and generally worse results than the V4
debug service.

Task-number: QTCREATORBUG-14931
Change-Id: Ic78d08a0b00cf7de3911b7b672ce229c6d779363
Reviewed-by: hjk <hjk@theqtcompany.com>

src/plugins/debugger/console/console.h

@@ -49,7 +49,7 @@ namespace Utils { class SavedAction; }
 namespace Debugger {
 namespace Internal {
 
-typedef std::function<bool(QString)> ScriptEvaluator;
+typedef std::function<void(QString)> ScriptEvaluator;
 
 class ConsoleItemModel;
 class ConsoleView;

src/plugins/debugger/debuggerengine.cpp

@@ -1743,12 +1743,6 @@ void DebuggerEngine::executeDebuggerCommand(const QString &, DebuggerLanguages)
     showStatusMessage(tr("This debugger cannot handle user input."));
 }
 
-bool DebuggerEngine::evaluateScript(const QString &)
-{
-    showStatusMessage(tr("This debugger cannot handle user scripts."));
-    return false;
-}
-
 BreakHandler *DebuggerEngine::breakHandler() const
 {
     return Internal::breakHandler();

src/plugins/debugger/debuggerengine.h

@@ -262,7 +262,6 @@ public:
 
     virtual bool acceptsDebuggerCommands() const { return true; }
     virtual void executeDebuggerCommand(const QString &command, DebuggerLanguages languages);
-    virtual bool evaluateScript(const QString &expression);
 
     virtual void assignValueInDebugger(WatchItem *item,
         const QString &expr, const QVariant &value);

src/plugins/debugger/qml/qmlengine.cpp

@@ -213,6 +213,7 @@ public:
     QList<quint32> queryIds;
     bool retryOnConnectFail = false;
     bool automaticConnect = false;
+    bool unpausedEvaluate = false;
 
     QTimer connectionTimer;
     QmlDebug::QmlDebugConnection *connection;
@@ -282,8 +283,8 @@ QmlEngine::QmlEngine(const DebuggerRunParameters &startParameters, DebuggerEngin
         d->automaticConnect = true;
     }
 
-    debuggerConsole()->setScriptEvaluator([this](const QString &expr) -> bool {
-        return evaluateScript(expr);
+    debuggerConsole()->setScriptEvaluator([this](const QString &expr) {
+        executeDebuggerCommand(expr, QmlLanguage);
     });
 
     d->connectionTimer.setInterval(4000);
@@ -1116,37 +1117,23 @@ void QmlEngine::executeDebuggerCommand(const QString &command, DebuggerLanguages
     if (!(languages & QmlLanguage))
         return;
 
-    StackHandler *handler = stackHandler();
-    if (handler->isContentsValid() && handler->currentFrame().isUsable()) {
+    if (state() == InferiorStopOk) {
+        StackHandler *handler = stackHandler();
+        if (handler->isContentsValid() && handler->currentFrame().isUsable()) {
+            d->evaluate(command, CB(d->handleExecuteDebuggerCommand));
+        } else {
+            // Paused but no stack? Something is wrong
+            d->engine->showMessage(_("Cannot evaluate %1. The stack trace is broken.").arg(command),
+                                   ConsoleOutput);
+        }
+    } else if (d->unpausedEvaluate) {
         d->evaluate(command, CB(d->handleExecuteDebuggerCommand));
     } else {
-        //Currently cannot evaluate if not in a javascript break
-        d->engine->showMessage(QString(_("Cannot evaluate %1 in current stack frame")).arg(
-                                   command), ConsoleOutput);
+        d->engine->showMessage(_("The application has to be paused in order to evaluate "
+                                 "expressions").arg(command), ConsoleOutput);
     }
 }
 
-bool QmlEngine::evaluateScript(const QString &expression)
-{
-    bool didEvaluate = true;
-    // Evaluate expression based on engine state
-    // When engine->state() == InferiorStopOk, the expression is sent to debuggerClient.
-    if (state() != InferiorStopOk) {
-        QModelIndex currentIndex = inspectorView()->currentIndex();
-        quint32 queryId = d->inspectorAgent.queryExpressionResult
-                (watchHandler()->watchItem(currentIndex)->id, expression);
-        if (queryId) {
-            d->queryIds.append(queryId);
-        } else {
-            didEvaluate = false;
-            debuggerConsole()->printItem(ConsoleItem::ErrorType, _("Error evaluating expression."));
-        }
-    } else {
-        executeDebuggerCommand(expression, QmlLanguage);
-    }
-    return didEvaluate;
-}
-
 void QmlEnginePrivate::updateScriptSource(const QString &fileName, int lineOffset, int columnOffset,
                                           const QString &source)
 {
@@ -1330,12 +1317,14 @@ void QmlEnginePrivate::evaluate(const QString expr, const QmlCallback &cb)
 
     // The Qt side Q_ASSERTs otherwise. So ignore the request and hope
     // it will be repeated soon enough (which it will, e.g. in updateLocals)
-    QTC_ASSERT(engine->state() == InferiorStopOk, return);
+    QTC_ASSERT(unpausedEvaluate || engine->state() == InferiorStopOk, return);
 
     DebuggerCommand cmd(EVALUATE);
 
     cmd.arg(EXPRESSION, expr);
-    cmd.arg(FRAME, engine->stackHandler()->currentIndex());
+    StackHandler *handler = engine->stackHandler();
+    if (handler->currentFrame().isUsable())
+        cmd.arg(FRAME, handler->currentIndex());
 
     runCommand(cmd, cb);
 }
@@ -2497,15 +2486,13 @@ void QmlEnginePrivate::stateChanged(State state)
         /// Start session.
         flushSendBuffer();
         runDirectCommand(CONNECT);
-        runCommand({VERSION}); // Only used for logging.
+        runCommand({VERSION}, CB(handleVersion));
     }
 }
 
 void QmlEnginePrivate::handleVersion(const QVariantMap &response)
 {
-    engine->showMessage(QString(_("Using V8 Version: %1")).arg(
-                                response.value(_(BODY)).toMap().
-                                value(_("V8Version")).toString()), LogOutput);
+    unpausedEvaluate = response.value(_(BODY)).toMap().value(_("UnpausedEvaluate"), false).toBool();
 }
 
 void QmlEnginePrivate::flushSendBuffer()

src/plugins/debugger/qml/qmlengine.h

@@ -130,7 +130,6 @@ private:
     void expandItem(const QByteArray &iname) override;
     void selectWatchData(const QByteArray &iname) override;
     void executeDebuggerCommand(const QString &command, DebuggerLanguages languages) override;
-    bool evaluateScript(const QString &expression) override;
 
     bool hasCapability(unsigned) const override;
     void quitDebugger() override;