Debugger: Force LLDB round trip between stack and locals update

The stack might produce data (such as as the QML context in
native mixed debugging) that is needed for locals display.
While this doesn't work yet with LLDB anyway, the change
suppresses one soft access when accessing the top frame of
an empty stack (the usual case on the first update).

Change-Id: If931fbe940b8cda01cc6cc34429a2fcb33cd8d19
Reviewed-by: Christian Stenger <christian.stenger@theqtcompany.com>

src/plugins/debugger/lldb/lldbengine.cpp

@@ -460,6 +460,8 @@ void LldbEngine::handleResponse(const QByteArray &response)
             refreshMemory(item);
         else if (name == "full-backtrace")
             showFullBacktrace(item);
+        else if (name == "continuation")
+            handleContinuation(item);
         else if (name == "statusmessage") {
             QString msg = QString::fromUtf8(item.data());
             if (msg.size())
@@ -469,6 +471,15 @@ void LldbEngine::handleResponse(const QByteArray &response)
     }
 }
 
+void LldbEngine::handleContinuation(const GdbMi &data)
+{
+    if (data.data() == "updateLocals") {
+        updateLocals();
+        return;
+    }
+    QTC_ASSERT(false, qDebug() << "Unknown continuation: " << data.data());
+}
+
 void LldbEngine::showFullBacktrace(const GdbMi &data)
 {
     Internal::openTextEditor(_("Backtrace $"),
@@ -524,10 +535,10 @@ void LldbEngine::activateFrame(int frameIndex)
     DebuggerCommand cmd("activateFrame");
     cmd.arg("index", frameIndex);
     cmd.arg("thread", threadsHandler()->currentThread().raw());
+    cmd.arg("continuation", "updateLocals");
     runCommand(cmd);
 
     reloadRegisters();
-    updateLocals();
 }
 
 void LldbEngine::selectThread(ThreadId threadId)
@@ -793,8 +804,12 @@ bool LldbEngine::setToolTipExpression(TextEditor::TextEditorWidget *editorWidget
 void LldbEngine::updateAll()
 {
     reloadRegisters();
-    updateStack();
-    updateLocals();
+
+    DebuggerCommand cmd("reportStack");
+    cmd.arg("nativeMixed", isNativeMixedActive());
+    cmd.arg("stacklimit", action(MaximalStackDepth)->value().toInt());
+    cmd.arg("continuation", "updateLocals");
+    runCommand(cmd);
 }
 
 void LldbEngine::reloadFullStack()
@@ -805,14 +820,6 @@ void LldbEngine::reloadFullStack()
     runCommand(cmd);
 }
 
-void LldbEngine::updateStack()
-{
-    DebuggerCommand cmd("reportStack");
-    cmd.arg("nativeMixed", isNativeMixedActive());
-    cmd.arg("stacklimit", action(MaximalStackDepth)->value().toInt());
-    runCommand(cmd);
-}
-
 //////////////////////////////////////////////////////////////////////
 //
 // Watch specific stuff