Debugger: Reverse gdb stack traces when creating full back traces

By default, threads are sorted in descending order. This change brings
thread 1, which is ususally the most interesting frame, to the front.

Change-Id: Ie8b0d6b849da8b8d816bca907e5a8efa7e46c473
Reviewed-by: hjk <hjk@qt.io>

src/plugins/debugger/gdb/gdbengine.cpp

@@ -4235,13 +4235,43 @@ void GdbEngine::notifyInferiorSetupFailedHelper(const QString &msg)
     notifyEngineSetupFailed();
 }
 
+static QString reverseBacktrace(const QString &trace)
+{
+    static const QRegularExpression threadPattern(R"(Thread \d+ \(Thread )");
+    Q_ASSERT(threadPattern.isValid());
+
+    if (!trace.contains(threadPattern)) // Pattern mismatch fallback
+        return trace;
+
+    const QStringView traceView{trace};
+    QList<QStringView> threadTraces;
+    const auto traceSize = traceView.size();
+    for (qsizetype pos = 0; pos < traceSize; ) {
+        auto nextThreadPos = traceView.indexOf(threadPattern, pos + 1);
+        if (nextThreadPos == -1)
+            nextThreadPos = traceSize;
+        threadTraces.append(traceView.sliced(pos, nextThreadPos - pos));
+        pos = nextThreadPos;
+    }
+
+    QString result;
+    result.reserve(traceSize);
+    for (auto it = threadTraces.crbegin(), end = threadTraces.crend(); it != end; ++it) {
+        result += *it;
+        if (result.endsWith('\n'))
+            result += '\n';
+    }
+    return result;
+}
+
 void GdbEngine::createFullBacktrace()
 {
     DebuggerCommand cmd("thread apply all bt full", NeedsTemporaryStop | ConsoleCommand);
     cmd.callback = [](const DebuggerResponse &response) {
         if (response.resultClass == ResultDone) {
             Internal::openTextEditor("Backtrace$",
-                response.consoleStreamOutput + response.logStreamOutput);
+                                     reverseBacktrace(response.consoleStreamOutput)
+                                     + response.logStreamOutput);
         }
     };
     runCommand(cmd);