QtWebEnginePage initialization seems to disable CrtDbgReport'ing

  • We use _CrtDbgReportW to help us pop up a window during asserting. However, we've recently started working with QtWebEngine, and noticed that as soon as you work with a QtWebEnginePage, it seems to disable _CrtDbgReportW.

    Is there something I'm doing wrong? It seems weird to set the command line argument "--disable-breakpad" however there's not much documentation on whether it should indeed be set. Any suggestions would be a big help:

    #include <QtWidgets\QMainWindow>
    #include <QtWidgets\QApplication>
    #include <QtWebEngineWidgets\QtWebEngineWidgets>
    #include <QtWidgets\QMenuBar>
    // custom assert mechanism
    bool MyAssert(
    	const char* const pSzExpr,		//expression
    	const char* szFile, const unsigned nLine, const char* szFunc
    	size_t len = 0;
    	std::wstring wsFile(strlen(szFile)+1, L'#');
    	mbstowcs_s(&len, &wsFile[0], wcslen(wsFile.c_str()), szFile, strlen(szFile) + 1);
    	std::wstring wsMsg(strlen(pSzExpr)+1, L'#');
    	mbstowcs_s(&len, &wsMsg[0], wcslen(wsMsg.c_str()), pSzExpr, strlen(pSzExpr) + 1);
    	return _CrtDbgReportW(_CRT_ASSERT, wsFile.c_str(), nLine, nullptr, wsMsg.c_str()) != 1;
    #define ASSERT( EXPR ) (( !!(EXPR) || MyAssert((#EXPR),__FILE__,__LINE__,__FUNCTION__) ) || (_CrtDbgBreak(), 0) )
    // qtwebengine's chromium disables ASSERTing via _CrtDbgReportW inside process_startup_helper.cc::SetupCRT
    // by setting _CrtSetReportMode(_CRT_ASSERT, 0) when !command_line.HasSwitch(switches::kDisableBreakpad)
    // ie. command line argument "--disable-breakpad" needs to be _set_
    int main( int argc, char *argv[] )
    	QApplication app( argc, argv );
    	QMainWindow* mainWin = new QMainWindow();
    	QWebEngineView* pView = new QWebEngineView(mainWin);
    	ASSERT(false && "Pre-WebEnginePage"); // asserts here (and anytime before)...
    	auto pPage = pView->page(); 
    	ASSERT(false && "Post-WebEnginePage"); // ... but does not assert here (or hereafter)
    	pPage->setUrl( QUrl("http://www.google.com") );
    	// setup rest of the application and basic menu controls
    	QMenu* pQFile = mainWin->menuBar()->addMenu( QIcon(), "&File" );
    	mainWin->addAction( pQFile->addAction( QIcon(), "&Quit", qApp, SLOT( quit() ), Qt::Key_Q ) );
    	mainWin->setCentralWidget( pView );
    	mainWin->resize( 1024, 750 );
    	auto result = app.exec();
    	// tidy up and quit
    	delete pView;
    	delete mainWin;
    	ASSERT(false && "Done"); // does not assert here either
    	return result;

  • Rather than re-directing to CrtDbgReport, I can simplify the problem even further, and fail to assert post-initialization by using the pre-existing "_ASSERT" macro:

    	QWebEngineView* pView = new QWebEngineView(mainWin);
    	_ASSERT(false && "Pre-WebEnginePage"); // asserts here (and anytime before)...
    	auto pPage = pView->page();
    	_ASSERT(false && L"Post-WebEnginePage"); // ... but does not assert here (or hereafter)

    Any comments would be appreciated. I have also filed a bug: https://bugreports.qt.io/browse/QTBUG-57634

  • Fun update for anyone interested, searching for "breakpad chromium" is much more informative than "disable-breakpad chromium." Apparently "breakpad" is a crash reporting tool used by chromium, which suppresses CRT's ASSERTs when it is active (which is by default).

    Pass in "--disable-breakpad" as a commandline argument in the main method (it is detected by the win32 ::GetCommandLineW call), or consider saving the crt report mode before the web engine page initializes, and then restore it immediately afterwards.

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