wasm: add DialogExec hack back with warning

Previously, this was implemented in QEventLoop. By moving
it to the event dispatcher we can target the warning message
better and provide a suggested workaround for the dialog
case.

The behavior is the same as before: call emscripten_sleep(),
which throws a Javascript exception and returns control
to the browser while leaking the content of the stack.

Pick-to: 6.2
Change-Id: I2979fe4fe5923c27713e85b6725614b60a693e93
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

1 files changed, 10 insertions, 0 deletions

diff --git a/src/plugins/platforms/wasm/qwasmeventdispatcher.cpp b/src/plugins/platforms/wasm/qwasmeventdispatcher.cpp
index 29dbf96883..69a38ecd68 100644
--- a/src/plugins/platforms/wasm/qwasmeventdispatcher.cpp
+++ b/src/plugins/platforms/wasm/qwasmeventdispatcher.cpp
@@ -91,6 +91,16 @@ bool QWasmEventDispatcher::processEvents(QEventLoop::ProcessEventsFlags flags)
     if (!(flags & QEventLoop::EventLoopExec))
         return QUnixEventDispatcherQPA::processEvents(flags);
 
+    if (flags & QEventLoop::DialogExec) {
+        qWarning() << "Warning: dialog exec() is not supported on Qt for WebAssembly, please use"
+                   << "show() instead. When using exec() the dialog will show, the user can interact"
+                   << "with it and the appropriate signals will be emitted on close. However, the"
+                   << "exec() call never returns, stack content at the time of the exec() call"
+                   << "is leaked, and the exec() call may interfere with input event processing";
+
+        emscripten_sleep(1); // This call never returns
+    }
+
     // Handle processEvents from QEventLoop::exec():
     //
     // At this point the application has created its root objects on