bevy_egui file dialog not working

[AlpineVibrations]

When i run the example on my Mac it runs fine.
If i copy the code to a new project and run it then it fails. It just does a spinning ball and hangs for ever. Cannot even quit the app (have to kill the terminal) and there is No error in the console..

i had a minimal example that show the problem.
https://github.com/AlpineVibrations/test-egui-file

[vladbat00]

hi! I wasn't able to reproduce the issue on your repo. Tested it on Windows 11: I ran the app and dragged some files onto it - everything seems to be working fine, no hanging or freezes. I also removed some unused dependencies so my Cargo.toml looked as follows:

[package]
name = "test-file-egui"
version = "0.1.0"
edition = "2024"

[dependencies]
bevy = "0.16.1"
bevy_egui = {version = "0.36", default-features = true, features = ["render"]}
rfd = "0.15.4"

(I don't think the Cargo.toml difference is the reason but mentioning it just in case.)

Is there anything I'm missing in the repro steps maybe?

[AlpineVibrations]

It's on the Open File Dialog not the drag and drop. And it's only on Mac OSX so far. I tested it and it runs fine on Linux.

[vladbat00]

Seems like the pick_folder call deadlocks on MacOS, as it attempts to build the modal on the main thread.

Not sure why it's implemented like that and how to make the async variant work with Bevy, but I don't think the issue is bevy_egui-related.
I'd probably ask around in the Bevy discord or the rfd repo, as I can't help with this issue unfortunately.

But if you learn how to make the async variant work, please share, I'm actually curious about this one.

[AlpineVibrations]

cool. will do. and thank you for finding the cause.

[plorefice]

I've stumbled upon the same problem today, so I did some additional digging. Turns out that the issue is the multi_threaded feature in Bevy: macOS probably doesn't like the file dialog to be spawned in a thread other than the main one.

The examples in this crate don't trigger the problem because the crate disables default features and doesn't depend on it, but it is among Bevy's default features, so it is encountered in a fresh project.

A workaround I've found (since I'm depending on another crate that requires multi_threaded) is to add NonSendMarker as a parameter to the system that spawns the file dialog. This forces the system to run on the main thread and everything works fine, including pick_folder.