This error uses jargon that most Flutter developers won't know. This might frustrate users.

Perhaps we should add more context? Maybe something like:

runApp requires an implicit view.

runApp renders the widget tree into a view provided by the platform,
called the "implicit view". However, the platform did not provide an
implicit view.

Try using runWidget instead of runApp.

See: https://flutter.dev/to/web-runwidget

Since it's a public API, I think we should not assume it 100% comes from runApp. Maybe

The app requested an implicit view, but the platform doesn't have one.

This is likely because the app called runApp to start up, which expects the platform to provide a default view to render into ("the implicit view"), while the engine has multi-view mode enabled, which requires the app handle view creation.

Try using runWidget instead of runApp. See also https://flutter.dev/to/web-runwidget

@loic-sharma @dkwingsmt I ended up with something like this, I hope it makes more sense!

The app is attempting to render into a default View that isn't available (platformDispatcher.implicitView == null).
This is likely because the platform has multi-view mode enabled, but the app is calling runApp to render its root Widget.
Try using runWidget instead of runApp to start your app. runWidget allows you to provide a View widget, without requiring a default on the platform.
See: https://flutter.dev/to/web-multiview-runwidget

(Tried to use lingo closer to that in the wrapWithDefaultView method docs.)

I slightly prefer Tong's wording.

Some context:

1. On desktop, the north star is that the app will call runApp even though there's no implicit view. runApp will know how to create a window to host the widget tree.
2. On desktop, you can have multiple views while also having an implicit view. Thus, on desktop you can call runApp even if you have multi-view mode enabled

Since it's a public API, I think we should not assume it 100% comes from runApp.

Should we move this error to runApp then and then make wrapWithDefaultView assert that platformDispatcher.implicitView != null?

What do y'all think about this? I tried to merge bits from all our messages :)

The app requested an implicit view, but the platform did not provide one.

runApp expects the platform to provide a default view to render into ("the implicit view").
However, the platform did not provide a default "implicit" view, likely because it has multi-view mode enabled.

Try using runWidget instead of runApp to start your app. runWidget allows you to provide a View widget, without requiring a default view.
See: https://flutter.dev/to/web-multiview-runwidget

Looks good!

I think checking it in wrapWithDefaultView is better than runApp since wrapWithDefaultView is also a public API and users can still call it incorrectly (which is a user error and you shouldn't assert on).

I applied @loic-sharma's suggestion! If @dkwingsmt is happy, I'm happy too, let's autosubmit this :P

(Off-topic)

runApp will know how to create a window to host the widget tree.
...
you can have multiple views while also having an implicit view

We need to discuss this elsewhere, I'm interested :P