When does terminal.size() return an error?

[Bunch-of-cells]

The type signature of CrosstermBackend::size() is (&self) -> io::Result<Rect>, so when does it return an error?

[PierreAntoineGuillaume]

I don't know for sure because I don't know tui-rs much, but an exemple is :

When it runs whithout being attached to a terminal.

for instance, you run it in a subshell

var=$(cargo run --exemple demo)

for more info, I guess you could read into TTYs.