Tricky type definition can cause inhabitedness check to go into an infinite loop.

[canndrew]

This code:

struct Foo<'a, T: 'a> {
    ph: std::marker::PhantomData<T>,
    foo: &'a Foo<'a, (T, T)>,
}

fn wub(f: Foo<!>) {
    match f {}
}

Causes rustc to stack overflow. This should be pretty easy to "fix" by just putting a recursion limit in is_uninhabited_from and returning false when it gets hit. What's a suitable limit here? Presumably there are other limits like this in other places in the compiler.

[canndrew]

This is fixed in #39680