Unable to easily check for equality between trait objects within an Arc

[pwnorbitals]

I tried this code (reference StackOverflow question) :

let a : Arc<dyn SomeTrait> = getA();
let b : Arc<dyn SomeTrait> = getB();

// The following two approaches don't work as expected
let eq1 = std::ptr::eq(a.as_ref(), b.as_ref()); 
let eq2 = Arc::ptr_eq(&a, &b);

I expected to see this happen:
trait object comparison works as expected, with no false positives or false negatives.

Instead, this happened:
see StackOverflow explanation. Fat pointer comparison is a complex topic and I believe it's a papercut issue that the developper has to understand the internals of fat pointer layout to be able to check for equality

[jonas-schievink]

duplicate of #63021

[pwnorbitals]

Then this would in turn be a duplicate of #46139