The documentation of many methods reads: "Panics if the new capacity overflows usize."

However it seems that the source of such panic is the internal Vec. Its documentation reads: "Panics if the new capacity exceeds isize::MAX bytes."

(For example, compare https://docs.rs/slab/latest/slab/struct.Slab.html#method.reserve with https://doc.rust-lang.org/alloc/vec/struct.Vec.html#method.reserve or https://doc.rust-lang.org/std/vec/struct.Vec.html#method.reserve.)