parse arguments is safe. It takes arguments: *const AnyObject and argc, and calls slice::from raw parts(arguments, argc as usize).

It does not check that arguments is non-null and aligned, or that argc elements are initialized. Safe Rust can pass a null pointer or a length past the allocation. The maintainer confirmed this on 2026-10-03, including a debug abort on Rust 1.78+ when Ruby calls an arity -1 method (to s via format, puts, or Array#join) with a NULL argv and argc of 0.