Function rlang_stop_internal 

extern "C" fn rlang_stop_internal(
    func: *const c_char,
    fmt: *const c_char,
)

rlang_stop_internal — abort with an internal error message.

Signature: void rlang_stop_internal(const char* fn, const char* fmt, ...)

In rlang, this is r_no_return. It calls Rf_error which longjmps. Since this is called from C code inside _minir_call_protected, the longjmp is safe (only crosses C frames).