SIGSEGV at compile time: compound assignment through a property pair under a nested field of deref(p + k) #17

Compound assignment through a property pair (operator .s / operator .s:=) whose base is a nested field of deref(p + k) crashes the compiler with SIGSEGV before main runs. A plain store, a plain field, deref(p), deref(q) after var q = p + 2, and an array element all work.

daScript at c4e4906 (lookibed fork), linux x86_64, interpreter (the crash is at compile time, so every tier).

Repro (z_n.das, run with daslang z_n.das; prints nothing, exit code 139):

options gen2
struct U {
    x : int
}
def operator .s(u : U) : int {
    return u.x
}
def operator .s:=(var u : U; v : int) {
    u.x = v
}
struct S {
    u : U
}
var arr : S[4]
[export]
def main {
    to_log(LOG_ERROR, "start\n")
    unsafe {
        var p : S? = addr(arr[0])
        deref(p + 2).u.s += 1
        to_log(LOG_ERROR, "{arr[2].u.s}\n")
    }
}

Forms that compile and run as expected:

deref(p).u.s += 1
var q = p + 2
deref(q).u.s += 1
arr[2].u.s += 1
deref(p + 2).u.x += 1
deref(p + 2).u.s = 5
deref(p + 2).s += 1

Forms that crash: deref(p + 2).u.s += 1, deref(p + k).u.s += 1 with k a variable, and the same through a [c_bitfields]-style generated property pair.

Found by c2das-re (a C to daslang converter): C p[2].u.s++ on a bitfield member reached through pointer arithmetic. The converter now spells the step as x = x + 1 to avoid it.