C error and random values when handling option for aliased fixed array

[gechandesu]

V doctor:

V full version: V 0.4.8 5ec9bb5.9f6150e
OS: linux, Linux version 6.6.8-arch1-1 (linux@archlinux) (gcc (GCC) 13.2.1 20230801, GNU ld (GNU Binutils) 2.41.0) #1 SMP PREEMPT_DYNAMIC Thu, 21 Dec 2023 19:01:01 +0000
Processor: 16 cpus, 64bit, little endian, 12th Gen Intel(R) Core(TM) i5-1240P

getwd: /home/ge/Code/v/netaddr/fixed_array_issues
vexe: /home/ge/.vlang/v
vexe mtime: 2024-11-20 22:55:01

vroot: OK, value: /home/ge/.vlang
VMODULES: OK, value: /home/ge/.vmodules
VTMP: OK, value: /tmp/v_1000

Git version: git version 2.46.1
Git vroot status: weekly.2024.47-4-g9f6150ee
.git/config present: true

CC version: cc (GCC) 14.2.1 20240910
emcc version: N/A
thirdparty/tcc status: thirdparty-linux-amd64 0134e9b9

What did you do?
./v -g -o vdbg cmd/v && ./vdbg fixed_array_option_return_handling_right.v

module main

import encoding.binary

pub type Addr = [4]u8

pub fn Addr.from_u32(a u32) Addr {
	mut bytes := [4]u8{}
	binary.big_endian_put_u32_fixed(mut bytes, a)
	return Addr(bytes)
}

pub fn (a Addr) u32() u32 {
	return binary.big_endian_u32_fixed(a)
}

struct Net {
	netaddr   Addr
	broadcast Addr
}

// returns Nth IP-address from the network if exists, else none
fn (n Net) nth(num i64) ?Addr {
	mut addr := Addr{}
	if num >= 0 {
		addr = Addr.from_u32(n.netaddr.u32() + u32(num))
	} else {
		addr = Addr.from_u32(n.broadcast.u32() + u32(num))
	}
	if !(n.netaddr.u32() < addr.u32() && addr.u32() < n.broadcast.u32()) {
		return none
	}
	return addr
}

fn main() {
	net := Net{
		netaddr:   Addr([u8(172), 16, 16, 0]!)
		broadcast: Addr([u8(172), 16, 16, 3]!)
	}
	res1 := net.nth(1) or { Addr([4]u8{}) } // Compiles, but res1 have random value on each run
	res2 := net.nth(1) or { Addr{} } // C error
	assert res1 == [u8(172), 16, 16, 1]!
	assert res2 == [u8(172), 16, 16, 1]!
}

What did you expect to see?

Assertion passed. No C errors.

What did you see instead?

================== C compilation error (from tcc): ==============
cc: /tmp/v_1000/fixed_array_option_return_handling_right.01JD5WK42AMV2XB24P1JAK56SA.tmp.c:14382: warning: cast between pointer and integer of different size
cc: /tmp/v_1000/fixed_array_option_return_handling_right.01JD5WK42AMV2XB24P1JAK56SA.tmp.c:14403: error: lvalue expected
... (the original output was 3 lines long, and was truncated to 2 lines)
=================================================================
(You can pass `-cg`, or `-show-c-output` as well, to print all the C error messages).
builder error: 
==================
C error found. It should never happen, when compiling pure V code.
This is a V compiler bug, please report it using `v bug file.v`,
or goto https://github.com/vlang/v/issues/new/choose .
You can also use #help on Discord: https://discord.gg/vlang .

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_{Huly®: V_0.6-21369}

[gechandesu]

I was in a hurry with the report, the error with the random result was already fixed here #22912 and is also not reproduced in the current example, but I have an example where this behavior persists, I will update the example.

[gechandesu]

I was in a hurry with the report, the error with the random result was already fixed here #22912 and is also not reproduced in the current example, but I have an example where this behavior persists, I will update the example.

Example updated.