packed struct can not handle arbitrary bit-width integers (more than 16 bit) correctly

[WoodyAtHome]

zig version 0.6.0+e1186c88e

const std = @import("std");

pub fn main() void {
    const Can = packed struct {
        const CR = packed struct {
            init: u1, lo: u1, mode: u3, reserved1: u3, reserved2: u17
        };
        cr: CR,
    };

    var can = Can{
        .cr = Can.CR{
            .init = 1,
            .lo = 0,
            .mode = 7,
            .reserved1 = 0,
            .reserved2 = 0,
        },
    };
    std.debug.warn("sizeOf(Can.CR) = {} bytes.\n", .{@sizeOf(Can.CR)});
}

Now play with the size of reserved2.

reserved2: u1..u16: Compiler and sizeOf output ok.

reserved2: u17..u23: strange compiler output and sizeOf(Can.CR) should be 4 bytes.

zig run main.zig 
<unknown>:0: error: invalid number of bytes
<unknown>:0: error: invalid number of bytes
sizeOf(Can.CR) = 5 bytes.

reserved2: u24: compiler crashes

zig run main.zig 
Assertion failed at /deps/zig/src/analyze.cpp:8386 in resolve_llvm_types_struct. This is a bug in the Zig compiler.
Unable to dump stack trace: debug info stripped

reserved2: u25:Compiler and sizeOf output ok.

[pixelherodev]

This is a known bug, I believe, though I do not remember the exact issue off-hand. If you search for "packed," you'll notice a number of bugs :(

[WoodyAtHome]

I couldn't find this bug I searched before.

[WoodyAtHome]

My workaround is now to use

reserved21: u8,
reserved22: u8,
reserved23: u8,

insteadof
reserved2: u24

[MasterQ32]

Yes this is a known issue, see #2627 and #3133