stage2: @sizeOf packed struct is not working as in stage1

[igor84]

Zig Version

0.10.0-dev.3664+02070ae26

Steps to Reproduce

const Rgb24 = packed struct {
    r: u8,
    g: u8,
    b: u8,
};

test {
    try std.testing.expectEqual(@as(usize, 3), @sizeOf(Rgb24));
}

Expected Behavior

The above test should pass.

Some time ago I fixed issues with packed struct in stage1 so that @sizeOf(Rgb24) would return 3 and if I have pixels: []Rgb24 I could use reader.readAll(std.mem.sliceAsBytes(pixels)) to load tightly packed Rgb24 data.

Actual Behavior

Now in stage2 @sizeOf(Rgb24) returns 4 and the array also isn't tightly packed but has additional byte of padding for each element which breaks readAll code.

[nektro]

the issue still stands, but for your mentioned use case you likely want extern struct not packed

[Vexu]

Working as intended, the self-hosted compiler implements #5049

[igor84]

@Vexu As far as I know stage1 doesn't compile with packed struct(u24) so is there a way to write code so it works with both stage1 and stage2?

@nektro I would say I need packed because I also have Rgb565{u5, u6, u5} for example and extern will not work for that.

[Vexu]

As far as I know stage1 doesn't compile with packed struct(u24) so is there a way to write code so it works with both stage1 and stage2?

You can use @import("builtin").zig_backend to check what you are using but I recommend sticking to either stage1 or stage2.