Get third party project "zigimg" working successfully with self-hosted.

[mlarouche]

Zig Version

0.10.0-dev.3757+ae8d26a6a

Steps to Reproduce

1. git clone https://github.com/zigimg/zigimg zigimg
2. git clone https://github.com/zigimg/test-suite test-suite
3. cd zigimg
4. git checkout stage2_compat
5. Remove zig_backend check in tests/image_test.zig line 350-352, test "Test Colorf32 iterator". There is another similar test skipped as well in tests/octree_quantizer_test.zig line 34-36
6. Do zig build test to run the test-suite

Expected Behavior

All the tests should pass.

Actual Behavior

Test [101/106] test.Test Colorf32 iterator... thread 23952 panic: switch on corrupt value
C:\Programmation\Zig\zigimg\zigimg\src\color.zig:809:66: 0x7ff7a6c6484b in next (zigimgtest.exe.obj)
            .rgba64 => |data| data[self.current_index].toColorf32(),
                                                                 ^
C:\Programmation\Zig\zigimg\zigimg\tests\image_test.zig:373:19: 0x7ff7a6c64468 in test.Test Colorf32 iterator (zigimgtest.exe.obj)
    while (it.next()) |actual| {
                  ^
C:\Programmation\Zig\zig\stage3\lib\zig\test_runner.zig:79:28: 0x7ff7a6c2165a in main (zigimgtest.exe.obj)
        } else test_fn.func();
                           ^
C:\Programmation\Zig\zig\stage3\lib\zig\std\start.zig:347:41: 0x7ff7a6c21277 in WinStartup (zigimgtest.exe.obj)
    std.debug.maybeEnableSegfaultHandler();

Something is corrupting the color iterator and the test fails. While looking at disassembly I found something weird (copied by hand from VS Code disassembly view)

374:               const expected = expectedColors[i];

lea rcx, [rbp+200h]
lea rdx, [rbp+0B0h]
mov r8d, 80h                  # This is the weird part, why it is trying to copy 128 bytes for a 16 bytes struct?
call memcpy

Contact BaroqueLarouche on zig Discord if you need any assistance with the setup. Thanks :) le

[mlarouche]

I found a workaround but the core of the issue is #12638.

pub fn iterator(self: Image) color.PixelStorageIterator {
    return color.PixelStorageIterator.init(&self.pixels);
}

@sizeof(Image) is 104 bytes

If Image is passed by copy, I am taking a pointer to a temporary value. Before on stage1, Image was passed by *const pointer behind the scene and never caused an issue.

[andrewrk]

Note that the snippet is indeed a bug because while zig is supposed to make choices according to perf, it is technically allowed to pass the arg either way. So passing as *const Image is not only a workaround, but a bug fix in zigimg:

pub fn iterator(self: *const Image) color.PixelStorageIterator {
    return color.PixelStorageIterator.init(&self.pixels);
}