qwidget.Show(window) seg faults

[le0flo]

os: NixOS 25.11
qt6 version: 6.10.1
libqt6zig commit: 7655ada

I'm using the qtbase package from nixpkgs, and this custom build script, instead of the one from examples

const std = @import("std");

const base_libs = [_][]const u8{
    "Qt6Core",
    "Qt6Gui",
    "Qt6Widgets",
};

const static_libs = [_][]const u8{
    "qapplication",
    "qwidget",
    "qlayout",
    "qboxlayout",
    "qstackedwidget",
    "qlabel",
    "qlineedit",
    "qabstractbutton",
    "qpushbutton",
};

pub fn build(b: *std.Build) void {
    const allocator = b.allocator;

    const target = b.standardTargetOptions(.{});
    const optimize = b.standardOptimizeOption(.{});

    const extra_paths: []const []const u8 = &.{ std.process.getEnvVarOwned(allocator, "QT6_PATH") catch "" };

    // Modules
    const qt6zig = b.dependency("libqt6zig", .{
        .target = target,
        .optimize = optimize,
        .@"extra-paths" = extra_paths,
    });

    const ui_module = b.addModule("ui", .{
        .root_source_file = b.path("src/ui/root.zig"),
    });

    const exe = b.addExecutable(.{
        .name = "navigator",
        .root_module = b.createModule(.{
            .root_source_file = b.path("src/main.zig"),
            .target = target,
            .optimize = optimize,
        }),
    });

    // Imports
    ui_module.addImport("libqt6zig", qt6zig.module("libqt6zig"));

    exe.root_module.addImport("libqt6zig", qt6zig.module("libqt6zig"));
    exe.root_module.addImport("ui", ui_module);

    // Linking
    const sub_paths = [_][]const u8{ "/bin", "/lib", "" };

    for (extra_paths) |path| {
        for (sub_paths) |sub_path| {
            const extra_path = b.fmt("{s}{s}", .{ path, sub_path });

            std.fs.cwd().access(extra_path, .{}) catch {
                continue;
            };

            exe.root_module.addLibraryPath(std.Build.LazyPath{ .cwd_relative = extra_path });
        }
    }

    for (base_libs) |lib| {
        exe.root_module.linkSystemLibrary(lib, .{});
    }

    for (static_libs) |lib| {
        exe.root_module.linkLibrary(qt6zig.artifact(lib));
    }

    // Install
    b.installArtifact(exe);

    // Run step
    const run_step = b.step("run", "Run the app");
    const run_cmd = b.addRunArtifact(exe);

    run_step.dependOn(&run_cmd.step);
    run_cmd.step.dependOn(b.getInstallStep());

    if (b.args) |args| {
        run_cmd.addArgs(args);
    }
}

The application compiles fine, links fine (I checked with ldd to see if the correct libs where linked, and they were), but when I run the program, it segfaults every time on qwidget.Show(). This is the error:

Segmentation fault at address 0x21
???:?:?: 0x7ffff75c1685 in ??? (libQt6Core.so.6)
Unwind information for `libQt6Core.so.6:0x7ffff75c1685` was not available, trace may be incomplete

???:?:?: 0x7ffff2c5e674 in ??? (libQt6XcbQpa.so.6)
???:?:?: 0x7ffff2c5f869 in ??? (libQt6XcbQpa.so.6)
???:?:?: 0x7ffff2c7de55 in ??? (libQt6XcbQpa.so.6)
???:?:?: 0x7ffff2c608fa in ??? (libQt6XcbQpa.so.6)
???:?:?: 0x7ffff6a75765 in ??? (libQt6Gui.so.6)
???:?:?: 0x7ffff60028d2 in ??? (libQt6Widgets.so.6)
???:?:?: 0x7ffff6002fc3 in ??? (libQt6Widgets.so.6)
???:?:?: 0x7ffff60125ca in ??? (libQt6Widgets.so.6)
/home/leo/.cache/zig/p/libqt6zig-6.8.2-OSXtXH2yhhZ-QseoeW8-SWd81AkVQxzWSv7wlIfdx_2k/include/libqwidget.zig:2629:25: 0x117fee1 in Show (libqt6.zig)
        qtc.QWidget_Show(@ptrCast(self));
                        ^
/home/leo/Desktop/leoflo/navigator/src/main.zig:28:17: 0x117cef6 in main (main.zig)
    qwidget.Show(window.widget);
                ^
/nix/store/iyv5lnq9cwlsixg357zv8zcp4pv2q7ml-zig-0.15.2/lib/zig/std/start.zig:627:37: 0x117d591 in main (std.zig)
            const result = root.main() catch |err| {
                                    ^
???:?:?: 0x7ffff7c2a4d7 in ??? (libc.so.6)
???:?:?: 0x7ffff7c2a59a in ??? (libc.so.6)
???:?:?: 0x11bbd34 in ??? (???)

The following is the snippet of code involved:

const argc = std.os.argv.len;
const argv = std.os.argv.ptr;

const app = qapplication.New(argc, argv);
defer qapplication.QDelete(app);

const window = try ui.Window.New(allocator);
defer qwidget.QDelete(window.widget);

qwidget.Show(window.widget);

_ = qapplication.Exec();

I thought the problem was with my nixos developer shell, but I tried downloading the libqt6zig-examples repo, opened my shell from and it compiled and ran without problems.

The problem is probably within the build script, as I cut down everything I thought was unnecessary from the libqt6zig-examples one, but I cant find what's (probably) missing.

The full repo of the project, is here

[rcalixte]

Hi! Thanks for the interest!

The problem is probably within the build script, as I cut down everything I thought was unnecessary from the libqt6zig-examples one, but I cant find what's (probably) missing.

Take a look at the demo for a simpler build system. It was designed for this purpose.

The application compiles fine, links fine (I checked with ldd to see if the correct libs where linked, and they were), but when I run the program, it segfaults every time on qwidget.Show(). This is the error:

The issue is that the Debug build mode is currently not supported. Any of the release options work. Beautiful app so far!

The Debug build mode did work on Zig 0.13 but has regressed since Zig 0.14. I hope to be able to restore it at some point because it was such a great development and debugging experience that I want others to experience too.