exportFn fails during semantic analysis

[galli-miro]

I've tried to build a simple shared module using the exportFn in a comptime block. Using zig version v0.11.0-dev.1638+7199d7c77 it fails with the following error:

/home/galli/repos/git.sr.ht/~hubidubi/river-lua/zig/lib/ziglua/src/ziglua-5.4/lib.zig:2021:13: error: TODO implement exporting arbitrary Value objects
    @export(declaration, .{ .name = "luaopen_" ++ name, .linkage = .Strong });

Since there is a TODO, I'm assuming this will be fixed at some point. But git blame tells me this TODO has been there for over 2 years, so who knows when that will happen.

build.zig:

const std = @import("std");
const ziglua = @import("lib/ziglua/build.zig");

pub fn build(b: *std.Build) void {
    // Standard release options allow the person running `zig build` to select
    // between Debug, ReleaseSafe, ReleaseFast, and ReleaseSmall.
    const target = b.standardTargetOptions(.{});
    const optimize = b.standardOptimizeOption(.{});

    const lib = b.addSharedLibrary(.{
        .name = "test",
        .root_source_file = .{ .path = "src/main.zig" },
        .target = target,
        .optimize = optimize,
    });
    lib.addModule("ziglua", ziglua.compileAndCreateModule(b, lib, .{ .shared = true }));
    lib.install();
}

main.zig:

const std = @import("std");
const ziglua = @import("ziglua");

usingnamespace ziglua;

fn hello(lua: *ziglua.Lua) i32 {
    _ = lua;
    std.debug.print("hello world\n", .{});
    return 1;
}

fn module(lua: *ziglua.Lua) i32 {
    var fns = [_]ziglua.FnReg{ .{ .name = "hello", .func = ziglua.wrap(hello) }, .{ .name = "", .func = null } };
    lua.newLib(fns[0..]);
    return 1;
}

comptime {
    ziglua.exportFn("hello", module);
}

My current fix is to do the exporting and wrapping by hand, but maybe I'm missing something:

export fn luaopen_module(L: *ziglua.LuaState) callconv(.C) c_int {
    var fns = [_]ziglua.FnReg{ .{ .name = "hello", .func = ziglua.wrap(hello) }, .{ .name = "", .func = null } };

    var lua = ziglua.Lua{ .state = L };
    lua.newLib(fns[0..]);

    return 1;
}

[natecraddock]

Hi! Thanks for reporting. I'll look into this later today. I haven't tested exportFn() with the newest version of Zig, and it has always been a bit messy.

[natecraddock]

I looked into this a bit more. This is indeed an issue with Zig. I might try fixing this in Zig (sounds like a small but fun challenge!)

Until then, your solution is the best way. I'll be sure to document this better.

Also, because this is Zig and we can know the size of arrays passed into functions, no need to end the FnReg array with a sentinel .{ .name = "", .func = null }.

[galli-miro]

Thanks for having a closer look and also for the tip with the array :)

[hryx]

There is now a work-in-progress PR that should address this: ziglang/zig#14796

[natecraddock]

The Zig MR is now merged, so I'll look into this in the next couple days

[natecraddock]

It looks like the PR only partially fixed this. There is no longer a semantic analysis error, and the code compiles. But the symbol is not found in the output object. I'll look again at this later

[natecraddock]

I found another Zig / Lua bindings project that seems to have solved this. Linking here to check on it later: https://github.com/truemedian/lunaro