toSlice

pub fn toSlice(a: Args, arena: Allocator) ToSliceError![]const [:0]const u8 {
    if (native_os == .windows) {
        var it = try a.iterateAllocator(arena);
        var contents: std.ArrayList(u8) = .empty;
        var slice_list: std.ArrayList(usize) = .empty;
        while (it.next()) |arg| {
            try contents.appendSlice(arena, arg[0 .. arg.len + 1]);
            try slice_list.append(arena, arg.len);
        }
        const contents_slice = contents.items;
        const slice_sizes = slice_list.items;
        const slice_list_bytes = std.math.mul(usize, @sizeOf([]u8), slice_sizes.len) catch return error.OutOfMemory;
        const total_bytes = std.math.add(usize, slice_list_bytes, contents_slice.len) catch return error.OutOfMemory;
        const buf = try arena.alignedAlloc(u8, .of([]u8), total_bytes);
        errdefer arena.free(buf);

        const result_slice_list = std.mem.bytesAsSlice([:0]u8, buf[0..slice_list_bytes]);
        const result_contents = buf[slice_list_bytes..];
        @memcpy(result_contents[0..contents_slice.len], contents_slice);

        var contents_index: usize = 0;
        for (slice_sizes, 0..) |len, i| {
            const new_index = contents_index + len;
            result_slice_list[i] = result_contents[contents_index..new_index :0];
            contents_index = new_index + 1;
        }

        return result_slice_list;
    } else if (native_os == .wasi and !builtin.link_libc) {
        var count: usize = undefined;
        var buf_size: usize = undefined;

        switch (std.os.wasi.args_sizes_get(&count, &buf_size)) {
            .SUCCESS => {},
            else => |err| return std.posix.unexpectedErrno(err),
        }

        if (count == 0) return &.{};

        const argv = try arena.alloc([*:0]u8, count);
        const argv_buf = try arena.alloc(u8, buf_size);

        switch (std.os.wasi.args_get(argv.ptr, argv_buf.ptr)) {
            .SUCCESS => {},
            else => |err| return std.posix.unexpectedErrno(err),
        }

        const args = try arena.alloc([:0]const u8, count);
        for (args, argv) |*dst, src| dst.* = std.mem.sliceTo(src, 0);
        return args;
    } else {
        const args = try arena.alloc([:0]const u8, a.vector.len);
        for (args, a.vector) |*dst, src| dst.* = std.mem.sliceTo(src, 0);
        return args;
    }
}