formatJoin

fn formatJoin(paths: []const []const u8, w: *std.Io.Writer) std.Io.Writer.Error!void {
    const first_path_idx = for (paths, 0..) |p, idx| {
        if (p.len != 0) break idx;
    } else return;

    try w.writeAll(paths[first_path_idx]); // first component
    var prev_path = paths[first_path_idx];
    for (paths[first_path_idx + 1 ..]) |this_path| {
        if (this_path.len == 0) continue; // skip empty components
        const prev_sep = isSep(prev_path[prev_path.len - 1]);
        const this_sep = isSep(this_path[0]);
        if (!prev_sep and !this_sep) {
            try w.writeByte(sep);
        }
        if (prev_sep and this_sep) {
            try w.writeAll(this_path[1..]); // skip redundant separator
        } else {
            try w.writeAll(this_path);
        }
        prev_path = this_path;
    }
}