Multiple line addition with comments

[xTachyon]

fn f() {
    const S: usize = 4 + // id
1 + // direction
5; // something
}

I've been trying to explain where my constant comes from with comments, but that seems to break the way this is formatted. I was expecting something more like what clang format does:

void f() {
    constexpr auto S = 4 + // id
                       1 + // direction
                       5;  // something
}

I see now that there's the following error printed when I ask for it, but I don't feel like it's justified. I just want some alignment for the expressions to look a little nicer. I realize that I can put the comment on the next line, but it felt more informative and less easy to forget to update the way I did it.

error[internal]: not formatted because a comment would be lost
 --> \\?\D:\repos\dune\x.rs:2
  |
2 |     const S: usize = 4 + // id
  |
  = note: set `error_on_unformatted = false` to suppress the warning against comments or string literals

[ytmimi]

Thanks for reaching out, but going to close this as a duplicate of #3591 and #3167. The issue is that we don't handle comments in binary expressions. rustfmt wants to rewrite your code as const S: usize = 4 + 1 + 5;, but doing so would remove the comment and therefore rustfmt leaves the code unformatted.