Hi Katie,

Kate Deplaix <kit-ty-kate@outlook.com> writes:

> With diffutils 3.10, "diff -Naur a b" returns:
>
> diff -Naur a/test b/test
> --- a/test   2025-02-20 14:50:07.870258052 +0000
> +++ b/test   2025-02-20 14:50:18.957287641 +0000
> @@ -0,0 +1 @@
> +content
>
> but with diffutils 3.11, the same command returns:
>
> File a/test is a regular empty file while file b/test is a regular file

Good catch.

CC'ing Paul Eggert since I think that I found the cause and it appears
unintentional to me.

Commit e016d12581ac4ea6be1ded88279527ceface74e1 has the following
ChangeLog:

    diff: improve symlink handling, avoiding a race
    [...]
    (compare_prepped_files): Use filetype and stat macros, not detype.
    [...]

Where filetype refers to a constant string returned by Gnulib's
c_file_type function. The relevant lines are here:

  if (S_ISREG (st->st_mode))
    return st->st_size == 0 ? N_("regular empty file") : N_("regular file");

So empty files will be treated as different file types because of that
change.

I have attached a patch to check for this condition.

Collin