tsort: show error if directory is specified

[cakebaker]

GNU tsort shows an error if a directory is specified and returns 1 as exit code:

$ tsort dir
tsort: dir: read error: Is a directory
$ echo $?
1

uutils tsort, on the other hand, doesn't fail:

$ cargo run tsort dir
$ echo $?
0

[mtimaN]

I cannot replicate this.

$ which tsort 
/usr/bin/tsort
$ tsort dir
$ echo $?
0

[SaHHiiLL]

I cannot replicate this.

$ which tsort 
/usr/bin/tsort
$ tsort dir
$ echo $?
0

I can replicate this.

$ tsort $HOME/Downloads
tsort: Downloads: read error: Is a directory

Version

$ tsort --version
tsort (GNU coreutils) 9.4
Copyright (C) 2023 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by Mark Kettenis.

[SaHHiiLL]

This seems like a simple fix I can create a pr, path.is_dir() check and early return should fix and give the expected behavior.