Improve error message description when trying to compress a folder with a multiple single file formats

[marcospb19]

Version

e377dd3 (latest)

Description

Ouch is not giving a correct error message when trying to compress a folder with multiple single formats:

$ ouch compress linux.pkg linux.xz.gz.zst

Current Behavior

thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', src/commands/mod.rs:102:49
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Expected Behavior

Something like this, when we just pass ".xz".

$ ouch compress linux-5.17.5.arch1-1-x86_64.pkg linux.xz
[ERROR] Cannot compress to 'linux.xz'.
 - You are trying to compress multiple files.
 - The compression format 'xz' cannot receive multiple files.
 - The only supported formats that archive files into an archive are .tar and .zip.

hint: Try inserting '.tar' or '.zip' before 'xz'.
hint: From: linux.xz
hint: To:   linux.tar.xz

Additional Information

It would be beneficial, while solving this, to write integration tests that check what is the output given.

[marcospb19]

This is still not working properly:

ouch c empty-folder/ a.gz
[ERROR] failed to read from file `/home/marcospb19/ouch/empty-folder`

I think I have detected where the problem is tho.