Add -s/--squeeze and --squeeze-limit.

[eth-p]

After some reconsideration towards #762, I decided to try adding support for bat -s.

While I personally think that having the option to squeeze empty lines goes against the Unix philosophy, cat itself has the feature on every distro (and even MacOS). For the sake of maintaining drop-in replacement compatibility, I added support to bat.

Another benefit of including it rather than relying on sed would be to show the correct line numbers in the sidebar.

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This pull request adds:

• bat --squeeze/bat -s
• bat --squeeze-limit=<number> -- to set the maximum number of consecutive empty lines when using -s
• PrettyPrinter::squeeze_empty_lines

[sharkdp]

Thank you for the implementation!

I haven't looked at -s in the past (for drop-in compatibility) because it's not part of the POSIX standard, see https://pubs.opengroup.org/onlinepubs/9699919799/utilities/cat.html (I just now saw the "RATIONALE" section: "The -s option was omitted because it corresponds to different functions in BSD and System V-based systems.").

That said, I am happy to consider adding this to bat. We should definitely add some tests though before merging this.

[sharkdp]

Can we expand this a bit to explain what happens if it is set to None? Also, maybe an example wouldn't hurt? My understanding would be that Some(3) would mean that

1 something
2 like
3 
4 
5 
6 this

would be printed unchanged, while

1 something
2 like
3
4
5
6
7 this

would be squeezed (to one empty line or to three empty lines?).

[eth-p]

To three empty lines.

I had a hard time trying to describe how it worked in only a few comments. The example would definitely be a good idea, thanks!

[eth-p]

I haven't looked at -s in the past (for drop-in compatibility) because it's not part of the POSIX standard, see https://pubs.opengroup.org/onlinepubs/9699919799/utilities/cat.html (I just now saw the "RATIONALE" section: "The -s option was omitted because it corresponds to different functions in BSD and System V-based systems.").

It seems that -s on System V is just for silencing messages. I think it would be safe to implement the BSD/GNU behavior for bat.

Without -s, it would be equally incompatible with System V cat as it would be with the option. We won't really be losing anything from adding it, I think.

That said, I am happy to consider adding this to bat. We should definitely add some tests though before merging this.

Will do.

[sharkdp]

Closing this for now. We can always come back and reopen it later.