Allow users of picocli-shell-jline3 to use clear command and a nicer help command

[sualeh]

Allow users of picocli-shell-jline3 to use clear command and a nicer help command.

• The clear screen command is provided out of the box by jline2, and similarly should be built into picocli.shell.jline3.PicocliCommands. This change allows users of PicocliCommands to include a clear screen command with a single line: picocliCommands.includeClearScreenCommand(reader); - see the example.
• The help command is provided by jline3 by default, but picocli help is much nicer. This change allows users of PicocliCommands to override the jline3 help command with a single line: systemRegistry.register("help", picocliCommands); - see the example.

[sualeh]

@remkop - any thoughts on this?

[remkop]

@sualeh I finally had time to look at this in more detail.

I have an idea for keeping things more declarative, can you take a look and let me know your thoughts?

[codecov-io]

Codecov Report

Merging #1265 (c026772) into master (e5033e1) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #1265   +/-   ##
=========================================
  Coverage     93.82%   93.82%           
  Complexity      462      462           
=========================================
  Files             2        2           
  Lines          6852     6852           
  Branches       1842     1842           
=========================================
  Hits           6429     6429           
  Misses          138      138           
  Partials        285      285           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update e5033e1...a0db671. Read the comment docs.

[sualeh]

@remkop - thanks for the last snippet. I think I have finally understood (sorry for being dense), and pushed what I think are the final changes. Please take a look. Thanks.

[remkop]

Great! Let me check when I get to my PC.

[remkop]

Thank you for the changes, @sualeh, this looks pretty good now!

For finishing touches, can you add some javadoc?
Also I believe the factory and the clear-screen subcommand should require a LineReaderImpl; this is not great, but we cannot call clearScreen on any LineReader. This is also something we should probably raise with the JLine maintainers: they should consider adding the clearScreen method to the LineReader interface.

[sualeh]

@remkop - I have made the clean-up changes you suggested.

• I want to remove workDir from PicocliCommands. Please let me know if you need a separate pull request for that, or if I can include it in the same PR.
• I will test the suggestion in Expose clearScreen on LineReader jline/jline3#610 and see if that works - then we can go back to using LineReader

[remkop]

I'm fine with removing workDir (thanks! :-)), no need for a separate pull request.

Happy to use the LineReader interface if possible, let me know how it goes.

[sualeh]

@remkop - I think we are done. I have removed workDir, and the clear screen is not working - see my comments on jline/jline3#610

[remkop]

This looks good, thank you!

I will merge this soon.
This will be included in the upcoming picocli 4.6 release.

Thank you again for the contribution!

[remkop]

Ah very nice!
Using a public API like Terminal is a lot nicer than having to use internal API like LineReaderImpl.
Thanks for following up!

[remkop]

Merged.
Thank you again for the contribution!