Alias that returns modified command

[anki-code]

Motivation

After deep dive into How make sudo expand aliases? I understood that we want to modify command before execution but we can't achieve this because all we can is to use callable alias to wrap the command into it. But callable alias is a complex "process wrapper" and using it with subprocess operators has requirements on managing threading, capturing and std manually. Implementing this is high bar for inexperienced users who just want to play with command itself.

Thus we need the way between simple string aliases and callable aliases. I implemented this way as "Alias that returns modified command".

Before

No way to create alias that returns modified command before execution.

After

@aliases.register('xsudo')
@aliases.return_command
def _xsudo(args):
    return ['sudo', '--', *aliases.eval_alias(args), aliases.CUT_ARGS]

aliases['cow'] = 'echo mooo'  

xsudo cow tooo
# Password:
# mooo tooo

xsudo cow tooo | grep m
# mooo tooo

Tag CUT_ARGS is additional tag to have an ability to rid from the tail of arguments. It's needed sometimes in other aliases too (#5452).

Closes #2618 #2893

Notes

• It's uncomfortable work with aliases object when we have dict aliases for Windows in tests. We need to change it some day: Refactoring: aliases #5452

For community

⬇️ Please click the 👍 reaction instead of leaving a +1 or 👍 comment

[anki-code]

Hey @bennyyip! I moved your comment to the sudo thread with proposal to make a xontrib. Thank you for sharing this!
As you can read first message of this PR the motivation to add "return cmd alias" is more bigger than just solve sudo case. We need a way to modify command before execution and without proxies and wrappers.

[anki-code]

I've changed api to more clear and putted CUT_ARGS to aliases to avoid remembering by jnoortheen ;)
@gforsyth It's ready to review ;)

[anki-code]

@gforsyth here is the new issue where in fact people want to use commands without wrapping it into the callable alias to avoid capturing/tty issues - #5512 (comment) but now they need to wrap it into the callable alias and facing with questions about managing the TTY.

[anki-code]

@gforsyth here is another one issue where user tries to generate command using python subprocess and have fail with management std - #4792