document how to use powershell and elvish completions

[jyn514]

i added support for these in #2945 but wasn't able to figure out how to actually use them in the respective shells. it would be nice to document how to do that; i don't use these shells so i don't know.

Invoke-Expression looks like the right thing for powershell, but when i try Invoke-Expression [String]$(cargo r -- util completion powershell) it complains that it doesn't like the using token. i'm not sure if that's specific to powershell on windows or something like that?

elvish i couldn't get working at all, it complained about invalid syntax. i think ubuntu might package an ancient version or something like that.

Originally posted by @jyn514 in https://github.com/martinvonz/jj/pull/2945#discussion_r1477437430

[martinvonz]

For elvish, maybe you ran into https://github.com/clap-rs/clap/issues/4265? (Oh, look, I filed that issue. I have no memory of that.)

[c00t]

Current Version

• jj 0.14.0-8e4d1af98eccf1ed8a79a7ddf9500467aa7684f5
• PowerShell 7.4.1

On powershell, only the . operator can be used (instead of Invoke-Expression), but I believe there are some encoding issue with the current implementation, here is my current profile file:

# jj completion
$jjc = [ScriptBlock]::Create([system.String]::Join("`n",$(jj util completion powershell).split("`n")))
# can't do this
# $jjc = [ScriptBlock]::Create($(jj util completion powershell))
. $jjc

I can't create a ScriptBlock just from $(jj util completion powershell).

But writing the script to a file and then using the . operator is fine:

jj util completion powershell > jjc.ps1
. .\jjc.ps1

This could be a clap issue as well?

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Update

Aha! That problem has been solved by clap. (found by jj user actually)