Author here. This blog post is the result of my puzzling over how auto-complete works in the shell, and subsequently whether shell completion scripts could be written in Rust. It also introduces a new Rust crate, shell_completion[0], which is a library that exposes some low level primitives for writing shell completion scripts in Rust. shell_completion is certainly in its infancy, so I'd be happy to have contributors of any kind (both code and opinions are welcome).<p>[0]: <a href="https://github.com/joshmcguigan/shell_completion" rel="nofollow">https://github.com/joshmcguigan/shell_completion</a>
That sounds useful. I used to write tons of ZSH scripts when I used to obsessively make my Linux desktop experience nice and automated. Writing custom completions always felt awkward for me and unintuitive (like most ZSH programming).<p>Does your shell_completion library work with ZSH? I'm not familiar with how sh/bash differs here from ZSH but I'd image it'd be easy to make compatible.<p>I'm waiting patiently for Evlish to mature so I can use their Go-like (and Go-powered) scripting language and burn my old ZSH scripts in a fire. <a href="https://github.com/elves/elvish" rel="nofollow">https://github.com/elves/elvish</a>
Seeing this got me curious to know if any work has been done on generating completions for applications that make use of the clap command-line argument parser.<p><a href="https://github.com/clap-rs/clap" rel="nofollow">https://github.com/clap-rs/clap</a><p><a href="https://crates.io/crates/clap" rel="nofollow">https://crates.io/crates/clap</a><p>Among other things I found this currently open issue that has a lot of discussion and information in it:<p><a href="https://github.com/clap-rs/clap/issues/568" rel="nofollow">https://github.com/clap-rs/clap/issues/568</a><p>It might be of interest to you as well, OP?
If I'm understanding correctly, this is a shim that:<p>1) serializes the fields the bash completion API gives you (when you hit TAB)<p>2) exports them to Rust, then<p>3) passes the Rust program's results back to bash?<p>I've been working on similar problems, and I understand why that's appealing. Bash is a pretty bad language to write completion scripts in! It's really bad at string and array processing [1].<p>----<p>Though on a quick glance, if you're exporting $COMP_LINE and $COMP_POINT, then it's making the job of the completion script very hard, since you're passing off the responsibility of parsing shell to it:<p>In other words, if you have something like:<p><pre><code> mycommand --flag arg\ with\ spaces --flag2=<TAB>
</code></pre>
Then it's not desirable to pass the entire string. It would be better to parse it and pass:<p><pre><code> ["mycommand", "--flag", "arg with spaces", "--flag2="] # and indicate index 3 being completed
</code></pre>
Another common case is:<p><pre><code> echo $(dirname <TAB> # I don't need echo $( to complete
</code></pre>
I noticed this deficiency of bash while essentially cloning the bash API for Oil: <a href="https://www.oilshell.org/" rel="nofollow">https://www.oilshell.org/</a><p>One consequence of this is that the bash-completion project (maintained separately from bash) actually has an ad hoc bash parser in bash! This is really bad -- unsurprisingly it has obvious bugs, like not being able to complete inside command subs. An ad hoc bash parser in Rust would also be bad.<p>So instead Oil parses shell for you -- since it has a shell parser! -- and then it gives you the partial argv array. So then the plugin is only responsible for what it can reasonably do.<p>-----<p>Additional, I proposed that this could be made into a protocol that other shells consume. So instead of writing bash completions in Rust, you could write zsh/fish/bash/Oil completions in Rust.<p><a href="https://github.com/oilshell/oil/wiki/Shellac-Protocol-Proposal" rel="nofollow">https://github.com/oilshell/oil/wiki/Shellac-Protocol-Propos...</a><p>A lot of people are already "scraping" bash completions this way, i.e. to use in zsh or their own shells, so it should not be hard to come up with something "standard", given those working examples.<p><a href="https://github.com/oilshell/oil/wiki/Projects-Already-Doing-Something-Like-Shellac" rel="nofollow">https://github.com/oilshell/oil/wiki/Projects-Already-Doing-...</a><p>If you're interested in chatting about it please join <a href="https://oilshell.zulipchat.com/" rel="nofollow">https://oilshell.zulipchat.com/</a> .<p>I wouldn't say it's the #1 priority now because Oil already emulates bash quite well, but I think a bunch of people are motivated because they 1) don't want to write completions N times, for every shell and 2) Don't want to write completions in the bash language.<p>home page: main page: <a href="https://github.com/oilshell/oil/wiki/Shell-Autocompletion" rel="nofollow">https://github.com/oilshell/oil/wiki/Shell-Autocompletion</a><p>IMO it makes sense to write completions in whatever language the command line tool / flag parser is written in.<p>[1] <a href="https://www.oilshell.org/blog/2016/11/06.html" rel="nofollow">https://www.oilshell.org/blog/2016/11/06.html</a>
I did this <a href="https://github.com/xliiv/fui" rel="nofollow">https://github.com/xliiv/fui</a>
This is something different, but maybe someone could say it's sort of "completions"?
Fui also has a feature which allow to copy/dump a whole form (ctrl-k) string which can be pasted to bash.