Apply "Parsing With Derivatives" incremental parsing to Bash tab completion

[harveywi]

Overview

This PR adapts the Parsing With Derivatives (PwD) functional pearl to the problem of CLI tab completion. Currently, this is only supported for Bash tab completion, but it should be possible to use this routine for tab completion with other shells.

PwD for Incremental Parsing

For any zio.cli.Command instance, there is a corresponding regular language that contains all of the instance's valid sequences of command line arguments. We first build a data structure that represents this regular language, then use the PwD algorithm to incrementally update this data structure as a kind of incremental parsing.

As we process each user-provided command line argument from left to right, the PwD algorithm gives us a "residual language" that represents all of the valid arguments that can be provided to the right of the current argument. So all we have to do is calculate the residual language for everything to the left of the CLI cursor position, then return a list of all of the residual language's first tokens that share a prefix with the token at the cursor position.

Notes on Latency

Since the Bash complete machinery will call your binary to calculate tab completions, and satisfactory experience with tab completion requires low latency, we highly recommend building your binary using graalvm native-image --no-fallback.

[jdegoes]

@harveywi Can you bring this up to date so we can merge?

[harveywi]

@harveywi Can you bring this up to date so we can merge?

Yes - I'll set some time aside this weekend, or early next week if needed. I think there's just a merge conflict that (hopefully) won't be too challenging to resolve.

[harveywi]

@jdegoes I am almost done refreshing this PR - there was considerable code churn and I went on a side quest to upgrade zio-nio to use ZIO 2.0.0-RC3. The good news is that all the tests pass and the tab completion works as expected 🎉.

To speed things along, I may see if I can just mimic the one or two methods from zio-nio and pop them directly in this PR - I think they're only used in the unit tests anyways. I should be able to wrap this up soon.

[jdegoes]

Thanks for the update!

[harveywi]

Ok - I think that should do it. 🤷

[jdegoes]

Looks great! Can you resolve conflicts?

[harveywi]

Looks great! Can you resolve conflicts?

Did I miss some conflicts? I had rebased this PR off of the latest (as of now) master branch, and GitHub seems to think the PR has no merge conflicts ("This branch has no conflicts with the base branch").

[jdegoes]

Sorry must have been a stale browser window. Looks great, and all merged in! 💪