Consider switch to reedline crate

[bartlomieju]

Currently we use rustyline crate for the REPL. However there are shortcomings in that crate, mainly it gives us no control over "external prints".

If you have code like:

setInterval(() => {
  console.log("foo");
}, 1000);

Its output gonna be interleaved with prompt:

❯ deno
Deno 1.17.0
exit using ctrl+d or close()
> setInterval(() => console.log("foo"), 1000);
1
> barfoo
foo
foo

Uncaught ReferenceError: bar is not defined
    at <anonymous>:2:1
> foo
> bafoo
> barfoo
> barafoo
foo
foo
foo

Ideally the output would go into line above the prompt line.

https://docs.rs/reedline has all the necessary APIs to fit our purposes and seems to be more battle tested (it's the base for nushell.sh)

This switch would allow us to address: https://github.com/denoland/deno/issues/8049

CC @dsherret

[sophiajt]

Hi all - JT from the Nushell project.

Thanks for looking into reedline. I wanted to share a bit of "full disclosure" for reedline, as you're making your decision. Nushell currently, like deno, uses rustyline. We started up reedline, hopeful that it'd be a good replacement for rustyline for us. Currently, reedline is getting close (we're using it in our upcoming nushell engine rewrite to test it out), but there are a few gaps between it and reedline.

• rustyline currently is a bit more "battle-tested" as nushell isn't yet using reedline as its main line editor
• reedline has a few usability issues we're working on fixing around handling wrapping, multiline editing, and around rendering input and hints at the bottom of the terminal (compared to rustyline)
• that said, reedline should be pretty hack-able, as we wrote it with contributions in mind and welcome improvements

We've got a channel on the Nushell discord called #external-collab which is a great place to jump in and brainstorm with the Nushell and reedline folks about possible changes to reedline. We'd love to chat.

[bartlomieju]

Hi @jntrnr, thanks for reaching out!

We did some preliminary tests with reedline (CC @crowlKats) and found a major blocker at the moment, is that Reedline struct is neither Sync nor Send. In the REPL we're running the editor on a separate thread (becuase the editor interface is sync) and we use channels for completions (because Deno's LSP and executing code in V8 is an async operation).

I think we'll wait until engine-q and reedline are incorporated into main branch of nushell and get released before making the switch. That said, I'm a huge fan of both nushell and API for reedline and this is definitely something I want to explore in Q1 of 2022. I'll reach out on Discord for further conversation.

[sophiajt]

@bartlomieju - out of curiosity, which direction did you go for line editing?

[bartlomieju]

Hey @jntrnr, due to limited bandwidth we are sticking with rustyline for now, but we might revisit the topic in the future.