feat: add multiline editing in the REPL

[Snehil-Shah]

Resolves #2060

Description

What is the purpose of this pull request?

This pull request:

• adds support for manually adding a newline using CTRL+O keybinding.
• adds support for navigating through lines using arrow keys.
• adds support for continuous backspaces.

Related Issues

Does this pull request have any related issues?

This pull request:

• resolves [RFC]: add support for multi-line editing to the REPL #2060

Questions

Any questions for reviewers of this pull request?

Testing strategy?

Other

Any other information relevant to this pull request? This may include screenshots, references, and/or implementation notes.

I wanted to clarify a mistake in the original RFC and that hitting the up arrow auto-completes the previous commands only if the line is empty. After this PR, this behavior is preserved. Only when you have an empty input, the up arrow completions will work.

I will add the ability to cycle through multiline commands using the up arrow, in a separate PR.

Checklist

Please ensure the following tasks are completed before submitting this pull request.

• Read, understood, and followed the contributing guidelines.

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@stdlib-js/reviewers

[kgryte]

@Snehil-Shah After pulling this down and playing with things, I was able to get the REPL into a state where I was stuck in multi-line edit mode and the command cache was not being cleared. Even after executing subsequent commands, anytime I hit enter from a new command prompt, rather than execute an empty statement, the REPL would re-enter multi-line mode. Looks like some edge cases are not being fully handled.

[kgryte]

Also, when I did the following

In [1]: {<|>}

and hit Ctrl+E, the REPL did not break the line at the cursor. Instead, it did

In [1]: {}
<|>

which is not what is typically desired..

[Snehil-Shah]

@kgryte I think I found out what's really going on. So, the thing is, I have been testing this out with CTRL+O combination all this time because apparently CTRL+E was clashing with my editor's internal keybinding (yes I got lazy there in changing my editor preferences, I apologize). I now tried CTRL+E. Apparently, in node's readline, CTRL+E has a default keypress action of "to end of line". So everytime we do ctrl+e, we go to the end of the line and then we enter multiline editing. That's the reason your curly braces example is doing what it's doing.
I suggest we change to CTRL+O as the keybinding. Or move CTRL+E check to beforeKeypress handler and overwrite default behaviour. Again, so sorry for the oversight.

rather than execute an empty statement, the REPL would re-enter multi-line mode. Looks like some edge cases are not being fully handled.

That was intentional and not a problem with the cache. I thought empty statements don't mean anything so it would be better to assume they are trying to type more, maybe to have equal indentation by starting from below the prompt and they can always use backspace to go back.

In [1]: 
function a(){
// ...
}

I'll change it if it's not desired or correct.

[kgryte]

Re: keybinding. Ctrl-O is fine.

Re: empty statements. I found the updated behavior surprising. My feeling is that we should treat statements (including empty statements) consistently. Meaning,

In [1]: <|>

and

In [1]: a<|>

should behave consistently when hitting ENTER.

And to enter multi-line mode in both instances, one needs to use the Ctrl-O keybinding. Special casing empty statements doesn't seem like enough of a win to be worth the inconsistency.

[Snehil-Shah]

@kgryte done.

[kgryte]

LGTM. I pulled down locally and tested out. Seems to work as stated.

As stated in the OP, we'll want to figure out the previous command/history issue. And moving from processLine to a dedicated multi-line handler class significantly increases complexity, requiring fairly tight coupling between various components. This class is a good candidate for a future refactor in order to disentangle logic. For now, however, I'm fine with punting this to another day.

Thanks for working on this, @Snehil-Shah!