repl: Customizable subprompt for multiline input

[pckrishnadas88]

Description:
This PR adds the ability to customise the REPL subprompt for multiline input. Previously, the REPL always used the fixed | prompt for multiline statements. With this change, the subprompt can be customised. Once feature finalised doc can be updated.

Feature: Customisable subprompt for multiline input.
Fixes : #59401

// custom-repl-subprompt.js
'use strict';
const repl = require('repl').start({ prompt: '> ' });

// Default behavior
// > const foo = {
// | bar: 42,
// | baz: 100
// | }
// > foo
// { bar: 42, baz: 100 }

// Set a custom multiline prompt
repl.setMultilinePrompt('... ');

// Example with custom prompt
// > const obj = {
// ... x: 1,
// ... y: 2
// ... }
// > obj
// { x: 1, y: 2 }

// Set an emoji as multiline prompt (UTF-8)
repl.setMultilinePrompt('😎 ');

// Example with emoji prompt
// > const emojiObj = {
// 😎 mood: 'happy',
// 😎 energy: 'high'
// 😎 }
// > emojiObj
// { mood: 'happy', energy: 'high' }

[codecov]

Codecov Report

❌ Patch coverage is 84.84848% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.93%. Comparing base (4612c79) to head (02f1d5e).

Files with missing lines	Patch %	Lines
lib/internal/readline/interface.js	69.23%	4 Missing ⚠️
lib/repl.js	95.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #59566      +/-   ##
==========================================
- Coverage   88.25%   87.93%   -0.33%     
==========================================
  Files         703      703              
  Lines      207412   207433      +21     
  Branches    39893    39707     -186     
==========================================
- Hits       183052   182404     -648     
- Misses      16313    16987     +674     
+ Partials     8047     8042       -5     

Files with missing lines	Coverage Δ
lib/repl.js	86.95% <95.00%> (-7.32%)	⬇️
lib/internal/readline/interface.js	93.30% <69.23%> (-4.03%)	⬇️

... and 45 files with indirect coverage changes

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[BridgeAR]

Thanks for opening the PR. I think we should not add anything to readline, but we could add the option.

I also wonder if we just want to set that option to '| ' when we start the internal REPL and not do that for any other REPL instances. That way we would have the default behavior that we want and unbreak external REPLs, while still allowing them to opt-in to the other behavior, when appropriate.

[BridgeAR]

This is adding these methods to the readline interface, while we currently only use this in the REPL. I don't think we should regularly expose this API.

Since we already have the symbol anyway, I think we can just use those and directly set the symbol and remove this getter and setter.

[BridgeAR]

I believe this option is currently not used at all? I do think it would in fact be nicer if we used the repl options for defining the value. So we should probably do that?

[pckrishnadas88]

Hi I'm currently down with fever please give me a day or two. Usually where we discuss and finalize the requirements? I will make the changes soon.

[BridgeAR]

Get well soon! 🫖
Discussing things in the PR is fine.

[BridgeAR]

@pckrishnadas88 I hope you feel better again! Would you mind having another look? :)

[pckrishnadas88]

Sure will try to update it as soon as possible. Will ping you while coding in case I have questions.

[pckrishnadas88]

@BridgeAR I’ve updated the PR. My branch was behind main by over 200 commits due to a 2–3 week gap, and I got a bit lost on this issue. Could you please review the code and confirm if this aligns with your recommendations? Some tests are still failing, likely because I’m not entirely sure the rebase was completed correctly after encountering conflicts.