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repl: add syntax highlighting, auto-indentation, and signature hints#64443

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hemanth:repl/experimental-enhancements
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repl: add syntax highlighting, auto-indentation, and signature hints#64443
hemanth wants to merge 1 commit into
nodejs:mainfrom
hemanth:repl/experimental-enhancements

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@hemanth

@hemanth hemanth commented Jul 12, 2026 •
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Description

Add REPL enhancements enabled by default:

1. Inline Syntax Highlighting

Uses the Acorn tokenizer (already in deps/) to colorize JavaScript input in real-time:

  • Keywords (const, function, if, etc.) → Magenta
  • Strings → Green
  • Numbers → Yellow
  • Booleans/null/undefined → Yellow
  • Regular expressions → Red
  • Comments → Gray

Highlighting is applied at display time only — repl.line remains plain text, so cursor positioning and evaluation are unaffected.

2. Auto-Indentation

Automatically inserts 2-space indentation on continuation lines based on brace/bracket/paren depth when entering multiline input.

3. Function Signature Hints

When the user types functionName(, the function's parameter list is displayed as a dimmed hint below the input line. Uses the V8 Inspector protocol with throwOnSideEffect: true for safety.

Usage

These features are enabled by default when useColors and terminal are true. Individual features can be controlled via repl.start() options (e.g., syntaxHighlighting: false).

Motivation

This addresses the feature requests from #48164, which was closed as not planned. These are quality-of-life improvements that bring the Node.js REPL closer to modern shell experiences (Python's IPython, Ruby's Pry, etc.).

Refs: #48164

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nodejs-github-bot commented Jul 12, 2026

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Review requested:

  • @nodejs/config

@nodejs-github-bot nodejs-github-bot added c++ Issues and PRs that require attention from people who are familiar with C++. lib / src Issues and PRs related to general changes in the lib or src directory. needs-ci PRs that need a full CI run. labels Jul 12, 2026
@hemanth
hemanth force-pushed the repl/experimental-enhancements branch 4 times, most recently from 30413de to 14baff1 Compare July 12, 2026 07:02
@codecov

codecov Bot commented Jul 12, 2026 •
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Codecov Report

❌ Patch coverage is 73.65269% with 132 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.20%. Comparing base (14166a5) to head (eec5763).
⚠️ Report is 21 commits behind head on main.

Files with missing lines Patch % Lines
lib/internal/repl/utils.js 70.79% 131 Missing and 1 partial ⚠️
Additional details and impacted files 
@@            Coverage Diff             @@
##             main   #64443      +/-   ##
==========================================
- Coverage   90.23%   90.20%   -0.03%     
==========================================
  Files         741      741              
  Lines      241375   242165     +790     
  Branches    45483    45628     +145     
==========================================
+ Hits       217800   218454     +654     
- Misses      15129    15247     +118     
- Partials     8446     8464      +18
Files with missing lines Coverage Δ
lib/repl.js 94.19% <100.00%> (+0.18%) ⬆️
src/node_options.cc 76.65% <100.00%> (-0.08%) ⬇️
src/node_options.h 98.02% <100.00%> (+<0.01%) ⬆️
lib/internal/repl/utils.js 87.56% <70.79%> (-8.83%) ⬇️

... and 56 files with indirect coverage changes

🚀 New features to boost your workflow:
  • ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
  • 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

@hemanth
hemanth force-pushed the repl/experimental-enhancements branch 2 times, most recently from 16ee02c to b749718 Compare July 12, 2026 20:37
avivkeller
avivkeller requested changes Jul 12, 2026
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can these be idiomatic PRs?

@hemanth

hemanth commented Jul 12, 2026

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@avivkeller for sure! having some challenges on my local machine, so depending on the GH CI to report me the build time errors.

@hemanth
hemanth force-pushed the repl/experimental-enhancements branch 2 times, most recently from 1e7bcec to 088a905 Compare July 13, 2026 00:01
@hemanth
hemanth requested a review from avivkeller July 13, 2026 02:34
@edsadr

edsadr commented Jul 13, 2026

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this one has been in my list forever; I thik this should dogfood util.styleText and make use of everything about coloring already existing in core

@hemanth

hemanth commented Jul 13, 2026

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Agree. util.styleText reminded me of #43371

@hemanth
hemanth force-pushed the repl/experimental-enhancements branch from 088a905 to eec5763 Compare July 13, 2026 17:38
@hemanth hemanth mentioned this pull request Jul 13, 2026
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RafaelGSS
RafaelGSS reviewed Jul 14, 2026
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@avivkeller

avivkeller commented Jul 14, 2026

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Also note that #64034 makes some behind-the-scenes improvements as well, and may conflict with these idiomatic PRs code-wise

@hemanth
hemanth force-pushed the repl/experimental-enhancements branch 2 times, most recently from ea23882 to 192fcb1 Compare July 18, 2026 20:57
@hemanth
repl: add syntax highlighting, auto-indentation, and signature hints
a7bf2be 
Signed-off-by: hemanth <hemanth.hm@gmail.com>
@hemanth
hemanth force-pushed the repl/experimental-enhancements branch from 192fcb1 to a7bf2be Compare July 18, 2026 21:10
@hemanth

hemanth commented Jul 18, 2026

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Rebased on main, removed the --experimental-repl-enhancements flag — features are now on by default.

Highlighting, auto-indent, and signature hints are all display-only (repl.line stays plain text), so they are safe to ship ungated. Each can still be disabled via repl.start() options or TERM=dumb.

Adapted to the new getReplInspector API and the refactored line queue from recent main changes.

cc @avivkeller @RafaelGSS @edsadr

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@hemanth @nodejs-github-bot @edsadr @avivkeller @RafaelGSS