repl: don't use deprecated `domain` module #55204

avivkeller · 2024-10-01T00:26:55Z

This PR refactors the REPL module by eliminating the deprecated node:domain module. It replaces its functionality with a modern approach using a try/catch block and process listener.

Why?

The domain module has been deprecated for a while, and its use is discouraged. Despite this, Node.js still relies on it in a key component: the REPL. To lead by example and promote best practices, this PR updates the REPL module to use more up-to-date error-handling mechanisms, completely removing reliance on the deprecated domain module.

Additionally, this update simplifies the REPL's code and results in a slight performance improvement—though the gains are give-or-take a few ticks and may not be noticeable.

Breaking Changes

This PR is marked as semver-major PRs that contain breaking changes and should be released in the next major version. because it introduces functional changes to the REPL:

Removal of options.domain: This undocumented feature is removed (without a formal deprecation cycle, given the domain module itself is deprecated, and the feature was never documented nor tested).
Removal of ERR_INVALID_REPL_INPUT: This error is no longer needed, as after this change, there are no restricted inputs.

This PR is also marked needs-citgm PRs that need a CITGM CI run. in case any of the above cause breakages.

CC @nodejs/repl
CC @nodejs/tsc due to semver-major PRs that contain breaking changes and should be released in the next major version.

doc/api/repl.md

lib/repl.js

test/parallel/test-repl-save-load.js

test/parallel/test-repl-tab-complete-nested-repls.js

test/parallel/test-repl-tab.js

test/parallel/test-repl-top-level-await.js

codecov · 2024-10-01T01:53:51Z

Codecov Report

Attention: Patch coverage is 92.94118% with 6 lines in your changes missing coverage. Please review.

Project coverage is 88.42%. Comparing base (fa8f149) to head (b0d6991).
Report is 229 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/repl.js	92.94%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main   #55204    +/-   ##
========================================
  Coverage   88.41%   88.42%            
========================================
  Files         652      654     +2     
  Lines      186918   187688   +770     
  Branches    36072    36126    +54     
========================================
+ Hits       165270   165956   +686     
- Misses      14891    14963    +72     
- Partials     6757     6769    +12

Files with missing lines	Coverage Δ
lib/internal/errors.js	`96.99% <ø> (-0.01%)`	⬇️
lib/repl.js	`94.72% <92.94%> (-0.25%)`	⬇️

... and 139 files with indirect coverage changes

---- 🚨 Try these New Features:

Flaky Tests Detection - Detect and resolve failed and flaky tests
JS Bundle Analysis - Avoid shipping oversized bundles

doc/api/errors.md

lib/repl.js

mcollina

I have a rough feeling that you'd need to add
a FinalizationRegistry to clear up any instances

test/parallel/test-repl-uncaught-exception-async.js

lib/repl.js

avivkeller · 2024-10-07T21:13:27Z

I have a rough feeling that you'd need to add a FinalizationRegistry to clear up any instances

Why? Is unsetting the callback on close() not enough?

lib/repl.js

mcollina

lgtm

I'm convinced.

nodejs-github-bot · 2024-10-26T10:56:34Z

CI: https://ci.nodejs.org/job/node-test-pull-request/63292/

aduh95 · 2024-11-03T11:11:38Z

Can someone start a CITGM if they thinks it's necessary. IMO we can use the most recent main branch CITGM for comparison

I doubt we have any package on CITGM that use repl, do we?

avivkeller · 2024-11-04T20:10:52Z

Got it! I've removed the label. IIRC semver-major PRs need two TSC approvals to land, would you mind reviewing?

nodejs-github-bot · 2024-11-10T20:10:36Z

CI: https://ci.nodejs.org/job/node-test-pull-request/63504/

nodejs-github-bot · 2024-11-12T17:42:45Z

CI: https://ci.nodejs.org/job/node-test-pull-request/63530/

mcollina · 2024-11-18T18:50:29Z

@nodejs/tsc add it to the agenda for visibility.

addaleax · 2024-11-18T19:50:33Z

doc/api/repl.md

-
-* Uncaught exceptions only emit the [`'uncaughtException'`][] event in the
-  standalone REPL. Adding a listener for this event in a REPL within
-  another Node.js program results in [`ERR_INVALID_REPL_INPUT`][].


I'd replace this section with one that describes the new behavior and amend the changes: YAML entry instead of dropping it (since the new behavior is definitely one that doesn't matter to some users but will have a significant negative impact on users who rely on it)

I don't think a specific section is needed, IMO there's nothing to document. it adds a listener to the process object, what negative impact does that have?

@redyetidev Well, before this change, uncaughtException listeners wouldn't have seen uncaught exceptions coming from the REPL, and now they do, right? It's not a massive change or anything, but I'd still document it somewhere. If you feel that no separate section is necessary, I'd still keep the changes: block to document the change in behavior over time

That's incorrect. Before this change, uncaughtException listeners still saw REPL exceptions

Oops. Nevermind then!

I am confused about this change. As far as I see it in the code, only the stand alone repl works with the uncaughtException listeners. In case more than a single REPL instance is running, it is not possible to identify the correct listeners, so none receive the errors.

addaleax

Needs docs; I'd also add a test for the specific behavior that we now have when two separate REPL instances receive the same uncaught exception.

There's probably even room for a way to restore the current behavior (which is imo the clearly correct one, even if it makes use of code that's deprecated for good reasons) – we'd a) need to make the REPL take an option that tells it whether to install the global process.on('uncaughtException') listener and b) allow users to set that flag to off, and start a REPL within a domain on their own + move errors from the domain to the REPL instance. That's not too complex, I think. I probably misread the code and the current logic is trying to re-establish this behavior, all good.

avivkeller · 2024-11-20T13:19:16Z

I'd also add a test for the specific behavior that we now have when two separate REPL instances receive the same uncaught exception.

That won't happen. It's specifically set up so that an uncaught exception triggered from REPL (A) won't affect REPL (B). A test to ensure this is https://github.com/nodejs/node/pull/55204/files#diff-ca6f6e3faa6e2dc3fba74eabfc212f36fa2f84b7a17e3f73662d24b678d18f73 (although it doesn't check two REPLs, rather it verifies that an uncaught exception triggered from outside the REPL does not affect the REPL, which [testing-wise] is a similar test)

BridgeAR

This is definitely nice work, I still think there are a few open parts though.

BridgeAR · 2024-11-27T16:05:56Z

lib/repl.js

@@ -612,13 +626,8 @@ function REPLServer(prompt,
        }
      } catch (e) {
        err = e;


Nit: the assignment is AFAIK not needed anymore

BridgeAR · 2024-12-05T19:21:18Z

lib/repl.js

+  },
+});
+
+let kHasSetUncaughtListener = false;


This is not a constant, so I would name the variable different.

Suggested change

let kHasSetUncaughtListener = false;

let hasUncaughtExceptionListener = false;

BridgeAR · 2024-12-05T19:42:51Z

lib/repl.js

+    }
+  };
+
+  self._onEvalError = function _onEvalError(e) {


It would be great not to expose this property.
I would just pass the instance to the method so that this method is a purely internal one.

For testing purposes, we would only have to verify that nothing else is written to REPLinstance.output.write().

BridgeAR · 2024-12-05T19:47:41Z

lib/repl.js

-  self._domain.on('error', function debugDomainError(e) {
-    debug('domain error');
+    try {
+      FunctionPrototypeApply(eval_, this, args);


eval_ could be an async function provided by the user. Would it be a good idea to await that method? I am not certain if that would improve things or if it makes it more difficult

BridgeAR · 2024-12-05T19:52:26Z

lib/repl.js


 const kBufferedCommandSymbol = Symbol('bufferedCommand');
 const kContextId = Symbol('contextId');
 const kLoadingSymbol = Symbol('loading');
+const kListeningREPLs = new SafeSet();
+const kAsyncREPLMap = new SafeMap();
+let kActiveREPL;


Suggested change

let kActiveREPL;

let activeREPL;

BridgeAR · 2024-12-05T19:59:53Z

lib/repl.js

+  if (kActiveREPL) {
+    kActiveREPL._onEvalError(er);


Are we definitely safe, that the active repl is definitely the correct one?
Let's say one repl starts an operation at time 0 and the operation needs 4 time intervals. A second repl instance start an operation at time 1 and that operation needs 2 intervals. The first instance fails after 2 intervals. Which repl instance is the error now reported upon? Do we maybe have a test for this?

BridgeAR · 2024-12-05T20:06:03Z

doc/api/repl.md

-
-* Uncaught exceptions only emit the [`'uncaughtException'`][] event in the
-  standalone REPL. Adding a listener for this event in a REPL within
-  another Node.js program results in [`ERR_INVALID_REPL_INPUT`][].


I am confused about this change. As far as I see it in the code, only the stand alone repl works with the uncaughtException listeners. In case more than a single REPL instance is running, it is not possible to identify the correct listeners, so none receive the errors.

avivkeller added the semver-major PRs that contain breaking changes and should be released in the next major version. label Oct 1, 2024

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repl: don't use deprecated domain module

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doc,lib: remove deprecated domain module #45839

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	let kHasSetUncaughtListener = false;
	let hasUncaughtExceptionListener = false;

repl: don't use deprecated domain module #55204

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repl: don't use deprecated domain module #55204

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Why?

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repl: don't use deprecated `domain` module #55204

repl: don't use deprecated `domain` module #55204

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