repl: emit uncaughtException #20803

BridgeAR · 2018-05-17T14:31:22Z

This was just a rough idea after looking into #19998.

I have no real opinion if this is a good idea or not and thought it might be good if others give their opinion. This way it seems like we would be able to actually report uncaughtException if a listener is attached.

If this is indeed something should could do, I'll also add tests.

Checklist

make -j4 test (UNIX), or vcbuild test (Windows) passes
tests and/or benchmarks are included
documentation is changed or added
commit message follows commit guidelines

addaleax · 2018-05-17T14:34:05Z

lib/repl.js

-    if (isError && e.stack) {
+    if (process.listenerCount('uncaughtException') !== 0) {
+      process.emit('uncaughtException', e);
+    } else if (isError && e.stack) {


I don’t think we want the event being emitted and information being written to stderr to be mutually exclusive? I’d generally expect that the REPL shows global errors that aren’t caught, even if there is an uncaughtException listener…

Hm, to me it's similar to the "regular" error: if there's no exception listener, the app will crash. In this context it's for me printing to the repl. If the listener is attached, it should only end up there and the user has to decide what to do with it.

apapirovski · 2018-05-17T14:34:07Z

This works in the opened repl but one of the main use cases domains serve in repl is in its programmatic usage where multiple repl instances can be created. This would pretty badly break that for anyone using uncaughtException.

To me the hard part is in distinguishing which errors should go to uncaughtException and which should be written out. Everyone will have different expectations around that. I don't think just always emitting and always logging is the right answer. Not convinced it's possible to please everyone and not break anyone.

BridgeAR · 2018-05-17T14:44:41Z

Is it actually possible to detect if the repl is opened or not? In that case we could just do it there?

AyushG3112 · 2018-05-17T15:29:09Z

The question which comes to my mind is whether we should allow one REPL session a look into uncaughtExceptions of another REPL session. I'd personally be against that as it will lead to unintended situations which would be potentially confusing to users.

BridgeAR · 2018-05-24T16:11:01Z

Is there interest in trying to pursue this further? I think it would make sense in case for the opened repl in case we can distinguish that from the programmatic usage. I just do not know if we have that information / if it is possible to get that information.

addaleax · 2018-05-24T16:14:47Z

@BridgeAR We do make some customizations for the Node.js main REPL, yes – lib/internal/repl.js is the one we use for that, rather than lib/repl.js

(Would also be okay with that, yes)

BridgeAR · 2018-08-21T01:17:51Z

PTAL

I just pushed another commit that limits this functionality strictly to the very first opened repl. In case a second one is opened, it will deactivate the behavior for all.

BridgeAR · 2018-08-26T12:06:03Z

@addaleax @apapirovski @AyushG3112 what do you think about the approach?

lib/repl.js

jasnell · 2018-10-17T16:33:08Z

Ping @BridgeAR ... what's the status on this?

BridgeAR · 2018-12-02T23:34:43Z

CI https://ci.nodejs.org/job/node-test-pull-request/19139/

PTAL. I guess this is actually getting somewhere. I am just not to sure how to write a test for this.

lib/repl.js

Trott · 2018-12-04T04:19:17Z

@nodejs/repl This could use some reviews. Any takesr? Even someone blocking it would be more useful than it languishing with no approvals and no requests for changes, IMO.

BridgeAR · 2018-12-05T21:52:30Z

Resumed build https://ci.nodejs.org/job/node-test-commit/24000/
CI https://ci.nodejs.org/job/node-test-pull-request/19477/

BridgeAR · 2018-12-13T08:16:46Z

@nodejs/repl @nodejs/tsc PTAL

targos · 2018-12-15T10:35:53Z

@BridgeAR can you post an example repl session that shows the impact of this change?

apapirovski · 2019-01-23T16:05:02Z

Yeah, that's fair. I'm having a look myself right now.

apapirovski

SGTM but is there a way to add a test?

doc/api/repl.md

BridgeAR · 2019-01-27T01:52:28Z

I just reworked some code here due to @apapirovski request for a test because I realized that adding an uncaughtException listener in an repl instance which is not run as standalone program is going to silence all main application errors without any chance to get any kind of notification for it.

Therefore I added some more code to fix that behavior as well: it is from now on going to throw an error if the listener is added in such a case. I could theoretically move that part into a separate PR but for me it felt right here.

While writing tests I also noticed that the former way of detecting if the REPL was run as standalone program or not was not sufficient. Currently there's no way to detect if it's the internal repl or not, so I added an internal symbol to detect that as well.

Therefore I'll ask everyone who had a look at this so far to take another look. Thanks.

BridgeAR · 2019-01-27T15:14:29Z

CI https://ci.nodejs.org/job/node-test-pull-request/20347/

@nodejs/tsc PTAL as this is now also fixing a nasty "bug" that could be triggered when using uncaughtException in the repl (silencing the main application errors).

doc/api/errors.md

doc/api/repl.md

Trott · 2019-01-27T19:34:22Z

Since it's semver-major, should we run CITGM at this time?

lib/internal/errors.js

lib/internal/repl.js

lib/repl.js

addaleax · 2019-01-27T19:35:55Z

Since it's semver-major, should we run CITGM at this time?

I don’t think we have modules in CITGM that test the default REPL (aka Node’s “interactive” mode) in any way, so I’m not sure it’s worth it?

Adding an `uncaughtException` listener in an REPL instance suppresses errors in the whole application. Closing the instance won't remove those listeners either.

The internal default repl will from now on trigger `uncaughtException` handlers instead of ignoring them. The regular error output is suppressed in that case.

BridgeAR · 2019-04-07T14:39:52Z

I updated the PR and incorporated the feedback. I also added a known issue test that highlights one of the problems this PR partially fixes (using the uncaughtException listener from an REPL instance silences all errors in the application that started that instance).

PTAL

nodejs-github-bot · 2019-04-07T14:40:46Z

CI: https://ci.nodejs.org/job/node-test-pull-request/22267/

test/known_issues/known_issues.status

BridgeAR · 2019-04-09T13:58:31Z

Superseded by #27151

I found a way to also handle the async cases properly and this PR changed multiple times, so it felt better to open a new one instead of keeping this one around.

lance

I was a little late on the review here. But I will submit it anyway. It's been sitting unsubmitted in my browser for a couple of days.

lance · 2019-04-08T16:02:08Z

doc/api/errors.md

+<a id="ERR_INVALID_REPL_INPUT"></a>
+### ERR_INVALID_REPL_INPUT
+
+The input can or may not be used in the [`REPL`][]. All prohibited inputs are


I don't understand what is meant by "can or may not be used".

I thought I'll keep it broad so that it could be used for different REPL input. So far it will only be used for uncaught exception listeners, so only the may part applies. I am happy to change it to only may or what ever you have as alternative.

lance · 2019-04-08T16:03:59Z

doc/api/repl.md

-* Uncaught exceptions do not emit the [`'uncaughtException'`][] event.
+* Uncaught exceptions only emit the [`'uncaughtException'`][] event if the
+  `repl` is used as standalone program. If the `repl` is included anywhere in
+  another application, adding this event synchronous will throw an


What is meant by "adding this event synchronous"?

This is actually outdated in the other PR. In this version I was not able to actually handle listeners that were added asynchronously. E.g., setTimeout(() => process.on("uncaughtException", () => {})) was not detected here. This is fixed in the latest implementation.

lance · 2019-04-08T16:05:37Z

doc/api/repl.md

+
+```js
+process.on('uncaughtException', () => console.log('Uncaught'));
+// TypeError [ERR_INVALID_REPL_INPUT]: Unhandled exception listeners can not be


Nit: perhaps "Listeners for uncaughtException cannot be used in the REPL" is a bit clearer.

lance · 2019-04-08T16:12:29Z

test/parallel/test-repl-pretty-custom-stack.js

@@ -40,8 +39,6 @@ process.on('uncaughtException', (e) => {
  throw e;
 });

-process.on('exit', () => (Error.prepareStackTrace = origPrepareStackTrace));


This seems unrelated to the PR changes. What am I missing?

It is somewhat unrelated. In a former PR this test was impacted as well and I noticed that this is actually not necessary, so I just went ahead and removed it.

BridgeAR added wip Issues and PRs that are still a work in progress. semver-major PRs that contain breaking changes and should be released in the next major version. labels May 17, 2018

BridgeAR requested a review from addaleax May 17, 2018 14:31

nodejs-github-bot added the repl Issues and PRs related to the REPL subsystem. label May 17, 2018

addaleax reviewed May 17, 2018

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BridgeAR force-pushed the repl-add-uncaught-exception branch from ca99566 to 630f80f Compare December 2, 2018 23:26

BridgeAR changed the title ~~WIP repl: emit uncaughtException~~ repl: emit uncaughtException Dec 2, 2018

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CI failures: 20181201-20181205 nodejs/reliability#19

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BridgeAR force-pushed the repl-add-uncaught-exception branch from 630f80f to f2083ed Compare December 13, 2018 07:01

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BridgeAR mentioned this pull request Jan 27, 2019

repl: minor improvements #25731

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addaleax mentioned this pull request Feb 18, 2019

Should Node.js standard library throw custom Error subclasses? #8342

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BridgeAR added 2 commits April 7, 2019 15:53

test: add known issue

1aaa6b7

Adding an `uncaughtException` listener in an REPL instance suppresses errors in the whole application. Closing the instance won't remove those listeners either.

repl: emit uncaughtException

88306b2

The internal default repl will from now on trigger `uncaughtException` handlers instead of ignoring them. The regular error output is suppressed in that case.

BridgeAR force-pushed the repl-add-uncaught-exception branch from 0c848e1 to 88306b2 Compare April 7, 2019 14:32

BridgeAR requested review from Fishrock123, richardlau, Trott, addaleax, lance and antsmartian April 7, 2019 14:38

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fixup! test: add known issue

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repl: emit uncaughtException #20803

repl: emit uncaughtException #20803

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repl: emit uncaughtException #20803

repl: emit uncaughtException #20803

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