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promise: better stack traces for --trace-warnings #9525

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promise: better stack traces for --trace-warnings #9525

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991d9e2
promise: better stack traces for --trace-warnings
addaleax Nov 9, 2016
de662ae
address nit
addaleax Nov 9, 2016
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17 changes: 15 additions & 2 deletions lib/internal/process/promises.js
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,11 @@ let lastPromiseId = 1;

exports.setup = setupPromises;

function getAsynchronousRejectionWarningObject(uid) {
return new Error('Promise rejection was handled ' +
`asynchronously (rejection id: ${uid})`);
}
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Perhaps this could reduce late promise handling performance slightly but... oh well, maybe we can make that an option if people complain. ¯\_(ツ)_/¯ Good defaults are more important for this kind of thing.

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Maybe, but I think it’s okay. This should not be a hot path anyway.


function setupPromises(scheduleMicrotasks) {
process._setupPromises(function(event, promise, reason) {
if (event === promiseRejectEvent.unhandled)
Expand All @@ -31,10 +36,15 @@ function setupPromises(scheduleMicrotasks) {
const uid = promiseToGuidProperty.get(promise);
promiseToGuidProperty.delete(promise);
if (hasBeenNotified === true) {
let warning = null;
if (!process.listenerCount('rejectionHandled')) {
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Won't this always be hit because of the default listener?

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@Fishrock123 Are you referring to the code in the block below this one? That’s not technically a listener, so it isn’t counted here. Also, at least a quick check in the REPL yields process.listenerCount('rejectionHandled') === 0 by default.

// Generate the warning object early to get a good stack trace.
warning = getAsynchronousRejectionWarningObject(uid);
}
process.nextTick(function() {
if (!process.emit('rejectionHandled', promise)) {
const warning = new Error('Promise rejection was handled ' +
`asynchronously (rejection id: ${uid})`);
if (warning === null)
warning = getAsynchronousRejectionWarningObject(uid);
warning.name = 'PromiseRejectionHandledWarning';
warning.id = uid;
process.emitWarning(warning);
Expand All @@ -50,6 +60,9 @@ function setupPromises(scheduleMicrotasks) {
`(rejection id: ${uid}): ${reason}`);
warning.name = 'UnhandledPromiseRejectionWarning';
warning.id = uid;
if (reason instanceof Error) {
warning.stack = reason.stack;
}
process.emitWarning(warning);
if (!deprecationWarned) {
deprecationWarned = true;
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5 changes: 5 additions & 0 deletions test/message/unhandled_promise_trace_warnings.js
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@@ -0,0 +1,5 @@
// Flags: --trace-warnings
'use strict';
require('../common');
const p = Promise.reject(new Error('This was rejected'));
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I think the common module needs to be required here:

require('../common');

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@danbev right, done

setImmediate(() => p.catch(() => {}));
31 changes: 31 additions & 0 deletions test/message/unhandled_promise_trace_warnings.out
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@@ -0,0 +1,31 @@
(node:*) Error: This was rejected
at * (*test*message*unhandled_promise_trace_warnings.js:*)
at *
at *
at *
at *
at *
at *
at *
at *
at *
(node:*) DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
at *
at *
at *
at *
at *
at *
at *
at *
at *
(node:*) PromiseRejectionHandledWarning: Promise rejection was handled asynchronously (rejection id: 1)
at getAsynchronousRejectionWarningObject (internal/process/promises.js:*)
at rejectionHandled (internal/process/promises.js:*)
at *
at Promise.then (native)
at Promise.catch (native)
at Immediate.setImmediate (*test*message*unhandled_promise_trace_warnings.js:*)
at *
at *
at *