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Promises/better unhandled rejection message #17158

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Promises/better unhandled rejection message #17158

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a29fe91
Improved unhandled rejection message
MadaraUchiha Nov 20, 2017
ba4adc5
Make tests pass
MadaraUchiha Nov 20, 2017
ab45e60
Wrap reason with unsafeToString() if it's a string
MadaraUchiha Nov 20, 2017
bf06851
Add test for checking warnings about rejected numbers.
MadaraUchiha Nov 21, 2017
9d29f0c
Fix failing symbol rejection test.
MadaraUchiha Nov 21, 2017
481c7f1
Make test lines wrap at 80 characters or less.
MadaraUchiha Nov 22, 2017
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20 changes: 15 additions & 5 deletions lib/internal/process/promises.js
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Original file line number Diff line number Diff line change
@@ -1,7 +1,5 @@
'use strict';

const { safeToString } = process.binding('util');

const promiseRejectEvent = process._promiseRejectEvent;
const hasBeenNotifiedProperty = new WeakMap();
const promiseToGuidProperty = new WeakMap();
Expand Down Expand Up @@ -60,11 +58,23 @@ function setupPromises(scheduleMicrotasks) {
}

function emitWarning(uid, reason) {
try {
if (reason instanceof Error) {
process.emitWarning(reason.stack, 'UnhandledPromiseRejectionWarning');
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So I guess the only downfall to doing it this way is it won't include any additional properties added on to the Error object. Any reason to do this vs using util.inspect()?

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Just that I wasn't aware of util.inspect(). I went with what the rest of the code did in the same function.

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Namely, Node doesn't show this information for synchronous errors:

// test.js
var e = new Error("error");
e.foo = "bar";
throw e;
~/test/test.js:3
throw e;
^

Error: error
    at Object.<anonymous> (/Users/benjamin/Downloads/test.js:1:71)
    at Module._compile (module.js:573:30)
    at Object.Module._extensions..js (module.js:584:10)
    at Module.load (module.js:507:32)
    at tryModuleLoad (module.js:470:12)
    at Function.Module._load (module.js:462:3)
    at Function.Module.runMain (module.js:609:10)
    at startup (bootstrap_node.js:158:16)
    at bootstrap_node.js:598:3

} else {
process.emitWarning(reason, 'UnhandledPromiseRejectionWarning');
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@refack refack Nov 20, 2017 •
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So this still should be safeToString(reason), notice that emitWarning will only emit strings

D:\code\4node$ promise-warning.exe\node.exe -e "Promise.reject('a');Promise.reject(100)"
(node:18696) UnhandledPromiseRejectionWarning: a
(node:18696) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:18696) [DEP0018] 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.
(node:18696) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 2)

P.S. could you add a test for a non string rejection?

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What's the expected behavior when strings get rejected? I couldn't find a way to get the stack trace in that case.

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I'd assume the stack has been destroyed when this is reached. IMHO just printing the reason (after stringifying) is the best we can do.
So if it's an Error reason.stack else safeToString(reason).

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I think that test-promises-warning-on-unhandled-rejection.js implicitly checks for string rejections, please tell me if something else might be better.

I've pushed the commit to wrap the reason with safeToString().

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@refack refack Nov 20, 2017 •
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Yeah it's an awkward test... You could add a line just before last:

const p = Promise.reject(100);

then move case (2) to (3) add a case (2):

case 2:
      assert.strictEqual(warning.name, 'UnhandledPromiseRejectionWarning');
      assert(/100/.test(warning.message));
      break;

P.S. it's testing Strings because it checks the stringified output

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Sorry, should be p1 since p is used for the async handling check

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@refack Added the requested test, also added comments to make it clear what each state in the state machine means.

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💯

}
} catch (e) {
// ignored
}

const warning = new Error(
`Unhandled promise rejection (rejection id: ${uid}): ` +
safeToString(reason));
'Unhandled promise rejection. This error originated either by ' +
'throwing inside of an async function without a catch block, ' +
'or by rejecting a promise which was not handled with .catch(). ' +
`(rejection id: ${uid})`
);
warning.name = 'UnhandledPromiseRejectionWarning';
warning.id = uid;
try {
if (reason instanceof Error) {
warning.stack = reason.stack;
Expand Down
18 changes: 18 additions & 0 deletions test/message/unhandled_promise_trace_warnings.out
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Original file line number Diff line number Diff line change
@@ -1,3 +1,21 @@
(node:*) UnhandledPromiseRejectionWarning: Error: This was rejected
at * (*test*message*unhandled_promise_trace_warnings.js:*)
at *
at *
at *
at *
at *
at *
at *
at *
at *
at *
at *
at *
at *
at *
at *
at *
(node:*) Error: This was rejected
at * (*test*message*unhandled_promise_trace_warnings.js:*)
at *
Expand Down
7 changes: 5 additions & 2 deletions test/parallel/test-promises-unhandled-proxy-rejections.js
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Expand Up @@ -6,8 +6,11 @@ const expectedDeprecationWarning = 'Unhandled promise rejections are ' +
'rejections that are not handled will ' +
'terminate the Node.js process with a ' +
'non-zero exit code.';
const expectedPromiseWarning = 'Unhandled promise rejection (rejection id: ' +
'1): [object Object]';
const expectedPromiseWarning = 'Unhandled promise rejection. ' +
'This error originated either by throwing ' +
'inside of an async function without a catch ' +
'block, or by rejecting a promise which was ' +
'not handled with .catch(). (rejection id: 1)';

function throwErr() {
throw new Error('Error from proxy');
Expand Down
7 changes: 5 additions & 2 deletions test/parallel/test-promises-unhandled-symbol-rejections.js
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Original file line number Diff line number Diff line change
Expand Up @@ -6,8 +6,11 @@ const expectedDeprecationWarning = 'Unhandled promise rejections are ' +
'rejections that are not handled will ' +
'terminate the Node.js process with a ' +
'non-zero exit code.';
const expectedPromiseWarning = 'Unhandled promise rejection (rejection id: ' +
'1): Symbol()';
const expectedPromiseWarning = 'Unhandled promise rejection. ' +
'This error originated either by throwing ' +
'inside of an async function without a catch ' +
'block, or by rejecting a promise which was ' +
'not handled with .catch(). (rejection id: 1)';

common.expectWarning({
DeprecationWarning: expectedDeprecationWarning,
Expand Down
11 changes: 7 additions & 4 deletions test/parallel/test-promises-warning-on-unhandled-rejection.js
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Expand Up @@ -12,18 +12,21 @@ let b = 0;
process.on('warning', common.mustCall((warning) => {
switch (b++) {
case 0:
assert.strictEqual(warning.name, 'UnhandledPromiseRejectionWarning');
assert(/Unhandled promise rejection/.test(warning.message));
assert.strictEqual(warning.message, 'This was rejected');
break;
case 1:
assert.strictEqual(warning.name, 'DeprecationWarning');
assert.strictEqual(warning.name, 'UnhandledPromiseRejectionWarning');
assert(/Unhandled promise rejection/.test(warning.message), 'Expected warning message to contain "Unhandled promise rejection" but did not. Had "' + warning.message + '" instead.');
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these lines need to be line-wrapped at <= 80 chars

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How come make test's linter passes for me? I totally missed that.

break;
case 2:
assert.strictEqual(warning.name, 'DeprecationWarning');
break;
case 3:
assert.strictEqual(warning.name, 'PromiseRejectionHandledWarning');
assert(/Promise rejection was handled asynchronously/
.test(warning.message));
}
}, 3));
}, 4));

const p = Promise.reject('This was rejected');
setImmediate(common.mustCall(() => p.catch(() => {})));