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Give better stack traces for Unhandled Promise Rejection warnings #60235

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Mar 17, 2020
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Give better stack traces for Unhandled Promise Rejection warnings #60235

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12 changes: 12 additions & 0 deletions src/setup_node_env/exit_on_warning.js
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Original file line number Diff line number Diff line change
Expand Up @@ -35,4 +35,16 @@ if (process.noProcessWarnings !== true) {

process.exit(1);
});

// While the above warning listener would also be called on
// unhandledRejection warnings, we can give a better error message if we
// handle them separately:
process.on('unhandledRejection', function(reason) {
console.error('Unhandled Promise rejection detected:');
console.error();
console.error(reason);
console.error();
console.error('Terminating process...');
process.exit(1);
});
Comment on lines +42 to +49
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Isn't this already catched by the warning event?

From https://kibana-ci.elastic.co/blue/rest/organizations/jenkins/pipelines/elastic+kibana+pipeline-pull-request/runs/33334/nodes/28/steps/147/log/?start=0

Node.js process-warning detected:
[2020-03-16T08:30:26.360Z] 
[2020-03-16T08:30:26.360Z] UnhandledPromiseRejectionWarning: [object Object]
[2020-03-16T08:30:26.360Z]     at emitWarning (internal/process/promises.js:99:15)
[2020-03-16T08:30:26.360Z]     at emitPromiseRejectionWarnings (internal/process/promises.js:143:7)
[2020-03-16T08:30:26.360Z]     at process._tickCallback (internal/process/next_tick.js:69:34)
[2020-03-16T08:30:26.360Z] 
[2020-03-16T08:30:26.360Z] Terminating process...
[2020-03-16T08:30:26.360Z] Fatal error: jest exited with code 1�

Or will the reason catched by the unhandledRejection contains more info than what is catched by the warning handler?

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The stack trace available for the unhandled exception is just pointing back to a next-tick frame which doesn't show any of the user-land code. This makes the stack trace unusable and the reader can't see which Promise was not handled correctly.

By implementing an unhandledRejection listener we get access to the rejection reason, which hopefully always is an Error object with its own stack trace. We can use this stack trace to guide the developer towards the location where the Promise rejection wasn't handled.

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That was the question :) great then.

}