Vue.config.errorHandler cannot catch the error thrown by watcher whose user is true in the option if the callback returns a promise

[xixileng]

Version

2.6.8

Reproduction link

https://jsfiddle.net/fh5kz3r6/

Steps to reproduce

1.return a promise that reject one error in watch;
2.trigger the watcher in the step 1;

What is expected?

Vue.config.errorHandler can catch the error.

What is actually happening?

Vue.config.errorHandler not catch the error.

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I think changing the try {/.../} catch (e) {/.../} in the Vue.prototype.$watch and run function of the watcher to invokeWithErrorHandling can solve the problem.