webpack-dev-server hangs completely on error when failOnError: true

[limejoe]

• Operating System: Win10
• Node Version: 12.16.1
• NPM Version: 6.13.4
• webpack Version: 4.44.2
• eslint-webpack-plugin Version: 2.1.0

Expected Behavior

Build should be failed, webpack-dev-server job should exit or complete

Actual Behavior

The build is failed, but webpack-dev-server job hangs and does not finish

Code

webpack.common.config.js
https://gist.github.com/limejoe/04e87d012f0c27e1983a3a6da0c6be64

webpack.dev_ui_only.config.js
https://gist.github.com/limejoe/74cbb88a8e72d0852b799fcecb14f6a5

How Do We Reproduce?

run webpack-dev-server --open --config webpack.dev_ui_only.config.js

[Gusis93]

Adding to this issue, when failOnError is true, I get this on my build:

(node:7728) UnhandledPromiseRejectionWarning: TypeError: Cannot read property 'toString' of undefined
(node:7728) 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(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 1)
(node:7728) [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.

Unless I have fix: true, so it seems some promise is not being handled when an issue pops up.

[rnagy90]

Same hanging error when using the styleling-plugin.
The eslint error also occurs in a "create-react-app" project.