react-scripts no longer prints ESLint warnings

Describe the bug

After upgrading to react-scripts@4.0.2, react-scripts start no longer prints ESLint warnings (both to the terminal and browser console), while it still prints ESLint errors.

Did you try recovering your dependencies?

1.22.10

Which terms did you search for in User Guide?

None.

Environment

Environment Info:

  current version of create-react-app: 4.0.1
  running from /Users/erikmuller/.config/yarn/global/node_modules/create-react-app

  System:
    OS: macOS 11.2
    CPU: (8) x64 Intel(R) Core(TM) i5-8259U CPU @ 2.30GHz
  Binaries:
    Node: 14.15.1 - ~/.nvm/versions/node/v14.15.1/bin/node
    Yarn: 1.22.10 - /usr/local/bin/yarn
    npm: 6.14.8 - ~/.nvm/versions/node/v14.15.1/bin/npm
  Browsers:
    Chrome: 88.0.4324.150
    Edge: Not Found
    Firefox: 84.0.2
    Safari: 14.0.3
  npmPackages:
    react: Not Found
    react-dom: Not Found
    react-scripts: Not Found
  npmGlobalPackages:
    create-react-app: Not Found

Steps to reproduce

1. Make sure to have "@typescript-eslint/no-unused-vars": "warn" in the eslint config
2. Add unused variable somewhere in your code, e.g. const x = 42
3. Run yarn react-scripts start

Expected behavior

React Scripts prints both ESLint errors and warnings.

Actual behavior

React Scripts only prints ESLint errors but no warnings.

[miguelCT]

I’m not sure if what happens to me is the same but, even though I have the ESLINT_NO_DEV_ERRORS (v4.0.2) env variable set to true, and the ESlint errors are transformed to ESlint warnings, the build is still not successful and I get a Failed to compile. message.

For example, with this code:

const x = 42; 

And the rule:

"@typescript-eslint/no-unused-vars": "error"

I get the following console output:

And the following error in the App Overlay

What I understood about the ESLINT_NO_DEV_ERRORS env is that, even if I have ESlint errors in my code, those errors would be transformed to warnings and therefore the App compilation would be successful, printing those in console. Have I maybe misunderstood or is it possibly a bug?

[romamd]

This seems to be related to this release: https://github.com/webpack-contrib/eslint-webpack-plugin/releases/tag/v2.5.0

@miguelCT Running npm i eslint-webpack-plugin@2.4.3 --save-dev -E fixed it for me.