import/extensions ignores extension overrides if ignorePackages is set in object options #1248

node: v10.14.1
eslint: v5.10.0
eslint-plugin-import: v2.14.0

.eslintrc.js

module.exports = {
  plugins: ['import'],
  rules: {
    'import/extensions': ['error', 'always', {
      ignorePackages: true,
      js: 'never',
    }]
  }
}

./src/index.js

import app from './app';

Running eslint results in an error:

/Volumes/Projects/project/src/index.js
1:22  error  Missing file extension "js" for "./app"  import/extensions

The problem seems to be here https://github.com/benmosher/eslint-plugin-import/blob/1cd82eb27df85768fbd076e4ff6b7f36d6f652ce/src/rules/extensions.js#L36-L45

Plugin expects extensions overrides to be specified inside pattern property inside the options object if ignorePackages property is also specified. It's not documented here though.

So this configuration works correctly:

{
  rules: {
    'import/extensions': ['error', 'always', {
      ignorePackages: true,
      pattern: { // wrap extensions in the `pattern` object
        js: 'never',
      }
    }]
  }
}

Either documentation is lacking or pattern property should not be expected in options.