Change Request: explicitly handle undefined being passed as a config value #18259
Description
ESLint version
next
What problem do you want to solve?
Currently flat config does not have any special handling for undefined being passed in causing an "accessed property on undefined" error:
Oops! Something went wrong! :(
ESLint: 8.56.0
TypeError: Cannot read properties of undefined (reading 'ignores')
at FlatConfigArray.get ignores [as ignores] ([redacted]/node_modules/@humanwhocodes/config-array/api.js:648:15)
at FlatConfigArray.isDirectoryIgnored ([redacted]/node_modules/@humanwhocodes/config-array/api.js:1012:10)
at FlatConfigArray.getConfig ([redacted]/node_modules/@humanwhocodes/config-array/api.js:806:12)
at FlatConfigArray.isFileIgnored ([redacted]/node_modules/@humanwhocodes/config-array/api.js:962:15)
at [redacted]/node_modules/eslint/lib/eslint/eslint-helpers.js:312:49
at Array.reduce (<anonymous>)
at entryFilter ([redacted]/node_modules/eslint/lib/eslint/eslint-helpers.js:299:28)
at Object.isAppliedFilter ([redacted]/node_modules/@nodelib/fs.walk/out/readers/common.js:12:31)
at AsyncReader._handleEntry ([redacted]/node_modules/@nodelib/fs.walk/out/readers/async.js:86:20)
at [redacted]/node_modules/@nodelib/fs.walk/out/readers/async.js:65:22
This is confusing because undefined is commonly expected if you try to use a config that doesn't exist but the error message looks more like a potential bug in ESLint:
const jestPlugin = require('eslint-plugin-jest');
module.exports = [
{
// enable jest rules on test files
files: ['test/**'],
...jestPlugin.configs['flat/recommended'],
},
// explodes, as we're removing this in our next major!
jestPlugin.configs['flat/snapshots'],
];This is a real-world example of where I hit this as I was testing for eslint-plugin-jest's upcoming major in which we're removing the flat/snapshots config.
What do you think is the correct solution?
I'd like ESLint to explicitly check for undefined and raise an error along the lines of "you've passed undefined as a config - this usually happens when you're trying to reference a config that doesn't exist"
Participation
- I am willing to submit a pull request for this change.
Additional comments
Born from #18094 & #18094 (comment)