🐛 Cascaded ESLint configuration flags eslintrc files as unused

[pjonsson]

Prerequisites

• I'm using the latest version
• I've read the relevant documentation
• I've searched for existing issues
• I've checked the list of known issues
• I've read the issue reproduction guide

Reproduction url

https://knip.dev/reference/plugins/eslint#default-configuration

Reproduction access

• I've made sure the reproduction is publicly accessible

Description of the issue

The ESLint plugin default configuration at https://knip.dev/reference/plugins/eslint#default-configuration lists the config files as ".eslintrc", ".eslintrc.{js,json,cjs}", "eslintrc.{yml,yaml}", "package.json", but the old non-flat ESLint config format can have .eslintrc files appear in subdirectories (https://eslint.org/docs/v8.x/use/configure/configuration-files#cascading-and-hierarchy), so with this (minimized) knip.jsonc:

{
  "$schema": "https://unpkg.com/knip@5/schema-jsonc.json",
  "entry": ["test/**/*.{ts,tsx}"],
  "project": ["./**/*.{js,jsx,ts,tsx}"],
}

I get buildprocess/.eslintrc.js and test/.eslintrc.js flagged as unused, but not .eslintrc.js. If I change knip.jsonc to:

{
  "$schema": "https://unpkg.com/knip@5/schema-jsonc.json",
  "entry": ["test/**/*.{ts,tsx}"],
  "project": ["./**/*.{js,jsx,ts,tsx}"],
  "eslint": {
    "config": [
      "**/.eslintrc",
      "**/.eslintrc.{js,json,cjs}",
      "**/.eslintrc.{yml,yaml}",
      "package.json"
    ],
    "entry": [
      "eslint.config.{js,cjs,mjs}"
    ]
  }
}

I do not get the .eslintrc.js files in subdirectories flagged either.

[webpro]

Please provide an actual and minimal reproduction. Without, I can't see if there are workspaces or how the files are referencing each other, etc.

[pjonsson]

Here's a zip of a git repository: repro-knip-cascading-eslint-config.zip

I used the node:20 docker image for these commands: after yarn install, run yarn gulp lint to see that three lint errors appear, and yarn knip to get:

Unused files (2)
buildprocess/.eslintrc.js
test/.eslintrc.js

After that, add:

"eqeqeq": 0,

before "no-sync": 0 in buildprocess/.eslintrc.js and run yarn gulp lint to see that only two lint errors remain, so the ESLint config in that directory is used.

[webpro]

Thanks for the reproduction, that's clear.

The issue here is that Knip does not implement all the logic that ESLint itself has. So indeed the other .eslintrc.js on non-default locations are unused to Knip because there are no explicit references to it.

Here are the defaults for the ESLint plugin: https://knip.dev/reference/plugins/eslint

This an example of how it can be overridden (as you were already doing):

{
  "$schema": "https://unpkg.com/knip@5/schema-jsonc.json",
  "entry": [
    "gulpfile.js", "test/**/*Spec.js"
  ],
  "eslint": [".eslintrc.js", "buildprocess/.eslintrc.js", "test/.eslintrc.js"] // or ["**/.eslintrc.js"]
}

[pjonsson]

The issue here is that Knip does not implement all the logic that ESLint itself has.

As far as I can tell, the cascading configuration "logic" in ESLint is that any configuration file in a subdirectory to the directory of the root ESLint configuration file is used, as described in the paragraph directly under the first code block here: https://eslint.org/docs/v8.x/use/configure/configuration-files#cascading-and-hierarchy

So indeed the other .eslintrc.js on non-default locations are unused to Knip because there are no explicit references to it.

I don't see how the .eslintrc.js files differ in that respect, there are no explicit references to the root .eslintrc.js either.

If you don't want to add **/ before the non-flat configuration filenames in the ESLint plugin, could you at least add some documentation on the ESLint plugin webpage that mentions cascaded ESLint configurations are not supported?

[webpro]

You do have a point. My initial reluctance came from the fact that none of the Knip plugins have this "expensive" glob pattern for config files, and only few tools actually support config cascade.

However, ESLint v9 does not seem to have this feature. Adding a note to the docs.

Thanks, glad we got this cleared up.

[webpro]

🚀 This issue has been resolved in v5.45.0. See Release 5.45.0 for release notes.

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