no-unused-vars errors with parameters when parameter marked used later

[webOS101]

Tell us about your environment

• ESLint Version: 5.6.1
• Node Version: v9.4.0
• npm Version: 5.6.0

What parser (default, Babel-ESLint, etc.) are you using? babel-eslint

Please show your full configuration:

Configuration

{
	"parser": "babel-eslint",
	"plugins": [
		"babel",
		"react"
	],
	"extends": ["plugin:react/recommended"],
	"rules": {
		"no-unused-vars": 1
	}
}

What did you do? Please include the actual source code causing the issue, as well as the command that you used to run ESLint.

The eslint-plugin-react rule for jsx-uses-vars marks the Wrapped parameter as used. However, no-unused-vars doesn't update the status of config. The default for no-unused-vars should not warn on parameters before the first used parameter.

import React from 'react';
import foo from 'foo';

export const AccessibilityDecorator = foo((config, Wrapped) => {
	return class t extends React.Component {
		render () {
			return <Wrapped />;
		}
	};
});

eslint .

What did you expect to happen?

No warnings.

What actually happened? Please include the actual, raw output from ESLint.

/Users/.../.../test.js
  4:44  warning  'config' is defined but never used  no-unused-vars

✖ 1 problem (0 errors, 1 warning)

Linked issue: jsx-eslint/eslint-plugin-react#2009

[platinumazure]

Hi @webOS101, thanks for the issue.

Would you mind running ESLint with the --print-config option, passing in the path of the file you're trying to lint here? Curious to see if your configuration is being overridden somewhere (either in no-unused-vars, or react/jsx-uses-vars). Thanks!

[webOS101]

It's not that, sadly. I had checked that previously.

{
  "globals": {},
  "env": {},
  "rules": {
    "react/display-name": 2,
    "react/jsx-key": 2,
    "react/jsx-no-comment-textnodes": 2,
    "react/jsx-no-duplicate-props": 2,
    "react/jsx-no-target-blank": 2,
    "react/jsx-no-undef": 2,
    "react/jsx-uses-react": 2,
    "react/jsx-uses-vars": 2,
    "react/no-children-prop": 2,
    "react/no-danger-with-children": 2,
    "react/no-deprecated": 2,
    "react/no-direct-mutation-state": 2,
    "react/no-find-dom-node": 2,
    "react/no-is-mounted": 2,
    "react/no-render-return-value": 2,
    "react/no-string-refs": 2,
    "react/no-unescaped-entities": 2,
    "react/no-unknown-property": 2,
    "react/no-unsafe": 0,
    "react/prop-types": 2,
    "react/react-in-jsx-scope": 2,
    "react/require-render-return": 2,
    "no-unused-vars": 1
  },
  "parserOptions": {
    "ecmaFeatures": {
      "jsx": true
    }
  },
  "plugins": [
    "react",
    "babel"
  ],
  "parser": "/usr/local/lib/node_modules/babel-eslint/lib/index.js",
  "extends": [
    "plugin:react/recommended"
  ]
}

[webOS101]

It may be as simple as checking eslintUsed here:

eslint/lib/rules/no-unused-vars.js

Line 472 in 648a33a

return !posteriorParams.some(v => v.references.length > 0);

But I didn't actually test that.

[webOS101]

I confirmed that works. I was able to create a test case that fails and passes with that fix. I still have never figured out how to use a locally linked eslint to test with either global or local installs. I guess I'll figure it out someday. I'll create a PR shortly.

[platinumazure]

Thanks @webOS101 for digging further! I think I rewrote that code some time ago and this was an oversight on my part.

I've relabeled this as a bug, in accordance with your investigation results.