There is no formatter for 'json'/'jsonc' files installed.

[Joris914]

Some relevant settings:

  "editor.codeActionsOnSave": {
    "source.fixAll.eslint": "always"
  },
  "eslint.validate": [
    "javascript",
    "typescript",
    "json"
  ],
  "eslint.run": "onType",
  "eslint.format.enable": true,
  "eslint.useFlatConfig": true,
  // just for good measure, I don't think below should do anything
  "[json]": {
    "editor.defaultFormatter": "dbaeumer.vscode-eslint"
  },
  "[jsonc]": {
    "editor.defaultFormatter": "dbaeumer.vscode-eslint"
  },
  "json.format.enable": false, // disable the default vscode json formatter

If I set the last option to true, the error message changes to:

My eslint.config.mjs:

import { FlatCompat } from '@eslint/eslintrc'
import json from '@eslint/json'
import prettier from 'eslint-plugin-prettier'
import simpleImportSort from 'eslint-plugin-simple-import-sort'
import { dirname } from 'path'
import { fileURLToPath } from 'url'

const __filename = fileURLToPath(import.meta.url)
const __dirname = dirname(__filename)

const compat = new FlatCompat({
    baseDirectory: __dirname,
})

const eslintConfig = [
    ...compat.extends('next/core-web-vitals', 'next/typescript'),
    {
        languageOptions: {
            ecmaVersion: 'latest',
            sourceType: 'module',
        },
        plugins: {
            simpleImportSort,
            prettier,
            json,
        },
        rules: {
            'comma-dangle': ['error', 'always-multiline'],
            'react/prop-types': 'off',
            'no-unused-vars': 'warn',
            'simpleImportSort/imports': 'error',
            'simpleImportSort/exports': 'error',
            'prettier/prettier': 'warn',
            '@typescript-eslint/no-unused-vars': 'off',
            'json/no-duplicate-keys': 'error',
        },
    },
]

export default eslintConfig

I have tried separating the json-specific rules into its own block with file extension specifications, but that didn't help.
I saw one other issue about this but that was because of "eslint.format.enable": true not being set. I would appreciate some help here :)

[dbaeumer]

@Joris914 can you format the file in the terminal using --fix. If so, can you please provide me with a GitHub repository with a minimal setup that demos what you are seeing.

[Joris914]

Hmm, when I run it on command line I get the message 0:0 warning File ignored because no matching configuration was supplied
I guess that means it's not an extension issue, but an ESLint itself issue?