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MIGRATION.md

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Migration to flat config

Starting with version 11.0.0, this package exports the config in the new ESLint Flat Config format. This document aims to help migrating from the previous configuration format.

See https://eslint.org/docs/latest/use/configure/migration-guide for a more in-depth guide.

Extending base configs

All our base configs are flat configs themselves, meaning they are exported as arrays of configs. To extend them, just spread the configs in yours. Later config elements (in array order), override the previous ones.

import cheminfo from 'eslint-config-cheminfo';

export default [
  ...cheminfo,
  {
    // Custom config for the project, overrides.
  },
];

Warning

In previous versions, the default config cheminfo was the same as cheminfo/base. Now it exports the full config, including jsdoc and unicorn. If you don't want it, extend from the base config only: import cheminfo from 'eslint-config-cheminfo/base';. This is also the case for the eslint-config-cheminfo-typescript package.

Only one config file

The main thing about Flat Config is that a project now has only one configuration file that is put at the top-level. This file should be written in ESM and named eslint.config.mjs (eslint.config.js is possible if you are in a "type": "module" project).

When migrating, look for all .eslintrc.* file in your project and move their configs to the new file, then remove them. If you have a .eslintignore file, it should also be moved to the flat config.

How to migrate nested .eslintrc.* files?

Refs: glob-based configs.

In the old config format, a nested config file only applied to the directory where it was and its children. When moving it to the flat config, use files patterns:

export default [
  ...cheminfo,
  {
    files: ['scripts/**'],
    rules: {
      // Rules that only apply to the scripts directory.
    },
  },
];

How migrate .eslintignore?

Refs: ignoring files.

Add an object with an ignores field to the flat config.

export default [
  {
    ignores: ['**/build', 'src/generated/**'],
  },
  ...cheminfo,
];

Be careful that the new ignores should be written with glob syntax (previously it was gitignore syntax). The main difference is that to match directories or files at any depth, you need to have **/ at the beginning of the pattern.

What about the env field?

Refs: configuring language options.

Install and use the globals package:

import globals from 'globals';

export default [
  ...cheminfo,
  {
    languageOptions: {
      globals: {
        ...globals.node,
        ...globals.jest,
      },
    },
  },
];

Examples

Here are some example configs that were already migrated in our open source projects: