Bump eslint to ^9.11.1 and migrate to flat config (#4727)

We recently released new versions of our ESLint packages to rely on
ESLint 9. This PR bumps all of the ESLint-related packages in this repo
to match, and migrates the current ESLint config into the new flat
format. It also upgrades Prettier to v3.

---------

Co-authored-by: Elliot Winkler <[email protected]>

.depcheckrc.yml

@@ -16,10 +16,15 @@ ignores:
   - 'simple-git-hooks'
   - 'ts-node'
   - 'typedoc'
-  # Ignore plugins implicitly imported by tools
+  # Ignore plugins for tools
+  - '@typescript-eslint/*'
+  - 'babel-jest'
+  - 'eslint-config-*'
+  - 'eslint-plugin-*'
   - 'jest-silent-reporter'
   - 'prettier-plugin-packagejson'
-  # Ignore plugins we explicitly use with tools
-  - 'babel-jest'
+  - 'typescript-eslint'
+  # Ignore dependencies imported implicitly by tools
+  - 'eslint-import-resolver-typescript'
   # Ignore dependencies which plug into the NPM lifecycle
   - '@lavamoat/preinstall-always-fail'

eslint.config.mjs

@@ -0,0 +1,152 @@
+import base, { createConfig } from '@metamask/eslint-config';
+import nodejs from '@metamask/eslint-config-nodejs';
+import jest from '@metamask/eslint-config-jest';
+import typescript from '@metamask/eslint-config-typescript';
+
+const config = createConfig(
+  {
+    ignores: [
+      'yarn.lock',
+      '**/**.map',
+      '**/**.tsbuildinfo',
+      '**/*.json',
+      '**/*.md',
+      '**/LICENSE',
+      '**/*.sh',
+      '**/.DS_Store',
+      '**/dist/**',
+      '**/docs/**',
+      '**/coverage/**',
+      'merged-packages/**',
+      '.yarn/**',
+      'scripts/create-package/package-template/**',
+    ],
+  },
+  ...base,
+  {
+    rules: {
+      // Left disabled because various properties throughough this repo are snake_case because the
+      // names come from external sources or must comply with standards
+      // e.g. `txreceipt_status`, `signTypedData_v4`, `token_id`
+      camelcase: 'off',
+      'id-length': 'off',
+
+      // TODO: re-enble most of these rules
+      '@typescript-eslint/naming-convention': 'off',
+      'function-paren-newline': 'off',
+      'id-denylist': 'off',
+      'implicit-arrow-linebreak': 'off',
+      'import/no-anonymous-default-export': 'off',
+      'import/no-unassigned-import': 'off',
+      'lines-around-comment': 'off',
+      'n/no-sync': 'off',
+      'no-async-promise-executor': 'off',
+      'no-case-declarations': 'off',
+      'no-invalid-this': 'off',
+      'no-negated-condition': 'off',
+      'no-new': 'off',
+      'no-param-reassign': 'off',
+      'no-restricted-syntax': 'off',
+      radix: 'off',
+      'require-atomic-updates': 'off',
+      'jsdoc/match-description': [
+        'off',
+        { matchDescription: '^[A-Z`\\d_][\\s\\S]*[.?!`>)}]$' },
+      ],
+    },
+    settings: {
+      jsdoc: {
+        mode: 'typescript',
+      },
+    },
+  },
+  {
+    files: [
+      '**/jest.config.js',
+      '**/jest.environment.js',
+      '**/tests/**/*.{ts,js}',
+      '*.js',
+      '*.test.{ts,js}',
+      'scripts/*.ts',
+      'scripts/create-package/*.ts',
+      'yarn.config.cjs',
+    ],
+    extends: [nodejs],
+  },
+  {
+    files: ['*.test.{ts,js}', '**/tests/**/*.{ts,js}'],
+    extends: [jest],
+  },
+  {
+    // These files are test helpers, not tests. We still use the Jest ESLint
+    // config here to ensure that ESLint expects a test-like environment, but
+    // various rules meant just to apply to tests have been disabled.
+    files: ['**/tests/**/*.{ts,js}', '!*.test.{ts,js}'],
+    rules: {
+      'jest/no-export': 'off',
+      'jest/require-top-level-describe': 'off',
+      'jest/no-if': 'off',
+    },
+  },
+  {
+    files: ['*.js', '*.cjs'],
+    parserOptions: {
+      sourceType: 'script',
+      ecmaVersion: '2020',
+    },
+  },
+  {
+    files: ['*.ts'],
+    extends: [typescript],
+    parserOptions: {
+      tsconfigRootDir: import.meta.dirname,
+      project: ['./tsconfig.packages.json'],
+    },
+    rules: {
+      // Enable rules that are disabled in `@metamask/eslint-config-typescript`
+      '@typescript-eslint/no-explicit-any': 'error',
+
+      // TODO: auto-fix breaks stuff
+      '@typescript-eslint/promise-function-async': 'off',
+
+      // TODO: re-enable most of these rules
+      '@typescript-eslint/no-unnecessary-type-assertion': 'off',
+      '@typescript-eslint/unbound-method': 'off',
+      '@typescript-eslint/prefer-enum-initializers': 'off',
+      '@typescript-eslint/prefer-nullish-coalescing': 'off',
+      '@typescript-eslint/prefer-optional-chain': 'off',
+      '@typescript-eslint/prefer-reduce-type-parameter': 'off',
+      'no-restricted-syntax': 'off',
+      'no-restricted-globals': 'off',
+    },
+  },
+  {
+    files: ['tests/setupAfterEnv/matchers.ts'],
+    parserOptions: {
+      sourceType: 'script',
+    },
+  },
+  {
+    files: ['*.d.ts'],
+    rules: {
+      '@typescript-eslint/naming-convention': 'warn',
+      'import/unambiguous': 'off',
+    },
+  },
+  {
+    files: ['scripts/*.ts'],
+    rules: {
+      // All scripts will have shebangs.
+      'n/shebang': 'off',
+    },
+  },
+  {
+    files: ['**/jest.environment.js'],
+    rules: {
+      // These files run under Node, and thus `require(...)` is expected.
+      'n/global-require': 'off',
+    },
+  },
+);
+
+export default config;