refactor: modernize ESLint configuration (#7080)

* refactor: modernize ESLint configuration

This changeset migrates the project to ESLint 9 and to its new
configuration format (`eslint.config.js`).

To do this, I more or less ditched our current shared configuration in
favor of using `recommended` presets from the plugins we use. We haven't
been maintaining our ESLint preset since early 2022 and it uses long-
outdated lint plugins (e.g. a version of the TypeScript ESLint plugin
that was published in mid 2023). Even though this change will likely
get rid of some rules we might find helpful and re-enable later, I think
on the whole this is a win and a foundation for making ESLint a more
useful tool going forward.

A few other noteworthy changes here:

- Cuts ESLint runtime from ~1 min to ~7s
- This update makes a few extraneous dev dependencies explicit. A lot of
  our ESLint dependencies (eslint, plugins, prettier, etc.) were
  transitive dependencies from `@netlify/eslint-config-node`, which is a
  pattern notorious for causing package resolution issues. This change
  makes these dependencies explicit.
- Replaced the lone custom ESLint rule (restricts the use of
  `process.cwd()`) with a built-in equivalent.
- Updated the `tsconfig.json` configuration to use a more accurate
  configuration for our version of node. (We specified targets, `lib`s,
  etc. that were outdated for Node 18.) This change was prompted by some
  lint errors that made no sense.
- Added the Vitest ESLint plugin.

* build: add lint, lint:fix npm scripts

These were added recently then reverted, so I'm adding them back here.

* refactor: remove unnecessary typescript `include` glob

* refactor: remove unnecessary eslint `ignores` glob

* deps: add missing npm-run-all2 dependency

Previously, this package was made available transitively--I think via
`@netlify/eslint-config-node`.

* ci: reduce indirection in lint CI step

* build: remove cross-env-shell

Not really sure why we even use this--we don't specify any environment
variables to these tasks.

* build: fix and de-complicate lint, format tasks

* style: fix formatting errors

Author: ndhoule

.eslintignore

@@ -40,9 +40,15 @@ jobs:
       - name: Install core dependencies
         run: npm ci --no-audit
         if: '${{!steps.release-check.outputs.IS_RELEASE}}'
+
+      - name: Formatting
+        run: npm run format:check
+        if: '${{!steps.release-check.outputs.IS_RELEASE}}'
+
       - name: Linting
-        run: npm run format:ci
+        run: npm run lint
         if: '${{!steps.release-check.outputs.IS_RELEASE}}'
+
       - name: Run unit tests
         uses: nick-fields/retry@v3
         with:

.eslintrc.cjs

@@ -1 +1,7 @@
-"@netlify/eslint-config-node/.prettierrc.json"
+{
+  "semi": false,
+  "singleQuote": true,
+  "printWidth": 120,
+  "proseWrap": "always",
+  "trailingComma": "all"
+}

.github/workflows/unit-tests.yml

@@ -0,0 +1,163 @@
+// @ts-check
+import * as path from 'node:path'
+import { fileURLToPath } from 'node:url'
+import eslint from '@eslint/js'
+import { includeIgnoreFile } from '@eslint/compat'
+import prettier from 'eslint-config-prettier'
+import node from 'eslint-plugin-n'
+import vitest from '@vitest/eslint-plugin'
+import tseslint from 'typescript-eslint'
+
+const __filename = fileURLToPath(import.meta.url)
+const __dirname = path.dirname(__filename)
+
+export default tseslint.config(
+  // Global rules and configuration
+  includeIgnoreFile(path.resolve(__dirname, '.gitignore')),
+  {
+    linterOptions: {
+      reportUnusedDisableDirectives: true,
+    },
+  },
+
+  // JavaScript-specific rules
+  eslint.configs.recommended,
+
+  // Typescript-specific rules
+  tseslint.configs.strictTypeChecked,
+  tseslint.configs.stylisticTypeChecked,
+  {
+    languageOptions: {
+      parserOptions: {
+        projectService: true,
+        tsconfigRootDir: __dirname,
+      },
+    },
+  },
+
+  {
+    files: ['**/*.?(c|m)js?(x)'],
+    ...tseslint.configs.disableTypeChecked,
+  },
+  node.configs['flat/recommended'],
+  {
+    rules: {
+      'n/no-extraneous-import': 'off',
+      'n/no-extraneous-require': 'off',
+      'n/no-missing-import': 'off',
+      'n/no-missing-require': 'off',
+      'n/no-unpublished-import': 'off',
+      'n/no-unpublished-require': 'off',
+    },
+  },
+
+  // Project-specific rules
+  {
+    ignores: ['.github/styles/', '**/__fixtures__/'],
+  },
+  {
+    files: ['**/*.?(c|m)ts?(x)'],
+    rules: {
+      // `interface` and `type` have different use cases, allow both
+      '@typescript-eslint/consistent-type-definitions': 'off',
+
+      // Ignore underscore-prefixed unused variables (mirrors tsc behavior)
+      '@typescript-eslint/no-unused-vars': [
+        'error',
+        {
+          args: 'all',
+          argsIgnorePattern: '^_',
+          caughtErrors: 'all',
+          caughtErrorsIgnorePattern: '^_',
+          destructuredArrayIgnorePattern: '^_',
+          ignoreRestSiblings: true,
+          varsIgnorePattern: '^_',
+        },
+      ],
+    },
+  },
+  {
+    rules: {
+      'no-restricted-imports': [
+        'error',
+        {
+          paths: [
+            {
+              name: 'node:process',
+              importNames: ['cwd'],
+              message: 'Use `command.workingDir` instead.',
+            },
+            {
+              name: 'process',
+              importNames: ['cwd'],
+              message: 'Use `command.workingDir` instead.',
+            },
+
+            {
+              name: 'chalk',
+              message:
+                'Use the safe chalk import that handles colors for json output: `import { chalk } from "src/utils/command-helpers.js"`',
+            },
+          ],
+        },
+      ],
+      'no-restricted-properties': [
+        'error',
+        {
+          object: 'process',
+          property: 'cwd',
+          message: '`process.cwd` is not permitted; use `command.workingDir` instead.',
+        },
+      ],
+    },
+  },
+
+  // Tests
+  {
+    files: ['**/*.test.?(c|m)[jt]s?(x)'],
+    plugins: { vitest },
+    rules: {
+      ...vitest.configs.recommended.rules,
+
+      'vitest/expect-expect': [
+        'error',
+        {
+          assertFunctionNames: [
+            // Defaults
+            'assert',
+            'expect',
+
+            // Fix issue where text-context-specific `expect()` calls trigger false positive
+            't.expect',
+            'ctx.expect',
+            'context.expect',
+
+            // Custom assertion functions
+            'assertNetlifyToml',
+          ],
+        },
+      ],
+    },
+  },
+
+  // XXX: Temporarily disabled rules: These rules are disabled because we have offending code that we haven't yet fixed.
+  {
+    rules: {
+      // Empty functions and blocks are useful (e.g `noop() {}`, `catch {}`) but can mask unintentionally omitted
+      // implementation. We should add explanatory comments like `// intentionally empty` and `// ignore error` in these
+      // scenarios to communicate intent.
+      'no-empty': 'off',
+      '@typescript-eslint/no-empty-function': 'off',
+
+      'n/no-unsupported-features/node-builtins': [
+        'error',
+        {
+          ignores: ['FormData', 'ReadableStream', 'Response', 'fetch', 'fs/promises.cp'],
+        },
+      ],
+    },
+  },
+
+  // Must be last
+  prettier,
+)