Add rootDir setting to eslint-plugin-next (vercel#27918)

## Introduction

This PR enables setting a `rootDir` for a Next.js project, and follows the same pattern used by [`@typescript-eslint/parser`](https://github.com/typescript-eslint/typescript-eslint/tree/master/packages/parser#parseroptionsproject).

## Details

Previously, users had to pass paths to the rule itself.
```js
module.exports = {
  rules: { 
    "@next/next/no-html-link-for-pages": [
      "error",
      // This could be a string, or array of strings.
      "/packages/my-app/pages",
    ],
  },
};
```

With this PR, this has been simplified (the previous implementation still works as expected).
```js
module.exports = {
  settings: { 
    next: {
      rootDir: "/packages/my-app",
    },
  },
  rules: { 
    "@next/next/no-html-link-for-pages": "error",
  },
};
```

Further, this rule allows the use of globs, again aligning with `@typescript-eslint/parser`.
```js
module.exports = {
  settings: { 
    next: {
      // Globs
      rootDir: "/packages/*",
      rootDir: "/packages/{app-a,app-b}",

      // Arrays
      rootDir: ["/app-a", "/app-b"],
      
      // Arrays with globs
      rootDir: ["/main-app", "/other-apps/*"],
  },
};
```

This enables users to either provide per-workspace configuration with overrides, or to use globs for situations like monorepos where the apps share a domain (micro-frontends).

This doesn't solve, but improves vercel#26330.

## Feature

- [x] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [x] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`

## Documentation / Examples

- [x] Make sure the linting passes

Author: mrmckeb

packages/eslint-plugin-next/README.md

@@ -0,0 +1,4 @@
+# `@next/eslint-plugin-next`
+
+Documentation for `@next/eslint-plugin-next` can be found at:
+https://nextjs.org/docs/basic-features/eslint#eslint-plugin

packages/eslint-plugin-next/jsconfig.json

@@ -0,0 +1,7 @@
+{
+  "compilerOptions": {
+    "module": "commonjs",
+    "target": "es2019"
+  },
+  "exclude": ["node_modules"]
+}

packages/eslint-plugin-next/lib/rules/google-font-display.js

@@ -1,4 +1,4 @@
-const NodeAttributes = require('../utils/nodeAttributes.js')
+const NodeAttributes = require('../utils/node-attributes.js')
 
 module.exports = {
   meta: {

packages/eslint-plugin-next/lib/rules/google-font-preconnect.js

@@ -1,4 +1,4 @@
-const NodeAttributes = require('../utils/nodeAttributes.js')
+const NodeAttributes = require('../utils/node-attributes.js')
 
 module.exports = {
   meta: {

packages/eslint-plugin-next/lib/rules/link-passhref.js

@@ -1,4 +1,4 @@
-const NodeAttributes = require('../utils/nodeAttributes.js')
+const NodeAttributes = require('../utils/node-attributes.js')
 
 module.exports = {
   meta: {

packages/eslint-plugin-next/lib/rules/no-html-link-for-pages.js

@@ -1,5 +1,7 @@
+// @ts-check
 const path = require('path')
 const fs = require('fs')
+const getRootDir = require('../utils/get-root-dirs')
 const {
   getUrlFromPagesDirectories,
   normalizeURL,
@@ -20,7 +22,7 @@ const fsExistsSyncCache = {}
 module.exports = {
   meta: {
     docs: {
-      description: 'Prohibit full page refresh for nextjs pages',
+      description: 'Prohibit full page refresh for Next.js pages',
       category: 'HTML',
       recommended: true,
     },
@@ -43,14 +45,27 @@ module.exports = {
     ],
   },
 
+  /**
+   * Creates an ESLint rule listener.
+   *
+   * @param {import('eslint').Rule.RuleContext} context - ESLint rule context
+   * @returns {import('eslint').Rule.RuleListener} An ESLint rule listener
+   */
   create: function (context) {
-    const [customPagesDirectory] = context.options
-    const pagesDirs = customPagesDirectory
-      ? [customPagesDirectory].flat()
-      : [
-          path.join(context.getCwd(), 'pages'),
-          path.join(context.getCwd(), 'src', 'pages'),
-        ]
+    /** @type {(string|string[])[]} */
+    const ruleOptions = context.options
+    const [customPagesDirectory] = ruleOptions
+
+    const rootDirs = getRootDir(context)
+
+    const pagesDirs = (customPagesDirectory
+      ? [customPagesDirectory]
+      : rootDirs.map((dir) => [
+          path.join(dir, 'pages'),
+          path.join(dir, 'src', 'pages'),
+        ])
+    ).flat()
+
     const foundPagesDirs = pagesDirs.filter((dir) => {
       if (fsExistsSyncCache[dir] === undefined) {
         fsExistsSyncCache[dir] = fs.existsSync(dir)

packages/eslint-plugin-next/lib/rules/no-page-custom-font.js

@@ -1,4 +1,4 @@
-const NodeAttributes = require('../utils/nodeAttributes.js')
+const NodeAttributes = require('../utils/node-attributes.js')
 
 module.exports = {
   meta: {

packages/eslint-plugin-next/lib/utils/get-root-dirs.js

@@ -0,0 +1,40 @@
+// @ts-check
+const glob = require('glob')
+
+/**
+ * Process a Next.js root directory glob.
+ *
+ * @param {string} rootDir - A Next.js root directory glob.
+ * @returns {string[]} - An array of Root directories.
+ */
+const processRootDir = (rootDir) => {
+  // Ensures we only match folders.
+  if (!rootDir.endsWith('/')) rootDir += '/'
+  return glob.sync(rootDir)
+}
+
+/**
+ * Gets one or more Root
+ *
+ * @param {import('eslint').Rule.RuleContext} context - ESLint rule context
+ * @returns An array of root directories.
+ */
+const getRootDirs = (context) => {
+  let rootDirs = [context.getCwd()]
+
+  /** @type {{rootDir?:string|string[]}|undefined} */
+  const nextSettings = context.settings.next || {}
+  let rootDir = nextSettings.rootDir
+
+  if (typeof rootDir === 'string') {
+    rootDirs = processRootDir(rootDir)
+  } else if (Array.isArray(rootDir)) {
+    rootDirs = rootDir
+      .map((dir) => (typeof dir === 'string' ? processRootDir(dir) : []))
+      .flat()
+  }
+
+  return rootDirs
+}
+
+module.exports = getRootDirs

packages/eslint-plugin-next/lib/utils/nodeAttributes.js renamed to packages/eslint-plugin-next/lib/utils/node-attributes.js

@@ -7,5 +7,14 @@
   "repository": {
     "url": "vercel/next.js",
     "directory": "packages/eslint-plugin-next"
+  },
+  "files": [
+    "lib"
+  ],
+  "dependencies": {
+    "glob": "7.1.7"
+  },
+  "devDependencies": {
+    "@types/eslint": "7.28.0"
   }
 }