feat(no-this-in-before-router-enter): create rule

docs/rules/README.md

@@ -313,6 +313,7 @@ For example:
 | [vue/no-restricted-v-bind](./no-restricted-v-bind.md) | disallow specific argument in `v-bind` |  |
 | [vue/no-static-inline-styles](./no-static-inline-styles.md) | disallow static inline `style` attributes |  |
 | [vue/no-template-target-blank](./no-template-target-blank.md) | disallow target="_blank" attribute without rel="noopener noreferrer" |  |
+| [vue/no-this-in-before-route-enter](./no-this-in-before-route-enter.md) | disallow this usage in a beforeRouteEnter method |  |
 | [vue/no-unregistered-components](./no-unregistered-components.md) | disallow using components that are not registered inside templates |  |
 | [vue/no-unsupported-features](./no-unsupported-features.md) | disallow unsupported Vue.js syntax on the specified version | :wrench: |
 | [vue/no-unused-properties](./no-unused-properties.md) | disallow unused properties |  |

docs/rules/no-this-in-before-route-enter.md

@@ -0,0 +1,115 @@
+---
+pageClass: rule-details
+sidebarDepth: 0
+title: vue/no-this-in-before-route-enter
+description: disallow this usage in a beforeRouteEnter method
+---
+# vue/no-this-in-before-route-enter
+
+> disallow this usage in a beforeRouteEnter method
+
+- :exclamation: <badge text="This rule has not been released yet." vertical="middle" type="error"> ***This rule has not been released yet.*** </badge>
+
+## Rule Details
+
+Because lack of `this` in the `beforeRouteEnter` [(docs)](https://router.vuejs.org/guide/advanced/navigation-guards.html#in-component-guards). This behavior isn't obvious, so it's pretty easy to make a `TypeError`. Especially during some refactor. 
+
+Bad:
+
+<eslint-code-block :rules="{'vue/no-this-in-before-route-enter': ['error']}">
+
+```vue
+<script>
+export default {
+  beforeRouteEnter() {
+    this.method(); // Uncaught TypeError: Cannot read property 'method' of undefined      
+  }   
+}
+</script>
+```
+
+</eslint-code-block>
+
+Bad:
+
+<eslint-code-block :rules="{'vue/no-this-in-before-route-enter': ['error']}">
+
+```vue
+<script>
+export default {
+  beforeRouteEnter() {
+    this.attribute = 42;
+  }   
+}
+</script>
+```
+
+</eslint-code-block>
+
+Bad:
+
+<eslint-code-block :rules="{'vue/no-this-in-before-route-enter': ['error']}">
+
+```vue
+<script>
+export default {
+  beforeRouteEnter() {
+    if (this.value === 42) {
+
+    }
+  }   
+}
+</script>
+```
+
+</eslint-code-block>
+
+
+Bad:
+
+<eslint-code-block :rules="{'vue/no-this-in-before-route-enter': ['error']}">
+
+```vue
+<script>
+export default {
+  beforeRouteEnter() {
+    this.attribute = this.method();
+  }   
+}
+</script>
+```
+
+</eslint-code-block>
+
+Good:
+
+<eslint-code-block :rules="{'vue/no-this-in-before-route-enter': ['error']}">
+
+```vue
+<script>
+export default {
+  beforeRouteEnter() {
+    // anything without this
+  }   
+}
+</script>
+```
+
+</eslint-code-block>
+
+### Options
+
+Nothing.
+
+## When Not To Use It
+
+When [vue-router](https://router.vuejs.org/) is not installed.
+
+## Further Reading
+
+[vue-router - in-component-guards](https://router.vuejs.org/guide/advanced/navigation-guards.html#in-component-guards)
+
+## :mag: Implementation
+
+- [Rule source](https://github.com/vuejs/eslint-plugin-vue/blob/master/lib/rules/no-this-in-before-route-enter.js)
+- [Test source](https://github.com/vuejs/eslint-plugin-vue/blob/master/tests/lib/rules/no-this-in-before-route-enter.js)

lib/index.js

@@ -113,6 +113,7 @@ module.exports = {
     'no-template-shadow': require('./rules/no-template-shadow'),
     'no-template-target-blank': require('./rules/no-template-target-blank'),
     'no-textarea-mustache': require('./rules/no-textarea-mustache'),
+    'no-this-in-before-route-enter': require('./rules/no-this-in-before-route-enter'),
     'no-unregistered-components': require('./rules/no-unregistered-components'),
     'no-unsupported-features': require('./rules/no-unsupported-features'),
     'no-unused-components': require('./rules/no-unused-components'),

lib/rules/no-this-in-before-route-enter.js

@@ -0,0 +1,91 @@
+/**
+ * @fileoverview Don't use this in a beforeRouteEnter method
+ * @author Przemyslaw Jan Beigert
+ */
+'use strict'
+
+// ------------------------------------------------------------------------------
+// Requirements
+// ------------------------------------------------------------------------------
+
+const utils = require('../utils')
+
+// ------------------------------------------------------------------------------
+// Rule Definition
+// ------------------------------------------------------------------------------
+
+module.exports = {
+  meta: {
+    type: 'problem',
+    docs: {
+      description: 'disallow this usage in a beforeRouteEnter method',
+      categories: null,
+      url: 'https://eslint.vuejs.org/rules/no-this-in-before-route-enter.html'
+    },
+    fixable: null,
+    schema: [],
+    messages: {
+      disallow:
+        "'beforeRouteEnter' does NOT have access to `this` component instance. https://router.vuejs.org/guide/advanced/navigation-guards.html#in-component-guards."
+    }
+  },
+  /** @param {RuleContext} context */
+  create(context) {
+    /**
+     * @typedef {object} ScopeStack
+     * @property {ScopeStack | null} upper
+     * @property {FunctionExpression | FunctionDeclaration} node
+     * @property {boolean} beforeRouteEnter
+     */
+    /** @type {Set<FunctionExpression>} */
+    const beforeRouteEnterFunctions = new Set()
+    /** @type {ScopeStack | null} */
+    let scopeStack = null
+
+    /**
+     * @param {FunctionExpression | FunctionDeclaration | ArrowFunctionExpression} node
+     */
+    function onFunctionEnter(node) {
+      if (node.type === 'ArrowFunctionExpression') {
+        return
+      }
+      scopeStack = {
+        upper: scopeStack,
+        node,
+        beforeRouteEnter: beforeRouteEnterFunctions.has(
+          /** @type {never} */ (node)
+        )
+      }
+    }
+
+    /**
+     * @param {FunctionExpression | FunctionDeclaration | ArrowFunctionExpression} node
+     */
+    function onFunctionExit(node) {
+      if (scopeStack && scopeStack.node === node) {
+        scopeStack = scopeStack.upper
+      }
+    }
+    return utils.defineVueVisitor(context, {
+      onVueObjectEnter(node) {
+        const beforeRouteEnter = utils.findProperty(node, 'beforeRouteEnter')
+        if (
+          beforeRouteEnter &&
+          beforeRouteEnter.value.type === 'FunctionExpression'
+        ) {
+          beforeRouteEnterFunctions.add(beforeRouteEnter.value)
+        }
+      },
+      ':function': onFunctionEnter,
+      ':function:exit': onFunctionExit,
+      ThisExpression(node) {
+        if (scopeStack && scopeStack.beforeRouteEnter) {
+          context.report({
+            node,
+            messageId: 'disallow'
+          })
+        }
+      }
+    })
+  }
+}