Add v-for-delimiter-style rule

docs/rules/README.md

@@ -312,6 +312,7 @@ For example:
 | [vue/script-indent](./script-indent.md) | enforce consistent indentation in `<script>` | :wrench: |
 | [vue/sort-keys](./sort-keys.md) | enforce sort-keys in a manner that is compatible with order-in-components |  |
 | [vue/static-class-names-order](./static-class-names-order.md) | enforce static class names order | :wrench: |
+| [vue/v-for-delimiter-style](./v-for-delimiter-style.md) | enforce `v-for` directive's delimiter style | :wrench: |
 | [vue/v-on-function-call](./v-on-function-call.md) | enforce or forbid parentheses after method calls without arguments in `v-on` directives | :wrench: |
 
 ### Extension Rules

docs/rules/v-for-delimiter-style.md

@@ -0,0 +1,65 @@
+---
+pageClass: rule-details
+sidebarDepth: 0
+title: vue/v-for-delimiter-style
+description: enforce `v-for` directive's delimiter style
+---
+# vue/v-for-delimiter-style
+> enforce `v-for` directive's delimiter style
+
+- :wrench: The `--fix` option on the [command line](https://eslint.org/docs/user-guide/command-line-interface#fixing-problems) can automatically fix some of the problems reported by this rule.
+
+## :book: Rule Details
+
+This rule enforces which delimiter (`in` or `of`) should be used in `v-for` directives.
+
+<eslint-code-block fix :rules="{'vue/v-for-delimiter-style': ['error']}">
+
+```vue
+<template>
+  <!-- ✓ GOOD -->
+  <div v-for="x in xs" />
+
+  <!-- ✗ BAD -->
+  <div v-for="x of xs" />
+</template>
+```
+
+</eslint-code-block>
+
+## :wrench: Options
+Default is set to `in`.
+
+```json
+{
+  "vue/v-for-delimiter-style": ["error", "in" | "of"]
+}
+```
+
+- `"in"` (default) ... requires using `in`.
+- `"of"` ... requires using `of`.
+
+### `"of"`
+
+<eslint-code-block fix :rules="{'vue/v-for-delimiter-style': ['error', 'of']}">
+
+```vue
+<template>
+  <!-- ✓ GOOD -->
+  <div v-for="x of xs" />
+
+  <!-- ✗ BAD -->
+  <div v-for="x in xs" />
+</template>
+```
+
+</eslint-code-block>
+
+## :books: Further Reading
+
+- [Guide - List Rendering](https://v3.vuejs.org/guide/list.html)
+
+## :mag: Implementation
+
+- [Rule source](https://github.com/vuejs/eslint-plugin-vue/blob/master/lib/rules/v-for-delimiter-style.js)
+- [Test source](https://github.com/vuejs/eslint-plugin-vue/blob/master/tests/lib/rules/v-for-delimiter-style.js)

lib/index.js

@@ -146,6 +146,7 @@ module.exports = {
     'this-in-template': require('./rules/this-in-template'),
     'use-v-on-exact': require('./rules/use-v-on-exact'),
     'v-bind-style': require('./rules/v-bind-style'),
+    'v-for-delimiter-style': require('./rules/v-for-delimiter-style'),
     'v-on-function-call': require('./rules/v-on-function-call'),
     'v-on-style': require('./rules/v-on-style'),
     'v-slot-style': require('./rules/v-slot-style'),

lib/rules/v-for-delimiter-style.js

@@ -0,0 +1,69 @@
+/**
+ * @fileoverview enforce `v-for` directive's delimiter style
+ * @author Flo Edelmann
+ * @copyright 2020 Flo Edelmann. All rights reserved.
+ * See LICENSE file in root directory for full license.
+ */
+'use strict'
+
+// ------------------------------------------------------------------------------
+// Requirements
+// ------------------------------------------------------------------------------
+
+const utils = require('../utils')
+
+// ------------------------------------------------------------------------------
+// Rule Definition
+// ------------------------------------------------------------------------------
+
+module.exports = {
+  meta: {
+    type: 'suggestion',
+    docs: {
+      description: "enforce `v-for` directive's delimiter style",
+      categories: undefined,
+      recommended: false,
+      url: 'https://eslint.vuejs.org/rules/v-for-delimiter-style.html'
+    },
+    fixable: 'code',
+    schema: [{ enum: ['in', 'of'] }]
+  },
+  /** @param {RuleContext} context */
+  create(context) {
+    const preferredDelimiter =
+      /** @type {string|undefined} */ (context.options[0]) || 'in'
+
+    return utils.defineTemplateBodyVisitor(context, {
+      /** @param {VForExpression} node */
+      VForExpression(node) {
+        const tokenStore =
+          context.parserServices.getTemplateBodyTokenStore &&
+          context.parserServices.getTemplateBodyTokenStore()
+
+        const delimiterToken = /** @type {Token} */ (tokenStore.getTokenAfter(
+          node.left.length
+            ? node.left[node.left.length - 1]
+            : tokenStore.getFirstToken(node),
+          (token) => token.type !== 'Punctuator' || token.value !== ')'
+        ))
+
+        if (delimiterToken.value === preferredDelimiter) {
+          return
+        }
+
+        context.report({
+          node,
+          loc: node.loc,
+          message: `Expected '{{preferredDelimiter}}' instead of '{{usedDelimiter}}' in 'v-for'.`,
+          data: {
+            preferredDelimiter,
+            usedDelimiter: delimiterToken.value
+          },
+          *fix(fixer) {
+            yield fixer.replaceText(delimiterToken, preferredDelimiter)
+          }
+        })
+      }
+    })
+  }
+}

tests/lib/rules/v-for-delimiter-style.js

@@ -0,0 +1,98 @@
+/**
+ * @fileoverview enforce `v-for` directive's delimiter style
+ * @author Flo Edelmann
+ * @copyright 2020 Flo Edelmann. All rights reserved.
+ * See LICENSE file in root directory for full license.
+ */
+'use strict'
+
+// ------------------------------------------------------------------------------
+// Requirements
+// ------------------------------------------------------------------------------
+
+const RuleTester = require('eslint').RuleTester
+const rule = require('../../../lib/rules/v-for-delimiter-style')
+
+// ------------------------------------------------------------------------------
+// Tests
+// ------------------------------------------------------------------------------
+
+const tester = new RuleTester({
+  parser: require.resolve('vue-eslint-parser'),
+  parserOptions: { ecmaVersion: 2015 }
+})
+
+tester.run('v-for-delimiter-style', rule, {
+  valid: [
+    {
+      filename: 'test.vue',
+      code: ''
+    },
+    {
+      filename: 'test.vue',
+      code: '<template><div v-for="x in xs"></div></template>'
+    },
+    {
+      filename: 'test.vue',
+      code: '<template><div v-for="x    in xs"></div></template>'
+    },
+    {
+      filename: 'test.vue',
+      code: '<template><div v-for="x in    xs"></div></template>'
+    },
+    {
+      filename: 'test.vue',
+      code: '<template><div v-for="x    in    xs"></div></template>'
+    },
+    {
+      filename: 'test.vue',
+      code: '<template><div v-for="x in xs"></div></template>',
+      options: ['in']
+    },
+    {
+      filename: 'test.vue',
+      code: '<template><div v-for="x of xs"></div></template>',
+      options: ['of']
+    }
+  ],
+  invalid: [
+    {
+      filename: 'test.vue',
+      code: '<template><div v-for="x of xs"></div></template>',
+      output: '<template><div v-for="x in xs"></div></template>',
+      errors: ["Expected 'in' instead of 'of' in 'v-for'."]
+    },
+    {
+      filename: 'test.vue',
+      code: '<template><div v-for="x    of xs"></div></template>',
+      output: '<template><div v-for="x    in xs"></div></template>',
+      errors: ["Expected 'in' instead of 'of' in 'v-for'."]
+    },
+    {
+      filename: 'test.vue',
+      code: '<template><div v-for="x of    xs"></div></template>',
+      output: '<template><div v-for="x in    xs"></div></template>',
+      errors: ["Expected 'in' instead of 'of' in 'v-for'."]
+    },
+    {
+      filename: 'test.vue',
+      code: '<template><div v-for="x    of    xs"></div></template>',
+      output: '<template><div v-for="x    in    xs"></div></template>',
+      errors: ["Expected 'in' instead of 'of' in 'v-for'."]
+    },
+    {
+      filename: 'test.vue',
+      options: ['in'],
+      code: '<template><div v-for="x of xs"></div></template>',
+      output: '<template><div v-for="x in xs"></div></template>',
+      errors: ["Expected 'in' instead of 'of' in 'v-for'."]
+    },
+    {
+      filename: 'test.vue',
+      options: ['of'],
+      code: '<template><div v-for="x in xs"></div></template>',
+      output: '<template><div v-for="x of xs"></div></template>',
+      errors: ["Expected 'of' instead of 'in' in 'v-for'."]
+    }
+  ]
+})