feat: Add vue/no-multiple-objects-in-class rule (#1218)

* feat: Add

* feat: Add rule, test, and docs

* chore: run update

* chore: rename no-multiple-objects-in-class

* chore: fix docs url

* docs: fix pattern

* fix: consider bind

* chore: remove unused function

Author: tyankatsu0105

Diff for: docs/rules/README.md

@@ -286,6 +286,7 @@ For example:
 | [vue/no-bare-strings-in-template](./no-bare-strings-in-template.md) | disallow the use of bare strings in `<template>` |  |
 | [vue/no-boolean-default](./no-boolean-default.md) | disallow boolean defaults | :wrench: |
 | [vue/no-duplicate-attr-inheritance](./no-duplicate-attr-inheritance.md) | enforce `inheritAttrs` to be set to `false` when using `v-bind="$attrs"` |  |
+| [vue/no-multiple-objects-in-class](./no-multiple-objects-in-class.md) | disallow to pass multiple objects into array to class |  |
 | [vue/no-potential-component-option-typo](./no-potential-component-option-typo.md) | disallow a potential typo in your component property |  |
 | [vue/no-reserved-component-names](./no-reserved-component-names.md) | disallow the use of reserved names in component definitions |  |
 | [vue/no-restricted-component-options](./no-restricted-component-options.md) | disallow specific component option |  |

Diff for: docs/rules/no-multiple-objects-in-class.md

@@ -0,0 +1,37 @@
+---
+pageClass: rule-details
+sidebarDepth: 0
+title: vue/no-multiple-objects-in-class
+description: disallow to pass multiple objects into array to class
+---
+# vue/no-multiple-objects-in-class
+> disallow to pass multiple objects into array to class
+
+## :book: Rule Details
+
+This rule disallows to pass multiple objects into array to class.  
+
+<eslint-code-block :rules="{'vue/no-multiple-objects-in-class': ['error']}">
+
+```vue
+<template>
+  <div>
+    <!-- ✓ GOOD -->
+    <div :class="[{'foo': isFoo, 'bar': isBar}]" />
+
+    <!-- ✗ BAD -->
+    <div :class="[{'foo': isFoo}, {'bar': isBar}]" />
+  </div>
+</template>
+```
+
+</eslint-code-block>
+
+## :wrench: Options
+
+Nothing.
+
+## :mag: Implementation
+
+- [Rule source](https://github.com/vuejs/eslint-plugin-vue/blob/master/lib/rules/no-multiple-objects-in-class.js)
+- [Test source](https://github.com/vuejs/eslint-plugin-vue/blob/master/tests/lib/rules/no-multiple-objects-in-class.js)

Diff for: lib/index.js

@@ -74,6 +74,7 @@ module.exports = {
     'no-irregular-whitespace': require('./rules/no-irregular-whitespace'),
     'no-lifecycle-after-await': require('./rules/no-lifecycle-after-await'),
     'no-multi-spaces': require('./rules/no-multi-spaces'),
+    'no-multiple-objects-in-class': require('./rules/no-multiple-objects-in-class'),
     'no-multiple-slot-args': require('./rules/no-multiple-slot-args'),
     'no-multiple-template-root': require('./rules/no-multiple-template-root'),
     'no-mutating-props': require('./rules/no-mutating-props'),

Diff for: lib/rules/no-multiple-objects-in-class.js

@@ -0,0 +1,59 @@
+/**
+ * @author tyankatsu <https://github.com/tyankatsu0105>
+ * See LICENSE file in root directory for full license.
+ */
+'use strict'
+
+// ------------------------------------------------------------------------------
+// Requirements
+// ------------------------------------------------------------------------------
+
+const { defineTemplateBodyVisitor } = require('../utils')
+
+// ------------------------------------------------------------------------------
+// Rule Definition
+// ------------------------------------------------------------------------------
+
+/**
+ * count ObjectExpression element
+ * @param {VAttribute} node
+ * @return {number}
+ */
+function countObjectExpression(node) {
+  return node.value.expression.elements.filter(
+    (element) => element.type === 'ObjectExpression'
+  ).length
+}
+
+module.exports = {
+  meta: {
+    type: 'suggestion',
+    docs: {
+      description: 'disallow to pass multiple objects into array to class',
+      categories: undefined,
+      url: 'https://eslint.vuejs.org/rules/no-multiple-objects-in-class.html'
+    },
+    fixable: null,
+    schema: [],
+    messages: {
+      unexpected: 'Unexpected multiple objects. Merge objects.'
+    }
+  },
+  /** @param {RuleContext} context */
+  create(context) {
+    return defineTemplateBodyVisitor(context, {
+      /** @param {VAttribute} node */
+      'VAttribute[directive=true][key.argument.name="class"][key.name.name="bind"][value.expression.type="ArrayExpression"]'(
+        node
+      ) {
+        if (countObjectExpression(node) > 1) {
+          context.report({
+            node,
+            loc: node.loc,
+            messageId: 'unexpected'
+          })
+        }
+      }
+    })
+  }
+}

Diff for: tests/lib/rules/no-multiple-objects-in-class.js

@@ -0,0 +1,48 @@
+/**
+ * @author tyankatsu <https://github.com/tyankatsu0105>
+ */
+'use strict'
+
+// ------------------------------------------------------------------------------
+// Requirements
+// ------------------------------------------------------------------------------
+
+const rule = require('../../../lib/rules/no-multiple-objects-in-class')
+const RuleTester = require('eslint').RuleTester
+
+// ------------------------------------------------------------------------------
+// Tests
+// ------------------------------------------------------------------------------
+
+const ruleTester = new RuleTester({
+  parser: require.resolve('vue-eslint-parser'),
+  parserOptions: { ecmaVersion: 2015, sourceType: 'module' }
+})
+
+ruleTester.run('no-multiple-objects-in-class', rule, {
+  valid: [
+    `<template><div :class="[{'foo': isFoo}]" /></template>`,
+    `<template><div :class="[{'foo': isFoo, 'bar': isBar}]" /></template>`,
+    `<template><div v-foo:class="[{'foo': isFoo}, {'bar': isBar}]" /></template>`
+  ],
+  invalid: [
+    {
+      code: `<template><div v-bind:class="[{'foo': isFoo}, {'bar': isBar}]" /></template>`,
+      errors: [
+        {
+          message: 'Unexpected multiple objects. Merge objects.',
+          type: 'VAttribute'
+        }
+      ]
+    },
+    {
+      code: `<template><div :class="[{'foo': isFoo}, {'bar': isBar}]" /></template>`,
+      errors: [
+        {
+          message: 'Unexpected multiple objects. Merge objects.',
+          type: 'VAttribute'
+        }
+      ]
+    }
+  ]
+})