Added valid-v-if-template-root rule.

Author: perrysong

docs/rules/index.md

@@ -118,6 +118,7 @@ Rules in this category are enabled for all presets provided by eslint-plugin-vue
 | [vue/valid-v-else](./valid-v-else.md) | enforce valid `v-else` directives |  | :three::two::warning: |
 | [vue/valid-v-for](./valid-v-for.md) | enforce valid `v-for` directives |  | :three::two::warning: |
 | [vue/valid-v-html](./valid-v-html.md) | enforce valid `v-html` directives |  | :three::two::warning: |
+| [vue/valid-v-if-template-root](./valid-v-if-template-root.md) | enforce valid `v-if` directives on root element |  | :three::two::warning: |
 | [vue/valid-v-if](./valid-v-if.md) | enforce valid `v-if` directives |  | :three::two::warning: |
 | [vue/valid-v-is](./valid-v-is.md) | enforce valid `v-is` directives |  | :three::warning: |
 | [vue/valid-v-memo](./valid-v-memo.md) | enforce valid `v-memo` directives |  | :three::warning: |

docs/rules/valid-template-root.md

@@ -46,4 +46,4 @@ This rule was introduced in eslint-plugin-vue v3.11.0
 ## :mag: Implementation
 
 - [Rule source](https://github.com/vuejs/eslint-plugin-vue/blob/master/lib/rules/valid-template-root.js)
-- [Test source](https://github.com/vuejs/eslint-plugin-vue/blob/master/tests/lib/rules/valid-template-root.js)
+- [Test source](https://github.com/vuejs/eslint-plugin-vue/blob/master/tests/lib/rules/valid-template-root.js)

docs/rules/valid-v-if-template-root.md

@@ -0,0 +1,40 @@
+---
+pageClass: rule-details
+sidebarDepth: 0
+title: vue/valid-v-if-template-root
+description: enforce valid `v-if` directives on root element
+---
+# vue/valid-v-if-template-root
+
+> enforce valid `v-if` directives on root element
+
+- :exclamation: <badge text="This rule has not been released yet." vertical="middle" type="error"> ***This rule has not been released yet.*** </badge>
+- :gear: This rule is included in all of `"plugin:vue/vue3-essential"`, `"plugin:vue/essential"`, `"plugin:vue/vue3-strongly-recommended"`, `"plugin:vue/strongly-recommended"`, `"plugin:vue/vue3-recommended"` and `"plugin:vue/recommended"`.
+
+This rule checks whether every template root is valid.
+
+## :book: Rule Details
+
+This rule reports the template root in the following cases:
+
+<eslint-code-block :rules="{'vue/valid-v-if-template-root': ['error']}">
+
+```vue
+<!--  `v-if` should not be used on root element without `v-else` -->
+<template>
+  <div v-if="foo"></div>
+</template>
+
+<template><custom-component v-if="shouldShow" /></template>
+```
+
+</eslint-code-block>
+
+## :wrench: Options
+
+Nothing.
+
+## :mag: Implementation
+
+- [Rule source](https://github.com/vuejs/eslint-plugin-vue/blob/master/lib/rules/valid-v-if-template-root.js)
+- [Test source](https://github.com/vuejs/eslint-plugin-vue/blob/master/tests/lib/rules/valid-v-if-template-root.js)

lib/configs/essential.js

@@ -62,6 +62,7 @@ module.exports = {
     'vue/valid-v-else': 'error',
     'vue/valid-v-for': 'error',
     'vue/valid-v-html': 'error',
+    'vue/valid-v-if-template-root': 'error',
     'vue/valid-v-if': 'error',
     'vue/valid-v-model': 'error',
     'vue/valid-v-on': 'error',

lib/configs/vue3-essential.js

@@ -77,6 +77,7 @@ module.exports = {
     'vue/valid-v-else': 'error',
     'vue/valid-v-for': 'error',
     'vue/valid-v-html': 'error',
+    'vue/valid-v-if-template-root': 'error',
     'vue/valid-v-if': 'error',
     'vue/valid-v-is': 'error',
     'vue/valid-v-memo': 'error',

lib/index.js

@@ -219,6 +219,7 @@ module.exports = {
     'valid-v-else': require('./rules/valid-v-else'),
     'valid-v-for': require('./rules/valid-v-for'),
     'valid-v-html': require('./rules/valid-v-html'),
+    'valid-v-if-template-root': require('./rules/valid-v-if-template-root'),
     'valid-v-if': require('./rules/valid-v-if'),
     'valid-v-is': require('./rules/valid-v-is'),
     'valid-v-memo': require('./rules/valid-v-memo'),

lib/rules/valid-v-if-template-root.js

@@ -0,0 +1,72 @@
+/**
+ * @author Perry Song
+ * @copyright 2023 Perry Song. All rights reserved.
+ * See LICENSE file in root directory for full license.
+ */
+'use strict'
+
+const utils = require('../utils')
+
+/**
+ * Get the number of root element directive
+ * @param {VNode[]} rootElements The start tag node to check.
+ * @param {string} directiveName The directive name to check.
+ */
+function getDirectiveLength(rootElements, directiveName) {
+  if (!directiveName) return 0
+  return rootElements.filter(
+    (element) =>
+      element.type === 'VElement' && utils.hasDirective(element, directiveName)
+  ).length
+}
+
+module.exports = {
+  meta: {
+    type: 'problem',
+    docs: {
+      description: 'enforce valid `v-if` directives on root element',
+      categories: ['vue3-essential', 'essential'],
+      url: 'https://eslint.vuejs.org/rules/valid-v-if-template-root.html'
+    },
+    fixable: null,
+    schema: []
+  },
+  /** @param {RuleContext} context */
+  create(context) {
+    const sourceCode = context.getSourceCode()
+
+    return {
+      /** @param {Program} program */
+      Program(program) {
+        const element = program.templateBody
+        if (element == null) {
+          return
+        }
+
+        const rootElements = []
+        for (const child of element.children) {
+          if (sourceCode.getText(child).trim() !== '') {
+            rootElements.push(child)
+          }
+        }
+
+        if (rootElements.length === 0) return
+        const hasRootVIfLength = getDirectiveLength(rootElements, 'if')
+        const hasRootVElseLength = getDirectiveLength(rootElements, 'else')
+        const hasRootVElseIfLength = getDirectiveLength(rootElements, 'else-if')
+        if (
+          hasRootVIfLength === 1 &&
+          hasRootVElseLength === 0 &&
+          hasRootVElseIfLength === 0
+        ) {
+          context.report({
+            node: element,
+            loc: element.loc,
+            message:
+              '`v-if` should not be used on root element without `v-else`.'
+          })
+        }
+      }
+    }
+  }
+}

tests/lib/rules/valid-v-if-template-root.js

@@ -0,0 +1,111 @@
+/**
+ * @author Perry Song
+ * @copyright 2023 Perry Song. All rights reserved.
+ * See LICENSE file in root directory for full license.
+ */
+'use strict'
+
+const RuleTester = require('eslint').RuleTester
+const rule = require('../../../lib/rules/valid-v-if-template-root')
+
+const tester = new RuleTester({
+  parser: require.resolve('vue-eslint-parser'),
+  parserOptions: { ecmaVersion: 2015 }
+})
+
+tester.run('valid-v-if-template-root', rule, {
+  valid: [
+    {
+      filename: 'test.vue',
+      code: ''
+    },
+    {
+      filename: 'test.vue',
+      code: '<template><div>abc</div></template>'
+    },
+    {
+      filename: 'test.vue',
+      code: '<template>\n    <div>abc</div>\n</template>'
+    },
+    {
+      filename: 'test.vue',
+      code: '<template>\n    <!-- comment -->\n    <div>abc</div>\n</template>'
+    },
+    {
+      filename: 'test.vue',
+      code: '<template>\n    <!-- comment -->\n    <div v-if="foo">abc</div>\n    <div v-else>abc</div>\n</template>'
+    },
+    {
+      filename: 'test.vue',
+      code: '<template>\n    <!-- comment -->\n    <div v-if="foo">abc</div>\n    <div v-else-if="bar">abc</div>\n    <div v-else>abc</div>\n</template>'
+    },
+    {
+      filename: 'test.vue',
+      code: `<template>\n    <c1 v-if="1" />\n    <c2 v-else-if="1" />\n    <c3 v-else />\n</template>`
+    },
+    {
+      filename: 'test.vue',
+      code: '<template><div v-if="foo"></div><div v-else-if="bar"></div></template>'
+    },
+    {
+      filename: 'test.vue',
+      code: '<template src="foo.html"></template>'
+    },
+    {
+      filename: 'test.vue',
+      code: '<template><div><textarea/>test</div></template>'
+    },
+    {
+      filename: 'test.vue',
+      code: '<template><table><custom-thead></custom-thead></table></template>'
+    },
+    {
+      filename: 'test.vue',
+      code: '<template><div></div><div></div></template>'
+    },
+    {
+      filename: 'test.vue',
+      code: '<template>\n    <div></div>\n    <div></div>\n</template>'
+    },
+    {
+      filename: 'test.vue',
+      code: '<template>{{a b c}}</template>'
+    },
+    {
+      filename: 'test.vue',
+      code: '<template><div></div>aaaaaa</template>'
+    },
+    {
+      filename: 'test.vue',
+      code: '<template>aaaaaa<div></div></template>'
+    },
+    {
+      filename: 'test.vue',
+      code: '<template><div v-for="x in list"></div></template>'
+    },
+    {
+      filename: 'test.vue',
+      code: '<template><slot></slot></template>'
+    },
+    {
+      filename: 'test.vue',
+      code: '<template><template></template></template>'
+    },
+    {
+      filename: 'test.vue',
+      code: '<template> <div v-if="mode === \'a\'"></div><div v-if="mode === \'b\'"></div></template>'
+    }
+  ],
+  invalid: [
+    {
+      filename: 'test.vue',
+      code: '<template><custom-component v-if="foo"></custom-component></template>',
+      errors: ['`v-if` should not be used on root element without `v-else`.']
+    },
+    {
+      filename: 'test.vue',
+      code: '<template><div v-if="foo"></div></template>',
+      errors: ['`v-if` should not be used on root element without `v-else`.']
+    }
+  ]
+})