Add vue/no-root-v-if rule

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/no-root-v-if](./no-root-v-if.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/no-root-v-if.md

@@ -0,0 +1,39 @@
+---
+pageClass: rule-details
+sidebarDepth: 0
+title: vue/no-root-v-if
+description: enforce valid `v-if` directives on root element
+---
+# vue/no-root-v-if
+
+> 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>
+
+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/no-root-v-if': ['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/no-root-v-if.js)
+- [Test source](https://github.com/vuejs/eslint-plugin-vue/blob/master/tests/lib/rules/no-root-v-if.js)

lib/index.js

@@ -220,6 +220,7 @@ 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'),
+    'no-root-v-if': require('./rules/no-root-v-if'),
     '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/no-root-v-if.js

@@ -0,0 +1,70 @@
+/**
+ * @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.
+ */
+function getDirectivesLength(rootElements) {
+  let ifLength = 0
+  let elseLength = 0
+  let elseIfLength = 0
+
+  for (const element of rootElements) {
+    if (element.type === 'VElement') {
+      if (utils.hasDirective(element, 'if')) ifLength += 1
+      if (utils.hasDirective(element, 'else')) elseLength += 1
+      if (utils.hasDirective(element, 'else-if')) elseIfLength += 1
+    }
+  }
+
+  return {
+    ifLength,
+    elseLength,
+    elseIfLength
+  }
+}
+
+module.exports = {
+  meta: {
+    type: 'problem',
+    docs: {
+      description: 'enforce valid `v-if` directives on root element',
+      categories: undefined,
+      url: 'https://eslint.vuejs.org/rules/no-root-v-if.html'
+    },
+    fixable: null,
+    schema: []
+  },
+  /** @param {RuleContext} context */
+  create(context) {
+    return {
+      /** @param {Program} program */
+      Program(program) {
+        const element = program.templateBody
+        if (element == null) {
+          return
+        }
+
+        const rootElements = element.children.filter(utils.isVElement)
+        if (rootElements.length === 0) return
+        const { ifLength, elseLength, elseIfLength } =
+          getDirectivesLength(rootElements)
+        if (ifLength === 1 && elseLength === 0 && elseIfLength === 0) {
+          context.report({
+            node: element,
+            loc: element.loc,
+            message:
+              '`v-if` should not be used on root element without `v-else`.'
+          })
+        }
+      }
+    }
+  }
+}

tests/lib/rules/no-root-v-if.js

@@ -0,0 +1,116 @@
+/**
+ * @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/no-root-v-if')
+
+const tester = new RuleTester({
+  parser: require.resolve('vue-eslint-parser'),
+  parserOptions: { ecmaVersion: 2015 }
+})
+
+tester.run('no-root-v-if', 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`.']
+    },
+    {
+      filename: 'test.vue',
+      code: '<template><div /><div v-if="foo" /></template>',
+      errors: ['`v-if` should not be used on root element without `v-else`.']
+    }
+  ]
+})