Add vue/no-root-v-if rule (#2138)

Co-authored-by: perrysong <perrysong@xiaoman.cn>
Co-authored-by: Flo Edelmann <git@flo-edelmann.de>

docs/rules/index.md

@@ -240,6 +240,7 @@ For example:
 | [vue/no-restricted-props](./no-restricted-props.md) | disallow specific props | :bulb: | :hammer: |
 | [vue/no-restricted-static-attribute](./no-restricted-static-attribute.md) | disallow specific attribute |  | :hammer: |
 | [vue/no-restricted-v-bind](./no-restricted-v-bind.md) | disallow specific argument in `v-bind` |  | :hammer: |
+| [vue/no-root-v-if](./no-root-v-if.md) | disallow `v-if` directives on root element |  | :hammer: |
 | [vue/no-static-inline-styles](./no-static-inline-styles.md) | disallow static inline `style` attributes |  | :hammer: |
 | [vue/no-template-target-blank](./no-template-target-blank.md) | disallow target="_blank" attribute without rel="noopener noreferrer" | :bulb: | :warning: |
 | [vue/no-this-in-before-route-enter](./no-this-in-before-route-enter.md) | disallow `this` usage in a `beforeRouteEnter` method |  | :warning: |

docs/rules/no-root-v-if.md

@@ -0,0 +1,37 @@
+---
+pageClass: rule-details
+sidebarDepth: 0
+title: vue/no-root-v-if
+description: disallow `v-if` directives on root element
+---
+
+# vue/no-root-v-if
+
+> disallow `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 reports template roots with `v-if`. Rendering of the whole component could be made conditional in the parent component (with a `v-if` there) instead.
+
+## :book: Rule Details
+
+This rule reports the template root in the following cases:
+
+<eslint-code-block :rules="{'vue/no-root-v-if': ['error']}">
+
+```vue
+<template>
+  <div v-if="foo"></div>
+</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

@@ -124,6 +124,7 @@ module.exports = {
     'no-restricted-static-attribute': require('./rules/no-restricted-static-attribute'),
     'no-restricted-syntax': require('./rules/no-restricted-syntax'),
     'no-restricted-v-bind': require('./rules/no-restricted-v-bind'),
+    'no-root-v-if': require('./rules/no-root-v-if'),
     'no-setup-props-destructure': require('./rules/no-setup-props-destructure'),
     'no-shared-component-data': require('./rules/no-shared-component-data'),
     'no-side-effects-in-computed-properties': require('./rules/no-side-effects-in-computed-properties'),

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

@@ -0,0 +1,46 @@
+/**
+ * @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')
+
+module.exports = {
+  meta: {
+    type: 'suggestion',
+    docs: {
+      description: 'disallow `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 === 1 &&
+          utils.hasDirective(rootElements[0], 'if')
+        ) {
+          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 +1,115 @@
+/**
+ * @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>'
+    },
+    {
+      filename: 'test.vue',
+      code: '<template><div /><div v-if="foo" /></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`.']
+    }
+  ]
+})