Add vue/no-useless-template-attributes rule (#1644)

docs/rules/README.md

@@ -325,6 +325,7 @@ For example:
 | [vue/no-unused-refs](./no-unused-refs.md) | disallow unused refs |  |
 | [vue/no-use-computed-property-like-method](./no-use-computed-property-like-method.md) | disallow use computed property like method |  |
 | [vue/no-useless-mustaches](./no-useless-mustaches.md) | disallow unnecessary mustache interpolations | :wrench: |
+| [vue/no-useless-template-attributes](./no-useless-template-attributes.md) | disallow useless attribute on `<template>` |  |
 | [vue/no-useless-v-bind](./no-useless-v-bind.md) | disallow unnecessary `v-bind` directives | :wrench: |
 | [vue/no-v-text](./no-v-text.md) | disallow use of v-text |  |
 | [vue/padding-line-between-blocks](./padding-line-between-blocks.md) | require or disallow padding lines between blocks | :wrench: |

docs/rules/no-useless-template-attributes.md

@@ -0,0 +1,64 @@
+---
+pageClass: rule-details
+sidebarDepth: 0
+title: vue/no-useless-template-attributes
+description: disallow useless attribute on `<template>`
+---
+# vue/no-useless-template-attributes
+
+> disallow useless attribute on `<template>`
+
+- :exclamation: <badge text="This rule has not been released yet." vertical="middle" type="error"> ***This rule has not been released yet.*** </badge>
+
+## :book: Rule Details
+
+This rule to prevent any useless attribute on `<template>` tags.
+
+<eslint-code-block :rules="{'vue/no-useless-template-attributes': ['error']}">
+
+```vue
+<template>
+  <!-- ✓ GOOD -->
+  <template v-if="foo">...</template>
+  <template v-if="foo">...</template>
+  <template v-else-if="foo">...</template>
+  <template v-else>...</template>
+  <template v-for="i in foo" :key="i">...</template>
+  <template v-slot:foo>...</template>
+  <!-- for Vue<=2.5 -->
+  <template slot="foo">...</template>
+  <template :slot="foo">...</template>
+  <template slot-scope="param">...</template>
+  <!-- for Vue<=2.4 -->
+  <template scope="param">...</template>
+
+  <!-- ✗ BAD -->
+  <template v-if="foo" class="heading">...</template>
+  <template v-for="i in foo" :bar="i">...</template>
+  <template v-slot:foo="foo" ref="input">...</template>
+  <template v-if="foo" @click="click">...</template>
+
+  <!-- Ignore -->
+  <template class="heading">...</template>
+  <template :bar="i">...</template>
+  <template ref="input">...</template>
+  <template @click="click">...</template>
+</template>
+```
+
+</eslint-code-block>
+
+## :wrench: Options
+
+Nothing.
+
+## :couple: Related Rules
+
+- [vue/no-lone-template]
+
+[vue/no-lone-template]: ./no-lone-template.md
+
+## :mag: Implementation
+
+- [Rule source](https://github.com/vuejs/eslint-plugin-vue/blob/master/lib/rules/no-useless-template-attributes.js)
+- [Test source](https://github.com/vuejs/eslint-plugin-vue/blob/master/tests/lib/rules/no-useless-template-attributes.js)

lib/index.js

@@ -129,6 +129,7 @@ module.exports = {
     'no-use-v-if-with-v-for': require('./rules/no-use-v-if-with-v-for'),
     'no-useless-concat': require('./rules/no-useless-concat'),
     'no-useless-mustaches': require('./rules/no-useless-mustaches'),
+    'no-useless-template-attributes': require('./rules/no-useless-template-attributes'),
     'no-useless-v-bind': require('./rules/no-useless-v-bind'),
     'no-v-for-template-key-on-child': require('./rules/no-v-for-template-key-on-child'),
     'no-v-for-template-key': require('./rules/no-v-for-template-key'),

lib/rules/no-useless-template-attributes.js

@@ -0,0 +1,121 @@
+/**
+ * @author Yosuke Ota
+ * See LICENSE file in root directory for full license.
+ */
+'use strict'
+
+// ------------------------------------------------------------------------------
+// Requirements
+// ------------------------------------------------------------------------------
+
+const utils = require('../utils')
+
+// ------------------------------------------------------------------------------
+// Helpers
+// ------------------------------------------------------------------------------
+
+// https://github.com/vuejs/vue-next/blob/64e2f4643602c5980361e66674141e61ba60ef70/packages/compiler-core/src/parse.ts#L405
+const SPECIAL_TEMPLATE_DIRECTIVES = new Set([
+  'if',
+  'else',
+  'else-if',
+  'for',
+  'slot'
+])
+
+// ------------------------------------------------------------------------------
+// Rule Definition
+// ------------------------------------------------------------------------------
+
+module.exports = {
+  meta: {
+    type: 'problem',
+    docs: {
+      description: 'disallow useless attribute on `<template>`',
+      // TODO Switch to `vue3-essential` and `essential` in the major version.
+      // categories: ['vue3-essential', 'essential'],
+      categories: undefined,
+      url: 'https://eslint.vuejs.org/rules/no-useless-template-attributes.html'
+    },
+    fixable: null,
+    schema: [],
+    messages: {
+      unexpectedAttr: 'Unexpected useless attribute on `<template>`.',
+      unexpectedDir: 'Unexpected useless directive on `<template>`.'
+    }
+  },
+  /** @param {RuleContext} context */
+  create(context) {
+    /**
+     * @param {VAttribute | VDirective} attr
+     */
+    function getKeyName(attr) {
+      if (attr.directive) {
+        if (attr.key.name.name !== 'bind') {
+          // no v-bind
+          return null
+        }
+        if (
+          !attr.key.argument ||
+          attr.key.argument.type === 'VExpressionContainer'
+        ) {
+          // unknown
+          return null
+        }
+        return attr.key.argument.name
+      }
+      return attr.key.name
+    }
+
+    /**
+     * @param {VAttribute | VDirective} attr
+     */
+    function isFragmentTemplateAttribute(attr) {
+      if (attr.directive) {
+        const directiveName = attr.key.name.name
+        if (SPECIAL_TEMPLATE_DIRECTIVES.has(directiveName)) {
+          return true
+        }
+        if (directiveName === 'slot-scope') {
+          // `slot-scope` is deprecated in Vue.js 2.6
+          return true
+        }
+        if (directiveName === 'scope') {
+          // `scope` is deprecated in Vue.js 2.5
+          return true
+        }
+      }
+
+      const keyName = getKeyName(attr)
+      if (keyName === 'slot') {
+        // `slot` is deprecated in Vue.js 2.6
+        return true
+      }
+
+      return false
+    }
+
+    return utils.defineTemplateBodyVisitor(context, {
+      /** @param {VStartTag} node */
+      "VElement[name='template'][parent.type='VElement'] > VStartTag"(node) {
+        if (!node.attributes.some(isFragmentTemplateAttribute)) {
+          return
+        }
+
+        for (const attr of node.attributes) {
+          if (isFragmentTemplateAttribute(attr)) {
+            continue
+          }
+          const keyName = getKeyName(attr)
+          if (keyName === 'key') {
+            continue
+          }
+          context.report({
+            node: attr,
+            messageId: attr.directive ? 'unexpectedDir' : 'unexpectedAttr'
+          })
+        }
+      }
+    })
+  }
+}

tests/lib/rules/no-useless-template-attributes.js

@@ -0,0 +1,156 @@
+/**
+ * @author Yosuke Ota
+ * See LICENSE file in root directory for full license.
+ */
+'use strict'
+
+const RuleTester = require('eslint').RuleTester
+const rule = require('../../../lib/rules/no-useless-template-attributes')
+
+const tester = new RuleTester({
+  parser: require.resolve('vue-eslint-parser'),
+  parserOptions: {
+    ecmaVersion: 2020,
+    sourceType: 'module'
+  }
+})
+
+tester.run('no-useless-template-attributes', rule, {
+  valid: [
+    {
+      filename: 'test.vue',
+      code: `
+      <template>
+        <template v-if="foo">...</template>
+        <template v-else-if="bar">...</template>
+        <template v-else>...</template>
+      </template>
+      `
+    },
+    {
+      filename: 'test.vue',
+      code: `
+      <template>
+        <template v-for="e in list">...</template>
+      </template>
+      `
+    },
+    {
+      filename: 'test.vue',
+      code: `
+      <template>
+        <template v-slot>...</template>
+      </template>
+      `
+    },
+    {
+      filename: 'test.vue',
+      code: `
+      <template>
+        <CoolButton>
+         <template slot="foo">...</template>
+        </CoolButton>
+      </template>
+      `
+    },
+    {
+      filename: 'test.vue',
+      code: `
+      <template>
+        <CoolButton>
+         <template slot-scope="foo">...</template>
+        </CoolButton>
+      </template>
+      `
+    },
+    {
+      filename: 'test.vue',
+      code: `
+      <template>
+        <CoolButton>
+         <template scope="foo">...</template>
+        </CoolButton>
+      </template>
+      `
+    },
+    {
+      filename: 'test.vue',
+      code: `
+      <template>
+        <!-- ignore -->
+        <template foo="a">...</template>
+        <template :foo="a">...</template>
+        <template v-unknown="a">...</template>
+      </template>
+      `
+    },
+    // not template
+    {
+      filename: 'test.vue',
+      code: `
+      <template>
+        <div v-if="foo" class="heading">...</div>
+        <div v-for="i in foo" :bar="i">...</div>
+        <div v-slot:foo="foo" ref="input">...</div>
+        <div v-if="foo" @click="click">...</div>
+      </template>
+      `
+    }
+  ],
+  invalid: [
+    {
+      filename: 'test.vue',
+      code: `
+      <template>
+        <!-- ✓ GOOD -->
+        <template v-if="foo">...</template>
+        <template v-if="foo">...</template>
+        <template v-else-if="foo">...</template>
+        <template v-else>...</template>
+        <template v-for="i in foo" :key="i">...</template>
+        <template v-slot:foo>...</template>
+        <!-- for Vue<=2.5 -->
+        <template slot="foo">...</template>
+        <template :slot="foo">...</template>
+        <template slot-scope="param">...</template>
+        <!-- for Vue<=2.4 -->
+        <template scope="param">...</template>
+
+        <!-- ✗ BAD -->
+        <template v-if="foo" class="heading">...</template>
+        <template v-for="i in foo" :bar="i">...</template>
+        <template v-slot:foo="foo" ref="input">...</template>
+        <template v-if="foo" @click="click">...</template>
+
+        <!-- Ignore -->
+        <template class="heading">...</template>
+        <template :bar="i">...</template>
+        <template ref="input">...</template>
+        <template @click="click">...</template>
+      </template>
+      `,
+      errors: [
+        {
+          message: 'Unexpected useless attribute on `<template>`.',
+          line: 18,
+          column: 30
+        },
+        {
+          message: 'Unexpected useless directive on `<template>`.',
+          line: 19,
+          column: 36
+        },
+        {
+          message: 'Unexpected useless attribute on `<template>`.',
+          line: 20,
+          column: 36
+        },
+        {
+          message: 'Unexpected useless directive on `<template>`.',
+          line: 21,
+          column: 30
+        }
+      ]
+    }
+  ]
+})