New: no-unused-vars (fixes #100)(#187)

Author: aladdin-add

docs/rules/no-unused-vars.md

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+# Disallow unused variable definitions of v-for directives or scope attributes. (no-unused-vars)
+
+This rule report variable definitions of v-for directives or scope attributes if those are not used.
+
+## :book: Rule Details
+
+:-1: Examples of **incorrect** code for this rule:
+
+```html
+<template>
+    <ol v-for="i in 5"><!-- "i" is defined but never used. -->
+        <li>item</li>
+    </ol>
+</template>
+```
+
+:+1: Examples of **correct** code for this rule:
+
+```html
+<template>
+    <ol v-for="i in 5">
+        <li>{{i}}</li><!-- "i" is defined and used. -->
+    </ol>
+</template>
+```
+
+## :wrench: Options
+
+Nothing.

lib/rules/no-unused-vars.js

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+/**
+ * @fileoverview warn variable definitions of v-for directives or scope attributes if those are not used.
+ * @author 薛定谔的猫<[email protected]>
+ */
+'use strict'
+
+const utils = require('../utils')
+
+/**
+ * Creates AST event handlers for require-v-for-key.
+ *
+ * @param {RuleContext} context - The rule context.
+ * @returns {Object} AST event handlers.
+ */
+function create (context) {
+  return utils.defineTemplateBodyVisitor(context, {
+    VElement (node) {
+      for (const variable of node.variables) {
+        if (variable.references.length === 0) {
+          context.report({
+            node: variable.id,
+            loc: variable.id.loc,
+            message: `'{{name}}' is defined but never used.`,
+            data: variable.id
+          })
+        }
+      }
+    }
+  })
+}
+
+// ------------------------------------------------------------------------------
+// Rule Definition
+// ------------------------------------------------------------------------------
+
+module.exports = {
+  create,
+  meta: {
+    docs: {
+      description: 'warn variable definitions of v-for directives or scope attributes if those are not used',
+      category: 'Possible Errors',
+      recommended: false
+    },
+    fixable: null,
+    schema: []
+  }
+}

tests/lib/rules/no-unused-vars.js

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+/**
+ * @author 薛定谔的猫<[email protected]>
+ * @copyright 2017 薛定谔的猫. All rights reserved.
+ * See LICENSE file in root directory for full license.
+ */
+'use strict'
+
+// ------------------------------------------------------------------------------
+// Requirements
+// ------------------------------------------------------------------------------
+
+const RuleTester = require('eslint').RuleTester
+const rule = require('../../../lib/rules/no-unused-vars')
+
+// ------------------------------------------------------------------------------
+// Tests
+// ------------------------------------------------------------------------------
+
+const tester = new RuleTester({
+  parser: 'vue-eslint-parser',
+  parserOptions: { ecmaVersion: 2015 }
+})
+
+tester.run('no-unused-vars', rule, {
+  valid: [
+    {
+      code: '<template><ol v-for="i in 5"><li>{{i}}</li></ol></template>'
+    },
+    {
+      code: '<template><ol v-for="i in 5"><li :prop="i"></li></ol></template>'
+    },
+    {
+      code: '<template v-for="i in 5"><comp v-for="j in 10">{{i}}{{j}}</comp></template>'
+    },
+    {
+      code: '<template><ol v-for="i in data"><li v-for="f in i">{{ f.bar.baz }}</li></ol></template>'
+    },
+    {
+      code: '<template scope="props">{{props}}</template>'
+    },
+    {
+      code: '<template scope="props"><span v-if="props"></span></template>'
+    }
+  ],
+  invalid: [
+    {
+      code: '<template><ol v-for="i in 5"><li></li></ol></template>',
+      errors: ['\'i\' is defined but never used.']
+    },
+    {
+      code: '<template scope="props"></template>',
+      errors: ['\'props\' is defined but never used.']
+    },
+    {
+      code: '<template v-for="i in 5"><comp v-for="j in 10">{{i}}{{i}}</comp></template>',
+      errors: ['\'j\' is defined but never used.']
+    },
+    {
+      code: '<template><ol v-for="i in data"><li v-for="f in i"></li></ol></template>',
+      errors: ['\'f\' is defined but never used.']
+    },
+    {
+      code: '<template><div v-for="(v, i, c) in foo"></div></template>',
+      errors: ['\'v\' is defined but never used.', '\'i\' is defined but never used.', '\'c\' is defined but never used.']
+    }
+  ]
+})