⭐️New: Add vue/v-on-parens rule (#481)

* Implement rule

* Get rid of spread operator, update error message in test

* Update meta

* Add output in tests

* Rename rule to `v-on-function-call`

* Don't add parantheses on fix

* Fix rule

Author: niklashigi

docs/rules/README.md

@@ -155,6 +155,7 @@ For example:
 | [vue/script-indent](./script-indent.md) | enforce consistent indentation in `<script>` | :wrench: |
 | [vue/space-infix-ops](./space-infix-ops.md) | require spacing around infix operators | :wrench: |
 | [vue/space-unary-ops](./space-unary-ops.md) | enforce consistent spacing before or after unary operators | :wrench: |
+| [vue/v-on-function-call](./v-on-function-call.md) | enforce or forbid parentheses after method calls without arguments in `v-on` directives | :wrench: |
 
 ## Deprecated
 

docs/rules/v-on-function-call.md

@@ -0,0 +1,77 @@
+---
+pageClass: rule-details
+sidebarDepth: 0
+title: vue/v-on-function-call
+description: enforce or forbid parentheses after method calls without arguments in `v-on` directives
+---
+# vue/v-on-function-call
+> enforce or forbid parentheses after method calls without arguments in `v-on` directives
+
+- :wrench: The `--fix` option on the [command line](https://eslint.org/docs/user-guide/command-line-interface#fixing-problems) can automatically fix some of the problems reported by this rule.
+
+## :book: Rule Details
+
+:-1: Example of **incorrect** code for this rule:
+
+```html
+<button v-on:click="closeModal()">
+  Close
+</button>
+```
+
+:+1: Example of **correct** code for this rule:
+
+```html
+<button v-on:click="closeModal">
+  Close
+</button>
+```
+
+## :wrench: Options
+
+Default is set to `never`.
+
+```
+'vue/v-on-parens': [2, 'always'|'never']
+```
+
+### `"always"` - Always use parentheses in `v-on` directives
+
+:-1: Example of **incorrect** code:
+
+```html
+<button v-on:click="closeModal">
+  Close
+</button>
+```
+
+:+1: Example of **correct** code:
+
+```html
+<button v-on:click="closeModal()">
+  Close
+</button>
+```
+
+### `"never"` - Never use parentheses in `v-on` directives for method calls without arguments
+
+:-1: Example of **incorrect** code:
+
+```html
+<button v-on:click="closeModal()">
+  Close
+</button>
+```
+
+:+1: Example of **correct** code:
+
+```html
+<button v-on:click="closeModal">
+  Close
+</button>
+```
+
+## :mag: Implementation
+
+- [Rule source](https://github.com/vuejs/eslint-plugin-vue/blob/master/lib/rules/v-on-function-call.js)
+- [Test source](https://github.com/vuejs/eslint-plugin-vue/blob/master/tests/lib/rules/v-on-function-call.js)

lib/index.js

@@ -68,6 +68,7 @@ module.exports = {
     'this-in-template': require('./rules/this-in-template'),
     'use-v-on-exact': require('./rules/use-v-on-exact'),
     'v-bind-style': require('./rules/v-bind-style'),
+    'v-on-function-call': require('./rules/v-on-function-call'),
     'v-on-style': require('./rules/v-on-style'),
     'valid-template-root': require('./rules/valid-template-root'),
     'valid-v-bind': require('./rules/valid-v-bind'),

lib/rules/v-on-function-call.js

@@ -0,0 +1,60 @@
+/**
+ * @author Niklas Higi
+ */
+'use strict'
+
+// ------------------------------------------------------------------------------
+// Requirements
+// ------------------------------------------------------------------------------
+
+const utils = require('../utils')
+
+// ------------------------------------------------------------------------------
+// Rule Definition
+// ------------------------------------------------------------------------------
+
+module.exports = {
+  meta: {
+    type: 'suggestion',
+    docs: {
+      description: 'enforce or forbid parentheses after method calls without arguments in `v-on` directives',
+      category: undefined,
+      url: 'https://eslint.vuejs.org/rules/v-on-function-call.html'
+    },
+    fixable: 'code',
+    schema: [
+      { enum: ['always', 'never'] }
+    ]
+  },
+
+  create (context) {
+    const always = context.options[0] === 'always'
+
+    return utils.defineTemplateBodyVisitor(context, {
+      "VAttribute[directive=true][key.name='on'][key.argument!=null] > VExpressionContainer > Identifier" (node) {
+        if (!always) return
+        context.report({
+          node,
+          loc: node.loc,
+          message: "Method calls inside of 'v-on' directives must have parentheses."
+        })
+      },
+
+      "VAttribute[directive=true][key.name='on'][key.argument!=null] VOnExpression > ExpressionStatement > *" (node) {
+        if (!always && node.type === 'CallExpression' && node.arguments.length === 0) {
+          context.report({
+            node,
+            loc: node.loc,
+            message: "Method calls without arguments inside of 'v-on' directives must not have parentheses.",
+            fix: fixer => {
+              const nodeString = context.getSourceCode().getText().substring(node.range[0], node.range[1])
+              // This ensures that parens are also removed if they contain whitespace
+              const parensLength = nodeString.match(/\(\s*\)\s*$/)[0].length
+              return fixer.removeRange([node.end - parensLength, node.end])
+            }
+          })
+        }
+      }
+    })
+  }
+}

tests/lib/rules/v-on-function-call.js

@@ -0,0 +1,72 @@
+/**
+ * @author Niklas Higi
+ */
+'use strict'
+
+// ------------------------------------------------------------------------------
+// Requirements
+// ------------------------------------------------------------------------------
+
+const RuleTester = require('eslint').RuleTester
+const rule = require('../../../lib/rules/v-on-function-call')
+
+// ------------------------------------------------------------------------------
+// Tests
+// ------------------------------------------------------------------------------
+
+const tester = new RuleTester({
+  parser: 'vue-eslint-parser',
+  parserOptions: { ecmaVersion: 2015 }
+})
+
+tester.run('v-on-function-call', rule, {
+  valid: [
+    {
+      filename: 'test.vue',
+      code: ''
+    },
+    {
+      filename: 'test.vue',
+      code: '<template><div @click="foo(123)"></div></template>',
+      options: ['always']
+    },
+    {
+      filename: 'test.vue',
+      code: '<template><div @click="foo(123)"></div></template>',
+      options: ['never']
+    },
+    {
+      filename: 'test.vue',
+      code: '<template><div @click="foo()"></div></template>',
+      options: ['always']
+    },
+    {
+      filename: 'test.vue',
+      code: '<template><div @click="foo"></div></template>',
+      options: ['never']
+    }
+  ],
+  invalid: [
+    {
+      filename: 'test.vue',
+      code: '<template><div @click="foo"></div></template>',
+      output: `<template><div @click="foo"></div></template>`,
+      errors: ["Method calls inside of 'v-on' directives must have parentheses."],
+      options: ['always']
+    },
+    {
+      filename: 'test.vue',
+      code: '<template><div @click="foo()"></div></template>',
+      output: `<template><div @click="foo"></div></template>`,
+      errors: ["Method calls without arguments inside of 'v-on' directives must not have parentheses."],
+      options: ['never']
+    },
+    {
+      filename: 'test.vue',
+      code: '<template><div @click="foo( )"></div></template>',
+      output: `<template><div @click="foo"></div></template>`,
+      errors: ["Method calls without arguments inside of 'v-on' directives must not have parentheses."],
+      options: ['never']
+    }
+  ]
+})