Add rule require-render-return.

Author: armano2

docs/rules/require-render-return.md

@@ -0,0 +1,37 @@
+# Enforces render function to always return value (require-render-return)
+
+This rule aims to enforce render function to allways return value
+
+## :book: Rule Details
+
+:-1: Examples of **incorrect** code for this rule:
+
+```js
+export default {
+  render () {
+  }
+}
+```
+```js
+export default {
+  render (h) {
+    if (foo) {
+      return
+    }
+  }
+}
+```
+
+:+1: Examples of **correct** code for this rule:
+
+```js
+export default {
+  render (h) {
+    return
+  }
+}
+```
+
+## :wrench: Options
+
+Nothing.

lib/rules/require-render-return.js

@@ -0,0 +1,47 @@
+/**
+ * @fileoverview Enforces render function to always return value.
+ * @author Armano
+ */
+'use strict'
+
+const utils = require('../utils')
+
+// ------------------------------------------------------------------------------
+// Rule Definition
+// ------------------------------------------------------------------------------
+
+module.exports = {
+  meta: {
+    docs: {
+      description: 'Enforces render function to always return value.',
+      category: 'Possible Errors',
+      recommended: false
+    },
+    fixable: null,  // or "code" or "whitespace"
+    schema: []
+  },
+
+  create (context) {
+    // ----------------------------------------------------------------------
+    // Public
+    // ----------------------------------------------------------------------
+
+    return utils.executeOnVue(context, obj => {
+      obj.properties
+        .filter(item => item.type === 'Property' &&
+          utils.getStaticPropertyName(item) === 'render' &&
+          (item.value.type === 'ArrowFunctionExpression' || item.value.type === 'FunctionExpression') &&
+          !item.value.expression // render: () => test
+        )
+        .forEach(item => {
+          const body = item.value.body
+          if (body.type === 'BlockStatement' && !body.body.find(item => item.type === 'ReturnStatement')) {
+            context.report({
+              node: item.key,
+              message: 'Expected to return a value in render function.'
+            })
+          }
+        })
+    })
+  }
+}

lib/utils/index.js

@@ -25,7 +25,7 @@ module.exports = {
      * this generates a warning.
      *
      * @param {RuleContext} context The rule context to use parser services.
-     * @param {object} visitor The visitor.
+     * @param {Object} visitor The visitor.
      * @returns {void}
      */
   registerTemplateBodyVisitor (context, visitor) {
@@ -272,6 +272,43 @@ module.exports = {
     return members.reverse()
   },
 
+    /**
+   * Gets the property name of a given node.
+   * @param {ASTNode} node - The node to get.
+   * @return {string|null} The property name if static. Otherwise, null.
+   */
+  getStaticPropertyName (node) {
+    let prop
+    switch (node && node.type) {
+      case 'Property':
+      case 'MethodDefinition':
+        prop = node.key
+        break
+      case 'MemberExpression':
+        prop = node.property
+        break
+      // no default
+    }
+
+    switch (prop && prop.type) {
+      case 'Literal':
+        return String(prop.value)
+      case 'TemplateLiteral':
+        if (prop.expressions.length === 0 && prop.quasis.length === 1) {
+          return prop.quasis[0].value.cooked
+        }
+        break
+      case 'Identifier':
+        if (!node.computed) {
+          return prop.name
+        }
+        break
+      // no default
+    }
+
+    return null
+  },
+
   /**
    * Get all computed properties by looking at all component's properties
    * @param {ObjectExpression} Object with component definition

tests/lib/rules/require-render-return.js

@@ -0,0 +1,91 @@
+/**
+ * @fileoverview Enforces render function to always return value.
+ * @author Armano
+ */
+'use strict'
+
+// ------------------------------------------------------------------------------
+// Requirements
+// ------------------------------------------------------------------------------
+
+const rule = require('../../../lib/rules/require-render-return')
+const RuleTester = require('eslint').RuleTester
+
+const parserOptions = {
+  ecmaVersion: 6,
+  sourceType: 'module',
+  ecmaFeatures: { experimentalObjectRestSpread: true, jsx: true }
+}
+
+// ------------------------------------------------------------------------------
+// Tests
+// ------------------------------------------------------------------------------
+
+const ruleTester = new RuleTester()
+ruleTester.run('require-render-return', rule, {
+  valid: [
+    {
+      code: `Vue.component('test', {
+        render() {
+          return {}
+        }
+      })`,
+      parserOptions
+    },
+    {
+      code: `Vue.component('test', {
+        render() {
+          return <div></div>
+        }
+      })`,
+      parserOptions
+    },
+    {
+      filename: 'test.vue',
+      code: `export default {
+        render() {
+          return {}
+        }
+      }`,
+      parserOptions
+    },
+    {
+      filename: 'test.vue',
+      code: `export default {
+        render: () => null
+      }`,
+      parserOptions
+    }
+  ],
+
+  invalid: [
+    {
+      filename: 'test.vue',
+      code: `export default {
+        render() {
+        }
+      }`,
+      parserOptions,
+      errors: [{
+        message: 'Expected to return a value in render function.',
+        type: 'Identifier',
+        line: 2
+      }]
+    },
+    {
+      code: `Vue.component('test', {
+        render: function () {
+          if (a) {
+            return
+          }
+        }
+      })`,
+      parserOptions,
+      errors: [{
+        message: 'Expected to return a value in render function.',
+        type: 'Identifier',
+        line: 2
+      }]
+    }
+  ]
+})