feat: add no-async-functions rule

Author: yyx990803

index.js

@@ -5,6 +5,7 @@ module.exports = {
     recommended: require('./config')
   },
   rules: {
-    'jsx-uses-vars': require('./rules/jsx-uses-vars')
+    'jsx-uses-vars': require('./rules/jsx-uses-vars'),
+    'no-async-functions': require('./rules/no-async-functions')
   }
 }

rules/no-async-functions.js

@@ -0,0 +1,27 @@
+module.exports = {
+  meta: {
+    docs: {
+      description: 'Disallow use of async functions (for codebases targeting Node 6.x)',
+      category: 'Custom',
+      recommended: false
+    },
+    schema: []
+  },
+
+  create (context) {
+    function report (node) {
+      if (node.async) {
+        context.report({
+          node,
+          message: "async functions are disallowed for Node 6.x compatibility."
+        })
+      }
+    }
+
+    return {
+      FunctionDeclaration: report,
+      FunctionExpression: report,
+      ArrowFunctionExpression: report
+    }
+  }
+}