[NEW RULE] Adding no-async-actions rule

Fixes ember-cli#418

[DO NOT MERGE]
1. Working for normal async actions
2. With decorators it is throwing errors, need to fix this.

lib/rules/no-async-actions.js

@@ -0,0 +1,61 @@
+'use strict';
+
+const utils = require('../utils/utils');
+
+
+//------------------------------------------------------------------------------
+// General rule - Don't use async actions
+//------------------------------------------------------------------------------
+
+
+const message = 'Do not use async actions';
+
+module.exports = {
+  meta: {
+    docs: {
+      description: 'Disallow usage of async actions in components',
+      category: 'Possible Errors',
+      recommended: true,
+      url: 'http://ember-concurrency.com/docs/tutorial'
+    },
+    fixable: null,
+  },
+
+  create(context) {
+    return {
+      Property(node) {
+        if (node.key.name === 'actions') {
+          const props = node.value.properties;
+
+          props.forEach((p) => {
+            const body = p.value.body.body;
+            if (p.value.async) {
+              context.report({
+                node: p,
+                message,
+              });
+            } else if (body.length === 1 && utils.isReturnStatement(body[0])) {
+              const retSt = body[0];
+              if (retSt.argument.type === 'CallExpression' &&
+                  retSt.argument.callee.property.name === 'then') {
+                context.report({
+                  node: retSt,
+                  message,
+                });
+              }
+            }
+          });
+        } else if (node.decorators) {
+          if (node.decorators.find(d => d.expression.name === 'action')) {
+            if (node.value.async) {
+              context.report({
+                node,
+                message: 'Do not use async actions'
+              });
+            }
+          }
+        }
+      }
+    };
+  }
+};

tests/lib/rules/no-async-actions.js

@@ -0,0 +1,96 @@
+'use strict';
+
+//------------------------------------------------------------------------------
+// Requirements
+//------------------------------------------------------------------------------
+
+const rule = require('../../../lib/rules/no-async-actions.js');
+const RuleTester = require('eslint').RuleTester;
+
+
+//------------------------------------------------------------------------------
+// Tests
+//------------------------------------------------------------------------------
+
+const message = 'Do not use async actions';
+
+const ruleTester = new RuleTester({
+  parserOptions: {
+    ecmaVersion: 2018,
+    sourceType: 'module',
+  }
+});
+
+ruleTester.run('no-async-actions', rule, {
+  valid: [
+    {
+      code: `
+      Component.extend({
+      actions: {
+      handleClick() {
+      // ...
+      }
+      }
+      });`,
+    }
+
+  ],
+
+  invalid: [
+    {
+      code: `Component.extend({
+        actions: {
+          async handleClick() {
+            // ...
+          }
+        }
+      });`,
+      output: null,
+      errors: [{
+        message,
+      }]
+    },
+    {
+      code: `Component.extend({
+        actions: {
+          handleClick() {
+            return something.then(() => { 
+              let hello = "world";
+            });
+          }
+        }
+      });`,
+      output: null,
+      errors: [{
+        message,
+      }]
+    },
+    {
+      code: `Component.extend({
+          @action
+          async handleClick() {
+            // ...
+          }
+      });`,
+      output: null,
+      errors: [{
+        message,
+      }]
+    },
+    {
+      code: `Component.extend({
+          @action
+          handleClick() {
+            return something.then(() => { 
+              let hello = "world";
+            });
+          }
+      });`,
+      output: null,
+      errors: [{
+        message,
+      }]
+    },
+
+  ]
+});