[Linter] Adding rule to warn about boolean type properties

src/core/AutoRest.Core/Properties/Resources.resx

@@ -323,4 +323,7 @@
   <data name="InvalidMutabilityValueForReadOnly" xml:space="preserve">
     <value>When property is modeled as "readOnly": true then x-ms-mutability extension can only have "read" value. When property is modeled as "readOnly": false then applying x-ms-mutability extension with only "read" value is not allowed. Extension contains invalid values: '{0}'.</value>
   </data>
+  <data name="BooleanPropertyNotRecommended" xml:space="preserve">
+    <value>Booleans are not descriptive and make them hard to use. Instead use string enums with allowed set of values defined: '{0}'.</value>
+  </data>
 </root>

src/modeler/AutoRest.Swagger.Tests/Swagger/Validation/boolean-properties.json

@@ -0,0 +1,61 @@
+{
+  "swagger": "2.0",
+  "info": {
+    "title": "Boolean properties not recommended in models",
+    "description": "Some documentation.",
+    "version": "2017-02-08"
+  },
+  "host": "management.azure.com",
+  "schemes": [
+    "https"
+  ],
+  "basePath": "/",
+  "produces": [
+    "application/json"
+  ],
+  "consumes": [
+    "application/json"
+  ],
+  "paths": {
+    "/foo": {
+      "post": {
+        "operationId": "PostFoo",
+        "summary": "Foo path",
+        "description": "Foo operation",
+        "responses": {
+          "default": {
+            "description": "Unexpected error"
+          }
+        }
+      }
+    }
+  },
+  "definitions": {
+    "Test1": {
+      "description": "Property for foo path 1",
+      "properties": {
+        "nameAvailable": {
+          "readOnly": true,
+          "type": "boolean",
+          "description": "Gets a boolean value that indicates whether the name is available for you to use. If true, the name is available. If false, the name has already been taken or invalid and cannot be used."
+        }
+      }
+    },
+    "parameters": {
+      "SubscriptionIdParameter": {
+        "name": "subscriptionId",
+        "in": "path",
+        "required": true,
+        "type": "string",
+        "description": "test subscription id"
+      },
+      "ApiVersion": {
+        "name": "api-version",
+        "in": "path",
+        "required": true,
+        "type": "string",
+        "description": "test api version"
+      }
+    }
+  }
+}

src/modeler/AutoRest.Swagger.Tests/SwaggerModelerValidationTests.cs

@@ -72,6 +72,14 @@ public void AvoidMsdnReferencesValidation()
             messages.AssertOnlyValidationMessage(typeof(AvoidMsdnReferences), 4);
         }
 
+        [Fact]
+        public void BooleanPropertiesValidation()
+        {
+            var messages = ValidateSwagger(Path.Combine("Swagger", "Validation", "boolean-properties.json"));
+
+            messages.AssertOnlyValidationMessage(typeof(BooleanPropertyNotRecommended));
+        }
+
         [Fact]
         public void DefaultValueInEnumValidation()
         {

src/modeler/AutoRest.Swagger/Model/ServiceDefinition.cs

@@ -94,7 +94,7 @@ public ServiceDefinition()
 
         /// <summary>
         /// Key is the object serviceTypeName and the value is swagger definition.
-        /// </summary>
+        [Rule(typeof(BooleanPropertyNotRecommended))]
         [Rule(typeof(ResourceModelValidation))]
         [Rule(typeof(TrackedResourceValidation))]
         [Rule(typeof(ResourceIsMsResourceValidation))]

src/modeler/AutoRest.Swagger/Validation/BooleanPropertyNotRecommended.cs

@@ -0,0 +1,58 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License. See License.txt in the project root for license information.
+
+using AutoRest.Core.Logging;
+using AutoRest.Core.Properties;
+using AutoRest.Core.Validation;
+using System.Collections.Generic;
+using AutoRest.Swagger.Model;
+
+namespace AutoRest.Swagger.Validation
+{
+    /// <summary>
+    /// Flags properties of boolean type as they are not recommended, unless it's the only option.
+    /// </summary>
+    public class BooleanPropertyNotRecommended : TypedRule<Dictionary<string, Schema>>
+    {
+        /// <summary>
+        /// The template message for this Rule. 
+        /// </summary>
+        /// <remarks>
+        /// This may contain placeholders '{0}' for parameterized messages.
+        /// </remarks>
+        public override string MessageTemplate => Resources.BooleanPropertyNotRecommended;
+
+        /// <summary>
+        /// The severity of this message (ie, debug/info/warning/error/fatal, etc)
+        /// </summary>
+        public override Category Severity => Category.Warning;
+
+        /// <summary>
+        /// Validates whether properties of type boolean exist.
+        /// </summary>
+        /// <param name="definitions">Operation Definition to validate</param>
+        /// <returns>true if there are propeties of type boolean, false otherwise.</returns>
+        public override bool IsValid(Dictionary<string, Schema> definitions, RuleContext context, out object[] formatParameters)
+        {
+            formatParameters = null;
+            List<string> booleanProperties = new List<string>();
+            foreach (string key in definitions.Keys)
+            {
+                Schema definitionSchema = definitions.GetValueOrNull(key);
+                if (definitionSchema.Properties != null)
+                {
+                    foreach (var property in definitionSchema.Properties)
+                    {
+                        if (property.Value.Type.ToString().ToLower().Equals("boolean"))
+                        {
+                            booleanProperties.Add(key + "/" + property.Key);
+
+                        }
+                    }
+                }
+            }
+            formatParameters = new[] { string.Join(", ", booleanProperties.ToArray()) };
+            return (booleanProperties.Count == 0);
+        }
+    }
+}