Set `ModelMetadata.TemplateHint` based on data annotations

- add `CachedDataAnnotationsMetadataAttributes.UIHint`
- set `ModelMetadata.TemplateHint` using `UIHintAttribute` or `HiddenInputAttribute`
- add doc comments for `TemplateHint`-related properties and methods
- add unit tests and use these attributes in functional tests

nits:
- cache and seal `CachedModelMetadata.IsCollectionType`
- correct doc comments for `ModelMetadata.RealModelType`
- add doc comments for `IsCollectionType`-related properties and methods
- add doc comments for `IsComplexType`-related properties and methods
- move `CachedModelMetadata.IsComplexType` right below `IsCollectionType`
 - same for related fields and methods

src/Microsoft.AspNet.Mvc.ModelBinding/Metadata/CachedDataAnnotationsMetadataAttributes.cs

@@ -1,7 +1,6 @@
 // Copyright (c) Microsoft Open Technologies, Inc. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-using System;
 using System.Collections.Generic;
 using System.ComponentModel.DataAnnotations;
 using System.Linq;
@@ -20,6 +19,8 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
             HiddenInput = attributes.OfType<HiddenInputAttribute>().FirstOrDefault();
             Required = attributes.OfType<RequiredAttribute>().FirstOrDefault();
             ScaffoldColumn = attributes.OfType<ScaffoldColumnAttribute>().FirstOrDefault();
+            UIHint = attributes.OfType<UIHintAttribute>().FirstOrDefault();
+
             BinderMetadata = attributes.OfType<IBinderMetadata>().FirstOrDefault();
             PropertyBindingPredicateProviders = attributes.OfType<IPropertyBindingPredicateProvider>();
             BinderModelNameProvider = attributes.OfType<IModelNameProvider>().FirstOrDefault();
@@ -82,7 +83,7 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
         public HiddenInputAttribute HiddenInput { get; protected set; }
 
         /// <summary>
-        /// Gets (or sets in subclasses) <see cref="IEnumerable{IPropertyBindingPredicateProvider}"/> found in 
+        /// Gets (or sets in subclasses) <see cref="IEnumerable{IPropertyBindingPredicateProvider}"/> found in
         /// collection passed to the <see cref="CachedDataAnnotationsMetadataAttributes(IEnumerable{object})"/>
         /// constructor, if any.
         /// </summary>
@@ -91,5 +92,11 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
         public RequiredAttribute Required { get; protected set; }
 
         public ScaffoldColumnAttribute ScaffoldColumn { get; protected set; }
+
+        /// <summary>
+        /// Gets (or sets in subclasses) <see cref="UIHintAttribute"/> found in collection passed to the
+        /// <see cref="CachedDataAnnotationsMetadataAttributes(IEnumerable{object})"/> constructor, if any.
+        /// </summary>
+        public UIHintAttribute UIHint { get; protected set; }
     }
 }

src/Microsoft.AspNet.Mvc.ModelBinding/Metadata/CachedDataAnnotationsModelMetadata.cs

@@ -9,8 +9,8 @@ using System.Reflection;
 
 namespace Microsoft.AspNet.Mvc.ModelBinding
 {
-    // Class does not override ComputeIsComplexType() because value calculated in ModelMetadata's base implementation
+    // Class does not override ComputeIsCollectionType() or ComputeIsComplexType() because values calculated in
-    // is correct.
+    // ModelMetadata's base implementation are correct. No data annotations override those calculations.
     public class CachedDataAnnotationsModelMetadata : CachedModelMetadata<CachedDataAnnotationsMetadataAttributes>
     {
         private static readonly string HtmlName = DataType.Html.ToString();
@@ -333,6 +333,31 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
                        : base.ComputeShowForEdit();
         }
 
+        /// <summary>
+        /// Calculate the <see cref="ModelMetadata.TemplateHint"/> value based on presence of a
+        /// <see cref="UIHintAttribute"/> and its <see cref="UIHintAttribute.UIHint"/> value or presence of a
+        /// <see cref="HiddenInputAttribute"/> when no <see cref="UIHintAttribute"/> exists.
+        /// </summary>
+        /// <returns>
+        /// Calculated <see cref="ModelMetadata.TemplateHint"/> value. <see cref="UIHintAttribute.UIHint"/> if a
+        /// <see cref="UIHintAttribute"/> exists. <c>"HiddenInput"</c> if a <see cref="HiddenInputAttribute"/> exists
+        /// and no <see cref="UIHintAttribute"/> exists. <c>null</c> otherwise.
+        /// </returns>
+        protected override string ComputeTemplateHint()
+        {
+            if (PrototypeCache.UIHint != null)
+            {
+                return PrototypeCache.UIHint.UIHint;
+            }
+
+            if (PrototypeCache.HiddenInput != null)
+            {
+                return "HiddenInput";
+            }
+
+            return base.ComputeTemplateHint();
+        }
+
         private static void ValidateDisplayColumnAttribute(DisplayColumnAttribute displayColumnAttribute,
             PropertyInfo displayColumnProperty, Type modelType)
         {

src/Microsoft.AspNet.Mvc.ModelBinding/Metadata/CachedModelMetadata.cs

@@ -25,13 +25,15 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
         private bool _hasNonDefaultEditFormat;
         private bool _hideSurroundingHtml;
         private bool _htmlEncode;
-        private bool _isReadOnly;
+        private bool _isCollectionType;
         private bool _isComplexType;
+        private bool _isReadOnly;
         private bool _isRequired;
         private string _nullDisplayText;
         private int _order;
         private bool _showForDisplay;
         private bool _showForEdit;
+        private string _templateHint;
         private IBinderMetadata _binderMetadata;
         private string _binderModelName;
         private IPropertyBindingPredicateProvider _propertyBindingPredicateProvider;
@@ -46,13 +48,15 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
         private bool _hasNonDefaultEditFormatComputed;
         private bool _hideSurroundingHtmlComputed;
         private bool _htmlEncodeComputed;
-        private bool _isReadOnlyComputed;
+        private bool _isCollectionTypeComputed;
         private bool _isComplexTypeComputed;
+        private bool _isReadOnlyComputed;
         private bool _isRequiredComputed;
         private bool _nullDisplayTextComputed;
         private bool _orderComputed;
         private bool _showForDisplayComputed;
         private bool _showForEditComputed;
+        private bool _templateHintComputed;
         private bool _isBinderMetadataComputed;
         private bool _isBinderModelNameComputed;
         private bool _isBinderTypeComputed;
@@ -320,6 +324,35 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
             }
         }
 
+        /// <inheritdoc />
+        public sealed override bool IsCollectionType
+        {
+            get
+            {
+                if (!_isCollectionTypeComputed)
+                {
+                    _isCollectionType = ComputeIsCollectionType();
+                    _isCollectionTypeComputed = true;
+                }
+
+                return _isCollectionType;
+            }
+        }
+
+        /// <inheritdoc />
+        public sealed override bool IsComplexType
+        {
+            get
+            {
+                if (!_isComplexTypeComputed)
+                {
+                    _isComplexType = ComputeIsComplexType();
+                    _isComplexTypeComputed = true;
+                }
+                return _isComplexType;
+            }
+        }
+
         /// <inheritdoc />
         public sealed override bool IsReadOnly
         {
@@ -358,20 +391,6 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
             }
         }
 
-        /// <inheritdoc />
-        public sealed override bool IsComplexType
-        {
-            get
-            {
-                if (!_isComplexTypeComputed)
-                {
-                    _isComplexType = ComputeIsComplexType();
-                    _isComplexTypeComputed = true;
-                }
-                return _isComplexType;
-            }
-        }
-
         /// <inheritdoc />
         public sealed override string NullDisplayText
         {
@@ -495,6 +514,27 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
             }
         }
 
+        /// <inheritdoc />
+        public sealed override string TemplateHint
+        {
+            get
+            {
+                if (!_templateHintComputed)
+                {
+                    _templateHint = ComputeTemplateHint();
+                    _templateHintComputed = true;
+                }
+
+                return _templateHint;
+            }
+
+            set
+            {
+                _templateHint = value;
+                _templateHintComputed = true;
+            }
+        }
+
         /// <inheritdoc />
         public sealed override Type BinderType
         {
@@ -605,6 +645,24 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
             return base.HtmlEncode;
         }
 
+        /// <summary>
+        /// Calculate the <see cref="IsCollectionType"/> value.
+        /// </summary>
+        /// <returns>Calculated <see cref="IsCollectionType"/> value.</returns>
+        protected virtual bool ComputeIsCollectionType()
+        {
+            return base.IsCollectionType;
+        }
+
+        /// <summary>
+        /// Calculate the <see cref="IsComplexType"/> value.
+        /// </summary>
+        /// <returns>Calculated <see cref="IsComplexType"/> value.</returns>
+        protected virtual bool ComputeIsComplexType()
+        {
+            return base.IsComplexType;
+        }
+
         protected virtual bool ComputeIsReadOnly()
         {
             return base.IsReadOnly;
@@ -615,11 +673,6 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
             return base.IsRequired;
         }
 
-        protected virtual bool ComputeIsComplexType()
-        {
-            return base.IsComplexType;
-        }
-
         /// <summary>
         /// Calculate the <see cref="NullDisplayText"/> value.
         /// </summary>
@@ -647,5 +700,14 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
         {
             return base.ShowForEdit;
         }
+
+        /// <summary>
+        /// Calculate the <see cref="TemplateHint"/> value.
+        /// </summary>
+        /// <returns>Calculated <see cref="TemplateHint"/> value.</returns>
+        protected virtual string ComputeTemplateHint()
+        {
+            return base.TemplateHint;
+        }
     }
 }

src/Microsoft.AspNet.Mvc.ModelBinding/Metadata/ModelMetadata.cs

@@ -142,11 +142,25 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
         /// </remarks>
         public virtual bool HideSurroundingHtml { get; set; }
 
+        /// <summary>
+        /// Gets a value indicating whether the <see cref="ModelType"/> is a collection <see cref="Type"/>.
+        /// </summary>
+        /// <remarks>
+        /// <c>true</c> if the <see cref="ModelType"/> is not <see cref="string"/> and is assignable to
+        /// <see cref="System.Collections.IEnumerable"/>; <c>false</c> otherwise.
+        /// </remarks>
         public virtual bool IsCollectionType
         {
             get { return TypeHelper.IsCollectionType(ModelType); }
         }
 
+        /// <summary>
+        /// Gets a value indicating whether the <see cref="ModelType"/> is a complex type.
+        /// </summary>
+        /// <remarks>
+        /// <c>false</c> if the <see cref="ModelType"/> has a direct conversion to <see cref="string"/>; <c>true</c>
+        /// otherwise.
+        /// </remarks>
         public virtual bool IsComplexType
         {
             get { return !TypeHelper.HasStringConverter(ModelType); }
@@ -238,8 +252,8 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
         protected IModelMetadataProvider Provider { get; set; }
 
         /// <returns>
-        /// Gets <c>T</c> if <see cref="ModelType"/> is <see cref="Nullable{T}"/>;
+        /// Gets runtime <see cref="Type"/> of <see cref="Model"/> if <see cref="Model"/> is non-<c>null</c> and
-        /// <see cref="ModelType"/> otherwise.
+        /// <see cref="ModelType"/> is not <see cref="Nullable{T}"/>; <see cref="ModelType"/> otherwise.
         /// </returns>
         public Type RealModelType
         {
@@ -294,6 +308,11 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
             set { _showForEdit = value; }
         }
 
+        /// <summary>
+        /// Gets or sets a hint that suggests what template to use for this model. Overrides <see cref="DataTypeName"/>
+        /// in that context but, unlike <see cref="DataTypeName"/>, this value is not used elsewhere.
+        /// </summary>
+        /// <value><c>null</c> unless set manually or through additional metadata e.g. attributes.</value>
         public virtual string TemplateHint { get; set; }
 
         internal EfficientTypePropertyKey<Type, string> CacheKey

test/Microsoft.AspNet.Mvc.ModelBinding.Test/Metadata/CachedDataAnnotationsMetadataAttributesTest.cs

@@ -32,6 +32,7 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
             Assert.Null(cache.HiddenInput);
             Assert.Null(cache.Required);
             Assert.Null(cache.ScaffoldColumn);
+            Assert.Null(cache.UIHint);
             Assert.Null(cache.BinderMetadata);
             Assert.Null(cache.BinderModelNameProvider);
             Assert.Empty(cache.PropertyBindingPredicateProviders);
@@ -51,6 +52,8 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
                     { new EditableAttribute(allowEdit: false), cache => cache.Editable },
                     { new HiddenInputAttribute(), cache => cache.HiddenInput },
                     { new RequiredAttribute(), cache => cache.Required },
+                    { new ScaffoldColumnAttribute(scaffold: true), cache => cache.ScaffoldColumn },
+                    { new UIHintAttribute("hintHint"), cache => cache.UIHint },
                     { new TestBinderMetadata(), cache => cache.BinderMetadata },
                     { new TestModelNameProvider(), cache => cache.BinderModelNameProvider },
                 };

test/Microsoft.AspNet.Mvc.ModelBinding.Test/Metadata/CachedDataAnnotationsModelMetadataProviderTest.cs

@@ -180,7 +180,7 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
         }
 
         [Fact]
-        public void HiddenInputWorksOnProperty()
+        public void HiddenInputWorksOnProperty_ForHideSurroundingHtml()
         {
             // Arrange
             var provider = new DataAnnotationsModelMetadataProvider();
@@ -195,7 +195,7 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
         }
 
         [Fact]
-        public void HiddenInputWorksOnPropertyType()
+        public void HiddenInputWorksOnPropertyType_ForHideSurroundingHtml()
         {
             // Arrange
             var provider = new DataAnnotationsModelMetadataProvider();
@@ -209,6 +209,36 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
             Assert.True(result);
         }
 
+        [Fact]
+        public void HiddenInputWorksOnProperty_ForTemplateHint()
+        {
+            // Arrange
+            var provider = new DataAnnotationsModelMetadataProvider();
+            var metadata = provider.GetMetadataForType(modelAccessor: null, modelType: typeof(ClassWithHiddenProperties));
+            var property = metadata.Properties["DirectlyHidden"];
+
+            // Act
+            var result = property.TemplateHint;
+
+            // Assert
+            Assert.Equal("HiddenInput", result);
+        }
+
+        [Fact]
+        public void HiddenInputWorksOnPropertyType_ForTemplateHint()
+        {
+            // Arrange
+            var provider = new DataAnnotationsModelMetadataProvider();
+            var metadata = provider.GetMetadataForType(modelAccessor: null, modelType: typeof(ClassWithHiddenProperties));
+            var property = metadata.Properties["OfHiddenType"];
+
+            // Act
+            var result = property.TemplateHint;
+
+            // Assert
+            Assert.Equal("HiddenInput", result);
+        }
+
         [Fact]
         public void GetMetadataForProperty_WithNoBinderMetadata_GetsItFromType()
         {

test/Microsoft.AspNet.Mvc.ModelBinding.Test/Metadata/CachedDataAnnotationsModelMetadataTest.cs

@@ -109,7 +109,10 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
                         new DisplayFormatAttribute { NullDisplayText = "value" }, metadata => metadata.NullDisplayText
                     },
                     {
-                        new TestModelNameProvider() { Name = "value" }, metadata => metadata.BinderModelName
+                        new TestModelNameProvider { Name = "value" }, metadata => metadata.BinderModelName
+                    },
+                    {
+                         new UIHintAttribute("value"), metadata => metadata.TemplateHint
                     },
                 };
             }
@@ -208,6 +211,11 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
                         metadata => metadata.HideSurroundingHtml,
                         false
                     },
+                    {
+                        new HiddenInputAttribute(),
+                        metadata => string.Equals("HiddenInput", metadata.TemplateHint, StringComparison.Ordinal),
+                        true
+                    },
                     {
                         new RequiredAttribute(),
                         metadata => metadata.IsRequired,
@@ -466,6 +474,28 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
             Assert.Null(metadata.EditFormatString);
         }
 
+        [Fact]
+        public void TemplateHint_AttributesHaveExpectedPrecedence()
+        {
+            // Arrange
+            var expected = "this is a hint";
+            var hidden = new HiddenInputAttribute();
+            var uiHint = new UIHintAttribute(expected);
+            var provider = new DataAnnotationsModelMetadataProvider();
+            var metadata = new CachedDataAnnotationsModelMetadata(
+                provider,
+                containerType: null,
+                modelType: typeof(object),
+                propertyName: null,
+                attributes: new Attribute[] { hidden, uiHint });
+
+            // Act
+            var result = metadata.TemplateHint;
+
+            // Assert
+            Assert.Equal(expected, result);
+        }
+
         [Fact]
         public void Constructor_FindsBinderTypeProviders_Null()
         {

test/WebSites/MvcTagHelpersWebSite/Models/Person.cs

@@ -2,11 +2,13 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System.ComponentModel.DataAnnotations;
+using Microsoft.AspNet.Mvc;
 
 namespace MvcTagHelpersWebSite.Models
 {
     public class Person
     {
+        [HiddenInput(DisplayValue = false)]
         [Range(1, 100)]
         public int Number
         {
@@ -28,6 +30,7 @@ namespace MvcTagHelpersWebSite.Models
         }
 
         [EnumDataType(typeof(Gender))]
+        [UIHint("GenderUsingTagHelpers")]
         public Gender Gender
         {
             get;

test/WebSites/MvcTagHelpersWebSite/Views/MvcTagHelper_Home/EditWarehouse.cshtml

@@ -42,7 +42,7 @@
             }
             @Html.DropDownListFor(m => m.Employee.OfficeNumber, offices)
         </div>
-        @Html.HiddenFor(m => m.Employee.Number)
+        @Html.EditorFor(m => m.Employee.Number)
         @Html.ValidationSummary()
         <input type="submit" />
     </form>