Reduce allocations during HTML generation

- #3918
- precompute size of `StringBuilder` in `ExpressionHelper`
- reduce `string` allocations in `ViewDataEvaluator`
 - also get rid of `Enumeration` state machines
- reduce the size of a few objects; use more expression-valued properties
 - e.g. don't store `_modelType` in `ModelExplorer`
- add `EmptyArray<TElement>`; make empty arrays consistently `static`
- avoid `string.Split()` in HTML and tag helpers

nits:
- make `ExpressionHelperTest` tests more stringent
- correct `Message` for an `ArgumentNullException`
- remove excess `using`s in classes I touched (but often ended up leaving otherwise unchanged)
- improve doc comments
- remove `ToString()` call on a `string`
- avoid encoding `string.Empty`
- fix test file name
- remove useless variables
- correct spelling
- improve whitespace

src/Microsoft.AspNetCore.Mvc.Abstractions/ModelBinding/ModelStateDictionary.cs

@@ -169,7 +169,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
             }
         }
 
-        // Flag that indiciates if TooManyModelErrorException has already been added to this dictionary.
+        // Flag that indicates if TooManyModelErrorException has already been added to this dictionary.
         private bool HasRecordedMaxModelError { get; set; }
 
         /// <summary>
@@ -625,7 +625,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         }
 
         /// <summary>
-        /// Removes all keys and values from ths instance of <see cref="ModelStateDictionary"/>.
+        /// Removes all keys and values from this instance of <see cref="ModelStateDictionary"/>.
         /// </summary>
         public void Clear()
         {

src/Microsoft.AspNetCore.Mvc.Abstractions/ModelBinding/ModelStateEntry.cs

@@ -11,6 +11,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
     public abstract class ModelStateEntry
     {
         private ModelErrorCollection _errors;
+
         /// <summary>
         /// Gets the raw value from the request associated with this entry.
         /// </summary>

src/Microsoft.AspNetCore.Mvc.Core/BindAttribute.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using Microsoft.AspNetCore.Mvc.Internal;
 #if NETSTANDARD1_6
 using System.Reflection;
 #endif
@@ -83,7 +84,7 @@ namespace Microsoft.AspNetCore.Mvc
         {
             if (string.IsNullOrEmpty(original))
             {
-                return new string[0];
+                return EmptyArray<string>.Instance;
             }
 
             var split = original.Split(',').Select(piece => piece.Trim()).Where(piece => !string.IsNullOrEmpty(piece));

src/Microsoft.AspNetCore.Mvc.Core/ChallengeResult.cs

@@ -20,7 +20,7 @@ namespace Microsoft.AspNetCore.Mvc
         /// Initializes a new instance of <see cref="ChallengeResult"/>.
         /// </summary>
         public ChallengeResult()
-            : this(new string[] { })
+            : this(EmptyArray<string>.Instance)
         {
         }
 
@@ -51,7 +51,7 @@ namespace Microsoft.AspNetCore.Mvc
         /// <param name="properties"><see cref="AuthenticationProperties"/> used to perform the authentication
         /// challenge.</param>
         public ChallengeResult(AuthenticationProperties properties)
-            : this(new string[] { }, properties)
+            : this(EmptyArray<string>.Instance, properties)
         {
         }
 

src/Microsoft.AspNetCore.Mvc.Core/ConsumesAttribute.cs

@@ -53,7 +53,7 @@ namespace Microsoft.AspNetCore.Mvc
         // The value used is a non default value so that it avoids getting mixed with other action constraints
         // with default order.
         /// <inheritdoc />
-        int IActionConstraint.Order { get; } = ConsumesActionConstraintOrder;
+        int IActionConstraint.Order => ConsumesActionConstraintOrder;
 
         /// <summary>
         /// Gets or sets the supported request content types. Used to select an action when there would otherwise be

src/Microsoft.AspNetCore.Mvc.Core/Filters/MiddlewareFilterAttribute.cs

@@ -35,7 +35,7 @@ namespace Microsoft.AspNetCore.Mvc
         public int Order { get; set; }
 
         /// <inheritdoc />
-        public bool IsReusable { get; } = true;
+        public bool IsReusable => true;
 
         /// <inheritdoc />
         public IFilterMetadata CreateInstance(IServiceProvider serviceProvider)

src/Microsoft.AspNetCore.Mvc.Core/ForbidResult.cs

@@ -20,7 +20,7 @@ namespace Microsoft.AspNetCore.Mvc
         /// Initializes a new instance of <see cref="ForbidResult"/>.
         /// </summary>
         public ForbidResult()
-            : this(new string[] { })
+            : this(EmptyArray<string>.Instance)
         {
         }
 
@@ -51,7 +51,7 @@ namespace Microsoft.AspNetCore.Mvc
         /// <param name="properties"><see cref="AuthenticationProperties"/> used to perform the authentication
         /// challenge.</param>
         public ForbidResult(AuthenticationProperties properties)
-            : this(new string[] { }, properties)
+            : this(EmptyArray<string>.Instance, properties)
         {
         }
 

src/Microsoft.AspNetCore.Mvc.Core/Formatters/FormatterMappings.cs

@@ -4,7 +4,6 @@
 using System;
 using System.Collections.Generic;
 using Microsoft.AspNetCore.Mvc.Core;
-using Microsoft.Extensions.Primitives;
 using Microsoft.Net.Http.Headers;
 
 namespace Microsoft.AspNetCore.Mvc.Formatters
@@ -18,7 +17,7 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
             new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
 
         /// <summary>
-        /// Sets mapping for the format to specified media type. 
+        /// Sets mapping for the format to specified media type.
         /// If the format already exists, the media type will be overwritten with the new value.
         /// </summary>
         /// <param name="format">The format value.</param>
@@ -39,7 +38,7 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
         }
 
         /// <summary>
-        /// Sets mapping for the format to specified media type. 
+        /// Sets mapping for the format to specified media type.
         /// If the format already exists, the media type will be overwritten with the new value.
         /// </summary>
         /// <param name="format">The format value.</param>

src/Microsoft.AspNetCore.Mvc.Core/Internal/ClientValidatorCache.cs

@@ -11,8 +11,6 @@ namespace Microsoft.AspNetCore.Mvc.Internal
 {
     public class ClientValidatorCache
     {
-        private readonly IReadOnlyList<IClientModelValidator> EmptyArray = new IClientModelValidator[0];
-
         private readonly ConcurrentDictionary<ModelMetadata, CacheEntry> _cacheEntries = new ConcurrentDictionary<ModelMetadata, CacheEntry>();
 
         public IReadOnlyList<IClientModelValidator> GetValidators(ModelMetadata metadata, IClientModelValidatorProvider validatorProvider)
@@ -106,7 +104,7 @@ namespace Microsoft.AspNetCore.Mvc.Internal
 
             if (count == 0)
             {
-                return EmptyArray;
+                return EmptyArray<IClientModelValidator>.Instance;
             }
 
             var validators = new IClientModelValidator[count];

src/Microsoft.AspNetCore.Mvc.Core/Internal/ControllerActionInvokerCache.cs

@@ -3,7 +3,6 @@
 
 using System.Collections.Concurrent;
 using System.Collections.Generic;
-using System.Diagnostics;
 using System.Linq;
 using Microsoft.AspNetCore.Mvc.Abstractions;
 using Microsoft.AspNetCore.Mvc.Filters;
@@ -13,8 +12,6 @@ namespace Microsoft.AspNetCore.Mvc.Internal
 {
     public class ControllerActionInvokerCache
     {
-        private readonly IFilterMetadata[] EmptyFilterArray = new IFilterMetadata[0];
-
         private readonly IActionDescriptorCollectionProvider _collectionProvider;
         private readonly IFilterProvider[] _filterProviders;
 
@@ -134,7 +131,7 @@ namespace Microsoft.AspNetCore.Mvc.Internal
 
             if (count == 0)
             {
-                return EmptyFilterArray;
+                return EmptyArray<IFilterMetadata>.Instance;
             }
             else
             {

src/Microsoft.AspNetCore.Mvc.Core/Internal/EmptyArray.cs

@@ -0,0 +1,19 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+#if !NET451
+using System;
+#endif
+
+namespace Microsoft.AspNetCore.Mvc.Internal
+{
+    public static class EmptyArray<TElement>
+    {
+        public static TElement[] Instance { get; } =
+#if NET451
+            new TElement[0];
+#else
+            Array.Empty<TElement>();
+#endif
+    }
+}

src/Microsoft.AspNetCore.Mvc.Core/Internal/FileResultExecutorBase.cs

@@ -41,7 +41,7 @@ namespace Microsoft.AspNetCore.Mvc.Internal
         private void SetContentType(ActionContext context, FileResult result)
         {
             var response = context.HttpContext.Response;
-            response.ContentType = result.ContentType.ToString();
+            response.ContentType = result.ContentType;
         }
 
         protected static ILogger CreateLogger<T>(ILoggerFactory factory)

src/Microsoft.AspNetCore.Mvc.Core/Internal/PrefixContainer.cs

@@ -14,7 +14,6 @@ namespace Microsoft.AspNetCore.Mvc.Internal
     /// </summary>
     public class PrefixContainer
     {
-        private static readonly string[] EmptyArray = new string[0];
         private static readonly char[] Delimiters = new char[] { '[', '.' };
 
         private readonly ICollection<string> _originalValues;
@@ -31,7 +30,7 @@ namespace Microsoft.AspNetCore.Mvc.Internal
 
             if (_originalValues.Count == 0)
             {
-                _sortedValues = EmptyArray;
+                _sortedValues = EmptyArray<string>.Instance;
             }
             else
             {

src/Microsoft.AspNetCore.Mvc.Core/Internal/ValidatorCache.cs

@@ -11,8 +11,6 @@ namespace Microsoft.AspNetCore.Mvc.Internal
 {
     public class ValidatorCache
     {
-        private readonly IReadOnlyList<IModelValidator> EmptyArray = new IModelValidator[0];
-
         private readonly ConcurrentDictionary<ModelMetadata, CacheEntry> _cacheEntries = new ConcurrentDictionary<ModelMetadata, CacheEntry>();
 
         public IReadOnlyList<IModelValidator> GetValidators(ModelMetadata metadata, IModelValidatorProvider validatorProvider)
@@ -105,7 +103,7 @@ namespace Microsoft.AspNetCore.Mvc.Internal
 
             if (count == 0)
             {
-                return EmptyArray;
+                return EmptyArray<IModelValidator>.Instance;
             }
 
             var validators = new IModelValidator[count];

src/Microsoft.AspNetCore.Mvc.Core/ModelBinding/Binders/ArrayModelBinder.cs

@@ -5,6 +5,7 @@ using System;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
+using Microsoft.AspNetCore.Mvc.Internal;
 
 namespace Microsoft.AspNetCore.Mvc.ModelBinding.Binders
 {
@@ -36,7 +37,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Binders
         {
             Debug.Assert(targetType == typeof(TElement[]), "GenericModelBinder only creates this binder for arrays.");
 
-            return new TElement[0];
+            return EmptyArray<TElement>.Instance;
         }
 
         /// <inheritdoc />

src/Microsoft.AspNetCore.Mvc.Core/ModelBinding/Binders/FormCollectionModelBinder.cs

@@ -7,7 +7,6 @@ using System.Collections.Generic;
 using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Http;
-using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
 using Microsoft.Extensions.Primitives;
 
 namespace Microsoft.AspNetCore.Mvc.ModelBinding.Binders
@@ -36,7 +35,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Binders
             {
                 model = new EmptyFormCollection();
             }
-            
+
             bindingContext.Result = ModelBindingResult.Success(model);
         }
 

src/Microsoft.AspNetCore.Mvc.Localization/LocalizedHtmlString.cs

@@ -3,9 +3,9 @@
 
 using System;
 using System.IO;
-using System.Text;
 using System.Text.Encodings.Web;
 using Microsoft.AspNetCore.Html;
+using Microsoft.AspNetCore.Mvc.Internal;
 
 namespace Microsoft.AspNetCore.Mvc.Localization
 {
@@ -14,11 +14,6 @@ namespace Microsoft.AspNetCore.Mvc.Localization
     /// </summary>
     public class LocalizedHtmlString : IHtmlContent
     {
-#if NETSTANDARD1_4
-        private static readonly object[] EmptyArguments = Array.Empty<object>();
-#else
-        private static readonly object[] EmptyArguments = new object[0];
-#endif
         private readonly object[] _arguments;
 
         /// <summary>
@@ -27,7 +22,7 @@ namespace Microsoft.AspNetCore.Mvc.Localization
         /// <param name="name">The name of the string resource.</param>
         /// <param name="value">The string resource.</param>
         public LocalizedHtmlString(string name, string value)
-            : this(name, value, isResourceNotFound: false, arguments: EmptyArguments)
+            : this(name, value, isResourceNotFound: false, arguments: EmptyArray<string>.Instance)
         {
         }
 
@@ -38,7 +33,7 @@ namespace Microsoft.AspNetCore.Mvc.Localization
         /// <param name="value">The string resource.</param>
         /// <param name="isResourceNotFound">A flag that indicates if the resource is not found.</param>
         public LocalizedHtmlString(string name, string value, bool isResourceNotFound)
-            : this(name, value, isResourceNotFound, arguments: EmptyArguments)
+            : this(name, value, isResourceNotFound, arguments: EmptyArray<string>.Instance)
         {
         }
 

src/Microsoft.AspNetCore.Mvc.Razor/Internal/CompilerCacheResult.cs

@@ -5,6 +5,7 @@ using System;
 using System.Collections.Generic;
 using System.Linq.Expressions;
 using System.Reflection;
+using Microsoft.AspNetCore.Mvc.Internal;
 using Microsoft.AspNetCore.Mvc.Razor.Compilation;
 using Microsoft.Extensions.Primitives;
 
@@ -22,7 +23,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
         /// <param name="relativePath">Path of the view file relative to the application base.</param>
         /// <param name="compilationResult">The <see cref="Compilation.CompilationResult"/>.</param>
         public CompilerCacheResult(string relativePath, CompilationResult compilationResult)
-            : this(relativePath, compilationResult, new IChangeToken[0])
+            : this(relativePath, compilationResult, EmptyArray<IChangeToken>.Instance)
         {
         }
 
@@ -86,6 +87,5 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
         /// Gets a delegate that creates an instance of the <see cref="IRazorPage"/>.
         /// </summary>
         public Func<IRazorPage> PageFactory { get; }
-
     }
 }

src/Microsoft.AspNetCore.Mvc.Razor/RazorViewEngine.cs

@@ -7,6 +7,7 @@ using System.Diagnostics;
 using System.Globalization;
 using System.Linq;
 using System.Text.Encodings.Web;
+using Microsoft.AspNetCore.Mvc.Internal;
 using Microsoft.AspNetCore.Mvc.Razor.Internal;
 using Microsoft.AspNetCore.Mvc.ViewEngines;
 using Microsoft.Extensions.Caching.Memory;
@@ -31,8 +32,6 @@ namespace Microsoft.AspNetCore.Mvc.Razor
 
         private const string ControllerKey = "controller";
         private const string AreaKey = "area";
-        private static readonly ViewLocationCacheItem[] EmptyViewStartLocationCacheItems =
-            new ViewLocationCacheItem[0];
         private static readonly TimeSpan _cacheExpirationDuration = TimeSpan.FromMinutes(20);
 
         private readonly IRazorPageFactoryProvider _pageFactory;
@@ -415,7 +414,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor
                 // Only need to lookup _ViewStarts for the main page.
                 var viewStartPages = isMainPage ?
                     GetViewStartPages(relativePath, expirationTokens) :
-                    EmptyViewStartLocationCacheItems;
+                    EmptyArray<ViewLocationCacheItem>.Instance;
 
                 return new ViewLocationCacheResult(
                     new ViewLocationCacheItem(factoryResult.RazorPageFactory, relativePath),

src/Microsoft.AspNetCore.Mvc.TagHelpers/Internal/GlobbingUrlBuilder.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Mvc.Internal;
 using Microsoft.Extensions.Caching.Memory;
 using Microsoft.Extensions.FileProviders;
 using Microsoft.Extensions.FileSystemGlobbing;
@@ -18,13 +19,6 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers.Internal
     /// </summary>
     public class GlobbingUrlBuilder
     {
-        private static readonly IReadOnlyList<string> EmptyList =
-#if NET451
-            new string[0];
-#else
-            Array.Empty<string>();
-#endif
-
         // Valid whitespace characters defined by the HTML5 spec.
         private static readonly char[] ValidAttributeWhitespaceChars =
             new[] { '\t', '\n', '\u000C', '\r', ' ' };
@@ -116,7 +110,7 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers.Internal
         {
             if (string.IsNullOrEmpty(include))
             {
-                return EmptyList;
+                return EmptyArray<string>.Instance;
             }
 
             var cacheKey = new GlobbingUrlKey(include, exclude);
@@ -130,7 +124,7 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers.Internal
             var includeEnumerator = includeTokenizer.GetEnumerator();
             if (!includeEnumerator.MoveNext())
             {
-                return EmptyList;
+                return EmptyArray<string>.Instance;
             }
 
             var options = new MemoryCacheEntryOptions();

src/Microsoft.AspNetCore.Mvc.ViewFeatures/Internal/DefaultDisplayTemplates.cs

@@ -119,7 +119,6 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures.Internal
             {
                 htmlHelper.ViewData.TemplateInfo.HtmlFieldPrefix = string.Empty;
 
-                var fieldNameBase = oldPrefix;
                 var result = new HtmlContentBuilder();
                 var viewEngine = serviceProvider.GetRequiredService<ICompositeViewEngine>();
                 var viewBufferScope = serviceProvider.GetRequiredService<IViewBufferScope>();
@@ -138,7 +137,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures.Internal
                         container: htmlHelper.ViewData.ModelExplorer,
                         metadata: itemMetadata,
                         model: item);
-                    var fieldName = string.Format(CultureInfo.InvariantCulture, "{0}[{1}]", fieldNameBase, index++);
+                    var fieldName = string.Format(CultureInfo.InvariantCulture, "{0}[{1}]", oldPrefix, index++);
 
                     var templateBuilder = new TemplateBuilder(
                         viewEngine,

src/Microsoft.AspNetCore.Mvc.ViewFeatures/Internal/DefaultEditorTemplates.cs

@@ -86,7 +86,6 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures.Internal
             {
                 viewData.TemplateInfo.HtmlFieldPrefix = string.Empty;
 
-                var fieldNameBase = oldPrefix;
                 var result = new HtmlContentBuilder();
                 var viewEngine = serviceProvider.GetRequiredService<ICompositeViewEngine>();
                 var viewBufferScope = serviceProvider.GetRequiredService<IViewBufferScope>();
@@ -105,7 +104,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures.Internal
                         container: htmlHelper.ViewData.ModelExplorer,
                         metadata: itemMetadata,
                         model: item);
-                    var fieldName = string.Format(CultureInfo.InvariantCulture, "{0}[{1}]", fieldNameBase, index++);
+                    var fieldName = string.Format(CultureInfo.InvariantCulture, "{0}[{1}]", oldPrefix, index++);
 
                     var templateBuilder = new TemplateBuilder(
                         viewEngine,

src/Microsoft.AspNetCore.Mvc.ViewFeatures/Internal/ExpressionHelper.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Diagnostics;
 using System.Globalization;
 using System.Linq;
 using System.Linq.Expressions;
@@ -37,86 +38,166 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures.Internal
                 return expressionText;
             }
 
+            // Determine size of string needed (length) and number of segments it contains (segmentCount). Put another
+            // way, segmentCount tracks the number of times the loop below should iterate. This avoids adding ".model"
+            // and / or an extra leading "." and then removing them after the loop. Other information collected in this
+            // first loop helps with length and segmentCount adjustments. containsIndexers is somewhat separate: If
+            // true, expression strings are not cached for the expression.
+            //
+            // After the corrections below the first loop, length is usually exactly the size of the returned string.
+            // However when containsIndexers is true, the calculation is approximate because either evaluating indexer
+            // expressions multiple times or saving indexer strings can get expensive. Optimizing for the common case
+            // of a collection (not a dictionary) with less than 100 elements. If that assumption proves to be
+            // incorrect, the StringBuilder will be enlarged but hopefully just once.
             var containsIndexers = false;
+            var lastIsModel = false;
+            var length = 0;
+            var segmentCount = 0;
+            var trailingMemberExpressions = 0;
+
             var part = expression.Body;
-
-            // Builder to concatenate the names for property/field accessors within an expression to create a string.
-            var builder = new StringBuilder();
-
             while (part != null)
             {
-                if (part.NodeType == ExpressionType.Call)
+                switch (part.NodeType)
                 {
-                    containsIndexers = true;
-                    var methodExpression = (MethodCallExpression)part;
-                    if (!IsSingleArgumentIndexer(methodExpression))
-                    {
+                    case ExpressionType.Call:
+                        var methodExpression = (MethodCallExpression)part;
+                        if (IsSingleArgumentIndexer(methodExpression))
+                        {
+                            containsIndexers = true;
+                            lastIsModel = false;
+                            length += "[99]".Length;
+                            part = methodExpression.Object;
+                            segmentCount++;
+                            trailingMemberExpressions = 0;
+                        }
+                        else
+                        {
+                            // Unsupported.
+                            part = null;
+                        }
+                        break;
+
+                    case ExpressionType.ArrayIndex:
+                        var binaryExpression = (BinaryExpression)part;
+
+                        containsIndexers = true;
+                        lastIsModel = false;
+                        length += "[99]".Length;
+                        part = binaryExpression.Left;
+                        segmentCount++;
+                        trailingMemberExpressions = 0;
+                        break;
+
+                    case ExpressionType.MemberAccess:
+                        var memberExpressionPart = (MemberExpression)part;
+                        var name = memberExpressionPart.Member.Name;
+
+                        // If identifier contains "__", it is "reserved for use by the implementation" and likely
+                        // compiler- or Razor-generated e.g. the name of a field in a delegate's generated class.
+                        if (name.Contains("__"))
+                        {
+                            // Exit loop.
+                            part = null;
+                        }
+                        else
+                        {
+                            lastIsModel = string.Equals("model", name, StringComparison.OrdinalIgnoreCase);
+                            length += name.Length + 1;
+                            part = memberExpressionPart.Expression;
+                            segmentCount++;
+                            trailingMemberExpressions++;
+                        }
+                        break;
+
+                    case ExpressionType.Parameter:
+                        // Unsupported but indicates previous member access was not the view's Model.
+                        lastIsModel = false;
+                        part = null;
+                        break;
+
+                    default:
                         // Unsupported.
+                        part = null;
                         break;
-                    }
-
-                    InsertIndexerInvocationText(
-                        builder,
-                        methodExpression.Arguments.Single(),
-                        expression);
-
-                    part = methodExpression.Object;
                 }
-                else if (part.NodeType == ExpressionType.ArrayIndex)
+            }
+
+            // If name would start with ".model", then strip that part away.
+            if (lastIsModel)
+            {
+                length -= ".model".Length;
+                segmentCount--;
+                trailingMemberExpressions--;
+            }
+
+            // Trim the leading "." if present. The loop below special-cases the last property to avoid this addition.
+            if (trailingMemberExpressions > 0)
+            {
+                length--;
+            }
+
+            Debug.Assert(segmentCount >= 0);
+            if (segmentCount == 0)
+            {
+                Debug.Assert(!containsIndexers);
+                if (expressionTextCache != null)
                 {
-                    containsIndexers = true;
-                    var binaryExpression = (BinaryExpression)part;
-
-                    InsertIndexerInvocationText(
-                        builder,
-                        binaryExpression.Right,
-                        expression);
-
-                    part = binaryExpression.Left;
+                    expressionTextCache.Entries.TryAdd(expression, string.Empty);
                 }
-                else if (part.NodeType == ExpressionType.MemberAccess)
-                {
-                    var memberExpressionPart = (MemberExpression)part;
-                    var name = memberExpressionPart.Member.Name;
 
-                    // If identifier contains "__", it is "reserved for use by the implementation" and likely compiler-
-                    // or Razor-generated e.g. the name of a field in a delegate's generated class.
-                    if (name.Contains("__"))
-                    {
-                        // Exit loop. Should have the entire name because previous MemberAccess has same name as the
-                        // leftmost expression node (a variable).
+                return string.Empty;
+            }
+
+            var builder = new StringBuilder(length);
+            part = expression.Body;
+            while (part != null && segmentCount > 0)
+            {
+                segmentCount--;
+                switch (part.NodeType)
+                {
+                    case ExpressionType.Call:
+                        Debug.Assert(containsIndexers);
+                        var methodExpression = (MethodCallExpression)part;
+
+                        InsertIndexerInvocationText(builder, methodExpression.Arguments.Single(), expression);
+
+                        part = methodExpression.Object;
                         break;
-                    }
 
-                    builder.Insert(0, name);
-                    builder.Insert(0, '.');
-                    part = memberExpressionPart.Expression;
-                }
-                else
-                {
-                    break;
+                    case ExpressionType.ArrayIndex:
+                        Debug.Assert(containsIndexers);
+                        var binaryExpression = (BinaryExpression)part;
+
+                        InsertIndexerInvocationText(builder, binaryExpression.Right, expression);
+
+                        part = binaryExpression.Left;
+                        break;
+
+                    case ExpressionType.MemberAccess:
+                        var memberExpression = (MemberExpression)part;
+                        var name = memberExpression.Member.Name;
+                        Debug.Assert(!name.Contains("__"));
+
+                        builder.Insert(0, name);
+                        if (segmentCount > 0)
+                        {
+                            // One or more parts to the left of this part are coming.
+                            builder.Insert(0, '.');
+                        }
+
+                        part = memberExpression.Expression;
+                        break;
+
+                    default:
+                        // Should be unreachable due to handling in above loop.
+                        Debug.Assert(false);
+                        break;
                 }
             }
 
-            // If parts start with "model", then strip that part away.
-            if (part == null || part.NodeType != ExpressionType.Parameter)
-            {
-                var text = builder.ToString();
-                if (text.StartsWith(".model", StringComparison.OrdinalIgnoreCase))
-                {
-                    // 6 is the length of the string ".model".
-                    builder.Remove(0, 6);
-                }
-            }
-
-            if (builder.Length > 0)
-            {
-                // Trim the leading "." if present.
-                builder.Replace(".", string.Empty, 0, 1);
-            }
-
+            Debug.Assert(segmentCount == 0);
             expressionText = builder.ToString();
-
             if (expressionTextCache != null && !containsIndexers)
             {
                 expressionTextCache.Entries.TryAdd(expression, expressionText);

src/Microsoft.AspNetCore.Mvc.ViewFeatures/Internal/ExpressionTextCache.cs

@@ -15,7 +15,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures.Internal
     public class ExpressionTextCache
     {
         /// <inheritdoc />
-        public ConcurrentDictionary<LambdaExpression, string> Entries { get; } = 
+        public ConcurrentDictionary<LambdaExpression, string> Entries { get; } =
             new ConcurrentDictionary<LambdaExpression, string>(LambdaExpressionComparer.Instance);
 
         // This comparer is tightly coupled with the logic of ExpressionHelper.GetExpressionText.
@@ -30,7 +30,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures.Internal
                 {
                     return true;
                 }
-                // We will cache only pure member access expressions. Hence we compare two expressions 
+                // We will cache only pure member access expressions. Hence we compare two expressions
                 // to be equal only if they are identical member access expressions.
                 var expression1 = lambdaExpression1.Body;
                 var expression2 = lambdaExpression2.Body;
@@ -69,7 +69,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures.Internal
                             return false;
                         }
                     }
-                    else 
+                    else
                     {
                         return true;
                     }

src/Microsoft.AspNetCore.Mvc.ViewFeatures/Internal/MvcViewFeaturesLoggerExtensions.cs

@@ -5,6 +5,7 @@ using System;
 using System.Collections;
 using System.Collections.Generic;
 using System.Diagnostics;
+using Microsoft.AspNetCore.Mvc.Internal;
 using Microsoft.AspNetCore.Mvc.ViewComponents;
 using Microsoft.AspNetCore.Mvc.ViewEngines;
 using Microsoft.Extensions.Logging;
@@ -14,7 +15,6 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures.Internal
     internal static class MvcViewFeaturesLoggerExtensions
     {
         private static readonly double TimestampToTicks = TimeSpan.TicksPerSecond / (double)Stopwatch.Frequency;
-        private static readonly string[] EmptyArguments = new string[0];
 
         private static readonly Action<ILogger, string, string[], Exception> _viewComponentExecuting;
         private static readonly Action<ILogger, string, double, string, Exception> _viewComponentExecuted;
@@ -103,7 +103,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures.Internal
         {
             if (arguments == null || arguments.Length == 0)
             {
-                return EmptyArguments;
+                return EmptyArray<string>.Instance;
             }
 
             var formattedArguments = new string[arguments.Length];

src/Microsoft.AspNetCore.Mvc.ViewFeatures/Internal/ValidationHelpers.cs

@@ -3,14 +3,13 @@
 
 using System.Collections.Generic;
 using System.Diagnostics;
+using Microsoft.AspNetCore.Mvc.Internal;
 using Microsoft.AspNetCore.Mvc.ModelBinding;
 
 namespace Microsoft.AspNetCore.Mvc.ViewFeatures.Internal
 {
     public static class ValidationHelpers
     {
-        private static readonly ModelStateEntry[] EmptyModelStateEntries = new ModelStateEntry[0];
-
         public static string GetModelErrorMessageOrDefault(ModelError modelError)
         {
             Debug.Assert(modelError != null);
@@ -80,7 +79,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures.Internal
                 return entries;
             }
 
-            return EmptyModelStateEntries;
+            return EmptyArray<ModelStateEntry>.Instance;
         }
 
         private static void Visit(

src/Microsoft.AspNetCore.Mvc.ViewFeatures/ModelStateDictionaryExtensions.cs

@@ -154,7 +154,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         {
             // We check if expression is wrapped with conversion to object expression
             // and unwrap it if necessary, because Expression<Func<TModel, object>>
-            // automatically creates a convert to object expression for expresions
+            // automatically creates a convert to object expression for expressions
             // returning value types
             var unaryExpression = expression.Body as UnaryExpression;
 

src/Microsoft.AspNetCore.Mvc.ViewFeatures/RemoteAttribute.cs

@@ -7,6 +7,7 @@ using System.ComponentModel.DataAnnotations;
 using System.Globalization;
 using System.Linq;
 using Microsoft.AspNetCore.Mvc.DataAnnotations;
+using Microsoft.AspNetCore.Mvc.Internal;
 using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
 using Microsoft.AspNetCore.Mvc.Routing;
 using Microsoft.AspNetCore.Mvc.ViewFeatures;
@@ -26,7 +27,7 @@ namespace Microsoft.AspNetCore.Mvc
     public class RemoteAttribute : ValidationAttribute, IClientModelValidator
     {
         private string _additionalFields = string.Empty;
-        private string[] _additionalFieldsSplit = new string[0];
+        private string[] _additionalFieldsSplit = EmptyArray<string>.Instance;
         private bool _checkedForLocalizer;
         private IStringLocalizer _stringLocalizer;
 
@@ -275,7 +276,7 @@ namespace Microsoft.AspNetCore.Mvc
         {
             if (string.IsNullOrEmpty(original))
             {
-                return new string[0];
+                return EmptyArray<string>.Instance;
             }
 
             var split = original

src/Microsoft.AspNetCore.Mvc.ViewFeatures/Rendering/TagBuilder.cs

@@ -91,7 +91,7 @@ namespace Microsoft.AspNetCore.Mvc.Rendering
         }
 
         /// <summary>
-        /// Return valid HTML 4.01 "id" attribute for an element with the given <paramref name="name"/>.
+        /// Returns a valid HTML 4.01 "id" attribute value for an element with the given <paramref name="name"/>.
         /// </summary>
         /// <param name="name">The original element name.</param>
         /// <param name="invalidCharReplacement">
@@ -99,9 +99,11 @@ namespace Microsoft.AspNetCore.Mvc.Rendering
         /// <paramref name="name"/>.
         /// </param>
         /// <returns>
-        /// Valid HTML 4.01 "id" attribute for an element with the given <paramref name="name"/>.
+        /// Valid HTML 4.01 "id" attribute value for an element with the given <paramref name="name"/>.
         /// </returns>
-        /// <remarks>Valid "id" attributes are defined in http://www.w3.org/TR/html401/types.html#type-id</remarks>
+        /// <remarks>
+        /// Valid "id" attributes are defined in http://www.w3.org/TR/html401/types.html#type-id
+        /// </remarks>
         public static string CreateSanitizedId(string name, string invalidCharReplacement)
         {
             if (invalidCharReplacement == null)
@@ -205,7 +207,11 @@ namespace Microsoft.AspNetCore.Mvc.Rendering
                     writer.Write(" ");
                     writer.Write(key);
                     writer.Write("=\"");
-                    encoder.Encode(writer, attribute.Value ?? string.Empty);
+                    if (attribute.Value != null)
+                    {
+                        encoder.Encode(writer, attribute.Value);
+                    }
+
                     writer.Write("\"");
                 }
             }

src/Microsoft.AspNetCore.Mvc.ViewFeatures/Rendering/ViewContext.cs

@@ -83,7 +83,7 @@ namespace Microsoft.AspNetCore.Mvc.Rendering
             Writer = writer;
 
             FormContext = new FormContext();
-            
+
             ClientValidationEnabled = htmlHelperOptions.ClientValidationEnabled;
             Html5DateRenderingMode = htmlHelperOptions.Html5DateRenderingMode;
             ValidationSummaryMessageElement = htmlHelperOptions.ValidationSummaryMessageElement;
@@ -228,7 +228,7 @@ namespace Microsoft.AspNetCore.Mvc.Rendering
 
         public FormContext GetFormContextForClientValidation()
         {
-            return (ClientValidationEnabled) ? FormContext : null;
+            return ClientValidationEnabled ? FormContext : null;
         }
     }
 }

src/Microsoft.AspNetCore.Mvc.ViewFeatures/ViewFeatures/AttributeDictionary.cs

@@ -558,6 +558,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
             {
                 _attributes = attributes;
             }
+
             public int Count => _attributes.Count;
 
             public bool IsReadOnly => true;

src/Microsoft.AspNetCore.Mvc.ViewFeatures/ViewFeatures/DefaultHtmlGenerator.cs

@@ -404,10 +404,18 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
             var resolvedLabelText = labelText ??
                 modelExplorer.Metadata.DisplayName ??
                 modelExplorer.Metadata.PropertyName;
-            if (resolvedLabelText == null)
+            if (resolvedLabelText == null && expression != null)
             {
-                resolvedLabelText =
-                    string.IsNullOrEmpty(expression) ? string.Empty : expression.Split('.').Last();
+                var index = expression.LastIndexOf('.');
+                if (index == -1)
+                {
+                    // Expression does not contain a dot separator.
+                    resolvedLabelText = expression;
+                }
+                else
+                {
+                    resolvedLabelText = expression.Substring(index + 1);
+                }
             }
 
             if (string.IsNullOrEmpty(resolvedLabelText))
@@ -1289,8 +1297,9 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
                     object typeAttributeValue;
                     if (htmlAttributes != null && htmlAttributes.TryGetValue("type", out typeAttributeValue))
                     {
-                        if (string.Equals(typeAttributeValue.ToString(), "file", StringComparison.OrdinalIgnoreCase) ||
-                            string.Equals(typeAttributeValue.ToString(), "image", StringComparison.OrdinalIgnoreCase))
+                        var typeAttributeString = typeAttributeValue.ToString();
+                        if (string.Equals(typeAttributeString, "file", StringComparison.OrdinalIgnoreCase) ||
+                            string.Equals(typeAttributeString, "image", StringComparison.OrdinalIgnoreCase))
                         {
                             // 'value' attribute is not needed for 'file' and 'image' input types.
                             addValue = false;

src/Microsoft.AspNetCore.Mvc.ViewFeatures/ViewFeatures/HtmlHelper.cs

@@ -181,16 +181,17 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
         /// <summary>
         /// Creates a dictionary of HTML attributes from the input object,
         /// translating underscores to dashes in each public instance property.
-        ///
-        /// If the object is already an <see cref="IDictionary{String, Object}"/> instance, then it is
-        /// returned as-is.
+        /// </summary>
+        /// <param name="htmlAttributes">Anonymous object describing HTML attributes.</param>
+        /// <returns>A dictionary that represents HTML attributes.</returns>
+        /// <remarks>
+        /// If the object is already an <see cref="IDictionary{String, Object}"/> instance, then a shallow copy is
+        /// returned.
         /// <example>
         /// <c>new { data_name="value" }</c> will translate to the entry <c>{ "data-name", "value" }</c>
         /// in the resulting dictionary.
         /// </example>
-        /// </summary>
-        /// <param name="htmlAttributes">Anonymous object describing HTML attributes.</param>
-        /// <returns>A dictionary that represents HTML attributes.</returns>
+        /// </remarks>
         public static IDictionary<string, object> AnonymousObjectToHtmlAttributes(object htmlAttributes)
         {
             var dictionary = htmlAttributes as IDictionary<string, object>;
@@ -799,13 +800,21 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
             // we want to fall back to the field name rather than the ModelType.
             // This is similar to how the GenerateLabel get the text of a label.
             var resolvedDisplayName = modelExplorer.Metadata.DisplayName ?? modelExplorer.Metadata.PropertyName;
-            if (resolvedDisplayName == null)
+            if (resolvedDisplayName == null && expression != null)
             {
-                resolvedDisplayName =
-                    string.IsNullOrEmpty(expression) ? string.Empty : expression.Split('.').Last();
+                var index = expression.LastIndexOf('.');
+                if (index == -1)
+                {
+                    // Expression does not contain a dot separator.
+                    resolvedDisplayName = expression;
+                }
+                else
+                {
+                    resolvedDisplayName = expression.Substring(index + 1);
+                }
             }
 
-            return resolvedDisplayName;
+            return resolvedDisplayName ?? string.Empty;
         }
 
         protected virtual string GenerateDisplayText(ModelExplorer modelExplorer)
@@ -978,14 +987,13 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
             bool useViewData,
             object htmlAttributes)
         {
-            var tagBuilder =
-                _htmlGenerator.GenerateHidden(
-                    ViewContext,
-                    modelExplorer,
-                    expression,
-                    value,
-                    useViewData,
-                    htmlAttributes);
+            var tagBuilder = _htmlGenerator.GenerateHidden(
+                ViewContext,
+                modelExplorer,
+                expression,
+                value,
+                useViewData,
+                htmlAttributes);
             if (tagBuilder == null)
             {
                 return HtmlString.Empty;

src/Microsoft.AspNetCore.Mvc.ViewFeatures/ViewFeatures/IHtmlGenerator.cs

@@ -3,7 +3,6 @@
 
 using System.Collections.Generic;
 using Microsoft.AspNetCore.Html;
-using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
 using Microsoft.AspNetCore.Mvc.Rendering;
 
 namespace Microsoft.AspNetCore.Mvc.ViewFeatures

src/Microsoft.AspNetCore.Mvc.ViewFeatures/ViewFeatures/ModelExplorer.cs

@@ -20,7 +20,6 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
 
         private object _model;
         private Func<object, object> _modelAccessor;
-        private Type _modelType;
         private List<ModelExplorer> _properties;
 
         /// <summary>
@@ -30,8 +29,8 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
         /// <param name="metadata">The <see cref="ModelMetadata"/>.</param>
         /// <param name="model">The model object. May be <c>null</c>.</param>
         public ModelExplorer(
-            IModelMetadataProvider metadataProvider, 
-            ModelMetadata metadata, 
+            IModelMetadataProvider metadataProvider,
+            ModelMetadata metadata,
             object model)
         {
             if (metadataProvider == null)
@@ -172,29 +171,23 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
         {
             get
             {
-                if (_modelType == null)
+                if (Metadata.IsNullableValueType)
                 {
-                    if (Model == null)
-                    {
-                        // If the model is null, then use the declared model type;
-                        _modelType = Metadata.ModelType;
-                    }
-                    else if (Metadata.IsNullableValueType)
-                    {
-                        // We have a model, but if it's a nullable value type, then Model.GetType() will return
-                        // the non-nullable type (int? -> int). Since it's a value type, there's no subclassing,
-                        // just go with the declared type.
-                        _modelType = Metadata.ModelType;
-                    }
-                    else
-                    {
-                        // We have a model, and it's not a nullable so use the runtime type to handle
-                        // cases where the model is a subclass of the declared type and has extra data.
-                        _modelType = Model.GetType();
-                    }
+                    // We have a model, but if it's a nullable value type, then Model.GetType() will return
+                    // the non-nullable type (int? -> int). Since it's a value type, there's no subclassing,
+                    // just go with the declared type.
+                    return Metadata.ModelType;
                 }
 
-                return _modelType;
+                if (Model == null)
+                {
+                    // If the model is null, then use the declared model type;
+                    return Metadata.ModelType;
+                }
+
+                // We have a model, and it's not a nullable, so use the runtime type to handle
+                // cases where the model is a subclass of the declared type and has extra data.
+                return Model.GetType();
             }
         }
 
@@ -203,7 +196,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
         /// </summary>
         /// <remarks>
         /// Includes a <see cref="ModelExplorer"/> for each property of the <see cref="ModelMetadata"/>
-        /// for <see cref="ModelType"/>. 
+        /// for <see cref="ModelType"/>.
         /// </remarks>
         public IEnumerable<ModelExplorer> Properties
         {
@@ -260,8 +253,8 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
             }
 
             return Properties.FirstOrDefault(p => string.Equals(
-                p.Metadata.PropertyName, 
-                name, 
+                p.Metadata.PropertyName,
+                name,
                 StringComparison.Ordinal));
         }
 
@@ -383,7 +376,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
         /// <returns>A <see cref="ModelExplorer"/>.</returns>
         /// <remarks>
         /// <para>
-        /// A <see cref="ModelExplorer"/> created by 
+        /// A <see cref="ModelExplorer"/> created by
         /// <see cref="GetExplorerForExpression(Type, Func{object, object})"/>
         /// represents the result of executing an arbitrary expression against the model contained
         /// in the current <see cref="ModelExplorer"/> instance.
@@ -411,7 +404,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
         /// <returns>A <see cref="ModelExplorer"/>.</returns>
         /// <remarks>
         /// <para>
-        /// A <see cref="ModelExplorer"/> created by 
+        /// A <see cref="ModelExplorer"/> created by
         /// <see cref="GetExplorerForExpression(ModelMetadata, Func{object, object})"/>
         /// represents the result of executing an arbitrary expression against the model contained
         /// in the current <see cref="ModelExplorer"/> instance.
@@ -444,7 +437,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
         }
 
         private ModelExplorer CreateExplorerForProperty(
-            ModelMetadata propertyMetadata, 
+            ModelMetadata propertyMetadata,
             PropertyHelper propertyHelper)
         {
             if (propertyHelper == null)

src/Microsoft.AspNetCore.Mvc.ViewFeatures/ViewFeatures/SessionStateTempDataProvider.cs

@@ -9,6 +9,7 @@ using System.IO;
 using System.Linq;
 using System.Reflection;
 using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Mvc.Internal;
 using Microsoft.Extensions.Internal;
 using Newtonsoft.Json;
 using Newtonsoft.Json.Bson;
@@ -156,7 +157,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
             {
                 // Since we call Save() after the response has been sent, we need to initialize an empty session
                 // so that it is established before the headers are sent.
-                session.Set(TempDataSessionStateKey, new byte[] { });
+                session.Set(TempDataSessionStateKey, EmptyArray<byte>.Instance);
             }
 
             return tempDataDictionary ?? new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase);

src/Microsoft.AspNetCore.Mvc.ViewFeatures/ViewFeatures/TemplateBuilder.cs

@@ -42,7 +42,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures.Internal
 
             if (bufferScope == null)
             {
-                throw new ArgumentNullException(nameof(_bufferScope));
+                throw new ArgumentNullException(nameof(bufferScope));
             }
 
             if (viewContext == null)

src/Microsoft.AspNetCore.Mvc.ViewFeatures/ViewFeatures/ViewDataEvaluator.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Reflection;
 
 namespace Microsoft.AspNetCore.Mvc.ViewFeatures
@@ -98,57 +99,58 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
 
         private static ViewDataInfo InnerEvalComplexExpression(object indexableObject, string expression)
         {
-            foreach (var expressionPair in GetRightToLeftExpressions(expression))
+            Debug.Assert(expression != null);
+            var leftExpression = expression;
+            do
             {
-                var subExpression = expressionPair.Left;
-                var postExpression = expressionPair.Right;
-
-                var subTargetInfo = GetPropertyValue(indexableObject, subExpression);
-                if (subTargetInfo != null)
+                var targetInfo = GetPropertyValue(indexableObject, leftExpression);
+                if (targetInfo != null)
                 {
-                    if (string.IsNullOrEmpty(postExpression))
+                    if (leftExpression.Length == expression.Length)
                     {
-                        return subTargetInfo;
+                        // Nothing remaining in expression after leftExpression.
+                        return targetInfo;
                     }
 
-                    if (subTargetInfo.Value != null)
+                    if (targetInfo.Value != null)
                     {
-                        var potential = InnerEvalComplexExpression(subTargetInfo.Value, postExpression);
-                        if (potential != null)
+                        var rightExpression = expression.Substring(leftExpression.Length + 1);
+                        targetInfo = InnerEvalComplexExpression(targetInfo.Value, rightExpression);
+                        if (targetInfo != null)
                         {
-                            return potential;
+                            return targetInfo;
                         }
                     }
                 }
+
+                leftExpression = GetNextShorterExpression(leftExpression);
             }
+            while (!string.IsNullOrEmpty(leftExpression));
 
             return null;
         }
 
-        // Produces an enumeration of combinations of property names given a complex expression in the following order:
-        //  this["one.two.three.four"]
-        //  this["one.two.three][four"]
-        //  this["one.two][three.four"]
-        //  this["one][two.three.four"]
+        // Given "one.two.three.four" initially, calls return
+        //  "one.two.three"
+        //  "one.two"
+        //  "one"
+        //  ""
         // Recursion of InnerEvalComplexExpression() further sub-divides these cases to cover the full set of
         // combinations shown in Eval(ViewDataDictionary, string) comments.
-        private static IEnumerable<ExpressionPair> GetRightToLeftExpressions(string expression)
+        private static string GetNextShorterExpression(string expression)
         {
-            yield return new ExpressionPair(expression, string.Empty);
+            if (string.IsNullOrEmpty(expression))
+            {
+                return string.Empty;
+            }
 
             var lastDot = expression.LastIndexOf('.');
-
-            var subExpression = expression;
-            var postExpression = string.Empty;
-
-            while (lastDot > -1)
+            if (lastDot == -1)
             {
-                subExpression = expression.Substring(0, lastDot);
-                postExpression = expression.Substring(lastDot + 1);
-                yield return new ExpressionPair(subExpression, postExpression);
-
-                lastDot = subExpression.LastIndexOf('.');
+                return string.Empty;
             }
+
+            return expression.Substring(startIndex: 0, length: lastDot);
         }
 
         private static ViewDataInfo GetIndexedPropertyValue(object indexableObject, string key)
@@ -205,17 +207,5 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
 
             return new ViewDataInfo(container, propertyInfo);
         }
-
-        private struct ExpressionPair
-        {
-            public readonly string Left;
-            public readonly string Right;
-
-            public ExpressionPair(string left, string right)
-            {
-                Left = left;
-                Right = right;
-            }
-        }
     }
 }

src/Microsoft.AspNetCore.Mvc.WebApiCompatShim/OverloadActionConstraint.cs

@@ -21,7 +21,7 @@ namespace Microsoft.AspNetCore.Mvc.WebApiCompatShim
     public class OverloadActionConstraint : IActionConstraint
     {
         /// <inheritdoc />
-        public int Order { get; } = int.MaxValue;
+        public int Order => int.MaxValue;
 
         /// <inheritdoc />
         public bool Accept(ActionConstraintContext context)

test/Microsoft.AspNetCore.Mvc.Core.Test/Formatters/MediaTypeTest.cs

@@ -1,7 +1,6 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-using System.Linq;
 using Microsoft.Extensions.Primitives;
 using Xunit;
 

test/Microsoft.AspNetCore.Mvc.Core.Test/Formatters/StreamOutputFormatterTest.cs

@@ -3,10 +3,7 @@
 
 using System;
 using System.IO;
-using System.Text;
-using System.Threading.Tasks;
 using Microsoft.AspNetCore.Http;
-using Microsoft.AspNetCore.Http.Features;
 using Microsoft.Extensions.Primitives;
 using Xunit;
 

test/Microsoft.AspNetCore.Mvc.Core.Test/MediaTypeCollectionTest.cs

@@ -1,7 +1,6 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-using Microsoft.Extensions.Primitives;
 using Microsoft.Net.Http.Headers;
 using Xunit;
 

test/Microsoft.AspNetCore.Mvc.Core.Test/ModelBinding/CompositeValueProviderTest.cs

@@ -4,7 +4,6 @@
 using System;
 using System.Collections.Generic;
 using System.Globalization;
-using System.Threading.Tasks;
 using Microsoft.Extensions.Primitives;
 using Moq;
 using Xunit;

test/Microsoft.AspNetCore.Mvc.Core.Test/ModelBinding/EnumerableValueProviderTest.cs

@@ -4,7 +4,6 @@
 using System.Collections.Generic;
 using System.Globalization;
 using System.Linq;
-using System.Threading.Tasks;
 using Microsoft.Extensions.Primitives;
 using Xunit;
 

test/Microsoft.AspNetCore.Mvc.TagHelpers.Test/AnchorTagHelperTest.cs

@@ -134,7 +134,7 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
             generator.Verify();
             Assert.Equal("a", output.TagName);
             Assert.Empty(output.Attributes);
-            Assert.True(output.Content.GetContent().Length == 0);
+            Assert.Empty(output.Content.GetContent());
         }
 
         [Fact]
@@ -185,7 +185,7 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
             generator.Verify();
             Assert.Equal("a", output.TagName);
             Assert.Empty(output.Attributes);
-            Assert.True(output.Content.GetContent().Length == 0);
+            Assert.Empty(output.Content.GetContent());
         }
 
         [Fact]
@@ -242,7 +242,7 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
 
             Assert.Equal("a", output.TagName);
             Assert.Empty(output.Attributes);
-            Assert.True(output.Content.GetContent().Length == 0);
+            Assert.Empty(output.Content.GetContent());
         }
 
         [Fact]
@@ -300,7 +300,7 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
 
             Assert.Equal("a", output.TagName);
             Assert.Empty(output.Attributes);
-            Assert.True(output.Content.GetContent().Length == 0);
+            Assert.Empty(output.Content.GetContent());
         }
 
         [Fact]
@@ -357,7 +357,7 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
 
             Assert.Equal("a", output.TagName);
             Assert.Empty(output.Attributes);
-            Assert.True(output.Content.GetContent().Length == 0);
+            Assert.Empty(output.Content.GetContent());
         }
 
         [Theory]

test/Microsoft.AspNetCore.Mvc.TagHelpers.Test/ValidationMessageTagHelperTest.cs

@@ -149,7 +149,9 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
         [InlineData("\r\n  \r\n", "\r\n Something Else \r\n", "\r\n Something Else \r\n")]
         [InlineData("\r\n  \r\n", "Some Content", "Some Content")]
         public async Task ProcessAsync_DoesNotOverrideOutputContent(
-            string childContent, string outputContent, string expectedOutputContent)
+            string childContent,
+            string outputContent,
+            string expectedOutputContent)
         {
             // Arrange
             var tagBuilder = new TagBuilder("span2");
@@ -209,7 +211,8 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
         [InlineData("Content of validation message", "Content of validation message")]
         [InlineData("\r\n  \r\n", "New HTML")]
         public async Task ProcessAsync_MergesTagBuilderFromGenerateValidationMessage(
-            string childContent, string expectedOutputContent)
+            string childContent,
+            string expectedOutputContent)
         {
             // Arrange
             var tagBuilder = new TagBuilder("span2");

test/Microsoft.AspNetCore.Mvc.TestCommon/MediaTypeAssert.cs

@@ -1,4 +1,6 @@
-using System;
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
 using Microsoft.Extensions.Primitives;
 using Microsoft.Net.Http.Headers;
 using Xunit.Sdk;

test/Microsoft.AspNetCore.Mvc.ViewFeatures.Test/Internal/ExpressionHelperTest.cs

@@ -157,8 +157,8 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures.Internal
                         (Expression<Func<TestModel, string>>)(m => value)
                     },
                     {
-                        // These two expressions are not actually equivalent. However ExpressionHelper returns 
-                        // string.Empty for these two expressions and hence they are considered as equivalent by the 
+                        // These two expressions are not actually equivalent. However ExpressionHelper returns
+                        // string.Empty for these two expressions and hence they are considered as equivalent by the
                         // cache.
                         (Expression<Func<TestModel, string>>)(m => Model),
                         (Expression<Func<TestModel, TestModel>>)(m => m)
@@ -206,10 +206,6 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures.Internal
                         (Expression<Func<IDictionary<string, TestModel>, string>>)(model => model[key].SelectedCategory.CategoryName.MainCategory),
                         (Expression<Func<TestModel, Category>>)(model => model.SelectedCategory)
                     },
-                    {
-                        (Expression<Func<IList<TestModel>, Category>>)(model => model[2].SelectedCategory),
-                        (Expression<Func<IList<TestModel>, Category>>)(model => model[2].SelectedCategory)
-                    },
                     {
                         (Expression<Func<TestModel, string>>)(m => Model),
                         (Expression<Func<TestModel, string>>)(m => m.Model)
@@ -226,10 +222,6 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures.Internal
                         (Expression<Func<TestModel, string>>)(m => key),
                         (Expression<Func<TestModel, string>>)(m => value)
                     },
-                    {
-                        (Expression<Func<IDictionary<string, TestModel>, string>>)(model => model[key].SelectedCategory.CategoryName.MainCategory),
-                        (Expression<Func<IDictionary<string, TestModel>, string>>)(model => model[key].SelectedCategory.CategoryName.MainCategory)
-                    },
                 };
             }
         }
@@ -256,7 +248,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures.Internal
             var text2 = ExpressionHelper.GetExpressionText(expression, _expressionTextCache);
 
             // Assert
-            Assert.Same(text1, text2); // Cached
+            Assert.Same(text1, text2); // cached
         }
 
         [Theory]
@@ -270,6 +262,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures.Internal
             var text2 = ExpressionHelper.GetExpressionText(expression, _expressionTextCache);
 
             // Assert
+            Assert.Equal(text1, text2, StringComparer.Ordinal);
             Assert.NotSame(text1, text2); // not cached
         }
 
@@ -284,7 +277,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures.Internal
             var text2 = ExpressionHelper.GetExpressionText(expression2, _expressionTextCache);
 
             // Assert
-            Assert.Same(text1, text2);
+            Assert.Same(text1, text2); // cached
         }
 
         [Theory]
@@ -298,6 +291,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures.Internal
             var text2 = ExpressionHelper.GetExpressionText(expression2, _expressionTextCache);
 
             // Assert
+            Assert.NotEqual(text1, text2, StringComparer.Ordinal);
             Assert.NotSame(text1, text2);
         }
 

test/Microsoft.AspNetCore.Mvc.ViewFeatures.Test/Rendering/HtmlHelperFormTest.cs

@@ -6,7 +6,6 @@ using System.Collections.Generic;
 using System.IO;
 using System.Linq;
 using System.Text.Encodings.Web;
-using Microsoft.AspNetCore.Html;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Mvc.Routing;
 using Microsoft.AspNetCore.Mvc.ViewFeatures;

test/Microsoft.AspNetCore.Mvc.ViewFeatures.Test/Rendering/HtmlHelperHiddenTest.cs

@@ -20,12 +20,12 @@ namespace Microsoft.AspNetCore.Mvc.Rendering
             get
             {
                 var expected1 = @"<input baz=""HtmlEncode[[BazValue]]"" id=""HtmlEncode[[Property1]]"" name=""HtmlEncode[[Property1]]"" type=""HtmlEncode[[hidden]]"" " +
-                                @"value=""HtmlEncode[[ModelStateValue]]"" />";
+                    @"value=""HtmlEncode[[ModelStateValue]]"" />";
                 yield return new object[] { new Dictionary<string, object> { { "baz", "BazValue" } }, expected1 };
                 yield return new object[] { new { baz = "BazValue" }, expected1 };
 
                 var expected2 = @"<input foo-baz=""HtmlEncode[[BazValue]]"" id=""HtmlEncode[[Property1]]"" name=""HtmlEncode[[Property1]]"" type=""HtmlEncode[[hidden]]"" " +
-                                @"value=""HtmlEncode[[ModelStateValue]]"" />";
+                    @"value=""HtmlEncode[[ModelStateValue]]"" />";
                 yield return new object[] { new Dictionary<string, object> { { "foo-baz", "BazValue" } }, expected2 };
                 yield return new object[] { new { foo_baz = "BazValue" }, expected2 };
             }
@@ -151,7 +151,7 @@ namespace Microsoft.AspNetCore.Mvc.Rendering
         {
             // Arrange
             var expected = @"<input id=""HtmlEncode[[Property1]]"" key=""HtmlEncode[[value]]"" name=""HtmlEncode[[Property1]]"" type=""HtmlEncode[[hidden]]"" " +
-                           @"value=""HtmlEncode[[test]]"" />";
+                @"value=""HtmlEncode[[test]]"" />";
             var attributes = new { key = "value" };
             var helper = DefaultTemplatesUtilities.GetHtmlHelper(GetViewDataWithNullModelAndNonNullViewData());
 
@@ -167,7 +167,7 @@ namespace Microsoft.AspNetCore.Mvc.Rendering
         {
             // Arrange
             var expected = @"<input data-key=""HtmlEncode[[value]]"" id=""HtmlEncode[[Property1]]"" name=""HtmlEncode[[Property1]]"" type=""HtmlEncode[[hidden]]"" " +
-                           @"value=""HtmlEncode[[test]]"" />";
+                @"value=""HtmlEncode[[test]]"" />";
             var attributes = new Dictionary<string, object> { { "data-key", "value" } };
             var helper = DefaultTemplatesUtilities.GetHtmlHelper(GetViewDataWithNullModelAndNonNullViewData());
 
@@ -292,7 +292,7 @@ namespace Microsoft.AspNetCore.Mvc.Rendering
         {
             // Arrange
             var expected = @"<input baz=""HtmlEncode[[BazValue]]"" id=""HtmlEncode[[keyNotFound]]"" name=""HtmlEncode[[keyNotFound]]"" type=""HtmlEncode[[hidden]]"" " +
-                           @"value="""" />";
+                @"value="""" />";
             var helper = DefaultTemplatesUtilities.GetHtmlHelper(GetViewDataWithModelStateAndModelAndViewDataValues());
             var attributes = new Dictionary<string, object> { { "baz", "BazValue" } };
 

test/Microsoft.AspNetCore.Mvc.ViewFeatures.Test/Rendering/HtmlHelperLabelExtensionsTest.cs

@@ -38,6 +38,7 @@ namespace Microsoft.AspNetCore.Mvc.Core
         public void LabelHelpers_DisplayPropertyName()
         {
             // Arrange
+            var expectedLabel = "<label for=\"HtmlEncode[[Property1]]\">HtmlEncode[[Property1]]</label>";
             var helper = DefaultTemplatesUtilities.GetHtmlHelper();
 
             // Act
@@ -45,14 +46,15 @@ namespace Microsoft.AspNetCore.Mvc.Core
             var labelForResult = helper.LabelFor(m => m.Property1);
 
             // Assert
-            Assert.Equal("<label for=\"HtmlEncode[[Property1]]\">HtmlEncode[[Property1]]</label>", HtmlContentUtilities.HtmlContentToString(labelResult));
-            Assert.Equal("<label for=\"HtmlEncode[[Property1]]\">HtmlEncode[[Property1]]</label>", HtmlContentUtilities.HtmlContentToString(labelForResult));
+            Assert.Equal(expectedLabel, HtmlContentUtilities.HtmlContentToString(labelResult));
+            Assert.Equal(expectedLabel, HtmlContentUtilities.HtmlContentToString(labelForResult));
         }
 
         [Fact]
         public void LabelHelpers_DisplayPropertyName_ForNestedProperty()
         {
             // Arrange
+            var expectedLabel = "<label for=\"HtmlEncode[[Inner_Id]]\">HtmlEncode[[Id]]</label>";
             var helper = DefaultTemplatesUtilities.GetHtmlHelper<OuterClass>(model: null);
 
             // Act
@@ -60,8 +62,8 @@ namespace Microsoft.AspNetCore.Mvc.Core
             var labelForResult = helper.LabelFor(m => m.Inner.Id);
 
             // Assert
-            Assert.Equal("<label for=\"HtmlEncode[[Inner_Id]]\">HtmlEncode[[Id]]</label>", HtmlContentUtilities.HtmlContentToString(labelResult));
-            Assert.Equal("<label for=\"HtmlEncode[[Inner_Id]]\">HtmlEncode[[Id]]</label>", HtmlContentUtilities.HtmlContentToString(labelForResult));
+            Assert.Equal(expectedLabel, HtmlContentUtilities.HtmlContentToString(labelResult));
+            Assert.Equal(expectedLabel, HtmlContentUtilities.HtmlContentToString(labelForResult));
         }
 
         [Fact]

test/Microsoft.AspNetCore.Mvc.ViewFeatures.Test/Rendering/HtmlHelperPasswordTest.cs

@@ -469,7 +469,7 @@ namespace Microsoft.AspNetCore.Mvc.Rendering
             Expression<Func<PasswordModel, string>> expression,
             string expected)
         {
-            // Arrange            
+            // Arrange
             var model = new PasswordModel();
             var helper = DefaultTemplatesUtilities.GetHtmlHelper(model);
             helper.ViewData.TemplateInfo.HtmlFieldPrefix = "pre";
@@ -489,7 +489,7 @@ namespace Microsoft.AspNetCore.Mvc.Rendering
             // Act
             var result = helper.PasswordFor(expression);
 
-            // Assert 
+            // Assert
             Assert.Equal(expected, HtmlContentUtilities.HtmlContentToString(result));
         }
 

test/Microsoft.AspNetCore.Mvc.ViewFeatures.Test/Rendering/HtmlHelperTextAreaTest.cs

@@ -15,14 +15,14 @@ namespace Microsoft.AspNetCore.Mvc.Rendering
         [Fact]
         public void TextAreaFor_GeneratesPlaceholderAttribute_WhenDisplayAttributePromptIsSetAndTypeIsValid()
         {
-            // Arrange            
+            // Arrange
             var model = new TextAreaModelWithAPlaceholder();
             var helper = DefaultTemplatesUtilities.GetHtmlHelper(model);
 
             // Act
             var textArea = helper.TextAreaFor(m => m.Property1);
 
-            // Assert 
+            // Assert
             var result = HtmlContentUtilities.HtmlContentToString(textArea);
             Assert.Contains(@"placeholder=""HtmlEncode[[placeholder]]""", result, StringComparison.Ordinal);
         }
@@ -30,14 +30,14 @@ namespace Microsoft.AspNetCore.Mvc.Rendering
         [Fact]
         public void TextAreaFor_DoesNotGeneratePlaceholderAttribute_WhenNoPlaceholderPresentInModel()
         {
-            // Arrange            
+            // Arrange
             var model = new TextAreaModelWithoutAPlaceholder();
             var helper = DefaultTemplatesUtilities.GetHtmlHelper(model);
 
             // Act
             var textArea = helper.TextAreaFor(m => m.Property1);
 
-            // Assert 
+            // Assert
             var result = HtmlContentUtilities.HtmlContentToString(textArea);
             Assert.DoesNotContain(@"placeholder=""HtmlEncode[[placeholder]]""", result, StringComparison.Ordinal);
         }

test/Microsoft.AspNetCore.Mvc.ViewFeatures.Test/Rendering/HtmlHelperTextBoxTest.cs

@@ -21,14 +21,14 @@ namespace Microsoft.AspNetCore.Mvc.Rendering
         [InlineData("number")]
         public void TextBoxFor_GeneratesPlaceholderAttribute_WhenDisplayAttributePromptIsSetAndTypeIsValid(string type)
         {
-            // Arrange            
+            // Arrange
             var model = new TextBoxModel();
             var helper = DefaultTemplatesUtilities.GetHtmlHelper(model);
 
             // Act
             var textBox = helper.TextBoxFor(m => m.Property1, new { type });
 
-            // Assert 
+            // Assert
             var result = HtmlContentUtilities.HtmlContentToString(textBox);
             Assert.Contains(@"placeholder=""HtmlEncode[[placeholder]]""", result, StringComparison.Ordinal);
         }
@@ -48,14 +48,14 @@ namespace Microsoft.AspNetCore.Mvc.Rendering
         [InlineData("file")]
         public void TextBoxFor_DoesNotGeneratePlaceholderAttribute_WhenDisplayAttributePromptIsSetAndTypeIsInvalid(string type)
         {
-            // Arrange            
+            // Arrange
             var model = new TextBoxModel();
             var helper = DefaultTemplatesUtilities.GetHtmlHelper(model);
 
             // Act
             var textBox = helper.TextBoxFor(m => m.Property1, new { type });
 
-            // Assert 
+            // Assert
             var result = HtmlContentUtilities.HtmlContentToString(textBox);
             Assert.DoesNotContain(@"placeholder=""HtmlEncode[[placeholder]]""", result, StringComparison.Ordinal);
         }