From fa8c2eac3ef7c9ab149495dd88aeea2813c32c7c Mon Sep 17 00:00:00 2001
From: Doug Bunting <dougbu@microsoft.com>
Date: Thu, 7 Jan 2016 09:09:16 -0800
Subject: [PATCH] Check encoded and unencoded values against element body in
 `OptionTagHelper` - #3386 - initialize comparison `HashSet` with unencoded
 values to ensure both are checked - address perf and correctness issues in
 this code   - `context.Items[typeof(SelectTagHelper)]` entry read as
 `ICollection` but written as `IReadOnlyCollection`     -
 `IReadOnlyCollection` worse because it does not include `Contains()`, causing
 Linq use   - every `<option>` element recalculated the encoded values and
 created a `HashSet` to contain them     - add `CurrentValues` type to cache
 this `HashSet` in `context.Items`   - each `OptionTagHelper` created the
 additional `HashSet` even if `Value` was bound

---
 .../Internal/CurrentValues.cs                 | 21 ++++++
 .../OptionTagHelper.cs                        | 54 ++++++++++------
 .../SelectTagHelper.cs                        |  6 +-
 .../ViewFeatures/DefaultHtmlGenerator.cs      | 10 ++-
 .../ViewFeatures/IHtmlGenerator.cs            | 10 +--
 .../OptionTagHelperTest.cs                    | 64 ++++++++++---------
 .../SelectTagHelperTest.cs                    |  7 +-
 7 files changed, 107 insertions(+), 65 deletions(-)
 create mode 100644 src/Microsoft.AspNet.Mvc.TagHelpers/Internal/CurrentValues.cs

diff --git a/src/Microsoft.AspNet.Mvc.TagHelpers/Internal/CurrentValues.cs b/src/Microsoft.AspNet.Mvc.TagHelpers/Internal/CurrentValues.cs
new file mode 100644
index 0000000000..cf0389f423
--- /dev/null
+++ b/src/Microsoft.AspNet.Mvc.TagHelpers/Internal/CurrentValues.cs
@@ -0,0 +1,21 @@
+// 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.Collections.Generic;
+using System.Diagnostics;
+
+namespace Microsoft.AspNet.Mvc.TagHelpers.Internal
+{
+    public class CurrentValues
+    {
+        public CurrentValues(ICollection<string> values)
+        {
+            Debug.Assert(values != null);
+            Values = values;
+        }
+
+        public ICollection<string> Values { get; }
+
+        public ICollection<string> ValuesAndEncodedValues { get; set; }
+    }
+}
diff --git a/src/Microsoft.AspNet.Mvc.TagHelpers/OptionTagHelper.cs b/src/Microsoft.AspNet.Mvc.TagHelpers/OptionTagHelper.cs
index b897eb580e..1603bad918 100644
--- a/src/Microsoft.AspNet.Mvc.TagHelpers/OptionTagHelper.cs
+++ b/src/Microsoft.AspNet.Mvc.TagHelpers/OptionTagHelper.cs
@@ -5,6 +5,7 @@ using System;
 using System.Collections.Generic;
 using System.Threading.Tasks;
 using Microsoft.AspNet.Mvc.Rendering;
+using Microsoft.AspNet.Mvc.TagHelpers.Internal;
 using Microsoft.AspNet.Mvc.ViewFeatures;
 using Microsoft.AspNet.Razor.TagHelpers;
 
@@ -55,8 +56,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
         /// <inheritdoc />
         /// <remarks>
         /// Does nothing unless <see cref="TagHelperContext.Items"/> contains a
-        /// <see cref="SelectTagHelper"/> <see cref="Type"/> entry and that entry is a non-empty
-        /// <see cref="ICollection{string}"/> instance. Also does nothing if the associated &lt;option&gt; is already
+        /// <see cref="SelectTagHelper"/> <see cref="Type"/> entry and that entry is a non-<c>null</c>
+        /// <see cref="CurrentValues"/> instance. Also does nothing if the associated &lt;option&gt; is already
         /// selected.
         /// </remarks>
         public override async Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
@@ -85,32 +86,43 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                 context.Items.TryGetValue(typeof(SelectTagHelper), out formDataEntry);
 
                 // ... And did the SelectTagHelper determine any selected values?
-                var selectedValues = formDataEntry as ICollection<string>;
-                if (selectedValues != null && selectedValues.Count != 0)
+                var currentValues = formDataEntry as CurrentValues;
+                if (currentValues?.Values != null && currentValues.Values.Count != 0)
                 {
-                    // Encode all selected values for comparison with element content.
-                    var encodedValues = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
-                    foreach (var selectedValue in selectedValues)
-                    {
-                        encodedValues.Add(Generator.Encode(selectedValue));
-                    }
-
-                    // Select this <option/> element if value attribute or content matches a selected value. Callers
-                    // encode values as-needed while executing child content. But TagHelperOutput itself
-                    // encodes attribute values later, when start tag is generated.
+                    // Select this <option/> element if value attribute or (if no value attribute) body matches a
+                    // selected value. Body is encoded as-needed while executing child content. But TagHelperOutput
+                    // itself encodes attribute values later, when start tag is generated.
                     bool selected;
                     if (Value != null)
                     {
-                        selected = selectedValues.Contains(Value);
-                    }
-                    else if (output.IsContentModified)
-                    {
-                        selected = encodedValues.Contains(output.Content.GetContent());
+                        selected = currentValues.Values.Contains(Value);
                     }
                     else
                     {
-                        var childContent = await output.GetChildContentAsync();
-                        selected = encodedValues.Contains(childContent.GetContent());
+                        if (currentValues.ValuesAndEncodedValues == null)
+                        {
+                            // Include encoded versions of all selected values when comparing with body.
+                            var allValues = new HashSet<string>(currentValues.Values, StringComparer.OrdinalIgnoreCase);
+                            foreach (var selectedValue in currentValues.Values)
+                            {
+                                allValues.Add(Generator.Encode(selectedValue));
+                            }
+
+                            currentValues.ValuesAndEncodedValues = allValues;
+                        }
+
+                        TagHelperContent childContent;
+                        if (output.IsContentModified)
+                        {
+                            // Another tag helper has modified the body. Use what they wrote.
+                            childContent = output.Content;
+                        }
+                        else
+                        {
+                            childContent = await output.GetChildContentAsync();
+                        }
+
+                        selected = currentValues.ValuesAndEncodedValues.Contains(childContent.GetContent());
                     }
 
                     if (selected)
diff --git a/src/Microsoft.AspNet.Mvc.TagHelpers/SelectTagHelper.cs b/src/Microsoft.AspNet.Mvc.TagHelpers/SelectTagHelper.cs
index ee00d9c94a..9cd4023a15 100644
--- a/src/Microsoft.AspNet.Mvc.TagHelpers/SelectTagHelper.cs
+++ b/src/Microsoft.AspNet.Mvc.TagHelpers/SelectTagHelper.cs
@@ -8,6 +8,7 @@ using System.Linq;
 using System.Reflection;
 using Microsoft.AspNet.Mvc.ModelBinding;
 using Microsoft.AspNet.Mvc.Rendering;
+using Microsoft.AspNet.Mvc.TagHelpers.Internal;
 using Microsoft.AspNet.Mvc.ViewFeatures;
 using Microsoft.AspNet.Razor.TagHelpers;
 
@@ -22,7 +23,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
         private const string ForAttributeName = "asp-for";
         private const string ItemsAttributeName = "asp-items";
         private bool _allowMultiple;
-        private IReadOnlyCollection<string> _currentValues;
+        private ICollection<string> _currentValues;
 
         /// <summary>
         /// Creates a new <see cref="SelectTagHelper"/>.
@@ -94,7 +95,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
 
             // Whether or not (not being highly unlikely) we generate anything, could update contained <option/>
             // elements. Provide selected values for <option/> tag helpers.
-            context.Items[typeof(SelectTagHelper)] = _currentValues;
+            var currentValues = _currentValues == null ? null : new CurrentValues(_currentValues);
+            context.Items[typeof(SelectTagHelper)] = currentValues;
         }
 
         /// <inheritdoc />
diff --git a/src/Microsoft.AspNet.Mvc.ViewFeatures/ViewFeatures/DefaultHtmlGenerator.cs b/src/Microsoft.AspNet.Mvc.ViewFeatures/ViewFeatures/DefaultHtmlGenerator.cs
index 1dbefb93c1..f40f7ad036 100644
--- a/src/Microsoft.AspNet.Mvc.ViewFeatures/ViewFeatures/DefaultHtmlGenerator.cs
+++ b/src/Microsoft.AspNet.Mvc.ViewFeatures/ViewFeatures/DefaultHtmlGenerator.cs
@@ -511,7 +511,7 @@ namespace Microsoft.AspNet.Mvc.ViewFeatures
             string optionLabel,
             string expression,
             IEnumerable<SelectListItem> selectList,
-            IReadOnlyCollection<string> currentValues,
+            ICollection<string> currentValues,
             bool allowMultiple,
             object htmlAttributes)
         {
@@ -886,7 +886,7 @@ namespace Microsoft.AspNet.Mvc.ViewFeatures
         }
 
         /// <inheritdoc />
-        public virtual IReadOnlyCollection<string> GetCurrentValues(
+        public virtual ICollection<string> GetCurrentValues(
             ViewContext viewContext,
             ModelExplorer modelExplorer,
             string expression,
@@ -1026,9 +1026,7 @@ namespace Microsoft.AspNet.Mvc.ViewFeatures
                 }
             }
 
-            // HashSet<> implements IReadOnlyCollection<> as of 4.6, but does not for 4.5.1. If the runtime cast succeeds,
-            // avoid creating a new collection.
-            return (currentValues as IReadOnlyCollection<string>) ?? currentValues.ToArray();
+            return currentValues;
         }
 
         internal static string EvalString(ViewContext viewContext, string key, string format)
@@ -1407,7 +1405,7 @@ namespace Microsoft.AspNet.Mvc.ViewFeatures
         private static IEnumerable<SelectListItem> UpdateSelectListItemsWithDefaultValue(
             ModelExplorer modelExplorer,
             IEnumerable<SelectListItem> selectList,
-            IReadOnlyCollection<string> currentValues)
+            ICollection<string> currentValues)
         {
             // Perform deep copy of selectList to avoid changing user's Selected property values.
             var newSelectList = new List<SelectListItem>();
diff --git a/src/Microsoft.AspNet.Mvc.ViewFeatures/ViewFeatures/IHtmlGenerator.cs b/src/Microsoft.AspNet.Mvc.ViewFeatures/ViewFeatures/IHtmlGenerator.cs
index 81379f8f9e..994a36e9a9 100644
--- a/src/Microsoft.AspNet.Mvc.ViewFeatures/ViewFeatures/IHtmlGenerator.cs
+++ b/src/Microsoft.AspNet.Mvc.ViewFeatures/ViewFeatures/IHtmlGenerator.cs
@@ -273,7 +273,7 @@ namespace Microsoft.AspNet.Mvc.ViewFeatures
         /// <c>ViewContext.ViewData[expression]</c>.
         /// </param>
         /// <param name="currentValues">
-        /// An <see cref="IReadOnlyCollection{string}"/> containing values for &lt;option&gt; elements to select. If
+        /// An <see cref="ICollection{string}"/> containing values for &lt;option&gt; elements to select. If
         /// <c>null</c>, selects &lt;option&gt; elements based on <see cref="SelectListItem.Selected"/> values in
         /// <paramref name="selectList"/>.
         /// </param>
@@ -303,7 +303,7 @@ namespace Microsoft.AspNet.Mvc.ViewFeatures
             string optionLabel,
             string expression,
             IEnumerable<SelectListItem> selectList,
-            IReadOnlyCollection<string> currentValues,
+            ICollection<string> currentValues,
             bool allowMultiple,
             object htmlAttributes);
 
@@ -361,8 +361,8 @@ namespace Microsoft.AspNet.Mvc.ViewFeatures
         /// </param>
         /// <returns>
         /// <para>
-        /// <c>null</c> if no <paramref name="expression"/> result is found. Otherwise an
-        /// <see cref="IReadOnlyCollection{string}"/> containing current values for the given
+        /// <c>null</c> if no <paramref name="expression"/> result is found. Otherwise a
+        /// <see cref="ICollection{string}"/> containing current values for the given
         /// <paramref name="expression"/>.
         /// </para>
         /// <para>
@@ -380,7 +380,7 @@ namespace Microsoft.AspNet.Mvc.ViewFeatures
         /// <remarks>
         /// See <see cref="GenerateSelect"/> for information about how the return value may be used.
         /// </remarks>
-        IReadOnlyCollection<string> GetCurrentValues(
+        ICollection<string> GetCurrentValues(
             ViewContext viewContext,
             ModelExplorer modelExplorer,
             string expression,
diff --git a/test/Microsoft.AspNet.Mvc.TagHelpers.Test/OptionTagHelperTest.cs b/test/Microsoft.AspNet.Mvc.TagHelpers.Test/OptionTagHelperTest.cs
index b4829d14c0..264d07dc2f 100644
--- a/test/Microsoft.AspNet.Mvc.TagHelpers.Test/OptionTagHelperTest.cs
+++ b/test/Microsoft.AspNet.Mvc.TagHelpers.Test/OptionTagHelperTest.cs
@@ -5,6 +5,7 @@ using System.Collections.Generic;
 using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.AspNet.Mvc.ModelBinding;
+using Microsoft.AspNet.Mvc.TagHelpers.Internal;
 using Microsoft.AspNet.Razor.TagHelpers;
 using Xunit;
 
@@ -14,11 +15,11 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
     {
         // Original content, selected attribute, value attribute, selected values (to place in TagHelperContext.Items)
         // and expected tag helper output.
-        public static TheoryData<string, string, string, IEnumerable<string>, TagHelperOutput> GeneratesExpectedDataSet
+        public static TheoryData<string, string, string, CurrentValues, TagHelperOutput> GeneratesExpectedDataSet
         {
             get
             {
-                return new TheoryData<string, string, string, IEnumerable<string>, TagHelperOutput>
+                return new TheoryData<string, string, string, CurrentValues, TagHelperOutput>
                 {
                     // original content, selected, value, selected values,
                     // expected tag helper output - attributes, content
@@ -53,7 +54,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                             "")
                     },
                     {
-                        null, null, "value", Enumerable.Empty<string>(),
+                        null, null, "value", new CurrentValues(new HashSet<string>()),
                         GetTagHelperOutput(
                             "not-option",
                             new TagHelperAttributeList
@@ -63,7 +64,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                             "")
                     },
                     {
-                        null, null, "value", new [] { string.Empty, },
+                        null, null, "value", new CurrentValues(new HashSet<string>(new [] { string.Empty, })),
                         GetTagHelperOutput(
                             "not-option",
                             new TagHelperAttributeList
@@ -73,7 +74,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                             "")
                     },
                     {
-                        null, string.Empty, "value", new [] { string.Empty, },
+                        null, string.Empty, "value", new CurrentValues(new HashSet<string>(new [] { string.Empty, })),
                         GetTagHelperOutput(
                             "not-option",
                             new TagHelperAttributeList
@@ -83,7 +84,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                             "")
                     },
                     {
-                        null, null, "value", new [] { "value", },
+                        null, null, "value", new CurrentValues(new HashSet<string>(new [] { "value", })),
                         GetTagHelperOutput(
                             "not-option",
                             new TagHelperAttributeList
@@ -93,7 +94,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                             "")
                     },
                     {
-                        null, null, "value", new [] { string.Empty, "value", },
+                        null, null, "value", new CurrentValues(new HashSet<string>(new [] { string.Empty, "value", })),
                         GetTagHelperOutput(
                             "not-option",
                             new TagHelperAttributeList
@@ -133,7 +134,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                             "")
                     },
                     {
-                        string.Empty, null, null, Enumerable.Empty<string>(),
+                        string.Empty, null, null, new CurrentValues(new HashSet<string>()),
                         GetTagHelperOutput(
                             "not-option",
                             new TagHelperAttributeList
@@ -143,7 +144,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                             "")
                     },
                     {
-                        string.Empty, null, null, new [] { string.Empty, },
+                        string.Empty, null, null, new CurrentValues(new HashSet<string>(new [] { string.Empty, })),
                         GetTagHelperOutput(
                             "not-option",
                             new TagHelperAttributeList
@@ -153,7 +154,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                             "")
                     },
                     {
-                        string.Empty, string.Empty, null, new [] { string.Empty, },
+                        string.Empty, string.Empty, null,
+                        new CurrentValues(new HashSet<string>(new [] { string.Empty, })),
                         GetTagHelperOutput(
                             "not-option",
                             new TagHelperAttributeList
@@ -163,7 +165,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                             "")
                     },
                     {
-                        string.Empty, null, null, new [] { "text", },
+                        string.Empty, null, null, new CurrentValues(new HashSet<string>(new [] { "text", })),
                         GetTagHelperOutput(
                             "not-option",
                             new TagHelperAttributeList
@@ -173,7 +175,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                             "")
                     },
                     {
-                        string.Empty, null, null, new [] { string.Empty, "text", },
+                        string.Empty, null, null,
+                        new CurrentValues(new HashSet<string>(new [] { string.Empty, "text", })),
                         GetTagHelperOutput(
                             "not-option",
                             new TagHelperAttributeList
@@ -213,7 +216,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                             "text")
                     },
                     {
-                        "text", null, null, Enumerable.Empty<string>(),
+                        "text", null, null, new CurrentValues(new HashSet<string>()),
                         GetTagHelperOutput(
                             "not-option",
                             new TagHelperAttributeList
@@ -223,7 +226,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                             "text")
                     },
                     {
-                        "text", null, null, new [] { string.Empty, },
+                        "text", null, null, new CurrentValues(new HashSet<string>(new [] { string.Empty, })),
                         GetTagHelperOutput(
                             "not-option",
                             new TagHelperAttributeList
@@ -233,7 +236,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                             "text")
                     },
                     {
-                        "HtmlEncode[[text]]", null, null, new [] { "text", },
+                        "HtmlEncode[[text]]", null, null, new CurrentValues(new HashSet<string>(new [] { "text", })),
                         GetTagHelperOutput(
                             "not-option",
                             new TagHelperAttributeList
@@ -243,7 +246,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                             "HtmlEncode[[text]]")
                     },
                     {
-                        "text", string.Empty, null, new [] { "text", },
+                        "text", string.Empty, null, new CurrentValues(new HashSet<string>(new [] { "text", })),
                         GetTagHelperOutput(
                             "not-option",
                             new TagHelperAttributeList
@@ -253,7 +256,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                             "text")
                     },
                     {
-                        "HtmlEncode[[text]]", null, null, new [] { string.Empty, "text", },
+                        "HtmlEncode[[text]]", null, null,
+                        new CurrentValues(new HashSet<string>(new [] { string.Empty, "text", })),
                         GetTagHelperOutput(
                             "not-option",
                             new TagHelperAttributeList
@@ -283,7 +287,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                             "text")
                     },
                     {
-                        "text", null, "value", Enumerable.Empty<string>(),
+                        "text", null, "value", new CurrentValues(new HashSet<string>()),
                         GetTagHelperOutput(
                             "not-option",
                             new TagHelperAttributeList
@@ -293,7 +297,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                             "text")
                     },
                     {
-                        "text", null, "value", new [] { string.Empty, },
+                        "text", null, "value", new CurrentValues(new HashSet<string>(new [] { string.Empty, })),
                         GetTagHelperOutput(
                             "not-option",
                             new TagHelperAttributeList
@@ -303,7 +307,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                             "text")
                     },
                     {
-                        "text", string.Empty, "value", new [] { string.Empty, },
+                        "text", string.Empty, "value",
+                        new CurrentValues(new HashSet<string>(new [] { string.Empty, })),
                         GetTagHelperOutput(
                             "not-option",
                             new TagHelperAttributeList
@@ -313,7 +318,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                             "text")
                     },
                     {
-                        "text", null, "value", new [] { "text", },
+                        "text", null, "value", new CurrentValues(new HashSet<string>(new [] { "text", })),
                         GetTagHelperOutput(
                             "not-option",
                             new TagHelperAttributeList
@@ -323,7 +328,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                             "text")
                     },
                     {
-                        "text", null, "value", new [] { "value", },
+                        "text", null, "value", new CurrentValues(new HashSet<string>(new [] { "value", })),
                         GetTagHelperOutput(
                             "not-option",
                             new TagHelperAttributeList
@@ -333,7 +338,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                             "text")
                     },
                     {
-                        "text", null, "value", new [] { string.Empty, "value", },
+                        "text", null, "value",
+                        new CurrentValues(new HashSet<string>(new [] { string.Empty, "value", })),
                         GetTagHelperOutput(
                             "not-option",
                             new TagHelperAttributeList
@@ -354,7 +360,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             get
             {
                 return GeneratesExpectedDataSet.Where(
-                    entry => (entry[1] != null || entry[3] == null || (entry[3] as ICollection<string>).Count == 0));
+                    entry => (entry[1] != null || entry[3] == null || ((CurrentValues)(entry[3])).Values.Count == 0));
             }
         }
 
@@ -375,7 +381,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             string originalContent,
             string selected,
             string value,
-            IEnumerable<string> selectedValues,
+            CurrentValues currentValues,
             TagHelperOutput expectedTagHelperOutput)
         {
             // Arrange
@@ -420,7 +426,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                 model: null,
                 htmlGenerator: htmlGenerator,
                 metadataProvider: metadataProvider);
-            tagHelperContext.Items[typeof(SelectTagHelper)] = selectedValues;
+            tagHelperContext.Items[typeof(SelectTagHelper)] = currentValues;
             var tagHelper = new OptionTagHelper(htmlGenerator)
             {
                 Value = value,
@@ -446,7 +452,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             string originalContent,
             string selected,
             string value,
-            IEnumerable<string> selectedValues,
+            CurrentValues currentValues,
             TagHelperOutput ignored)
         {
             // Arrange
@@ -491,7 +497,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
                 model: null,
                 htmlGenerator: htmlGenerator,
                 metadataProvider: metadataProvider);
-            tagHelperContext.Items[typeof(SelectTagHelper)] = selectedValues;
+            tagHelperContext.Items[typeof(SelectTagHelper)] = currentValues;
             var tagHelper = new OptionTagHelper(htmlGenerator)
             {
                 Value = value,
@@ -509,7 +515,7 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             string originalContent,
             string selected,
             string value,
-            IEnumerable<string> ignoredValues,
+            CurrentValues ignoredValues,
             TagHelperOutput ignoredOutput)
         {
             // Arrange
diff --git a/test/Microsoft.AspNet.Mvc.TagHelpers.Test/SelectTagHelperTest.cs b/test/Microsoft.AspNet.Mvc.TagHelpers.Test/SelectTagHelperTest.cs
index 3716847e44..630a6286ed 100644
--- a/test/Microsoft.AspNet.Mvc.TagHelpers.Test/SelectTagHelperTest.cs
+++ b/test/Microsoft.AspNet.Mvc.TagHelpers.Test/SelectTagHelperTest.cs
@@ -8,6 +8,7 @@ using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.AspNet.Mvc.ModelBinding;
 using Microsoft.AspNet.Mvc.Rendering;
+using Microsoft.AspNet.Mvc.TagHelpers.Internal;
 using Microsoft.AspNet.Mvc.TestCommon;
 using Microsoft.AspNet.Mvc.ViewFeatures;
 using Microsoft.AspNet.Razor.TagHelpers;
@@ -544,7 +545,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var keyValuePair = Assert.Single(
                 tagHelperContext.Items,
                 entry => (Type)entry.Key == typeof(SelectTagHelper));
-            Assert.Same(currentValues, keyValuePair.Value);
+            var actualCurrentValues = Assert.IsType<CurrentValues>(keyValuePair.Value);
+            Assert.Same(currentValues, actualCurrentValues.Values);
         }
 
         [Theory]
@@ -618,7 +620,8 @@ namespace Microsoft.AspNet.Mvc.TagHelpers
             var keyValuePair = Assert.Single(
                 tagHelperContext.Items,
                 entry => (Type)entry.Key == typeof(SelectTagHelper));
-            Assert.Same(currentValues, keyValuePair.Value);
+            var actualCurrentValues = Assert.IsType<CurrentValues>(keyValuePair.Value);
+            Assert.Same(currentValues, actualCurrentValues.Values);
         }
 
         public class NameAndId