Add AllowedChildTagDescriptor.

- Changed the `AllowedChildTags` collection on `TagHelperDescriptor` to have a custom object type to represent child tags.
- Created comparers and builders to work with the child tag descriptor.
- Removed the validation methods on `TagHelperDescriptorBuilder` since there's no longer any bits to validate (they're contained within the sub-properties).
- Unit tested the `DisplayName`.

#1493

src/Microsoft.AspNetCore.Razor.Language/AllowedChildTagDescriptor.cs

@@ -0,0 +1,45 @@
+// 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;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
+
+namespace Microsoft.AspNetCore.Razor.Language
+{
+    [DebuggerDisplay("{DisplayName,nq}")]
+    public abstract class AllowedChildTagDescriptor : IEquatable<AllowedChildTagDescriptor>
+    {
+        public string Name { get; protected set; }
+
+        public string DisplayName { get; protected set; }
+
+        public IReadOnlyList<RazorDiagnostic> Diagnostics { get; protected set; }
+
+        public bool HasErrors
+        {
+            get
+            {
+                var errors = Diagnostics.Any(diagnostic => diagnostic.Severity == RazorDiagnosticSeverity.Error);
+
+                return errors;
+            }
+        }
+
+        public bool Equals(AllowedChildTagDescriptor other)
+        {
+            return AllowedChildTagDescriptorComparer.Default.Equals(this, other);
+        }
+
+        public override bool Equals(object obj)
+        {
+            return Equals(obj as AllowedChildTagDescriptor);
+        }
+
+        public override int GetHashCode()
+        {
+            return AllowedChildTagDescriptorComparer.Default.GetHashCode(this);
+        }
+    }
+}

src/Microsoft.AspNetCore.Razor.Language/AllowedChildTagDescriptorBuilder.cs

@@ -0,0 +1,17 @@
+// 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;
+
+namespace Microsoft.AspNetCore.Razor.Language
+{
+    public abstract class AllowedChildTagDescriptorBuilder
+    {
+        public abstract string Name { get; set; }
+
+        public abstract string DisplayName { get; set; }
+
+        public abstract RazorDiagnosticCollection Diagnostics { get; }
+        
+    }
+}

src/Microsoft.AspNetCore.Razor.Language/AllowedChildTagDescriptorComparer.cs

@@ -0,0 +1,73 @@
+// 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;
+using System.Collections.Generic;
+using System.Linq;
+using Microsoft.Extensions.Internal;
+
+namespace Microsoft.AspNetCore.Razor.Language
+{
+    internal class AllowedChildTagDescriptorComparer : IEqualityComparer<AllowedChildTagDescriptor>
+    {
+        /// <summary>
+        /// A default instance of the <see cref="AllowedChildTagDescriptorComparer"/>.
+        /// </summary>
+        public static readonly AllowedChildTagDescriptorComparer Default =
+            new AllowedChildTagDescriptorComparer();
+
+        /// <summary>
+        /// A default instance of the <see cref="AllowedChildTagDescriptorComparer"/> that does case-sensitive comparison.
+        /// </summary>
+        internal static readonly AllowedChildTagDescriptorComparer CaseSensitive =
+            new AllowedChildTagDescriptorComparer(caseSensitive: true);
+
+        private readonly StringComparer _stringComparer;
+        private readonly StringComparison _stringComparison;
+
+        private AllowedChildTagDescriptorComparer(bool caseSensitive = false)
+        {
+            if (caseSensitive)
+            {
+                _stringComparer = StringComparer.Ordinal;
+                _stringComparison = StringComparison.Ordinal;
+            }
+            else
+            {
+                _stringComparer = StringComparer.OrdinalIgnoreCase;
+                _stringComparison = StringComparison.OrdinalIgnoreCase;
+            }
+        }
+
+        /// <inheritdoc />
+        public virtual bool Equals(
+            AllowedChildTagDescriptor descriptorX,
+            AllowedChildTagDescriptor descriptorY)
+        {
+            if (object.ReferenceEquals(descriptorX, descriptorY))
+            {
+                return true;
+            }
+
+            if (descriptorX == null ^ descriptorY == null)
+            {
+                return false;
+            }
+
+            return descriptorX != null &&
+                string.Equals(descriptorX.Name, descriptorY.Name, _stringComparison) &&
+                string.Equals(descriptorX.DisplayName, descriptorY.DisplayName, StringComparison.Ordinal) &&
+                Enumerable.SequenceEqual(descriptorX.Diagnostics, descriptorY.Diagnostics);
+        }
+
+        /// <inheritdoc />
+        public virtual int GetHashCode(AllowedChildTagDescriptor descriptor)
+        {
+            var hashCodeCombiner = HashCodeCombiner.Start();
+            hashCodeCombiner.Add(descriptor.Name, _stringComparer);
+            hashCodeCombiner.Add(descriptor.DisplayName, StringComparer.Ordinal);
+
+            return hashCodeCombiner.CombinedHash;
+        }
+    }
+}

src/Microsoft.AspNetCore.Razor.Language/DefaultAllowedChildTagDescriptor.cs

@@ -0,0 +1,15 @@
+// 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.
+
+namespace Microsoft.AspNetCore.Razor.Language
+{
+    internal class DefaultAllowedChildTagDescriptor : AllowedChildTagDescriptor
+    {
+        public DefaultAllowedChildTagDescriptor(string name, string displayName, RazorDiagnostic[] diagnostics)
+        {
+            Name = name;
+            DisplayName = displayName;
+            Diagnostics = diagnostics;
+        }
+    }
+}

src/Microsoft.AspNetCore.Razor.Language/DefaultAllowedChildTagDescriptorBuilder.cs

@@ -0,0 +1,77 @@
+// 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;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Microsoft.AspNetCore.Razor.Language
+{
+    internal class DefaultAllowedChildTagDescriptorBuilder : AllowedChildTagDescriptorBuilder
+    {
+        private readonly DefaultTagHelperDescriptorBuilder _parent;
+        private DefaultRazorDiagnosticCollection _diagnostics;
+
+        public DefaultAllowedChildTagDescriptorBuilder(DefaultTagHelperDescriptorBuilder parent)
+        {
+            _parent = parent;
+        }
+
+        public override string Name { get; set; }
+
+        public override string DisplayName { get; set; }
+
+        public override RazorDiagnosticCollection Diagnostics
+        {
+            get
+            {
+                if (_diagnostics == null)
+                {
+                    _diagnostics = new DefaultRazorDiagnosticCollection();
+                }
+
+                return _diagnostics;
+            }
+        }
+
+        public AllowedChildTagDescriptor Build()
+        {
+            var validationDiagnostics = Validate();
+            var diagnostics = new HashSet<RazorDiagnostic>(validationDiagnostics);
+            if (_diagnostics != null)
+            {
+                diagnostics.UnionWith(_diagnostics);
+            }
+
+            var displayName = DisplayName ?? Name;
+            var descriptor = new DefaultAllowedChildTagDescriptor(
+                Name,
+                displayName,
+                diagnostics?.ToArray() ?? Array.Empty<RazorDiagnostic>());
+
+            return descriptor;
+        }
+
+        private IEnumerable<RazorDiagnostic> Validate()
+        {
+            if (string.IsNullOrWhiteSpace(Name))
+            {
+                var diagnostic = RazorDiagnosticFactory.CreateTagHelper_InvalidRestrictedChildNullOrWhitespace(_parent.GetDisplayName());
+
+                yield return diagnostic;
+            }
+            else if (Name != TagHelperMatchingConventions.ElementCatchAllName)
+            {
+                foreach (var character in Name)
+                {
+                    if (char.IsWhiteSpace(character) || HtmlConventions.InvalidNonWhitespaceHtmlCharacters.Contains(character))
+                    {
+                        var diagnostic = RazorDiagnosticFactory.CreateTagHelper_InvalidRestrictedChild(_parent.GetDisplayName(), Name, character);
+
+                        yield return diagnostic;
+                    }
+                }
+            }
+        }
+    }
+}

src/Microsoft.AspNetCore.Razor.Language/DefaultTagHelperDescriptor.cs

@@ -16,7 +16,7 @@ namespace Microsoft.AspNetCore.Razor.Language
             string tagOutputHint,
             TagMatchingRuleDescriptor[] tagMatchingRules,
             BoundAttributeDescriptor[] attributeDescriptors,
-            string[] allowedChildTags,
+            AllowedChildTagDescriptor[] allowedChildTags,
             Dictionary<string, string> metadata,
             RazorDiagnostic[] diagnostics) 
             : base(kind)

src/Microsoft.AspNetCore.Razor.Language/DefaultTagHelperDescriptorBuilder.cs

@@ -12,7 +12,7 @@ namespace Microsoft.AspNetCore.Razor.Language
         // Required values
         private readonly Dictionary<string, string> _metadata;
 
-        private HashSet<string> _allowedChildTags;
+        private List<DefaultAllowedChildTagDescriptorBuilder> _allowedChildTags;
         private List<DefaultBoundAttributeDescriptorBuilder> _attributeBuilders;
         private List<DefaultTagMatchingRuleDescriptorBuilder> _tagMatchingRuleBuilders;
         private DefaultRazorDiagnosticCollection _diagnostics;
@@ -38,19 +38,6 @@ namespace Microsoft.AspNetCore.Razor.Language
 
         public override string DisplayName { get; set; }
 
-        public override ICollection<string> AllowedChildTags
-        {
-            get
-            {
-                if (_allowedChildTags == null)
-                {
-                    _allowedChildTags = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
-                }
-
-                return _allowedChildTags;
-            }
-        }
-
         public override string TagOutputHint { get; set; }
 
         public override string Documentation { get; set; }
@@ -70,6 +57,16 @@ namespace Microsoft.AspNetCore.Razor.Language
             }
         }
 
+        public override IReadOnlyList<AllowedChildTagDescriptorBuilder> AllowedChildTags
+        {
+            get
+            {
+                EnsureAllowedChildTags();
+
+                return _allowedChildTags;
+            }
+        }
+
         public override IReadOnlyList<BoundAttributeDescriptorBuilder> BoundAttributes
         {
             get
@@ -90,6 +87,20 @@ namespace Microsoft.AspNetCore.Razor.Language
             }
         }
 
+        public override void AllowChildTag(Action<AllowedChildTagDescriptorBuilder> configure)
+        {
+            if (configure == null)
+            {
+                throw new ArgumentNullException(nameof(configure));
+            }
+
+            EnsureAllowedChildTags();
+
+            var builder = new DefaultAllowedChildTagDescriptorBuilder(this);
+            configure(builder);
+            _allowedChildTags.Add(builder);
+        }
+
         public override void BindAttribute(Action<BoundAttributeDescriptorBuilder> configure)
         {
             if (configure == null)
@@ -120,13 +131,24 @@ namespace Microsoft.AspNetCore.Razor.Language
 
         public override TagHelperDescriptor Build()
         {
-            var validationDiagnostics = Validate();
+            var diagnostics = new HashSet<RazorDiagnostic>();
-            var diagnostics = new HashSet<RazorDiagnostic>(validationDiagnostics);
             if (_diagnostics != null)
             {
                 diagnostics.UnionWith(_diagnostics);
             }
 
+            var allowedChildTags = Array.Empty<AllowedChildTagDescriptor>();
+            if (_allowedChildTags != null)
+            {
+                var allowedChildTagsSet = new HashSet<AllowedChildTagDescriptor>(AllowedChildTagDescriptorComparer.Default);
+                for (var i = 0; i < _allowedChildTags.Count; i++)
+                {
+                    allowedChildTagsSet.Add(_allowedChildTags[i].Build());
+                }
+
+                allowedChildTags = allowedChildTagsSet.ToArray();
+            }
+
             var tagMatchingRules = Array.Empty<TagMatchingRuleDescriptor>();
             if (_tagMatchingRuleBuilders != null)
             {
@@ -160,7 +182,7 @@ namespace Microsoft.AspNetCore.Razor.Language
                 TagOutputHint,
                 tagMatchingRules,
                 attributes,
-                _allowedChildTags?.ToArray() ?? Array.Empty<string>(),
+                allowedChildTags,
                 new Dictionary<string, string>(_metadata),
                 diagnostics.ToArray());
 
@@ -188,31 +210,11 @@ namespace Microsoft.AspNetCore.Razor.Language
             return this.GetTypeName() ?? Name;
         }
 
-        private IEnumerable<RazorDiagnostic> Validate()
+        private void EnsureAllowedChildTags()
         {
-            if (_allowedChildTags != null)
+            if (_allowedChildTags == null)
             {
-                foreach (var name in _allowedChildTags)
+                _allowedChildTags = new List<DefaultAllowedChildTagDescriptorBuilder>();
-                {
-                    if (string.IsNullOrWhiteSpace(name))
-                    {
-                        var diagnostic = RazorDiagnosticFactory.CreateTagHelper_InvalidRestrictedChildNullOrWhitespace(GetDisplayName());
-
-                        yield return diagnostic;
-                    }
-                    else if (name != TagHelperMatchingConventions.ElementCatchAllName)
-                    {
-                        foreach (var character in name)
-                        {
-                            if (char.IsWhiteSpace(character) || HtmlConventions.InvalidNonWhitespaceHtmlCharacters.Contains(character))
-                            {
-                                var diagnostic = RazorDiagnosticFactory.CreateTagHelper_InvalidRestrictedChild(GetDisplayName(), name, character);
-
-                                yield return diagnostic;
-                            }
-                        }
-                    }
-                }
             }
         }
 

src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs

@@ -855,7 +855,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                 {
                     AllowedChildren = Builder.BindingResult.Descriptors
                         .Where(descriptor => descriptor.AllowedChildTags != null)
-                        .SelectMany(descriptor => descriptor.AllowedChildTags)
+                        .SelectMany(descriptor => descriptor.AllowedChildTags.Select(childTag => childTag.Name))
                         .Distinct(StringComparer.OrdinalIgnoreCase)
                         .ToList();
                 }

src/Microsoft.AspNetCore.Razor.Language/TagHelperDescriptor.cs

@@ -28,7 +28,7 @@ namespace Microsoft.AspNetCore.Razor.Language
 
         public IEnumerable<BoundAttributeDescriptor> BoundAttributes { get; protected set; }
 
-        public IEnumerable<string> AllowedChildTags { get; protected set; }
+        public IEnumerable<AllowedChildTagDescriptor> AllowedChildTags { get; protected set; }
 
         public string Documentation { get; protected set; }
 
@@ -55,9 +55,13 @@ namespace Microsoft.AspNetCore.Razor.Language
         {
             if (_allDiagnostics == null)
             {
+                var allowedChildTagDiagnostics = AllowedChildTags.SelectMany(childTag => childTag.Diagnostics);
                 var attributeDiagnostics = BoundAttributes.SelectMany(attribute => attribute.Diagnostics);
                 var ruleDiagnostics = TagMatchingRules.SelectMany(rule => rule.GetAllDiagnostics());
-                var combinedDiagnostics = attributeDiagnostics.Concat(ruleDiagnostics).Concat(Diagnostics);
+                var combinedDiagnostics = allowedChildTagDiagnostics
+                    .Concat(attributeDiagnostics)
+                    .Concat(ruleDiagnostics)
+                    .Concat(Diagnostics);
                 _allDiagnostics = combinedDiagnostics.ToArray();
             }
 

src/Microsoft.AspNetCore.Razor.Language/TagHelperDescriptorBuilder.cs

@@ -54,16 +54,18 @@ namespace Microsoft.AspNetCore.Razor.Language
 
         public abstract string Documentation { get; set; }
 
-        public abstract ICollection<string> AllowedChildTags { get; }
-
         public abstract IDictionary<string, string> Metadata { get; }
 
         public abstract RazorDiagnosticCollection Diagnostics { get; }
 
+        public abstract IReadOnlyList<AllowedChildTagDescriptorBuilder> AllowedChildTags { get; }
+
         public abstract IReadOnlyList<BoundAttributeDescriptorBuilder> BoundAttributes { get; }
 
         public abstract IReadOnlyList<TagMatchingRuleDescriptorBuilder> TagMatchingRules { get; }
 
+        public abstract void AllowChildTag(Action<AllowedChildTagDescriptorBuilder> configure);
+
         public abstract void BindAttribute(Action<BoundAttributeDescriptorBuilder> configure);
 
         public abstract void TagMatchingRule(Action<TagMatchingRuleDescriptorBuilder> configure);

src/Microsoft.AspNetCore.Razor.Language/TagHelperDescriptorComparer.cs

@@ -23,6 +23,7 @@ namespace Microsoft.AspNetCore.Razor.Language
 
         private readonly StringComparer _stringComparer;
         private readonly StringComparison _stringComparison;
+        private readonly AllowedChildTagDescriptorComparer _AllowedChildTagDescriptorComparer;
         private readonly BoundAttributeDescriptorComparer _boundAttributeComparer;
         private readonly TagMatchingRuleDescriptorComparer _tagMatchingRuleComparer;
 
@@ -32,6 +33,7 @@ namespace Microsoft.AspNetCore.Razor.Language
             {
                 _stringComparer = StringComparer.Ordinal;
                 _stringComparison = StringComparison.Ordinal;
+                _AllowedChildTagDescriptorComparer = AllowedChildTagDescriptorComparer.CaseSensitive;
                 _boundAttributeComparer = BoundAttributeDescriptorComparer.CaseSensitive;
                 _tagMatchingRuleComparer = TagMatchingRuleDescriptorComparer.CaseSensitive;
             }
@@ -39,6 +41,7 @@ namespace Microsoft.AspNetCore.Razor.Language
             {
                 _stringComparer = StringComparer.OrdinalIgnoreCase;
                 _stringComparison = StringComparison.OrdinalIgnoreCase;
+                _AllowedChildTagDescriptorComparer = AllowedChildTagDescriptorComparer.Default;
                 _boundAttributeComparer = BoundAttributeDescriptorComparer.Default;
                 _tagMatchingRuleComparer = TagMatchingRuleDescriptorComparer.Default;
             }
@@ -71,9 +74,9 @@ namespace Microsoft.AspNetCore.Razor.Language
                 (descriptorX.AllowedChildTags != null &&
                 descriptorY.AllowedChildTags != null &&
                 Enumerable.SequenceEqual(
-                    descriptorX.AllowedChildTags.OrderBy(child => child, _stringComparer),
+                    descriptorX.AllowedChildTags.OrderBy(childTag => childTag.Name, _stringComparer),
-                    descriptorY.AllowedChildTags.OrderBy(child => child, _stringComparer),
+                    descriptorY.AllowedChildTags.OrderBy(childTag => childTag.Name, _stringComparer),
-                    _stringComparer))) &&
+                    _AllowedChildTagDescriptorComparer))) &&
                 string.Equals(descriptorX.Documentation, descriptorY.Documentation, StringComparison.Ordinal) &&
                 string.Equals(descriptorX.DisplayName, descriptorY.DisplayName, StringComparison.Ordinal) &&
                 string.Equals(descriptorX.TagOutputHint, descriptorY.TagOutputHint, _stringComparison) &&
@@ -95,6 +98,12 @@ namespace Microsoft.AspNetCore.Razor.Language
             hashCodeCombiner.Add(descriptor.Kind);
             hashCodeCombiner.Add(descriptor.AssemblyName, StringComparer.Ordinal);
 
+            var childTags = descriptor.AllowedChildTags.OrderBy(childTag => childTag.Name, _stringComparer);
+            foreach (var childTag in childTags)
+            {
+                hashCodeCombiner.Add(_AllowedChildTagDescriptorComparer.GetHashCode(childTag));
+            }
+
             var boundAttributes = descriptor.BoundAttributes.OrderBy(attribute => attribute.Name, _stringComparer);
             foreach (var attribute in boundAttributes)
             {
@@ -111,15 +120,6 @@ namespace Microsoft.AspNetCore.Razor.Language
             hashCodeCombiner.Add(descriptor.DisplayName, StringComparer.Ordinal);
             hashCodeCombiner.Add(descriptor.TagOutputHint, _stringComparer);
 
-            if (descriptor.AllowedChildTags != null)
-            {
-                var allowedChildren = descriptor.AllowedChildTags.OrderBy(child => child, _stringComparer);
-                foreach (var child in allowedChildren)
-                {
-                    hashCodeCombiner.Add(child, _stringComparer);
-                }
-            }
-
             return hashCodeCombiner.CombinedHash;
         }
     }

src/Microsoft.CodeAnalysis.Razor/DefaultTagHelperDescriptorFactory.cs

@@ -141,13 +141,13 @@ namespace Microsoft.CodeAnalysis.Razor
                 return;
             }
 
-            builder.AllowedChildTags.Add((string)restrictChildrenAttribute.ConstructorArguments[0].Value);
+            builder.AllowChildTag(childTagBuilder => childTagBuilder.Name = (string)restrictChildrenAttribute.ConstructorArguments[0].Value);
 
             if (restrictChildrenAttribute.ConstructorArguments.Length == 2)
             {
                 foreach (var value in restrictChildrenAttribute.ConstructorArguments[1].Values)
                 {
-                    builder.AllowedChildTags.Add((string)value.Value);
+                    builder.AllowChildTag(childTagBuilder => childTagBuilder.Name = (string)value.Value);
                 }
             }
         }

src/Microsoft.VisualStudio.LanguageServices.Razor/DefaultTagHelperCompletionService.cs

@@ -244,14 +244,9 @@ namespace Microsoft.VisualStudio.LanguageServices.Razor
 
             foreach (var descriptor in binding.Descriptors)
             {
-                if (descriptor.AllowedChildTags == null)
-                {
-                    continue;
-                }
-
                 foreach (var childTag in descriptor.AllowedChildTags)
                 {
-                    var prefixedName = string.Concat(prefix, childTag);
+                    var prefixedName = string.Concat(prefix, childTag.Name);
                     var descriptors = _tagHelperFactsService.GetTagHelpersGivenTag(
                         completionContext.DocumentContext,
                         prefixedName,

src/Microsoft.VisualStudio.LanguageServices.Razor/TagHelperDescriptorJsonConverter.cs

@@ -58,8 +58,8 @@ namespace Microsoft.VisualStudio.LanguageServices.Razor
 
             foreach (var childTag in childTags)
             {
-                var tagValue = childTag.Value<string>();
+                var tag = childTag.Value<JObject>();
-                builder.AllowedChildTags.Add(tagValue);
+                builder.AllowChildTag(childTagBuilder => ReadAllowedChildTag(childTagBuilder, tag, serializer));
             }
 
             foreach (var diagnostic in diagnostics)
@@ -133,6 +133,23 @@ namespace Microsoft.VisualStudio.LanguageServices.Razor
             }
         }
 
+        private void ReadAllowedChildTag(AllowedChildTagDescriptorBuilder builder, JObject childTag, JsonSerializer serializer)
+        {
+            var name = childTag[nameof(AllowedChildTagDescriptor.Name)].Value<string>();
+            var displayName = childTag[nameof(AllowedChildTagDescriptor.DisplayName)].Value<string>();
+            var diagnostics = childTag[nameof(AllowedChildTagDescriptor.Diagnostics)].Value<JArray>();
+
+            builder.Name = name;
+            builder.DisplayName = displayName;
+
+            foreach (var diagnostic in diagnostics)
+            {
+                var diagnosticReader = diagnostic.CreateReader();
+                var diagnosticObject = serializer.Deserialize<RazorDiagnostic>(diagnosticReader);
+                builder.Diagnostics.Add(diagnosticObject);
+            }
+        }
+
         private void ReadBoundAttribute(BoundAttributeDescriptorBuilder builder, JObject attribute, JsonSerializer serializer)
         {
             var descriptorKind = attribute[nameof(BoundAttributeDescriptor.Kind)].Value<string>();

test/Microsoft.AspNetCore.Razor.Language.Test/DefaultAllowedChildTagDescriptorBuilderTest.cs

@@ -0,0 +1,24 @@
+// 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 Xunit;
+
+namespace Microsoft.AspNetCore.Razor.Language
+{
+    public class DefaultAllowedChildTagDescriptorBuilderTest
+    {
+        [Fact]
+        public void Build_DisplayNameIsName()
+        {
+            // Arrange
+            var builder = new DefaultAllowedChildTagDescriptorBuilder(null);
+            builder.Name = "foo";
+
+            // Act
+            var descriptor = builder.Build();
+
+            // Assert
+            Assert.Equal("foo", descriptor.DisplayName);
+        }
+    }
+}

test/Microsoft.AspNetCore.Razor.Test.Common/Language/TestTagHelperDescriptorBuilderExtensions.cs

@@ -38,7 +38,7 @@ namespace Microsoft.AspNetCore.Razor.Language
                 throw new ArgumentNullException(nameof(builder));
             }
 
-            builder.AllowedChildTags.Add(allowedChild);
+            builder.AllowChildTag(childTagBuilder => childTagBuilder.Name = allowedChild);
 
             return builder;
         }

test/Microsoft.VisualStudio.LanguageServices.Razor.Test/Language/TestTagHelperDescriptorBuilderExtensions.cs

@@ -38,7 +38,7 @@ namespace Microsoft.AspNetCore.Razor.Language
                 throw new ArgumentNullException(nameof(builder));
             }
 
-            builder.AllowedChildTags.Add(allowedChild);
+            builder.AllowChildTag(childTagBuilder => childTagBuilder.Name = allowedChild);
 
             return builder;
         }