Added a copy constructor for tag helper descriptors. (#827)

src/Microsoft.AspNetCore.Razor.Runtime/Runtime/TagHelpers/TagHelperDescriptorResolver.cs

@@ -151,20 +151,10 @@ namespace Microsoft.AspNetCore.Razor.Runtime.TagHelpers
 
             if (!string.IsNullOrEmpty(tagHelperPrefix))
             {
-                return descriptors.Select(descriptor =>
+                return descriptors.Select(descriptor => new TagHelperDescriptor(descriptor)
-                    new TagHelperDescriptor
+                {
-                    {
+                    Prefix = tagHelperPrefix
-                        Prefix = tagHelperPrefix,
+                });
-                        TagName = descriptor.TagName,
-                        TypeName = descriptor.TypeName,
-                        AssemblyName = descriptor.AssemblyName,
-                        Attributes = descriptor.Attributes,
-                        RequiredAttributes = descriptor.RequiredAttributes,
-                        AllowedChildren = descriptor.AllowedChildren,
-                        RequiredParent = descriptor.RequiredParent,
-                        TagStructure = descriptor.TagStructure,
-                        DesignTimeDescriptor = descriptor.DesignTimeDescriptor
-                    });
             }
 
             return descriptors;

src/Microsoft.AspNetCore.Razor/Compilation/TagHelpers/TagHelperDescriptor.cs

@@ -23,6 +23,36 @@ namespace Microsoft.AspNetCore.Razor.Compilation.TagHelpers
         private IEnumerable<TagHelperRequiredAttributeDescriptor> _requiredAttributes =
             Enumerable.Empty<TagHelperRequiredAttributeDescriptor>();
 
+        /// <summary>
+        /// Creates a new <see cref="TagHelperDescriptor"/>. 
+        /// </summary>
+        public TagHelperDescriptor()
+        {
+        }
+
+        /// <summary>
+        /// Creates a shallow copy of the given <see cref="TagHelperDescriptor"/>.
+        /// </summary>
+        /// <param name="descriptor">The <see cref="TagHelperDescriptor"/> to copy.</param>
+        public TagHelperDescriptor (TagHelperDescriptor descriptor)
+        {
+            Prefix = descriptor.Prefix;
+            TagName = descriptor.TagName;
+            TypeName = descriptor.TypeName;
+            AssemblyName = descriptor.AssemblyName;
+            Attributes = descriptor.Attributes;
+            RequiredAttributes = descriptor.RequiredAttributes;
+            AllowedChildren = descriptor.AllowedChildren;
+            RequiredParent = descriptor.RequiredParent;
+            TagStructure = descriptor.TagStructure;
+            DesignTimeDescriptor = descriptor.DesignTimeDescriptor;
+
+            foreach (var property in descriptor.PropertyBag)
+            {
+                PropertyBag.Add(property.Key, property.Value);
+            }
+        }
+
         /// <summary>
         /// Text used as a required prefix when matching HTML start and end tags in the Razor source to available
         /// tag helpers.
@@ -219,4 +249,4 @@ namespace Microsoft.AspNetCore.Razor.Compilation.TagHelpers
             }
         }
     }
-}
+}

test/Microsoft.AspNetCore.Razor.Test/Compilation/TagHelpers/TagHelperDescriptorTest.cs

@@ -12,6 +12,49 @@ namespace Microsoft.AspNetCore.Razor.Compilation.TagHelpers
 {
     public class TagHelperDescriptorTest
     {
+        [Fact]
+        public void Constructor_CorrectlyCreatesCopy()
+        {
+            // Arrange
+            var descriptor = new TagHelperDescriptor
+            {
+                Prefix = "prefix",
+                TagName = "tag-name",
+                TypeName = "TypeName",
+                AssemblyName = "AsssemblyName",
+                Attributes = new List<TagHelperAttributeDescriptor>
+                {
+                    new TagHelperAttributeDescriptor
+                    {
+                        Name = "test-attribute",
+                        PropertyName = "TestAttribute",
+                        TypeName = "string"
+                    }
+                },
+                RequiredAttributes = new List<TagHelperRequiredAttributeDescriptor>
+                {
+                    new TagHelperRequiredAttributeDescriptor
+                    {
+                        Name = "test-required-attribute"
+                    }
+                },
+                AllowedChildren = new[] { "child" },
+                RequiredParent = "required parent",
+                TagStructure = TagStructure.NormalOrSelfClosing,
+                DesignTimeDescriptor = new TagHelperDesignTimeDescriptor()
+            };
+
+            descriptor.PropertyBag.Add("foo", "bar");
+
+            // Act
+            var copyDescriptor = new TagHelperDescriptor(descriptor);
+
+            // Assert
+            Assert.Equal(descriptor, copyDescriptor, CaseSensitiveTagHelperDescriptorComparer.Default);
+            Assert.Same(descriptor.Attributes, copyDescriptor.Attributes);
+            Assert.Same(descriptor.RequiredAttributes, copyDescriptor.RequiredAttributes);
+        }
+
         [Fact]
         public void TagHelperDescriptor_CanBeSerialized()
         {