Prerender select elements with value; move HtmlRenderer into Mvc.ViewFeatures (#12996)

src/Components/Components/ref/Microsoft.AspNetCore.Components.netcoreapp3.0.cs

@@ -363,30 +363,12 @@ namespace Microsoft.AspNetCore.Components.CompilerServices
 }
 namespace Microsoft.AspNetCore.Components.Rendering
 {
-    [System.Runtime.InteropServices.StructLayoutAttribute(System.Runtime.InteropServices.LayoutKind.Sequential)]
-    public readonly partial struct ComponentRenderedText
-    {
-        private readonly object _dummy;
-        private readonly int _dummyPrimitive;
-        public int ComponentId { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
-        public System.Collections.Generic.IEnumerable<string> Tokens { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
-    }
     public partial class EventFieldInfo
     {
         public EventFieldInfo() { }
         public int ComponentId { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute]set { } }
         public object FieldValue { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute]set { } }
     }
-    public partial class HtmlRenderer : Microsoft.AspNetCore.Components.Rendering.Renderer
-    {
-        public HtmlRenderer(System.IServiceProvider serviceProvider, Microsoft.Extensions.Logging.ILoggerFactory loggerFactory, System.Func<string, string> htmlEncoder) : base (default(System.IServiceProvider), default(Microsoft.Extensions.Logging.ILoggerFactory)) { }
-        public override Microsoft.AspNetCore.Components.Dispatcher Dispatcher { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
-        protected override void HandleException(System.Exception exception) { }
-        [System.Diagnostics.DebuggerStepThroughAttribute]
-        public System.Threading.Tasks.Task<Microsoft.AspNetCore.Components.Rendering.ComponentRenderedText> RenderComponentAsync(System.Type componentType, Microsoft.AspNetCore.Components.ParameterView initialParameters) { throw null; }
-        public System.Threading.Tasks.Task<Microsoft.AspNetCore.Components.Rendering.ComponentRenderedText> RenderComponentAsync<TComponent>(Microsoft.AspNetCore.Components.ParameterView initialParameters) where TComponent : Microsoft.AspNetCore.Components.IComponent { throw null; }
-        protected override System.Threading.Tasks.Task UpdateDisplayAsync(in Microsoft.AspNetCore.Components.Rendering.RenderBatch renderBatch) { throw null; }
-    }
     [System.Runtime.InteropServices.StructLayoutAttribute(System.Runtime.InteropServices.LayoutKind.Sequential)]
     public readonly partial struct RenderBatch
     {
@@ -405,6 +387,7 @@ namespace Microsoft.AspNetCore.Components.Rendering
         public virtual System.Threading.Tasks.Task DispatchEventAsync(ulong eventHandlerId, Microsoft.AspNetCore.Components.Rendering.EventFieldInfo fieldInfo, System.EventArgs eventArgs) { throw null; }
         public void Dispose() { }
         protected virtual void Dispose(bool disposing) { }
+        protected Microsoft.AspNetCore.Components.RenderTree.ArrayRange<Microsoft.AspNetCore.Components.RenderTree.RenderTreeFrame> GetCurrentRenderTreeFrames(int componentId) { throw null; }
         protected abstract void HandleException(System.Exception exception);
         protected Microsoft.AspNetCore.Components.IComponent InstantiateComponent(System.Type componentType) { throw null; }
         protected virtual void ProcessPendingRender() { }

src/Components/Components/ref/Microsoft.AspNetCore.Components.netstandard2.0.cs

@@ -363,30 +363,12 @@ namespace Microsoft.AspNetCore.Components.CompilerServices
 }
 namespace Microsoft.AspNetCore.Components.Rendering
 {
-    [System.Runtime.InteropServices.StructLayoutAttribute(System.Runtime.InteropServices.LayoutKind.Sequential)]
-    public readonly partial struct ComponentRenderedText
-    {
-        private readonly object _dummy;
-        private readonly int _dummyPrimitive;
-        public int ComponentId { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
-        public System.Collections.Generic.IEnumerable<string> Tokens { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
-    }
     public partial class EventFieldInfo
     {
         public EventFieldInfo() { }
         public int ComponentId { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute]set { } }
         public object FieldValue { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute]set { } }
     }
-    public partial class HtmlRenderer : Microsoft.AspNetCore.Components.Rendering.Renderer
-    {
-        public HtmlRenderer(System.IServiceProvider serviceProvider, Microsoft.Extensions.Logging.ILoggerFactory loggerFactory, System.Func<string, string> htmlEncoder) : base (default(System.IServiceProvider), default(Microsoft.Extensions.Logging.ILoggerFactory)) { }
-        public override Microsoft.AspNetCore.Components.Dispatcher Dispatcher { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
-        protected override void HandleException(System.Exception exception) { }
-        [System.Diagnostics.DebuggerStepThroughAttribute]
-        public System.Threading.Tasks.Task<Microsoft.AspNetCore.Components.Rendering.ComponentRenderedText> RenderComponentAsync(System.Type componentType, Microsoft.AspNetCore.Components.ParameterView initialParameters) { throw null; }
-        public System.Threading.Tasks.Task<Microsoft.AspNetCore.Components.Rendering.ComponentRenderedText> RenderComponentAsync<TComponent>(Microsoft.AspNetCore.Components.ParameterView initialParameters) where TComponent : Microsoft.AspNetCore.Components.IComponent { throw null; }
-        protected override System.Threading.Tasks.Task UpdateDisplayAsync(in Microsoft.AspNetCore.Components.Rendering.RenderBatch renderBatch) { throw null; }
-    }
     [System.Runtime.InteropServices.StructLayoutAttribute(System.Runtime.InteropServices.LayoutKind.Sequential)]
     public readonly partial struct RenderBatch
     {
@@ -405,6 +387,7 @@ namespace Microsoft.AspNetCore.Components.Rendering
         public virtual System.Threading.Tasks.Task DispatchEventAsync(ulong eventHandlerId, Microsoft.AspNetCore.Components.Rendering.EventFieldInfo fieldInfo, System.EventArgs eventArgs) { throw null; }
         public void Dispose() { }
         protected virtual void Dispose(bool disposing) { }
+        protected Microsoft.AspNetCore.Components.RenderTree.ArrayRange<Microsoft.AspNetCore.Components.RenderTree.RenderTreeFrame> GetCurrentRenderTreeFrames(int componentId) { throw null; }
         protected abstract void HandleException(System.Exception exception);
         protected Microsoft.AspNetCore.Components.IComponent InstantiateComponent(System.Type componentType) { throw null; }
         protected virtual void ProcessPendingRender() { }

src/Components/Components/src/Rendering/ComponentRenderedText.cs

@@ -1,29 +0,0 @@
-// 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;
-
-namespace Microsoft.AspNetCore.Components.Rendering
-{
-    /// <summary>
-    /// Represents the result of rendering a component into static html.
-    /// </summary>
-    public readonly struct ComponentRenderedText
-    {
-        internal ComponentRenderedText(int componentId, IEnumerable<string> tokens)
-        {
-            ComponentId = componentId;
-            Tokens = tokens;
-        }
-
-        /// <summary>
-        /// Gets the id associated with the component.
-        /// </summary>
-        public int ComponentId { get; }
-
-        /// <summary>
-        /// Gets the sequence of tokens that when concatenated represent the html for the rendered component.
-        /// </summary>
-        public IEnumerable<string> Tokens { get; }
-    }
-}

src/Components/Components/src/Rendering/Renderer.cs

@@ -93,7 +93,7 @@ namespace Microsoft.AspNetCore.Components.Rendering
         /// </summary>
         /// <param name="componentId">The id for the component.</param>
         /// <returns>The <see cref="RenderTreeBuilder"/> representing the current render tree.</returns>
-        private protected ArrayRange<RenderTreeFrame> GetCurrentRenderTreeFrames(int componentId) => GetRequiredComponentState(componentId).CurrentRenderTree.GetFrames();
+        protected ArrayRange<RenderTreeFrame> GetCurrentRenderTreeFrames(int componentId) => GetRequiredComponentState(componentId).CurrentRenderTree.GetFrames();
 
         /// <summary>
         /// Performs the first render for a root component, waiting for this component and all

src/Components/Components/test/Rendering/HtmlRendererTests.cs

@@ -1,16 +0,0 @@
-// 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 Microsoft.Extensions.Logging.Abstractions;
-
-namespace Microsoft.AspNetCore.Components.Rendering
-{
-    public class HtmlRendererTests : HtmlRendererTestBase
-    {
-        protected override HtmlRenderer GetHtmlRenderer(IServiceProvider serviceProvider)
-        {
-            return new HtmlRenderer(serviceProvider, NullLoggerFactory.Instance, _encoder);
-        }
-    }
-}

src/Components/Server/src/Circuits/DefaultCircuitFactory.cs

@@ -50,7 +50,6 @@ namespace Microsoft.AspNetCore.Components.Server.Circuits
             var components = ResolveComponentMetadata(httpContext);
 
             var scope = _scopeFactory.CreateScope();
-            var encoder = scope.ServiceProvider.GetRequiredService<HtmlEncoder>();
             var jsRuntime = (RemoteJSRuntime)scope.ServiceProvider.GetRequiredService<IJSRuntime>();
             var componentContext = (RemoteComponentContext)scope.ServiceProvider.GetRequiredService<IComponentContext>();
             jsRuntime.Initialize(client);
@@ -76,7 +75,6 @@ namespace Microsoft.AspNetCore.Components.Server.Circuits
                 _options,
                 jsRuntime,
                 client,
-                encoder,
                 _loggerFactory.CreateLogger<RemoteRenderer>());
 
             var circuitHandlers = scope.ServiceProvider.GetServices<CircuitHandler>()

src/Components/Server/src/Circuits/RemoteRenderer.cs

@@ -4,7 +4,6 @@
 using System;
 using System.Collections.Concurrent;
 using System.Linq;
-using System.Text.Encodings.Web;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Components.Rendering;
@@ -17,7 +16,7 @@ using Microsoft.JSInterop;
 
 namespace Microsoft.AspNetCore.Components.Web.Rendering
 {
-    internal class RemoteRenderer : HtmlRenderer
+    internal class RemoteRenderer : Renderer
     {
         private static readonly Task CanceledTask = Task.FromCanceled(new CancellationToken(canceled: true));
 
@@ -43,9 +42,8 @@ namespace Microsoft.AspNetCore.Components.Web.Rendering
             CircuitOptions options,
             IJSRuntime jsRuntime,
             CircuitClientProxy client,
-            HtmlEncoder encoder,
             ILogger logger)
-            : base(serviceProvider, loggerFactory, encoder.Encode)
+            : base(serviceProvider, loggerFactory)
         {
             _jsRuntime = jsRuntime;
             _client = client;

src/Components/Server/test/Circuits/CircuitHostTest.cs

@@ -5,10 +5,8 @@ using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Reflection;
-using System.Text.Encodings.Web;
 using System.Threading;
 using System.Threading.Tasks;
-using Microsoft.AspNetCore.Components.Web;
 using Microsoft.AspNetCore.Components.Web.Rendering;
 using Microsoft.AspNetCore.SignalR;
 using Microsoft.Extensions.DependencyInjection;
@@ -238,7 +236,7 @@ namespace Microsoft.AspNetCore.Components.Server.Circuits
         private class TestRemoteRenderer : RemoteRenderer
         {
             public TestRemoteRenderer(IServiceProvider serviceProvider, IJSRuntime jsRuntime, IClientProxy client)
-                : base(serviceProvider, NullLoggerFactory.Instance, new CircuitOptions(), jsRuntime, new CircuitClientProxy(client, "connection"), HtmlEncoder.Default, NullLogger.Instance)
+                : base(serviceProvider, NullLoggerFactory.Instance, new CircuitOptions(), jsRuntime, new CircuitClientProxy(client, "connection"), NullLogger.Instance)
             {
             }
 

src/Components/Server/test/Circuits/RemoteRendererTest.cs

@@ -4,10 +4,8 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
-using System.Text.Encodings.Web;
 using System.Threading;
 using System.Threading.Tasks;
-using Microsoft.AspNetCore.Components.Rendering;
 using Microsoft.AspNetCore.Components.Server;
 using Microsoft.AspNetCore.Components.Server.Circuits;
 using Microsoft.AspNetCore.SignalR;
@@ -20,23 +18,18 @@ using Xunit;
 
 namespace Microsoft.AspNetCore.Components.Web.Rendering
 {
-    public class RemoteRendererTest : HtmlRendererTestBase
+    public class RemoteRendererTest
     {
         // Nothing should exceed the timeout in a successful run of the the tests, this is just here to catch
         // failures.
         private static readonly TimeSpan Timeout = Debugger.IsAttached ? System.Threading.Timeout.InfiniteTimeSpan : TimeSpan.FromSeconds(10);
 
-        protected override HtmlRenderer GetHtmlRenderer(IServiceProvider serviceProvider)
-        {
-            return GetRemoteRenderer(serviceProvider, new CircuitClientProxy());
-        }
-
         [Fact]
         public void WritesAreBufferedWhenTheClientIsOffline()
         {
             // Arrange
             var serviceProvider = new ServiceCollection().BuildServiceProvider();
-            var renderer = (RemoteRenderer)GetHtmlRenderer(serviceProvider);
+            var renderer = GetRemoteRenderer(serviceProvider);
             var component = new TestComponent(builder =>
             {
                 builder.OpenElement(0, "my element");
@@ -57,7 +50,7 @@ namespace Microsoft.AspNetCore.Components.Web.Rendering
         public void NotAcknowledgingRenders_ProducesBatches_UpToTheLimit()
         {
             var serviceProvider = new ServiceCollection().BuildServiceProvider();
-            var renderer = (RemoteRenderer)GetHtmlRenderer(serviceProvider);
+            var renderer = GetRemoteRenderer(serviceProvider);
             var component = new TestComponent(builder =>
             {
                 builder.OpenElement(0, "my element");
@@ -81,7 +74,7 @@ namespace Microsoft.AspNetCore.Components.Web.Rendering
         public async Task NoNewBatchesAreCreated_WhenThereAreNoPendingRenderRequestsFromComponents()
         {
             var serviceProvider = new ServiceCollection().BuildServiceProvider();
-            var renderer = (RemoteRenderer)GetHtmlRenderer(serviceProvider);
+            var renderer = GetRemoteRenderer(serviceProvider);
             var component = new TestComponent(builder =>
             {
                 builder.OpenElement(0, "my element");
@@ -107,7 +100,7 @@ namespace Microsoft.AspNetCore.Components.Web.Rendering
         public async Task ProducesNewBatch_WhenABatchGetsAcknowledged()
         {
             var serviceProvider = new ServiceCollection().BuildServiceProvider();
-            var renderer = (RemoteRenderer)GetHtmlRenderer(serviceProvider);
+            var renderer = GetRemoteRenderer(serviceProvider);
             var i = 0;
             var component = new TestComponent(builder =>
             {
@@ -215,7 +208,7 @@ namespace Microsoft.AspNetCore.Components.Web.Rendering
                 .Returns<string, object[], CancellationToken>((n, v, t) => (long)v[1] == 2 ? firstBatchTCS.Task : secondBatchTCS.Task);
 
             // This produces the initial batch (id = 2)
-            var result = await renderer.RenderComponentAsync<AutoParameterTestComponent>(
+            await renderer.RenderComponentAsync<AutoParameterTestComponent>(
             ParameterView.FromDictionary(new Dictionary<string, object>
             {
                 [nameof(AutoParameterTestComponent.Content)] = initialContent,
@@ -278,7 +271,7 @@ namespace Microsoft.AspNetCore.Components.Web.Rendering
                 .Returns<string, object[], CancellationToken>((n, v, t) => (long)v[1] == 2 ? firstBatchTCS.Task : secondBatchTCS.Task);
 
             // This produces the initial batch (id = 2)
-            var result = await renderer.RenderComponentAsync<AutoParameterTestComponent>(
+            await renderer.RenderComponentAsync<AutoParameterTestComponent>(
             ParameterView.FromDictionary(new Dictionary<string, object>
             {
                 [nameof(AutoParameterTestComponent.Content)] = initialContent,
@@ -341,7 +334,7 @@ namespace Microsoft.AspNetCore.Components.Web.Rendering
             var trigger = new Trigger();
 
             // This produces the initial batch (id = 2)
-            var result = await renderer.RenderComponentAsync<AutoParameterTestComponent>(
+            await renderer.RenderComponentAsync<AutoParameterTestComponent>(
             ParameterView.FromDictionary(new Dictionary<string, object>
             {
                 [nameof(AutoParameterTestComponent.Content)] = initialContent,
@@ -398,7 +391,7 @@ namespace Microsoft.AspNetCore.Components.Web.Rendering
             var trigger = new Trigger();
 
             // This produces the initial batch (id = 2)
-            var result = await renderer.RenderComponentAsync<AutoParameterTestComponent>(
+            await renderer.RenderComponentAsync<AutoParameterTestComponent>(
             ParameterView.FromDictionary(new Dictionary<string, object>
             {
                 [nameof(AutoParameterTestComponent.Content)] = initialContent,
@@ -432,27 +425,7 @@ namespace Microsoft.AspNetCore.Components.Web.Rendering
                 exception.Message);
         }
 
-        [Fact]
+        private TestRemoteRenderer GetRemoteRenderer(IServiceProvider serviceProvider, CircuitClientProxy circuitClient = null)
-        public async Task PrerendersMultipleComponentsSuccessfully()
-        {
-            // Arrange
-            var serviceProvider = new ServiceCollection().BuildServiceProvider();
-
-            var renderer = GetRemoteRenderer(
-                serviceProvider,
-                new CircuitClientProxy());
-
-            // Act
-            var first = await renderer.RenderComponentAsync<TestComponent>(ParameterView.Empty);
-            var second = await renderer.RenderComponentAsync<TestComponent>(ParameterView.Empty);
-
-            // Assert
-            Assert.Equal(0, first.ComponentId);
-            Assert.Equal(1, second.ComponentId);
-            Assert.Equal(2, renderer._unacknowledgedRenderBatches.Count);
-        }
-
-        private RemoteRenderer GetRemoteRenderer(IServiceProvider serviceProvider, CircuitClientProxy circuitClientProxy)
         {
             var jsRuntime = new Mock<IJSRuntime>();
             jsRuntime.Setup(r => r.InvokeAsync<object>(
@@ -462,16 +435,30 @@ namespace Microsoft.AspNetCore.Components.Web.Rendering
                 It.IsAny<int>()))
                 .ReturnsAsync(Task.FromResult<object>(null));
 
-            return new RemoteRenderer(
+            return new TestRemoteRenderer(
                 serviceProvider,
                 NullLoggerFactory.Instance,
                 new CircuitOptions(),
                 jsRuntime.Object,
-                circuitClientProxy,
+                circuitClient ?? new CircuitClientProxy(),
-                HtmlEncoder.Default,
                 NullLogger.Instance);
         }
 
+        private class TestRemoteRenderer : RemoteRenderer
+        {
+            public TestRemoteRenderer(IServiceProvider serviceProvider, ILoggerFactory loggerFactory, CircuitOptions options, IJSRuntime jsRuntime, CircuitClientProxy client, ILogger logger)
+                : base(serviceProvider, loggerFactory, options, jsRuntime, client, logger)
+            {
+            }
+
+            public async Task RenderComponentAsync<TComponent>(ParameterView initialParameters)
+            {
+                var component = InstantiateComponent(typeof(TComponent));
+                var componentId = AssignRootComponentId(component);
+                await RenderRootComponentAsync(componentId, initialParameters);
+            }
+        }
+
         private class TestComponent : IComponent, IHandleAfterRender
         {
             private RenderHandle _renderHandle;

src/Components/Server/test/Circuits/TestCircuitHost.cs

@@ -3,7 +3,6 @@
 
 using System;
 using System.Collections.Generic;
-using System.Text.Encodings.Web;
 using Microsoft.AspNetCore.Components.Web.Rendering;
 using Microsoft.AspNetCore.SignalR;
 using Microsoft.Extensions.DependencyInjection;
@@ -40,7 +39,6 @@ namespace Microsoft.AspNetCore.Components.Server.Circuits
                     new CircuitOptions(),
                     jsRuntime,
                     clientProxy,
-                    HtmlEncoder.Default,
                     NullLogger.Instance);
             }
 

src/Components/Server/test/Microsoft.AspNetCore.Components.Server.Tests.csproj

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
     <TargetFramework>netcoreapp3.0</TargetFramework>
@@ -14,7 +14,6 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <Compile Include="..\..\Components\test\Rendering\HtmlRendererTestBase.cs" />
     <Compile Include="$(SignalRTestBase)HubMessageHelpers.cs" LinkBase="BlazorPack" />
     <Compile Include="$(SignalRTestBase)MessagePackHubProtocolTestBase.cs" LinkBase="BlazorPack" />
     <Compile Include="$(SignalRTestBase)TestBinder.cs" LinkBase="BlazorPack" />

src/Mvc/Mvc.ViewFeatures/src/RazorComponents/ComponentRenderedText.cs

@@ -0,0 +1,20 @@
+// 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;
+
+namespace Microsoft.AspNetCore.Components.Rendering
+{
+    internal readonly struct ComponentRenderedText
+    {
+        public ComponentRenderedText(int componentId, IEnumerable<string> tokens)
+        {
+            ComponentId = componentId;
+            Tokens = tokens;
+        }
+
+        public int ComponentId { get; }
+
+        public IEnumerable<string> Tokens { get; }
+    }
+}

src/Mvc/Mvc.ViewFeatures/src/RazorComponents/HtmlRenderer.cs

@@ -12,10 +12,7 @@ using Microsoft.Extensions.Logging;
 
 namespace Microsoft.AspNetCore.Components.Rendering
 {
-    /// <summary>
+    internal class HtmlRenderer : Renderer
-    /// A <see cref="Renderer"/> that produces HTML.
-    /// </summary>
-    public class HtmlRenderer : Renderer
     {
         private static readonly HashSet<string> SelfClosingElements = new HashSet<string>(StringComparer.OrdinalIgnoreCase)
         {
@@ -26,12 +23,6 @@ namespace Microsoft.AspNetCore.Components.Rendering
 
         private readonly Func<string, string> _htmlEncoder;
 
-        /// <summary>
-        /// Initializes a new instance of <see cref="HtmlRenderer"/>.
-        /// </summary>
-        /// <param name="serviceProvider">The <see cref="IServiceProvider"/> to use to instantiate components.</param>
-        /// <param name="loggerFactory">The <see cref="ILoggerFactory"/>.</param>
-        /// <param name="htmlEncoder">A <see cref="Func{T, TResult}"/> that will HTML encode the given string.</param>
         public HtmlRenderer(IServiceProvider serviceProvider, ILoggerFactory loggerFactory, Func<string, string> htmlEncoder)
             : base(serviceProvider, loggerFactory)
         {
@@ -58,30 +49,16 @@ namespace Microsoft.AspNetCore.Components.Rendering
             return CanceledRenderTask;
         }
 
-        /// <summary>
-        /// Renders a component into a sequence of <see cref="string"/> fragments that represent the textual representation
-        /// of the HTML produced by the component.
-        /// </summary>
-        /// <param name="componentType">The type of the <see cref="IComponent"/>.</param>
-        /// <param name="initialParameters">A <see cref="ParameterView"/> with the initial parameters to render the component.</param>
-        /// <returns>A <see cref="Task"/> that on completion returns a sequence of <see cref="string"/> fragments that represent the HTML text of the component.</returns>
         public async Task<ComponentRenderedText> RenderComponentAsync(Type componentType, ParameterView initialParameters)
         {
             var (componentId, frames) = await CreateInitialRenderAsync(componentType, initialParameters);
 
-            var result = new List<string>();
+            var context = new HtmlRenderingContext();
-            var newPosition = RenderFrames(result, frames, 0, frames.Count);
+            var newPosition = RenderFrames(context, frames, 0, frames.Count);
             Debug.Assert(newPosition == frames.Count);
-            return new ComponentRenderedText(componentId, result);
+            return new ComponentRenderedText(componentId, context.Result);
         }
 
-        /// <summary>
-        /// Renders a component into a sequence of <see cref="string"/> fragments that represent the textual representation
-        /// of the HTML produced by the component.
-        /// </summary>
-        /// <typeparam name="TComponent">The type of the <see cref="IComponent"/>.</typeparam>
-        /// <param name="initialParameters">A <see cref="ParameterView"/> with the initial parameters to render the component.</param>
-        /// <returns>A <see cref="Task"/> that on completion returns a sequence of <see cref="string"/> fragments that represent the HTML text of the component.</returns>
         public Task<ComponentRenderedText> RenderComponentAsync<TComponent>(ParameterView initialParameters) where TComponent : IComponent
         {
             return RenderComponentAsync(typeof(TComponent), initialParameters);
@@ -91,13 +68,13 @@ namespace Microsoft.AspNetCore.Components.Rendering
         protected override void HandleException(Exception exception)
             => ExceptionDispatchInfo.Capture(exception).Throw();
 
-        private int RenderFrames(List<string> result, ArrayRange<RenderTreeFrame> frames, int position, int maxElements)
+        private int RenderFrames(HtmlRenderingContext context, ArrayRange<RenderTreeFrame> frames, int position, int maxElements)
         {
             var nextPosition = position;
             var endPosition = position + maxElements;
             while (position < endPosition)
             {
-                nextPosition = RenderCore(result, frames, position, maxElements);
+                nextPosition = RenderCore(context, frames, position);
                 if (position == nextPosition)
                 {
                     throw new InvalidOperationException("We didn't consume any input.");
@@ -109,28 +86,27 @@ namespace Microsoft.AspNetCore.Components.Rendering
         }
 
         private int RenderCore(
-            List<string> result,
+            HtmlRenderingContext context,
             ArrayRange<RenderTreeFrame> frames,
-            int position,
+            int position)
-            int length)
         {
             ref var frame = ref frames.Array[position];
             switch (frame.FrameType)
             {
                 case RenderTreeFrameType.Element:
-                    return RenderElement(result, frames, position);
+                    return RenderElement(context, frames, position);
                 case RenderTreeFrameType.Attribute:
-                    return RenderAttributes(result, frames, position, 1);
+                    throw new InvalidOperationException($"Attributes should only be encountered within {nameof(RenderElement)}");
                 case RenderTreeFrameType.Text:
-                    result.Add(_htmlEncoder(frame.TextContent));
+                    context.Result.Add(_htmlEncoder(frame.TextContent));
                     return ++position;
                 case RenderTreeFrameType.Markup:
-                    result.Add(frame.MarkupContent);
+                    context.Result.Add(frame.MarkupContent);
                     return ++position;
                 case RenderTreeFrameType.Component:
-                    return RenderChildComponent(result, frames, position);
+                    return RenderChildComponent(context, frames, position);
                 case RenderTreeFrameType.Region:
-                    return RenderFrames(result, frames, position + 1, frame.RegionSubtreeLength - 1);
+                    return RenderFrames(context, frames, position + 1, frame.RegionSubtreeLength - 1);
                 case RenderTreeFrameType.ElementReferenceCapture:
                 case RenderTreeFrameType.ComponentReferenceCapture:
                     return ++position;
@@ -140,30 +116,57 @@ namespace Microsoft.AspNetCore.Components.Rendering
         }
 
         private int RenderChildComponent(
-            List<string> result,
+            HtmlRenderingContext context,
             ArrayRange<RenderTreeFrame> frames,
             int position)
         {
             ref var frame = ref frames.Array[position];
             var childFrames = GetCurrentRenderTreeFrames(frame.ComponentId);
-            RenderFrames(result, childFrames, 0, childFrames.Count);
+            RenderFrames(context, childFrames, 0, childFrames.Count);
             return position + frame.ComponentSubtreeLength;
         }
 
         private int RenderElement(
-            List<string> result,
+            HtmlRenderingContext context,
             ArrayRange<RenderTreeFrame> frames,
             int position)
         {
             ref var frame = ref frames.Array[position];
+            var result = context.Result;
             result.Add("<");
             result.Add(frame.ElementName);
-            var afterAttributes = RenderAttributes(result, frames, position + 1, frame.ElementSubtreeLength - 1);
+            var afterAttributes = RenderAttributes(context, frames, position + 1, frame.ElementSubtreeLength - 1, out var capturedValueAttribute);
+
+            // When we see an <option> as a descendant of a <select>, and the option's "value" attribute matches the
+            // "value" attribute on the <select>, then we auto-add the "selected" attribute to that option. This is
+            // a way of converting Blazor's select binding feature to regular static HTML.
+            if (context.ClosestSelectValueAsString != null
+                && string.Equals(frame.ElementName, "option", StringComparison.OrdinalIgnoreCase)
+                && string.Equals(capturedValueAttribute, context.ClosestSelectValueAsString, StringComparison.Ordinal))
+            {
+                result.Add(" selected");
+            }
+
             var remainingElements = frame.ElementSubtreeLength + position - afterAttributes;
             if (remainingElements > 0)
             {
                 result.Add(">");
-                var afterElement = RenderChildren(result, frames, afterAttributes, remainingElements);
+
+                var isSelect = string.Equals(frame.ElementName, "select", StringComparison.OrdinalIgnoreCase);
+                if (isSelect)
+                {
+                    context.ClosestSelectValueAsString = capturedValueAttribute;
+                }
+
+                var afterElement = RenderChildren(context, frames, afterAttributes, remainingElements);
+
+                if (isSelect)
+                {
+                    // There's no concept of nested <select> elements, so as soon as we're exiting one of them,
+                    // we can safely say there is no longer any value for this
+                    context.ClosestSelectValueAsString = null;
+                }
+
                 result.Add("</");
                 result.Add(frame.ElementName);
                 result.Add(">");
@@ -188,25 +191,29 @@ namespace Microsoft.AspNetCore.Components.Rendering
             }
         }
 
-        private int RenderChildren(List<string> result, ArrayRange<RenderTreeFrame> frames, int position, int maxElements)
+        private int RenderChildren(HtmlRenderingContext context, ArrayRange<RenderTreeFrame> frames, int position, int maxElements)
         {
             if (maxElements == 0)
             {
                 return position;
             }
 
-            return RenderFrames(result, frames, position, maxElements);
+            return RenderFrames(context, frames, position, maxElements);
         }
 
         private int RenderAttributes(
-            List<string> result,
+            HtmlRenderingContext context,
-            ArrayRange<RenderTreeFrame> frames, int position, int maxElements)
+            ArrayRange<RenderTreeFrame> frames, int position, int maxElements, out string capturedValueAttribute)
         {
+            capturedValueAttribute = null;
+
             if (maxElements == 0)
             {
                 return position;
             }
 
+            var result = context.Result;
+
             for (var i = 0; i < maxElements; i++)
             {
                 var candidateIndex = position + i;
@@ -216,6 +223,11 @@ namespace Microsoft.AspNetCore.Components.Rendering
                     return candidateIndex;
                 }
 
+                if (frame.AttributeName.Equals("value", StringComparison.OrdinalIgnoreCase))
+                {
+                    capturedValueAttribute = frame.AttributeValue as string;
+                }
+
                 switch (frame.AttributeValue)
                 {
                     case bool flag when flag:
@@ -247,6 +259,13 @@ namespace Microsoft.AspNetCore.Components.Rendering
 
             return (componentId, GetCurrentRenderTreeFrames(componentId));
         }
+
+        private class HtmlRenderingContext
+        {
+            public List<string> Result { get; } = new List<string>();
+
+            public string ClosestSelectValueAsString { get; set; }
+        }
     }
 }
 

src/Mvc/Mvc.ViewFeatures/test/RazorComponents/HtmlRendererTest.cs

@@ -6,23 +6,22 @@ using System.Collections.Generic;
 using System.Runtime.ExceptionServices;
 using System.Text.Encodings.Web;
 using System.Threading.Tasks;
-using Microsoft.AspNetCore.Components.RenderTree;
+using Microsoft.AspNetCore.Components;
+using Microsoft.AspNetCore.Components.Rendering;
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging.Abstractions;
 using Xunit;
 
-namespace Microsoft.AspNetCore.Components.Rendering
+namespace Microsoft.AspNetCore.Mvc.RazorComponents
 {
-    public abstract class HtmlRendererTestBase
+    public class HtmlRendererTest
     {
         protected readonly Func<string, string> _encoder = (string t) => HtmlEncoder.Default.Encode(t);
 
-        protected abstract HtmlRenderer GetHtmlRenderer(IServiceProvider serviceProvider);
-
         [Fact]
         public void RenderComponentAsync_CanRenderEmptyElement()
         {
             // Arrange
-
             var expectedHtml = new[] { "<", "p", ">", "</", "p", ">" };
             var serviceProvider = new ServiceCollection().AddSingleton(new RenderFragment(rtb =>
             {
@@ -99,7 +98,6 @@ namespace Microsoft.AspNetCore.Components.Rendering
             Assert.Equal(expectedHtml, result);
         }
 
-
         [Fact]
         public void RenderComponentAsync_CanRenderWithAttributes()
         {
@@ -272,6 +270,91 @@ namespace Microsoft.AspNetCore.Components.Rendering
             // Assert
             Assert.Equal(expectedHtml, result);
         }
+        
+        [Fact]
+        public void RenderComponentAsync_MarksSelectedOptionsAsSelected()
+        {
+            // Arrange
+            var expectedHtml = "<p>" +
+                @"<select unrelated-attribute-before=""a"" value=""b"" unrelated-attribute-after=""c"">" +
+                @"<option unrelated-attribute=""a"" value=""a"">Pick value a</option>" +
+                @"<option unrelated-attribute=""a"" value=""b"" selected>Pick value b</option>" +
+                @"<option unrelated-attribute=""a"" value=""c"">Pick value c</option>" +
+                "</select>" +
+                @"<option value=""b"">unrelated option</option>" +
+                "</p>";
+            var serviceProvider = new ServiceCollection().AddSingleton(new RenderFragment(rtb =>
+            {
+                rtb.OpenElement(0, "p");
+                rtb.OpenElement(1, "select");
+                rtb.AddAttribute(2, "unrelated-attribute-before", "a");
+                rtb.AddAttribute(3, "value", "b");
+                rtb.AddAttribute(4, "unrelated-attribute-after", "c");
+
+                foreach (var optionValue in new[] { "a", "b", "c"})
+                {
+                    rtb.OpenElement(5, "option");
+                    rtb.AddAttribute(6, "unrelated-attribute", "a");
+                    rtb.AddAttribute(7, "value", optionValue);
+                    rtb.AddContent(8, $"Pick value {optionValue}");
+                    rtb.CloseElement(); // option
+                }
+
+                rtb.CloseElement(); // select
+
+                rtb.OpenElement(9, "option"); // To show other value-matching options don't get marked as selected
+                rtb.AddAttribute(10, "value", "b");
+                rtb.AddContent(11, "unrelated option");
+                rtb.CloseElement(); // option
+
+                rtb.CloseElement(); // p
+            })).BuildServiceProvider();
+
+            var htmlRenderer = GetHtmlRenderer(serviceProvider);
+
+            // Act
+            var result = GetResult(htmlRenderer.Dispatcher.InvokeAsync(() => htmlRenderer.RenderComponentAsync<TestComponent>(ParameterView.Empty)));
+
+            // Assert
+            Assert.Equal(expectedHtml, string.Concat(result));
+        }
+
+        [Fact]
+        public void RenderComponentAsync_MarksSelectedOptionsAsSelected_WithOptGroups()
+        {
+            // Arrange
+            var expectedHtml =
+                @"<select value=""beta"">" +
+                @"<optgroup><option value=""alpha"">alpha</option></optgroup>" +
+                @"<optgroup><option value=""beta"" selected>beta</option></optgroup>" +
+                @"<optgroup><option value=""gamma"">gamma</option></optgroup>" +
+                "</select>";
+            var serviceProvider = new ServiceCollection().AddSingleton(new RenderFragment(rtb =>
+            {
+                rtb.OpenElement(0, "select");
+                rtb.AddAttribute(1, "value", "beta");
+
+                foreach (var optionValue in new[] { "alpha", "beta", "gamma" })
+                {
+                    rtb.OpenElement(2, "optgroup");
+                    rtb.OpenElement(3, "option");
+                    rtb.AddAttribute(4, "value", optionValue);
+                    rtb.AddContent(5, optionValue);
+                    rtb.CloseElement(); // option
+                    rtb.CloseElement(); // optgroup
+                }
+
+                rtb.CloseElement(); // select
+            })).BuildServiceProvider();
+
+            var htmlRenderer = GetHtmlRenderer(serviceProvider);
+
+            // Act
+            var result = GetResult(htmlRenderer.Dispatcher.InvokeAsync(() => htmlRenderer.RenderComponentAsync<TestComponent>(ParameterView.Empty)));
+
+            // Assert
+            Assert.Equal(expectedHtml, string.Concat(result));
+        }
 
         [Fact]
         public void RenderComponentAsync_CanRenderComponentAsyncWithChildrenComponents()
@@ -358,11 +441,11 @@ namespace Microsoft.AspNetCore.Components.Rendering
 
             // Act
             var result = GetResult(htmlRenderer.Dispatcher.InvokeAsync(() => htmlRenderer.RenderComponentAsync<ComponentWithParameters>(
-                new ParameterView(new[] {
+                ParameterView.FromDictionary(new Dictionary<string, object>
-                    RenderTreeFrame.Element(0,string.Empty),
+                {
-                    RenderTreeFrame.Attribute(1,"update",change),
+                    { "update", change },
-                    RenderTreeFrame.Attribute(2,"value",5)
+                    { "value", 5 }
-                }, 0))));
+                }))));
 
             // Assert
             Assert.Equal(expectedHtml, result);
@@ -499,6 +582,31 @@ namespace Microsoft.AspNetCore.Components.Rendering
             Assert.Equal(expectedHtml, result.Tokens);
         }
 
+        [Fact]
+        public async Task PrerendersMultipleComponentsSuccessfully()
+        {
+            // Arrange
+            var serviceProvider = new ServiceCollection().AddSingleton(new RenderFragment(rtb =>
+            {
+                rtb.OpenElement(0, "p");
+                rtb.AddMarkupContent(1, "<span>Hello world!</span>");
+                rtb.CloseElement();
+            })).BuildServiceProvider();
+            var renderer = GetHtmlRenderer(serviceProvider);
+
+            // Act
+            var first = await renderer.Dispatcher.InvokeAsync(() => renderer.RenderComponentAsync<TestComponent>(ParameterView.Empty));
+            var second = await renderer.Dispatcher.InvokeAsync(() => renderer.RenderComponentAsync<TestComponent>(ParameterView.Empty));
+
+            // Assert
+            Assert.Equal(0, first.ComponentId);
+            Assert.Equal(1, second.ComponentId);
+        }
+
+        private HtmlRenderer GetHtmlRenderer(IServiceProvider serviceProvider)
+        {
+            return new HtmlRenderer(serviceProvider, NullLoggerFactory.Instance, _encoder);
+        }
 
         private class NestedAsyncComponent : ComponentBase
         {