Add API to Renderer to trigger a UI refresh on hot reload

src/Components/Components/src/ComponentBase.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Threading.Tasks;
+using Microsoft.AspNetCore.Components.HotReload;
 using Microsoft.AspNetCore.Components.Rendering;
 
 namespace Microsoft.AspNetCore.Components
@@ -21,14 +22,15 @@ namespace Microsoft.AspNetCore.Components
     /// Optional base class for components. Alternatively, components may
     /// implement <see cref="IComponent"/> directly.
     /// </summary>
-    public abstract class ComponentBase : IComponent, IHandleEvent, IHandleAfterRender
+    public abstract class ComponentBase : IComponent, IHandleEvent, IHandleAfterRender, IReceiveHotReloadContext
     {
         private readonly RenderFragment _renderFragment;
         private RenderHandle _renderHandle;
         private bool _initialized;
         private bool _hasNeverRendered = true;
         private bool _hasPendingQueuedRender;
         private bool _hasCalledOnAfterRender;
+        private HotReloadContext? _hotReloadContext;
 
         /// <summary>
         /// Constructs an instance of <see cref="ComponentBase"/>.
@@ -102,7 +104,7 @@ protected void StateHasChanged()
                 return;
             }
 
-            if (_hasNeverRendered || ShouldRender())
+            if (_hasNeverRendered || ShouldRender() || (_hotReloadContext?.IsHotReloading ?? false))
             {
                 _hasPendingQueuedRender = true;
 
@@ -329,5 +331,10 @@ Task IHandleAfterRender.OnAfterRenderAsync()
             // have to use "async void" and do their own exception handling in
             // the case where they want to start an async task.
         }
+
+        void IReceiveHotReloadContext.Receive(HotReloadContext context)
+        {
+            _hotReloadContext = context;
+        }
     }
 }

src/Components/Components/src/HotReload/HotReloadContext.cs

@@ -0,0 +1,16 @@
+// 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.Components.HotReload
+{
+    /// <summary>
+    /// A context that indicates when a component is being rendered because of a hot reload operation.
+    /// </summary>
+    public sealed class HotReloadContext
+    {
+        /// <summary>
+        /// Gets a value that indicates if the application is re-rendering in response to a hot-reload change.
+        /// </summary>
+        public bool IsHotReloading { get; internal set; }
+    }
+}

src/Components/Components/src/HotReload/HotReloadEnvironment.cs

@@ -0,0 +1,22 @@
+// 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.Components.HotReload
+{
+    internal class HotReloadEnvironment
+    {
+        public static readonly HotReloadEnvironment Instance = new(Environment.GetEnvironmentVariable("DOTNET_MODIFIABLE_ASSEMBLIES") == "debug");
+
+        public HotReloadEnvironment(bool isHotReloadEnabled)
+        {
+            IsHotReloadEnabled = isHotReloadEnabled;
+        }
+
+        /// <summary>
+        /// Gets a value that determines if HotReload is configured for this application.
+        /// </summary>
+        public bool IsHotReloadEnabled { get; }
+    }
+}

src/Components/Components/src/HotReload/HotReloadManager.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;
+using System.Reflection;
+
+[assembly: AssemblyMetadata("ReceiveHotReloadDeltaNotification", "Microsoft.AspNetCore.Components.HotReload.HotReloadManager")]
+
+namespace Microsoft.AspNetCore.Components.HotReload
+{
+    internal static class HotReloadManager
+    {
+       internal static event Action? OnDeltaApplied;
+
+        public static void DeltaApplied()
+        {
+            OnDeltaApplied?.Invoke();
+        }
+    }
+}

src/Components/Components/src/HotReload/IReceiveHotReloadContext.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.
+
+namespace Microsoft.AspNetCore.Components.HotReload
+{
+    /// <summary>
+    /// Allows a component to receive a <see cref="HotReloadContext"/>.
+    /// </summary>
+    public interface IReceiveHotReloadContext : IComponent
+    {
+        /// <summary>
+        /// Configures a component to use the hot reload context.
+        /// </summary>
+        /// <param name="context">The hot reload context.</param>
+        void Receive(HotReloadContext context);
+    }
+}

src/Components/Components/src/Microsoft.AspNetCore.Components.csproj

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
     <TargetFramework>$(DefaultNetCoreTargetFramework)</TargetFramework>
@@ -33,6 +33,10 @@
     <SuppressBaselineReference Include="Microsoft.JSInterop" Condition=" '$(AspNetCoreMajorMinorVersion)' == '6.0' " />
   </ItemGroup>
 
+  <ItemGroup>
+    <EmbeddedResource Include="Properties\ILLink.Substitutions.xml" LogicalName="ILLink.Substitutions.xml" />
+  </ItemGroup>
+
   <Target Name="_GetNuspecDependencyPackageVersions">
     <MSBuild Targets="_GetPackageVersionInfo"
         BuildInParallel="$(BuildInParallel)"

src/Components/Components/src/ParameterView.cs

@@ -116,6 +116,21 @@ public IReadOnlyDictionary<string, object> ToDictionary()
             return result;
         }
 
+        internal ParameterView Clone()
+        {
+            if (ReferenceEquals(_frames, _emptyFrames))
+            {
+                return Empty;
+            }
+
+            var numEntries = GetEntryCount();
+            var cloneBuffer = new RenderTreeFrame[1 + numEntries];
+            cloneBuffer[0] = RenderTreeFrame.PlaceholderChildComponentWithSubtreeLength(1 + numEntries);
+            _frames.AsSpan(1, numEntries).CopyTo(cloneBuffer.AsSpan(1));
+
+            return new ParameterView(Lifetime, cloneBuffer, _ownerIndex);
+        }
+
         internal ParameterView WithCascadingParameters(IReadOnlyList<CascadingParameterState> cascadingParameters)
             => new ParameterView(_lifetime, _frames, _ownerIndex, cascadingParameters);
 
@@ -189,11 +204,7 @@ internal void CaptureSnapshot(ArrayBuilder<RenderTreeFrame> builder)
         {
             builder.Clear();
 
-            var numEntries = 0;
-            foreach (var entry in this)
-            {
-                numEntries++;
-            }
+            var numEntries = GetEntryCount();
 
             // We need to prefix the captured frames with an "owner" frame that
             // describes the length of the buffer so that ParameterView
@@ -207,6 +218,17 @@ internal void CaptureSnapshot(ArrayBuilder<RenderTreeFrame> builder)
             }
         }
 
+        private int GetEntryCount()
+        {
+            var numEntries = 0;
+            foreach (var _ in this)
+            {
+                numEntries++;
+            }
+
+            return numEntries;
+        }
+
         /// <summary>
         /// Creates a new <see cref="ParameterView"/> from the given <see cref="IDictionary{TKey, TValue}"/>.
         /// </summary>

src/Components/Components/src/Properties/AssemblyInfo.cs

@@ -8,5 +8,6 @@
 [assembly: InternalsVisibleTo("Microsoft.AspNetCore.Components.Tests, PublicKey=0024000004800000940000000602000000240000525341310004000001000100f33a29044fa9d740c9b3213a93e57c84b472c84e0b8a0e1ae48e67a9f8f6de9d5f7f3d52ac23e48ac51801f1dc950abe901da34d2a9e3baadb141a17c77ef3c565dd5ee5054b91cf63bb3c6ab83f72ab3aafe93d0fc3c2348b764fafb0b1c0733de51459aeab46580384bf9d74c4e28164b7cde247f891ba07891c9d872ad2bb")]
 [assembly: InternalsVisibleTo("Microsoft.AspNetCore.Components.Web.Tests, PublicKey=0024000004800000940000000602000000240000525341310004000001000100f33a29044fa9d740c9b3213a93e57c84b472c84e0b8a0e1ae48e67a9f8f6de9d5f7f3d52ac23e48ac51801f1dc950abe901da34d2a9e3baadb141a17c77ef3c565dd5ee5054b91cf63bb3c6ab83f72ab3aafe93d0fc3c2348b764fafb0b1c0733de51459aeab46580384bf9d74c4e28164b7cde247f891ba07891c9d872ad2bb")]
 [assembly: InternalsVisibleTo("Microsoft.AspNetCore.Components.ProtectedBrowserStorage.Tests, PublicKey=0024000004800000940000000602000000240000525341310004000001000100f33a29044fa9d740c9b3213a93e57c84b472c84e0b8a0e1ae48e67a9f8f6de9d5f7f3d52ac23e48ac51801f1dc950abe901da34d2a9e3baadb141a17c77ef3c565dd5ee5054b91cf63bb3c6ab83f72ab3aafe93d0fc3c2348b764fafb0b1c0733de51459aeab46580384bf9d74c4e28164b7cde247f891ba07891c9d872ad2bb")]
+[assembly: InternalsVisibleTo("Components.TestServer, PublicKey=0024000004800000940000000602000000240000525341310004000001000100f33a29044fa9d740c9b3213a93e57c84b472c84e0b8a0e1ae48e67a9f8f6de9d5f7f3d52ac23e48ac51801f1dc950abe901da34d2a9e3baadb141a17c77ef3c565dd5ee5054b91cf63bb3c6ab83f72ab3aafe93d0fc3c2348b764fafb0b1c0733de51459aeab46580384bf9d74c4e28164b7cde247f891ba07891c9d872ad2bb")]
 
 [assembly: InternalsVisibleTo("DynamicProxyGenAssembly2, PublicKey=0024000004800000940000000602000000240000525341310004000001000100c547cac37abd99c8db225ef2f6c8a3602f3b3606cc9891605d02baa56104f4cfc0734aa39b93bf7852f7d9266654753cc297e7d2edfe0bac1cdcf9f717241550e0a7b191195b7667bb4f64bcb8e2121380fd1d9d46ad2d92d2d15605093924cceaf74c4861eff62abf69b9291ed0a340e113be11e6a7d3113e92484cf7045cc7")]

src/Components/Components/src/Properties/ILLink.Substitutions.xml

@@ -0,0 +1,19 @@
+<linker>
+  <assembly fullname="Microsoft.AspNetCore.Components" >
+    <!-- HotReload will not be available in a trimmed app. We'll attempt to aggressively remove all references to it. -->
+    <type fullname="Microsoft.AspNetCore.Components.RenderTree.Renderer">
+      <method signature="System.Void RenderRootComponentsOnHotReload()" body="remove" />
+      <method signature="System.Void InitializeHotReload(System.IServiceProvider)" body="stub" />
+      <method signature="System.Void InstatiateComponentForHotReload(Microsoft.AspNetCore.Components.IComponent)" body="stub" />
+      <method signature="System.Void CaptureRootComponentForHotReload(Microsoft.AspNetCore.Components.ParameterView,Microsoft.AspNetCore.Components.Rendering.ComponentState)" body="stub" />
+      <method signature="System.Void DisposeForHotReload()" body="stub" />
+    </type>
+    <type fullname="Microsoft.AspNetCore.Components.HotReload.HotReloadContext">
+      <method signature="System.Boolean get_IsHotReloading()" body="stub" value="false" />
+      <method signature="System.Void set_IsHotReloading(System.Boolean)" body="remove" />
+    </type>
+    <type fullname="Microsoft.AspNetCore.Components.RenderTree.RenderTreeDiffBuilder">
+      <method signature="System.Boolean IsHotReloading(Microsoft.AspNetCore.Components.RenderTree.Renderer)" body="stub" value="false" />
+    </type>
+  </assembly>
+</linker>

src/Components/Components/src/PublicAPI.Unshipped.txt

@@ -8,6 +8,11 @@ Microsoft.AspNetCore.Components.ComponentApplicationState.PersistAsJson<TValue>(
 Microsoft.AspNetCore.Components.ComponentApplicationState.PersistState(string! key, byte[]! value) -> void
 Microsoft.AspNetCore.Components.ComponentApplicationState.TryTakeAsJson<TValue>(string! key, out TValue? instance) -> bool
 Microsoft.AspNetCore.Components.ComponentApplicationState.TryTakePersistedState(string! key, out byte[]? value) -> bool
+Microsoft.AspNetCore.Components.HotReload.HotReloadContext
+Microsoft.AspNetCore.Components.HotReload.HotReloadContext.HotReloadContext() -> void
+Microsoft.AspNetCore.Components.HotReload.HotReloadContext.IsHotReloading.get -> bool
+Microsoft.AspNetCore.Components.HotReload.IReceiveHotReloadContext
+Microsoft.AspNetCore.Components.HotReload.IReceiveHotReloadContext.Receive(Microsoft.AspNetCore.Components.HotReload.HotReloadContext! context) -> void
 Microsoft.AspNetCore.Components.Lifetime.ComponentApplicationLifetime
 Microsoft.AspNetCore.Components.Lifetime.ComponentApplicationLifetime.ComponentApplicationLifetime(Microsoft.Extensions.Logging.ILogger<Microsoft.AspNetCore.Components.Lifetime.ComponentApplicationLifetime!>! logger) -> void
 Microsoft.AspNetCore.Components.Lifetime.ComponentApplicationLifetime.PersistStateAsync(Microsoft.AspNetCore.Components.Lifetime.IComponentApplicationStateStore! store, Microsoft.AspNetCore.Components.RenderTree.Renderer! renderer) -> System.Threading.Tasks.Task!

src/Components/Components/src/RenderTree/RenderTreeDiffBuilder.cs

@@ -5,8 +5,6 @@
 
 using System;
 using System.Collections.Generic;
-using System.Diagnostics;
-using System.Runtime.CompilerServices;
 using Microsoft.AspNetCore.Components.Rendering;
 
 namespace Microsoft.AspNetCore.Components.RenderTree
@@ -535,15 +533,25 @@ private static void UpdateRetainedChildComponent(
             // comparisons it wants with the old values. Later we could choose to pass the
             // old parameter values if we wanted. By default, components always rerender
             // after any SetParameters call, which is safe but now always optimal for perf.
+
+            // When performing hot reload, we want to force all components to re-render.
+            // We do this using two mechanisms - we call SetParametersAsync even if the parameters
+            // are unchanged and we ignore ComponentBase.ShouldRender
+
             var oldParameters = new ParameterView(ParameterViewLifetime.Unbound, oldTree, oldComponentIndex);
             var newParametersLifetime = new ParameterViewLifetime(diffContext.BatchBuilder);
             var newParameters = new ParameterView(newParametersLifetime, newTree, newComponentIndex);
-            if (!newParameters.DefinitelyEquals(oldParameters))
+            if (!newParameters.DefinitelyEquals(oldParameters) || IsHotReloading(diffContext.Renderer))
             {
                 componentState.SetDirectParameters(newParameters);
             }
         }
 
+        /// <remarks>
+        /// Intentionally authored as a separate method so we can trim this code.
+        /// </remarks>
+        private static bool IsHotReloading(Renderer renderer) => renderer.HotReloadContext.IsHotReloading;
+
         private static int NextSiblingIndex(in RenderTreeFrame frame, int frameIndex)
         {
             switch (frame.FrameTypeField)
@@ -696,8 +704,8 @@ private static void AppendDiffEntriesForFramesWithSameSequence(
                         break;
                     }
 
-                    // We don't handle attributes here, they have their own diff logic.
-                    // See AppendDiffEntriesForAttributeFrame
+                // We don't handle attributes here, they have their own diff logic.
+                // See AppendDiffEntriesForAttributeFrame
                 default:
                     throw new NotImplementedException($"Encountered unsupported frame type during diffing: {newTree[newFrameIndex].FrameTypeField}");
             }