Retarget Microsoft.Extensions.DotNetDeltaApplier to netstandard2.1

src/Assets/TestProjects/WatchApp60/Program.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 System;
+using System.Diagnostics;
+using System.Threading;
+
+namespace ConsoleApplication
+{
+    public class Program
+    {
+        public static void Main(string[] args)
+        {
+            Console.WriteLine("Started");
+            // Process ID is insufficient because PID's may be reused.
+            Console.WriteLine($"Process identifier = {Process.GetCurrentProcess().Id}, {Process.GetCurrentProcess().StartTime:hh:mm:ss.FF}");
+            if (args.Length > 0 && args[0] == "--no-exit")
+            {
+                Thread.Sleep(Timeout.Infinite);
+            }
+            Console.WriteLine("Exiting");
+        }
+    }
+}

src/Assets/TestProjects/WatchApp60/WatchApp60.csproj

@@ -0,0 +1,8 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net60</TargetFramework>
+    <OutputType>exe</OutputType>
+  </PropertyGroup>
+
+</Project>

src/BuiltInTools/DotNetDeltaApplier/HotReloadAgent.cs

@@ -4,27 +4,53 @@
 using System;
 using System.Collections.Concurrent;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Linq;
 using System.Reflection;
-using System.Reflection.Metadata;
 
 namespace Microsoft.Extensions.HotReload
 {
     internal sealed class HotReloadAgent : IDisposable
     {
+        private delegate void ApplyUpdateDelegate(Assembly assembly, ReadOnlySpan<byte> metadataDelta, ReadOnlySpan<byte> ilDelta, ReadOnlySpan<byte> pdbDelta);
+
         private readonly Action<string> _log;
         private readonly AssemblyLoadEventHandler _assemblyLoad;
         private readonly ConcurrentDictionary<Guid, List<UpdateDelta>> _deltas = new();
         private readonly ConcurrentDictionary<Assembly, Assembly> _appliedAssemblies = new();
+        private readonly ApplyUpdateDelegate? _applyUpdate;
+        private readonly string? _capabilities;
         private volatile UpdateHandlerActions? _handlerActions;
 
         public HotReloadAgent(Action<string> log)
         {
+            var metadataUpdater = Type.GetType("System.Reflection.Metadata.MetadataUpdater, System.Runtime.Loader", throwOnError: false);
+
+            if (metadataUpdater != null)
+            {
+                _applyUpdate = (ApplyUpdateDelegate?)metadataUpdater.GetMethod("ApplyUpdate", BindingFlags.Public | BindingFlags.Static, binder: null,
+                    new[] { typeof(Assembly), typeof(ReadOnlySpan<byte>), typeof(ReadOnlySpan<byte>), typeof(ReadOnlySpan<byte>) }, modifiers: null)?.CreateDelegate(typeof(ApplyUpdateDelegate));
+
+                if (_applyUpdate != null)
+                {
+                    try
+                    {
+                        _capabilities = metadataUpdater.GetMethod("GetCapabilities", BindingFlags.NonPublic | BindingFlags.Static, binder: null, Type.EmptyTypes, modifiers: null)?.
+                            Invoke(obj: null, parameters: null) as string;
+                    }
+                    catch
+                    {
+                    }
+                }
+            }
+
             _log = log;
             _assemblyLoad = OnAssemblyLoad;
             AppDomain.CurrentDomain.AssemblyLoad += _assemblyLoad;
         }
 
+        public string Capabilities => _capabilities ?? string.Empty;
+
         private void OnAssemblyLoad(object? _, AssemblyLoadEventArgs eventArgs)
         {
             _handlerActions = null;
@@ -107,7 +133,7 @@ internal void GetHandlerActions(UpdateHandlerActions handlerActions, Type handle
 
             Action<Type[]?> CreateAction(MethodInfo update)
             {
-                Action<Type[]?> action = update.CreateDelegate<Action<Type[]?>>();
+                var action = (Action<Type[]?>)update.CreateDelegate(typeof(Action<Type[]?>));
                 return types =>
                 {
                     try
@@ -123,7 +149,7 @@ internal void GetHandlerActions(UpdateHandlerActions handlerActions, Type handle
 
             MethodInfo? GetUpdateMethod(Type handlerType, string name)
             {
-                if (handlerType.GetMethod(name, BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Static, new[] { typeof(Type[]) }) is MethodInfo updateMethod &&
+                if (handlerType.GetMethod(name, BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Static, binder: null, new[] { typeof(Type[]) }, modifiers: null) is MethodInfo updateMethod &&
                     updateMethod.ReturnType == typeof(void))
                 {
                     return updateMethod;
@@ -178,14 +204,17 @@ static void Visit(Assembly[] assemblies, Assembly assembly, List<Assembly> sorte
 
         public void ApplyDeltas(IReadOnlyList<UpdateDelta> deltas)
         {
+            Debug.Assert(Capabilities.Length > 0);
+            Debug.Assert(_applyUpdate != null);
+
             for (var i = 0; i < deltas.Count; i++)
             {
                 var item = deltas[i];
                 foreach (var assembly in AppDomain.CurrentDomain.GetAssemblies())
                 {
                     if (TryGetModuleId(assembly) is Guid moduleId && moduleId == item.ModuleId)
                     {
-                        MetadataUpdater.ApplyUpdate(assembly, item.MetadataDelta, item.ILDelta, ReadOnlySpan<byte>.Empty);
+                        _applyUpdate(assembly, item.MetadataDelta, item.ILDelta, ReadOnlySpan<byte>.Empty);
                     }
                 }
 
@@ -244,11 +273,13 @@ private Type[] GetMetadataUpdateTypes(IReadOnlyList<UpdateDelta> deltas)
 
         public void ApplyDeltas(Assembly assembly, IReadOnlyList<UpdateDelta> deltas)
         {
+            Debug.Assert(_applyUpdate != null);
+
             try
             {
                 foreach (var item in deltas)
                 {
-                    MetadataUpdater.ApplyUpdate(assembly, item.MetadataDelta, item.ILDelta, ReadOnlySpan<byte>.Empty);
+                    _applyUpdate(assembly, item.MetadataDelta, item.ILDelta, ReadOnlySpan<byte>.Empty);
                 }
 
                 _log("Deltas applied.");

src/BuiltInTools/DotNetDeltaApplier/Microsoft.Extensions.DotNetDeltaApplier.csproj

@@ -1,7 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <!-- Intentionally pinned. This feature is supported in projects targeting 6.0 or newer.-->
-    <TargetFramework>net7.0</TargetFramework>
+    <!--
+      dotnet-watch may inject this assembly to .NET 6.0+ app, so we can't target a newer version.
+      At the same time source build requires us to not target 6.0, so we fall back to netstandard.
+     -->
+    <TargetFramework>netstandard2.1</TargetFramework>
     <StrongNameKeyId>MicrosoftAspNetCore</StrongNameKeyId>
 
     <IsPackable>false</IsPackable>

src/BuiltInTools/DotNetDeltaApplier/StartupHook.cs

@@ -13,6 +13,9 @@ internal sealed class StartupHook
 {
     private static readonly bool LogDeltaClientMessages = Environment.GetEnvironmentVariable("HOTRELOAD_DELTA_CLIENT_LOG_MESSAGES") == "1";
 
+    /// <summary>
+    /// Invoked by the runtime when the containing assembly is listed in DOTNET_STARTUP_HOOKS.
+    /// </summary>
     public static void Initialize()
     {
         ClearHotReloadEnvironmentVariables(Environment.GetEnvironmentVariable, Environment.SetEnvironmentVariable);
@@ -77,7 +80,7 @@ public static async Task ReceiveDeltas(HotReloadAgent hotReloadAgent)
             return;
         }
 
-        var initPayload = new ClientInitializationPayload { Capabilities = GetApplyUpdateCapabilities() };
+        var initPayload = new ClientInitializationPayload(hotReloadAgent.Capabilities);
         Log("Writing capabilities: " + initPayload.Capabilities);
         initPayload.Write(pipeClient);
 
@@ -88,19 +91,9 @@ public static async Task ReceiveDeltas(HotReloadAgent hotReloadAgent)
 
             hotReloadAgent.ApplyDeltas(update.Deltas);
             pipeClient.WriteByte((byte)ApplyResult.Success);
-
         }
-        Log("Stopped received delta updates. Server is no longer connected.");
-    }
 
-    private static string GetApplyUpdateCapabilities()
-    {
-        var method = typeof(System.Reflection.Metadata.MetadataUpdater).GetMethod("GetCapabilities", BindingFlags.NonPublic | BindingFlags.Static, Type.EmptyTypes);
-        if (method is null)
-        {
-            return string.Empty;
-        }
-        return (string)method.Invoke(obj: null, parameters: null)!;
+        Log("Stopped received delta updates. Server is no longer connected.");
     }
 
     private static void Log(string message)

src/BuiltInTools/dotnet-watch/HotReload/DefaultDeltaApplier.cs

@@ -74,16 +74,11 @@ public async ValueTask<bool> Apply(DotNetWatchContext context, ImmutableArray<Wa
                 return false;
             }
 
-            var payload = new UpdatePayload
-            {
-                Deltas = ImmutableArray.CreateRange(solutionUpdate, c => new UpdateDelta
-                {
-                    ModuleId = c.ModuleId,
-                    ILDelta = c.ILDelta.ToArray(),
-                    MetadataDelta = c.MetadataDelta.ToArray(),
-                    UpdatedTypes = c.UpdatedTypes.ToArray(),
-                }),
-            };
+            var payload = new UpdatePayload(ImmutableArray.CreateRange(solutionUpdate, c => new UpdateDelta(
+                c.ModuleId,
+                metadataDelta: c.MetadataDelta.ToArray(),
+                ilDelta: c.ILDelta.ToArray(),
+                c.UpdatedTypes.ToArray())));
 
             await payload.WriteAsync(_pipe, cancellationToken);
             await _pipe.FlushAsync(cancellationToken);

src/BuiltInTools/dotnet-watch/HotReload/NamedPipeContract.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.IO;
+using System.Reflection;
 using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
@@ -14,8 +15,16 @@ internal readonly struct UpdatePayload
     {
         private static readonly byte Version = 1;
 
-        public IReadOnlyList<UpdateDelta> Deltas { get; init; }
+        public IReadOnlyList<UpdateDelta> Deltas { get; }
 
+        public UpdatePayload(IReadOnlyList<UpdateDelta> deltas)
+        {
+            Deltas = deltas;
+        }
+
+        /// <summary>
+        /// Called by the dotnet-watch.
+        /// </summary>
         public async ValueTask WriteAsync(Stream stream, CancellationToken cancellationToken)
         {
             await using var binaryWriter = new BinaryWriter(stream, Encoding.UTF8, leaveOpen: true);
@@ -54,6 +63,9 @@ static void WriteIntArray(BinaryWriter binaryWriter, int[] values)
             }
         }
 
+        /// <summary>
+        /// Called by delta applier.
+        /// </summary>
         public static async ValueTask<UpdatePayload> ReadAsync(Stream stream, CancellationToken cancellationToken)
         {
             using var binaryReader = new BinaryReader(stream, Encoding.UTF8, leaveOpen: true);
@@ -68,21 +80,15 @@ public static async ValueTask<UpdatePayload> ReadAsync(Stream stream, Cancellati
             var deltas = new UpdateDelta[count];
             for (var i = 0; i < count; i++)
             {
-                var delta = new UpdateDelta
-                {
-                    ModuleId = Guid.Parse(binaryReader.ReadString()),
-                    MetadataDelta = await ReadBytesAsync(binaryReader, cancellationToken),
-                    ILDelta = await ReadBytesAsync(binaryReader, cancellationToken),
-                    UpdatedTypes = ReadIntArray(binaryReader),
-                };
+                var moduleId = Guid.Parse(binaryReader.ReadString());
+                var metadataDelta = await ReadBytesAsync(binaryReader, cancellationToken);
+                var ilDelta = await ReadBytesAsync(binaryReader, cancellationToken);
+                var updatedTypes = ReadIntArray(binaryReader);
 
-                deltas[i] = delta;
+                deltas[i] = new UpdateDelta(moduleId, metadataDelta: metadataDelta, ilDelta: ilDelta, updatedTypes);
             }
 
-            return new UpdatePayload
-            {
-                Deltas = deltas,
-            };
+            return new UpdatePayload(deltas);
 
             static async ValueTask<byte[]> ReadBytesAsync(BinaryReader binaryReader, CancellationToken cancellationToken)
             {
@@ -121,10 +127,18 @@ static int[] ReadIntArray(BinaryReader binaryReader)
 
     internal readonly struct UpdateDelta
     {
-        public Guid ModuleId { get; init; }
-        public byte[] MetadataDelta { get; init; }
-        public byte[] ILDelta { get; init; }
-        public int[] UpdatedTypes { get; init; }
+        public Guid ModuleId { get; }
+        public byte[] MetadataDelta { get; }
+        public byte[] ILDelta { get; }
+        public int[] UpdatedTypes { get; }
+
+        public UpdateDelta(Guid moduleId, byte[] metadataDelta, byte[] ilDelta, int[] updatedTypes)
+        {
+            ModuleId = moduleId;
+            MetadataDelta = metadataDelta;
+            ILDelta = ilDelta;
+            UpdatedTypes = updatedTypes;
+        }
     }
 
     internal enum ApplyResult
@@ -137,8 +151,16 @@ internal readonly struct ClientInitializationPayload
     {
         private const byte Version = 0;
 
-        public string Capabilities { get; init; }
+        public string Capabilities { get; }
+
+        public ClientInitializationPayload(string capabilities)
+        {
+            Capabilities = capabilities;
+        }
 
+        /// <summary>
+        /// Called by delta applier.
+        /// </summary>
         public void Write(Stream stream)
         {
             using var binaryWriter = new BinaryWriter(stream, Encoding.UTF8, leaveOpen: true);
@@ -147,6 +169,9 @@ public void Write(Stream stream)
             binaryWriter.Flush();
         }
 
+        /// <summary>
+        /// Called by dotnet-watch.
+        /// </summary>
         public static ClientInitializationPayload Read(Stream stream)
         {
             using var binaryReader = new BinaryReader(stream, Encoding.UTF8, leaveOpen: true);
@@ -157,7 +182,7 @@ public static ClientInitializationPayload Read(Stream stream)
             }
 
             var capabilities = binaryReader.ReadString();
-            return new ClientInitializationPayload { Capabilities = capabilities };
+            return new ClientInitializationPayload(capabilities);
         }
     }
 }

src/Layout/redist/targets/GenerateLayout.targets

@@ -196,7 +196,7 @@
     <ItemGroup>
       <DotNetWatchFile Include="$(ArtifactsDir)bin\dotnet-watch\$(Configuration)\$(SdkTargetFramework)\**" />
       <DotNetWatchFile Include="$(ArtifactsDir)bin\Microsoft.AspNetCore.Watch.BrowserRefresh\$(Configuration)\netcoreapp3.1\*.dll" DeploymentSubpath="middleware" />
-      <DotNetWatchFile Include="$(ArtifactsDir)bin\Microsoft.Extensions.DotNetDeltaApplier\$(Configuration)\net7.0\*.dll" DeploymentSubpath="hotreload" />
+      <DotNetWatchFile Include="$(ArtifactsDir)bin\Microsoft.Extensions.DotNetDeltaApplier\$(Configuration)\netstandard2.1\*.dll" DeploymentSubpath="hotreload" />
       <DotNetWatchFile Include="$(ArtifactsDir)bin\DotNetWatchTasks\$(Configuration)\netstandard2.0\DotNetWatchTasks.dll" />
     </ItemGroup>
 

src/Layout/redist/targets/OverlaySdkOnLKG.targets

@@ -77,7 +77,7 @@
       <DotNetWatchOverlay Remove="$(ArtifactsDir)bin\dotnet-watch\$(Configuration)\$(SdkTargetFramework)\Microsoft.CodeAnalysis.CSharp.dll" />
       <DotNetWatchOverlay Remove="$(ArtifactsDir)bin\dotnet-watch\$(Configuration)\$(SdkTargetFramework)\Microsoft.CodeAnalysis.dll" />
       <DotNetWatchOverlay Include="$(ArtifactsDir)bin\Microsoft.AspNetCore.Watch.BrowserRefresh\$(Configuration)\netcoreapp3.1\*.dll" TargetDir="middleware" />
-      <DotNetWatchOverlay Include="$(ArtifactsDir)bin\Microsoft.Extensions.DotNetDeltaApplier\$(Configuration)\net7.0\*.dll" TargetDir="hotreload" />
+      <DotNetWatchOverlay Include="$(ArtifactsDir)bin\Microsoft.Extensions.DotNetDeltaApplier\$(Configuration)\netstandard2.1\*.dll" TargetDir="hotreload" />
       <DotNetWatchOverlay Include="$(ArtifactsDir)bin\DotNetWatchTasks\$(Configuration)\netstandard2.0\DotNetWatchTasks.dll" />
     </ItemGroup>
 

src/Tests/dotnet-watch.Tests/DotNetWatcherTests.cs

@@ -195,5 +195,18 @@ public async Task Run_WithHotReloadEnabled_DoesNotReadConsoleIn_InNonInteractive
             await standardInput.WriteLineAsync(inputString);
             await app.Process.GetOutputLineAsync($"Echo: {inputString}");
         }
+
+        [CoreMSBuildOnlyFact]
+        public async Task TargetNet60()
+        {
+            var testAsset = _testAssetsManager.CopyTestAsset("WatchApp60")
+                .WithSource()
+                .Path;
+
+            using var app = new WatchableApp(testAsset, _logger);
+
+            await app.StartWatcherAsync();
+            await app.GetProcessIdentifier();
+        }
     }
 }