Fix a couple of issues with dotnet-watch

src/BuiltInTools/DotNetDeltaApplier/HotReloadAgent.cs

@@ -14,7 +14,7 @@ internal class HotReloadAgent : IDisposable
     {
         private readonly Action<string> _log;
         private readonly AssemblyLoadEventHandler _assemblyLoad;
-        private readonly ConcurrentDictionary<Guid, IReadOnlyList<UpdateDelta>> _deltas = new();
+        private readonly ConcurrentDictionary<Guid, List<UpdateDelta>> _deltas = new();
         private readonly ConcurrentDictionary<Assembly, Assembly> _appliedAssemblies = new();
         private volatile UpdateHandlerActions? _handlerActions;
 
@@ -196,6 +196,10 @@ public void ApplyDeltas(IReadOnlyList<UpdateDelta> deltas)
                     {
                         System.Reflection.Metadata.AssemblyExtensions.ApplyUpdate(assembly, item.MetadataDelta, item.ILDelta, ReadOnlySpan<byte>.Empty);
                     }
+
+                    // Additionally stash the deltas away so it may be applied to assemblies loaded later.
+                    var cachedDeltas = _deltas.GetOrAdd(item.ModuleId, static _ => new());
+                    cachedDeltas.Add(item);
                 }
 
                 handlerActions.ClearCache.ForEach(a => a(updatedTypes));

src/BuiltInTools/DotNetDeltaApplier/StartupHook.cs

@@ -53,11 +53,6 @@ public static async Task ReceiveDeltas(HotReloadAgent hotReloadAgent)
             Log("Attempting to apply deltas.");
 
             hotReloadAgent.ApplyDeltas(update.Deltas);
-
-            // We want to base this off of mvids, but we'll figure that out eventually.
-            var applyResult = update.ChangedFile is string changedFile && changedFile.EndsWith(".razor", StringComparison.Ordinal) ?
-                ApplyResult.Success :
-                ApplyResult.Success_RefreshBrowser;
             pipeClient.WriteByte((byte)ApplyResult.Success);
 
         }

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

@@ -115,6 +115,8 @@ public async ValueTask<bool> TryHandleFileChange(DotNetWatchContext context, Fil
                 {
                     _reporter.Verbose("No deltas modified. Applying changes to clear diagnostics.");
                     await _deltaApplier.Apply(context, file.FilePath, updates, cancellationToken);
+                    // Even if there were diagnostics, continue treating this as a success
+                    _reporter.Output("No hot reload changes to apply.");
                 }
                 else
                 {
@@ -123,7 +125,8 @@ public async ValueTask<bool> TryHandleFileChange(DotNetWatchContext context, Fil
                 }
 
                 HotReloadEventSource.Log.HotReloadEnd(HotReloadEventSource.StartType.CompilationHandler);
-                // Even if there were diagnostics, continue treating this as a success
+                // Return true so that the watcher continues to keep the current hot reload session alive. If there were errors, this allows the user to fix errors and continue
+                // working on the running app.
                 return true;
             }
 
@@ -145,6 +148,11 @@ public async ValueTask<bool> TryHandleFileChange(DotNetWatchContext context, Fil
             var applyState = await _deltaApplier.Apply(context, file.FilePath, updates, cancellationToken);
             _reporter.Verbose($"Received {(applyState ? "successful" : "failed")} apply from delta applier.");
             HotReloadEventSource.Log.HotReloadEnd(HotReloadEventSource.StartType.CompilationHandler);
+            if (applyState)
+            {
+                _reporter.Output($"Hot reload of changes succeeded.");
+            }
+
             return applyState;
         }
 
@@ -171,7 +179,7 @@ private ImmutableArray<string> GetDiagnostics(Solution solution, CancellationTok
                     if (item.Severity == DiagnosticSeverity.Error)
                     {
                         var diagnostic = CSharpDiagnosticFormatter.Instance.Format(item);
-                        _reporter.Output(diagnostic);
+                        _reporter.Output("\x1B[40m\x1B[31m" + diagnostic);
                         projectDiagnostics = projectDiagnostics.Add(diagnostic);
                     }
                 }

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

@@ -17,10 +17,11 @@ namespace Microsoft.DotNet.Watcher.Tools
 {
     internal class DefaultDeltaApplier : IDeltaApplier
     {
+        private static readonly string _namedPipeName = Guid.NewGuid().ToString();
         private readonly IReporter _reporter;
-        private readonly string _namedPipeName = Guid.NewGuid().ToString();
         private Task _task;
         private NamedPipeServerStream _pipe;
+        private bool _refreshBrowserAfterFileChange;
 
         public DefaultDeltaApplier(IReporter reporter)
         {
@@ -29,14 +30,8 @@ public DefaultDeltaApplier(IReporter reporter)
 
         public bool SuppressBrowserRefreshAfterApply { get; init; }
 
-        public async ValueTask InitializeAsync(DotNetWatchContext context, CancellationToken cancellationToken)
+        public ValueTask InitializeAsync(DotNetWatchContext context, CancellationToken cancellationToken)
         {
-            if (_pipe is not null)
-            {
-                _pipe.Close();
-                await _pipe.DisposeAsync();
-            }
-
             _pipe = new NamedPipeServerStream(_namedPipeName, PipeDirection.InOut, 1, PipeTransmissionMode.Byte, PipeOptions.Asynchronous | PipeOptions.CurrentUserOnly);
             _task = _pipe.WaitForConnectionAsync(cancellationToken);
 
@@ -48,7 +43,15 @@ public async ValueTask InitializeAsync(DotNetWatchContext context, CancellationT
                 // Configure the app for EnC
                 context.ProcessSpec.EnvironmentVariables["DOTNET_MODIFIABLE_ASSEMBLIES"] = "debug";
                 context.ProcessSpec.EnvironmentVariables["DOTNET_HOTRELOAD_NAMEDPIPE_NAME"] = _namedPipeName;
+
+                // If there's any .razor file, we'll assume this is a blazor app and not cause a browser refresh.
+                if (!SuppressBrowserRefreshAfterApply)
+                {
+                    _refreshBrowserAfterFileChange = !context.FileSet.Any(f => f.FilePath.EndsWith(".razor", StringComparison.Ordinal));
+                }
             }
+
+            return default;
         }
 
         public async ValueTask<bool> Apply(DotNetWatchContext context, string changedFile, ImmutableArray<WatchHotReloadService.Update> solutionUpdate, CancellationToken cancellationToken)
@@ -110,11 +113,14 @@ public async ValueTask<bool> Apply(DotNetWatchContext context, string changedFil
 
             if (!SuppressBrowserRefreshAfterApply && context.BrowserRefreshServer is not null)
             {
-                if (result == ApplyResult.Success_RefreshBrowser)
+                // For a Web app, we have the option of either letting the app update the UI or
+                // refresh the browser. In general, for Blazor apps, we will choose not to refresh the UI
+                // and for other apps we'll always refresh
+                if (_refreshBrowserAfterFileChange)
                 {
                     await context.BrowserRefreshServer.ReloadAsync(cancellationToken);
                 }
-                else if (result == ApplyResult.Success)
+                else
                 {
                     await context.BrowserRefreshServer.SendJsonSerlialized(new HotReloadApplied());
                 }

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

@@ -98,6 +98,5 @@ internal enum ApplyResult
     {
         Failed = -1,
         Success = 0,
-        Success_RefreshBrowser = 1,
     }
 }

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

@@ -39,6 +39,7 @@ public async ValueTask<bool> TryHandleFileChange(DotNetWatchContext context, Fil
                 return false;
             }
             await HandleBrowserRefresh(context.BrowserRefreshServer, file, cancellationToken);
+            _reporter.Output("Hot reload of scoped css succeeded.");
             HotReloadEventSource.Log.HotReloadEnd(HotReloadEventSource.StartType.ScopedCssHandler);
             return true;
         }

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

@@ -33,6 +33,7 @@ public async ValueTask<bool> TryHandleFileChange(DotNetWatchContext context, Fil
             _reporter.Verbose($"Handling file change event for static content {file.FilePath}.");
             await HandleBrowserRefresh(context.BrowserRefreshServer, file, cancellationToken);
             HotReloadEventSource.Log.HotReloadEnd(HotReloadEventSource.StartType.StaticHandler);
+            _reporter.Output("Hot reload of static file succeeded.");
             return true;
         }
 

src/BuiltInTools/dotnet-watch/HotReloadDotNetWatcher.cs

@@ -128,8 +128,7 @@ public async Task WatchAsync(DotNetWatchContext context, CancellationToken cance
                             if (await hotReload.TryHandleFileChange(context, fileItem, combinedCancellationSource.Token))
                             {
                                 var totalTime = TimeSpan.FromTicks(Stopwatch.GetTimestamp() - start);
-                                _reporter.Output($"Hot reload of changes succeeded.");
-                                _reporter.Verbose($"Hot reload applied in {totalTime.TotalMilliseconds}ms.");
+                                _reporter.Verbose($"Hot reload change handled in {totalTime.TotalMilliseconds}ms.");
                             }
                             else
                             {

src/BuiltInTools/dotnet-watch/Program.cs

@@ -67,7 +67,13 @@ public Program(IConsole console, string workingDirectory)
             // AppContext.BaseDirectory = $sdkRoot\$sdkVersion\DotnetTools\dotnet-watch\$version\tools\net6.0\any\
             // MSBuild.dll is located at $sdkRoot\$sdkVersion\MSBuild.dll
             var sdkRootDirectory = Path.Combine(AppContext.BaseDirectory, "..", "..", "..", "..", "..", "..");
+#if DEBUG
+            // In the usual case, use the SDK that contains the dotnet-watch. However during local testing, it's
+            // much more common to run dotnet-watch from a different SDK. Use the ambient SDK in that case.
+            MSBuildLocator.RegisterDefaults();
+#else
             MSBuildLocator.RegisterMSBuildPath(sdkRootDirectory);
+#endif
 
             Ensure.NotNull(console, nameof(console));
             Ensure.NotNullOrEmpty(workingDirectory, nameof(workingDirectory));