[dotnet-watch] Separate build from run

eng/Versions.props

@@ -90,6 +90,10 @@
     <!-- Dependency from https://github.com/dotnet/arcade-services -->
     <MicrosoftDotNetDarcLibVersion>1.1.0-beta.24367.3</MicrosoftDotNetDarcLibVersion>
   </PropertyGroup>
+  <PropertyGroup>
+    <!-- Dependency from https://github.com/dotnet/aspire -->
+    <AspirePackageVersion>9.1.0-preview.1.24555.3</AspirePackageVersion>
+  </PropertyGroup>
   <PropertyGroup>
     <!-- Dependency from https://github.com/dotnet/winforms -->
     <MicrosoftDotnetWinFormsProjectTemplatesPackageVersion>9.0.0-rc.2.24474.1</MicrosoftDotnetWinFormsProjectTemplatesPackageVersion>

src/BuiltInTools/dotnet-watch/Aspire/AspireServiceFactory.cs

@@ -104,11 +104,11 @@ async ValueTask<string> IAspireServerEvents.StartProjectAsync(string dcpId, Proj
 
             var projectOptions = GetProjectOptions(projectLaunchInfo);
             var sessionId = Interlocked.Increment(ref _sessionIdDispenser).ToString(CultureInfo.InvariantCulture);
-            await StartProjectAsync(dcpId, sessionId, projectOptions, build: false, isRestart: false, cancellationToken);
+            await StartProjectAsync(dcpId, sessionId, projectOptions, isRestart: false, cancellationToken);
             return sessionId;
         }
 
-        public async ValueTask<RunningProject> StartProjectAsync(string dcpId, string sessionId, ProjectOptions projectOptions, bool build, bool isRestart, CancellationToken cancellationToken)
+        public async ValueTask<RunningProject> StartProjectAsync(string dcpId, string sessionId, ProjectOptions projectOptions, bool isRestart, CancellationToken cancellationToken)
         {
             ObjectDisposedException.ThrowIf(_isDisposed, this);
 
@@ -125,9 +125,8 @@ public async ValueTask<RunningProject> StartProjectAsync(string dcpId, string se
                     var writeResult = outputChannel.Writer.TryWrite(line);
                     Debug.Assert(writeResult);
                 },
-                restartOperation: (build, cancellationToken) =>
-                    StartProjectAsync(dcpId, sessionId, projectOptions, build, isRestart: true, cancellationToken),
-                build: build,
+                restartOperation: cancellationToken =>
+                    StartProjectAsync(dcpId, sessionId, projectOptions, isRestart: true, cancellationToken),
                 cancellationToken);
 
             if (runningProject == null)

src/BuiltInTools/dotnet-watch/FileItem.cs

@@ -7,12 +7,14 @@ namespace Microsoft.DotNet.Watcher
 {
     internal readonly record struct FileItem
     {
-        public string FilePath { get; init; }
+        public required string FilePath { get; init; }
 
         /// <summary>
         /// List of all projects that contain this file (does not contain duplicates).
+        /// Empty if <see cref="Change"/> is <see cref="ChangeKind.Add"/> and the
+        /// item has not been assigned to a project yet.
         /// </summary>
-        public List<string> ContainingProjectPaths { get; init; }
+        public required List<string> ContainingProjectPaths { get; init; }
 
         public string? StaticWebAssetPath { get; init; }
 

src/BuiltInTools/dotnet-watch/Filters/BuildEvaluator.cs

@@ -4,6 +4,7 @@
 
 using System.Diagnostics;
 using Microsoft.DotNet.Watcher.Internal;
+using Microsoft.Extensions.Tools.Internal;
 
 namespace Microsoft.DotNet.Watcher.Tools
 {
@@ -87,7 +88,7 @@ private async ValueTask<EvaluationResult> CreateEvaluationResult(CancellationTok
                 await FileWatcher.WaitForFileChangeAsync(
                     rootProjectFileSetFactory.RootProjectFile,
                     context.Reporter,
-                    startedWatching: () => context.Reporter.Warn("Fix the error to continue or press Ctrl+C to exit."),
+                    startedWatching: () => context.Reporter.Report(MessageDescriptor.FixBuildError),
                     cancellationToken);
             }
         }

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

@@ -74,7 +74,7 @@ public async ValueTask TerminateNonRootProcessesAndDispose(CancellationToken can
             Dispose();
         }
 
-        public ValueTask RestartSessionAsync(IReadOnlySet<ProjectId> projectsToBeRebuilt, CancellationToken cancellationToken)
+        public ValueTask RestartSessionAsync(ImmutableDictionary<ProjectId, string> projectsToBeRebuilt, CancellationToken cancellationToken)
         {
             // Remove previous updates to all modules that were affected by rude edits.
             // All running projects that statically reference these modules have been terminated.
@@ -84,7 +84,7 @@ public ValueTask RestartSessionAsync(IReadOnlySet<ProjectId> projectsToBeRebuilt
 
             lock (_runningProjectsAndUpdatesGuard)
             {
-                _previousUpdates = _previousUpdates.RemoveAll(update => projectsToBeRebuilt.Contains(update.ProjectId));
+                _previousUpdates = _previousUpdates.RemoveAll(update => projectsToBeRebuilt.ContainsKey(update.ProjectId));
             }
 
             _hotReloadService.EndSession();
@@ -276,7 +276,7 @@ private static void PrepareCompilations(Solution solution, string projectPath, C
             }
         }
 
-        public async ValueTask<(IReadOnlySet<ProjectId> projectsToBeRebuilt, IEnumerable<RunningProject> terminatedProjects)> HandleFileChangesAsync(
+        public async ValueTask<(ImmutableDictionary<ProjectId, string> projectsToRebuild, ImmutableArray<RunningProject> terminatedProjects)> HandleFileChangesAsync(
             Func<IEnumerable<Project>, CancellationToken, Task> restartPrompt,
             CancellationToken cancellationToken)
         {
@@ -292,14 +292,14 @@ private static void PrepareCompilations(Solution solution, string projectPath, C
             {
                 // If Hot Reload is blocked (due to compilation error) we ignore the current
                 // changes and await the next file change.
-                return (ImmutableHashSet<ProjectId>.Empty, []);
+                return (ImmutableDictionary<ProjectId, string>.Empty, []);
             }
 
             if (updates.Status == ModuleUpdateStatus.RestartRequired)
             {
                 if (!anyProcessNeedsRestart)
                 {
-                    return (ImmutableHashSet<ProjectId>.Empty, []);
+                    return (ImmutableDictionary<ProjectId, string>.Empty, []);
                 }
 
                 await restartPrompt.Invoke(updates.ProjectsToRestart, cancellationToken);
@@ -308,7 +308,7 @@ private static void PrepareCompilations(Solution solution, string projectPath, C
                 // except for the root process, which will terminate later on.
                 var terminatedProjects = await TerminateNonRootProcessesAsync(updates.ProjectsToRestart.Select(p => p.FilePath!), cancellationToken);
 
-                return (updates.ProjectsToRebuild.Select(p => p.Id).ToHashSet(), terminatedProjects);
+                return (updates.ProjectsToRebuild.ToImmutableDictionary(keySelector: p => p.Id, elementSelector: p => p.FilePath!), terminatedProjects);
             }
 
             Debug.Assert(updates.Status == ModuleUpdateStatus.Ready);
@@ -348,7 +348,7 @@ await ForEachProjectAsync(projectsToUpdate, async (runningProject, cancellationT
                 }
             }, cancellationToken);
 
-            return (ImmutableHashSet<ProjectId>.Empty, []);
+            return (ImmutableDictionary<ProjectId, string>.Empty, []);
         }
 
         private async ValueTask DisplayResultsAsync(WatchHotReloadService.Updates updates, CancellationToken cancellationToken)

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

@@ -31,7 +31,6 @@ public EnvironmentOptions EnvironmentOptions
         CancellationTokenSource processTerminationSource,
         Action<OutputLine>? onOutput,
         RestartOperation restartOperation,
-        bool build,
         CancellationToken cancellationToken)
     {
         var projectNode = projectMap.TryGetProjectNode(projectOptions.ProjectPath, projectOptions.TargetFramework);
@@ -58,9 +57,7 @@ public EnvironmentOptions EnvironmentOptions
             Executable = EnvironmentOptions.MuxerPath,
             WorkingDirectory = projectOptions.WorkingDirectory,
             OnOutput = onOutput,
-            Arguments = build || !CommandLineOptions.IsCodeExecutionCommand(projectOptions.Command)
-                ? [projectOptions.Command, .. projectOptions.CommandArguments]
-                : [projectOptions.Command, "--no-build", .. projectOptions.CommandArguments]
+            Arguments = [projectOptions.Command, "--no-build", .. projectOptions.CommandArguments]
         };
 
         var environmentBuilder = EnvironmentVariablesBuilder.FromCurrentEnvironment();

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

@@ -11,6 +11,7 @@ internal readonly struct ProjectNodeMap(ProjectGraph graph, IReporter reporter)
     {
         public readonly ProjectGraph Graph = graph;
 
+        // full path of proj file to list of nodes representing all target frameworks of the project:
         public readonly IReadOnlyDictionary<string, IReadOnlyList<ProjectGraphNode>> Map = 
             graph.ProjectNodes.GroupBy(n => n.ProjectInstance.FullPath).ToDictionary(
                 keySelector: static g => g.Key,

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

@@ -8,7 +8,7 @@
 
 namespace Microsoft.DotNet.Watcher.Tools
 {
-    internal delegate ValueTask<RunningProject> RestartOperation(bool build, CancellationToken cancellationToken);
+    internal delegate ValueTask<RunningProject> RestartOperation(CancellationToken cancellationToken);
 
     internal sealed class RunningProject(
         ProjectGraphNode projectNode,
@@ -68,7 +68,6 @@ public void Dispose()
         public async ValueTask WaitForProcessRunningAsync(CancellationToken cancellationToken)
         {
             await DeltaApplier.WaitForProcessRunningAsync(cancellationToken);
-            Reporter.Report(MessageDescriptor.BuildCompleted);
         }
     }
 }