Refactor dotnet-watch to isolate project.json dependency

src/Microsoft.DotNet.Watcher.Tools/CommandLineOptions.cs

@@ -1,11 +1,11 @@
 // 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.Collections.Generic;
 using System.IO;
 using Microsoft.DotNet.Cli.Utils;
 using Microsoft.DotNet.Watcher.Tools;
+using Microsoft.DotNet.Watcher.Internal;
 using Microsoft.Extensions.CommandLineUtils;
 
 namespace Microsoft.DotNet.Watcher
@@ -18,10 +18,7 @@ namespace Microsoft.DotNet.Watcher
         public IList<string> RemainingArguments { get; private set; }
         public static CommandLineOptions Parse(string[] args, TextWriter stdout, TextWriter stderr)
         {
-            if (args == null)
+            Ensure.NotNull(args, nameof(args));
-            {
-                throw new ArgumentNullException(nameof(args));
-            }
 
             var app = new CommandLineApplication(throwOnUnexpectedArg: false)
             {

src/Microsoft.DotNet.Watcher.Tools/DotNetWatcher.cs

@@ -1,12 +1,8 @@
 // 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.Collections.Generic;
-using System.IO;
 using System.Threading;
 using System.Threading.Tasks;
-using Microsoft.DotNet.Cli.Utils;
 using Microsoft.DotNet.Watcher.Internal;
 using Microsoft.Extensions.Logging;
 
@@ -14,163 +10,68 @@ namespace Microsoft.DotNet.Watcher
 {
     public class DotNetWatcher
     {
-        private readonly Func<IFileWatcher> _fileWatcherFactory;
-        private readonly Func<IProcessWatcher> _processWatcherFactory;
-        private readonly IProjectProvider _projectProvider;
-        private readonly ILoggerFactory _loggerFactory;
-
         private readonly ILogger _logger;
+        private readonly ProcessRunner _processRunner;
 
-        public DotNetWatcher(
+        public DotNetWatcher(ILogger logger)
-            Func<IFileWatcher> fileWatcherFactory,
-            Func<IProcessWatcher> processWatcherFactory,
-            IProjectProvider projectProvider,
-            ILoggerFactory loggerFactory)
         {
-            _fileWatcherFactory = fileWatcherFactory;
+            Ensure.NotNull(logger, nameof(logger));
-            _processWatcherFactory = processWatcherFactory;
-            _projectProvider = projectProvider;
-            _loggerFactory = loggerFactory;
 
-            _logger = _loggerFactory.CreateLogger(nameof(DotNetWatcher));
+            _logger = logger;
+            _processRunner = new ProcessRunner(logger);
         }
 
-        public async Task WatchAsync(string projectFile, IEnumerable<string> dotnetArguments, CancellationToken cancellationToken)
+        public async Task WatchAsync(ProcessSpec processSpec, IFileSetFactory fileSetFactory, CancellationToken cancellationToken)
         {
-            if (string.IsNullOrEmpty(projectFile))
+            Ensure.NotNull(processSpec, nameof(processSpec));
-            {
-                throw new ArgumentNullException(nameof(projectFile));
-            }
-            if (dotnetArguments == null)
-            {
-                throw new ArgumentNullException(nameof(dotnetArguments));
-            }
-            if (cancellationToken == null)
-            {
-                throw new ArgumentNullException(nameof(cancellationToken));
-            }
 
-            var dotnetArgumentsAsString = ArgumentEscaper.EscapeAndConcatenateArgArrayForProcessStart(dotnetArguments);
+            var cancelledTaskSource = new TaskCompletionSource<object>();
-
+            cancellationToken.Register(state => ((TaskCompletionSource<object>)state).TrySetResult(null), cancelledTaskSource);
-            var workingDir = Path.GetDirectoryName(projectFile);
 
             while (true)
             {
-                await WaitForValidProjectJsonAsync(projectFile, cancellationToken);
+                var fileSet = await fileSetFactory.CreateAsync(cancellationToken);
-                cancellationToken.ThrowIfCancellationRequested();
+                if (cancellationToken.IsCancellationRequested)
+                {
+                    return;
+                }
 
                 using (var currentRunCancellationSource = new CancellationTokenSource())
                 using (var combinedCancellationSource = CancellationTokenSource.CreateLinkedTokenSource(
                     cancellationToken,
                     currentRunCancellationSource.Token))
+                using (var fileSetWatcher = new FileSetWatcher(fileSet))
                 {
-                    var fileWatchingTask = WaitForProjectFileToChangeAsync(projectFile, combinedCancellationSource.Token);
+                    var fileSetTask = fileSetWatcher.GetChangedFileAsync(combinedCancellationSource.Token);
-                    var dotnetTask = WaitForDotnetToExitAsync(dotnetArgumentsAsString, workingDir, combinedCancellationSource.Token);
+                    var processTask = _processRunner.RunAsync(processSpec, combinedCancellationSource.Token);
 
-                    var tasksToWait = new Task[] { dotnetTask, fileWatchingTask };
+                    var finishedTask = await Task.WhenAny(processTask, fileSetTask, cancelledTaskSource.Task);
 
-                    int finishedTaskIndex = Task.WaitAny(tasksToWait, cancellationToken);
+                    // Regardless of the which task finished first, make sure everything is cancelled
-
-                    // Regardless of the outcome, make sure everything is cancelled
                     // and wait for dotnet to exit. We don't want orphan processes
                     currentRunCancellationSource.Cancel();
-                    Task.WaitAll(tasksToWait);
 
-                    cancellationToken.ThrowIfCancellationRequested();
+                    await Task.WhenAll(processTask, fileSetTask);
 
-                    string changedFile;
+                    if (finishedTask == cancelledTaskSource.Task || cancellationToken.IsCancellationRequested)
-                    if (finishedTaskIndex == 0)
-                    {
-                        // This is the dotnet task
-                        var dotnetExitCode = dotnetTask.Result;
-
-                        if (dotnetExitCode == 0)
-                        {
-                            _logger.LogInformation($"dotnet exit code: {dotnetExitCode}");
-                        }
-                        else
-                        {
-                            _logger.LogError($"dotnet exit code: {dotnetExitCode}");
-                        }
-
-                        _logger.LogInformation("Waiting for a file to change before restarting dotnet...");
-                        // Now wait for a file to change before restarting dotnet
-                        changedFile = await WaitForProjectFileToChangeAsync(projectFile, cancellationToken);
-                    }
-                    else
-                    {
-                        // This is a file watcher task
-                        changedFile = fileWatchingTask.Result;
-                    }
-
-                    if (!string.IsNullOrEmpty(changedFile))
-                    {
-                        _logger.LogInformation($"File changed: {changedFile}");
-                    }
-                }
-            }
-        }
-
-        private async Task<string> WaitForProjectFileToChangeAsync(string projectFile, CancellationToken cancellationToken)
-        {
-            using (var projectWatcher = CreateProjectWatcher(projectFile, watchProjectJsonOnly: false))
-            {
-                return await projectWatcher.WaitForChangeAsync(cancellationToken);
-            }
-        }
-
-        private Task<int> WaitForDotnetToExitAsync(string dotnetArguments, string workingDir, CancellationToken cancellationToken)
-        {
-            _logger.LogDebug($"Running dotnet with the following arguments: {dotnetArguments}");
-
-            var dotnetWatcher = _processWatcherFactory();
-            int dotnetProcessId = dotnetWatcher.Start("dotnet", dotnetArguments, workingDir);
-            _logger.LogInformation($"dotnet process id: {dotnetProcessId}");
-
-            return dotnetWatcher.WaitForExitAsync(cancellationToken);
-        }
-
-        private async Task WaitForValidProjectJsonAsync(string projectFile, CancellationToken cancellationToken)
-        {
-            while (true)
-            {
-                IProject project;
-                string errors;
-                if (_projectProvider.TryReadProject(projectFile, out project, out errors))
-                {
-                    return;
-                }
-
-                _logger.LogError($"Error(s) reading project file '{projectFile}': ");
-                _logger.LogError(errors);
-                _logger.LogInformation("Fix the error to continue.");
-
-                using (var projectWatcher = CreateProjectWatcher(projectFile, watchProjectJsonOnly: true))
-                {
-                    await projectWatcher.WaitForChangeAsync(cancellationToken);
-
-                    if (cancellationToken.IsCancellationRequested)
                     {
                         return;
                     }
 
-                    _logger.LogInformation($"File changed: {projectFile}");
+                    if (finishedTask == processTask)
+                    {
+                        _logger.LogInformation("Waiting for a file to change before restarting dotnet...");
+
+                        // Now wait for a file to change before restarting process
+                        await fileSetWatcher.GetChangedFileAsync(cancellationToken);
+                    }
+
+                    if (!string.IsNullOrEmpty(fileSetTask.Result))
+                    {
+                        _logger.LogInformation($"File changed: {fileSetTask.Result}");
+                    }
                 }
             }
         }
-
-        private ProjectWatcher CreateProjectWatcher(string projectFile, bool watchProjectJsonOnly)
-        {
-            return new ProjectWatcher(projectFile, watchProjectJsonOnly, _fileWatcherFactory, _projectProvider);
-        }
-
-        public static DotNetWatcher CreateDefault(ILoggerFactory loggerFactory)
-        {
-            return new DotNetWatcher(
-                fileWatcherFactory: () => new FileWatcher(),
-                processWatcherFactory: () => new ProcessWatcher(),
-                projectProvider: new ProjectProvider(),
-                loggerFactory: loggerFactory);
-        }
     }
 }

src/Microsoft.DotNet.Watcher.Tools/IFileSet.cs

@@ -1,10 +1,12 @@
 // 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.DotNet.Watcher.Internal
+using System.Collections.Generic;
+
+namespace Microsoft.DotNet.Watcher
 {
-    public interface IProjectProvider
+    public interface IFileSet : IEnumerable<string>
     {
-        bool TryReadProject(string projectFile, out IProject project, out string errors);
+        bool Contains(string filePath);
     }
 }

src/Microsoft.DotNet.Watcher.Tools/IFileSetFactory.cs

@@ -1,16 +1,13 @@
 // 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.Threading;
 using System.Threading.Tasks;
 
-namespace Microsoft.DotNet.Watcher.Internal
+namespace Microsoft.DotNet.Watcher
 {
-    public interface IProcessWatcher
+    public interface IFileSetFactory
     {
-        int Start(string executable, string arguments, string workingDir);
+        Task<IFileSet> CreateAsync(CancellationToken cancellationToken);
-
-        Task<int> WaitForExitAsync(CancellationToken cancellationToken);
     }
-}
+}

src/Microsoft.DotNet.Watcher.Tools/Internal/Ensure.cs

@@ -0,0 +1,30 @@
+// 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.DotNet.Watcher.Tools;
+
+namespace Microsoft.DotNet.Watcher.Internal
+{
+    internal static class Ensure
+    {
+        public static T NotNull<T>(T obj, string paramName)
+            where T : class
+        {
+            if (obj == null)
+            {
+                throw new ArgumentNullException(paramName);
+            }
+            return obj;
+        }
+
+        public static string NotNullOrEmpty(string obj, string paramName)
+        {
+            if (string.IsNullOrEmpty(obj))
+            {
+                throw new ArgumentException(Resources.Error_StringNullOrEmpty, paramName);
+            }
+            return obj;
+        }
+    }
+}

src/Microsoft.DotNet.Watcher.Tools/Internal/FileSet.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.Collections;
+using System.Collections.Generic;
+
+namespace Microsoft.DotNet.Watcher.Internal
+{
+    public class FileSet : IFileSet
+    {
+        private readonly HashSet<string> _files;
+
+        public FileSet(IEnumerable<string> files)
+        {
+            _files = new HashSet<string>(files, StringComparer.OrdinalIgnoreCase);
+        }
+
+        public bool Contains(string filePath) => _files.Contains(filePath);
+
+        public IEnumerator<string> GetEnumerator() => _files.GetEnumerator();
+        IEnumerator IEnumerable.GetEnumerator() => _files.GetEnumerator();
+    }
+}

src/Microsoft.DotNet.Watcher.Tools/Internal/FileSetWatcher.cs

@@ -0,0 +1,52 @@
+// 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.IO;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Microsoft.DotNet.Watcher.Internal
+{
+    public class FileSetWatcher : IDisposable
+    {
+        private readonly IFileWatcher _fileWatcher;
+        private readonly IFileSet _fileSet;
+
+        public FileSetWatcher(IFileSet fileSet)
+        {
+            _fileSet = fileSet;
+            _fileWatcher = new FileWatcher();
+        }
+
+        public async Task<string> GetChangedFileAsync(CancellationToken cancellationToken)
+        {
+            foreach (var file in _fileSet)
+            {
+                _fileWatcher.WatchDirectory(Path.GetDirectoryName(file));
+            }
+
+            var tcs = new TaskCompletionSource<string>();
+            cancellationToken.Register(() => tcs.TrySetResult(null));
+
+            Action<string> callback = path =>
+            {
+                if (_fileSet.Contains(path))
+                {
+                    tcs.TrySetResult(path);
+                }
+            };
+
+            _fileWatcher.OnFileChange += callback;
+            var changedFile = await tcs.Task;
+            _fileWatcher.OnFileChange -= callback;
+
+            return changedFile;
+        }
+
+        public void Dispose()
+        {
+            _fileWatcher.Dispose();
+        }
+    }
+}

src/Microsoft.DotNet.Watcher.Tools/Internal/FileWatcher/DotnetFileWatcher.cs

@@ -22,10 +22,8 @@ namespace Microsoft.DotNet.Watcher.Internal
 
         internal DotnetFileWatcher(string watchedDirectory, Func<string, FileSystemWatcher> fileSystemWatcherFactory)
         {
-            if (string.IsNullOrEmpty(watchedDirectory))
+            Ensure.NotNull(fileSystemWatcherFactory, nameof(fileSystemWatcherFactory));
-            {
+            Ensure.NotNullOrEmpty(watchedDirectory, nameof(watchedDirectory));
-                throw new ArgumentNullException(nameof(watchedDirectory));
-            }
 
             _watchedDirectory = watchedDirectory;
             _watcherFactory = fileSystemWatcherFactory;
@@ -38,10 +36,7 @@ namespace Microsoft.DotNet.Watcher.Internal
 
         private static FileSystemWatcher DefaultWatcherFactory(string watchedDirectory)
         {
-            if (string.IsNullOrEmpty(watchedDirectory))
+            Ensure.NotNullOrEmpty(watchedDirectory, nameof(watchedDirectory));
-            {
-                throw new ArgumentNullException(nameof(watchedDirectory));
-            }
 
             return new FileSystemWatcher(watchedDirectory);
         }
@@ -51,10 +46,7 @@ namespace Microsoft.DotNet.Watcher.Internal
             // Recreate the watcher
             CreateFileSystemWatcher();
 
-            if (OnError != null)
+            OnError?.Invoke(this, null);
-            {
-                OnError(this, null);
-            }
         }
 
         private void WatcherRenameHandler(object sender, RenamedEventArgs e)
@@ -81,11 +73,8 @@ namespace Microsoft.DotNet.Watcher.Internal
 
         private void NotifyChange(string fullPath)
         {
-            if (OnFileChange != null)
+            // Only report file changes
-            {
+            OnFileChange?.Invoke(this, fullPath);
-                // Only report file changes
-                OnFileChange(this, fullPath);
-            }
         }
 
         private void CreateFileSystemWatcher()

src/Microsoft.DotNet.Watcher.Tools/Internal/FileWatcher/PollingFileWatcher.cs

@@ -27,10 +27,7 @@ namespace Microsoft.DotNet.Watcher.Internal
 
         public PollingFileWatcher(string watchedDirectory)
         {
-            if (string.IsNullOrEmpty(watchedDirectory))
+            Ensure.NotNullOrEmpty(watchedDirectory, nameof(watchedDirectory));
-            {
-                throw new ArgumentNullException(nameof(watchedDirectory));
-            }
 
             _watchedDirectory = new DirectoryInfo(watchedDirectory);
 

src/Microsoft.DotNet.Watcher.Tools/Internal/IProject.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.Collections.Generic;
-
-namespace Microsoft.DotNet.Watcher.Internal
-{
-    public interface IProject
-    {
-        string ProjectFile { get; }
-
-        IEnumerable<string> Files { get; }
-
-        IEnumerable<string> ProjectDependencies { get; }
-    }
-}

src/Microsoft.DotNet.Watcher.Tools/Internal/Implementation/ProcessWatcher.cs

@@ -1,59 +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 System.Diagnostics;
-using System.Threading;
-using System.Threading.Tasks;
-using Microsoft.Extensions.Internal;
-
-namespace Microsoft.DotNet.Watcher.Internal
-{
-    public class ProcessWatcher : IProcessWatcher
-    {
-        private Process _runningProcess;
-
-        public int Start(string executable, string arguments, string workingDir)
-        {
-            // This is not thread safe but it will not run in a multithreaded environment so don't worry
-            if (_runningProcess != null)
-            {
-                throw new InvalidOperationException("The previous process is still running");
-            }
-
-            _runningProcess = new Process();
-            _runningProcess.StartInfo = new ProcessStartInfo()
-            {
-                FileName = executable,
-                Arguments = arguments,
-                UseShellExecute = false,
-                WorkingDirectory = workingDir
-            };
-
-            _runningProcess.Start();
-
-            return _runningProcess.Id;
-        }
-
-        public Task<int> WaitForExitAsync(CancellationToken cancellationToken)
-        {
-            cancellationToken.Register(() =>
-            {
-                if (_runningProcess != null)
-                {
-                    _runningProcess.KillTree();
-                }
-            });
-
-            return Task.Run(() =>
-            {
-                _runningProcess.WaitForExit();
-
-                var exitCode = _runningProcess.ExitCode;
-                _runningProcess = null;
-
-                return exitCode;
-            });
-        }
-    }
-}

src/Microsoft.DotNet.Watcher.Tools/Internal/IncludeContextExtensions.cs

@@ -1,7 +1,6 @@
 // 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.Collections.Generic;
 using System.Linq;
 using Microsoft.DotNet.ProjectModel.Files;
@@ -12,10 +11,7 @@ namespace Microsoft.DotNet.Watcher.Internal
     {
         public static IEnumerable<string> ResolveFiles(this IncludeContext context)
         {
-            if (context == null)
+            Ensure.NotNull(context, nameof(context));
-            {
-                throw new ArgumentNullException(nameof(context));
-            }
 
             return IncludeFilesResolver
                 .GetIncludeFiles(context, "/", diagnostics: null)

src/Microsoft.DotNet.Watcher.Tools/Internal/ProcessRunner.cs

@@ -0,0 +1,126 @@
+// 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;
+using System.Threading.Tasks;
+using Microsoft.Extensions.Internal;
+using Microsoft.DotNet.Cli.Utils;
+using Microsoft.Extensions.Logging;
+
+namespace Microsoft.DotNet.Watcher.Internal
+{
+    public class ProcessRunner
+    {
+        private readonly ILogger _logger;
+
+        public ProcessRunner(ILogger logger)
+        {
+            Ensure.NotNull(logger, nameof(logger));
+
+            _logger = logger;
+        }
+
+        // May not be necessary in the future. See https://github.com/dotnet/corefx/issues/12039
+        public async Task<int> RunAsync(ProcessSpec processSpec, CancellationToken cancellationToken)
+        {
+            Ensure.NotNull(processSpec, nameof(processSpec));
+
+            int exitCode;
+
+            using (var process = CreateProcess(processSpec))
+            using (var processState = new ProcessState(process))
+            {
+                cancellationToken.Register(() => processState.TryKill());
+
+                process.Start();
+                _logger.LogInformation("{execName} process id: {pid}", processSpec.ShortDisplayName(), process.Id);
+
+                await processState.Task;
+
+                exitCode = process.ExitCode;
+            }
+
+            LogResult(processSpec, exitCode);
+
+            return exitCode;
+        }
+
+        private Process CreateProcess(ProcessSpec processSpec)
+        {
+            var arguments = ArgumentEscaper.EscapeAndConcatenateArgArrayForProcessStart(processSpec.Arguments);
+
+            _logger.LogInformation("Running {execName} with the following arguments: {args}", processSpec.ShortDisplayName(), arguments);
+
+            var startInfo = new ProcessStartInfo
+            {
+                FileName = processSpec.Executable,
+                Arguments = arguments,
+                UseShellExecute = false,
+                WorkingDirectory = processSpec.WorkingDirectory
+            };
+            var process = new Process
+            {
+                StartInfo = startInfo,
+                EnableRaisingEvents = true
+            };
+            return process;
+        }
+
+        private void LogResult(ProcessSpec processSpec, int exitCode)
+        {
+            var processName = processSpec.ShortDisplayName();
+            if (exitCode == 0)
+            {
+                _logger.LogInformation("{execName} exit code: {code}", processName, exitCode);
+            }
+            else
+            {
+                _logger.LogError("{execName} exit code: {code}", processName, exitCode);
+            }
+        }
+
+        private class ProcessState : IDisposable
+        {
+            private readonly Process _process;
+            private readonly TaskCompletionSource<object> _tcs = new TaskCompletionSource<object>();
+            private volatile bool _disposed;
+
+            public ProcessState(Process process)
+            {
+                _process = process;
+                _process.Exited += OnExited;
+            }
+
+            public Task Task => _tcs.Task;
+
+            public void TryKill()
+            {
+                try
+                {
+                    if (!_process.HasExited)
+                    {
+                        _process.KillTree();
+                    }
+                }
+                catch
+                { }
+            }
+
+            private void OnExited(object sender, EventArgs args)
+                => _tcs.TrySetResult(null);
+
+            public void Dispose()
+            {
+                if (!_disposed)
+                {
+                    _disposed = true;
+                    TryKill();
+                    _process.Exited -= OnExited;
+                    _process.Dispose();
+                }
+            }
+        }
+    }
+}

src/Microsoft.DotNet.Watcher.Tools/Internal/Project.cs

@@ -1,16 +1,14 @@
 // 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.Collections.Generic;
 using System.IO;
 using System.Linq;
-using Microsoft.DotNet.ProjectModel.Files;
 using Microsoft.DotNet.ProjectModel.Graph;
 
 namespace Microsoft.DotNet.Watcher.Internal
 {
-    internal class Project : IProject
+    public class Project
     {
         public Project(ProjectModel.Project runtimeProject)
         {

src/Microsoft.DotNet.Watcher.Tools/Internal/ProjectJsonFileSet.cs

@@ -0,0 +1,95 @@
+// 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.Collections;
+using System.Collections.Generic;
+
+namespace Microsoft.DotNet.Watcher.Internal
+{
+    public class ProjectJsonFileSet : IFileSet
+    {
+        private readonly string _projectFile;
+        private ISet<string> _currentFiles;
+
+        public ProjectJsonFileSet(string projectFile)
+        {
+            _projectFile = projectFile;
+        }
+
+        public bool Contains(string filePath)
+        {
+            // if it was in the original list of files we were watching                 
+            if (_currentFiles?.Contains(filePath) == true)
+            {
+                return true;
+            }
+
+            // It's possible the new file was not in the old set but will be in the new set.
+            // Additions should be considered part of this.
+            RefreshFileList();
+
+            return _currentFiles.Contains(filePath);
+        }
+
+        public IEnumerator<string> GetEnumerator()
+        {
+            EnsureInitialized();
+            return _currentFiles.GetEnumerator();
+        }
+
+        IEnumerator IEnumerable.GetEnumerator()
+        {
+            EnsureInitialized();
+            return _currentFiles.GetEnumerator();
+        }
+
+        private void EnsureInitialized()
+        {
+            if (_currentFiles == null)
+            {
+                RefreshFileList();
+            }
+        }
+
+        private void RefreshFileList()
+        {
+            _currentFiles = new HashSet<string>(FindFiles(), StringComparer.OrdinalIgnoreCase);
+        }
+
+        private IEnumerable<string> FindFiles()
+        {
+            var projects = new HashSet<string>(); // temporary store to prevent re-parsing a project multiple times
+            return GetProjectFilesClosure(_projectFile, projects);
+        }
+
+        private IEnumerable<string> GetProjectFilesClosure(string projectFile, ISet<string> projects)
+        {
+            if (projects.Contains(projectFile))
+            {
+                yield break;
+            }
+
+            projects.Add(projectFile);
+
+            Project project;
+            string errors;
+
+            if (ProjectReader.TryReadProject(projectFile, out project, out errors))
+            {
+                foreach (var file in project.Files)
+                {
+                    yield return file;
+                }
+
+                foreach (var dependency in project.ProjectDependencies)
+                {
+                    foreach (var file in GetProjectFilesClosure(dependency, projects))
+                    {
+                        yield return file;
+                    }
+                }
+            }
+        }
+    }
+}

src/Microsoft.DotNet.Watcher.Tools/Internal/ProjectJsonFileSetFactory.cs

@@ -0,0 +1,51 @@
+// 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.Threading;
+using System.Threading.Tasks;
+using Microsoft.Extensions.Logging;
+
+namespace Microsoft.DotNet.Watcher.Internal
+{
+    public class ProjectJsonFileSetFactory : IFileSetFactory
+    {
+        private readonly ILogger _logger;
+        private readonly string _projectFile;
+        public ProjectJsonFileSetFactory(ILogger logger, string projectFile)
+        {
+            Ensure.NotNull(logger, nameof(logger));
+            Ensure.NotNullOrEmpty(projectFile, nameof(projectFile));
+
+            _logger = logger;
+            _projectFile = projectFile;
+        }
+
+        public async Task<IFileSet> CreateAsync(CancellationToken cancellationToken)
+        {
+            while (true)
+            {
+                cancellationToken.ThrowIfCancellationRequested();
+
+                Project project;
+                string errors;
+                if (ProjectReader.TryReadProject(_projectFile, out project, out errors))
+                {
+                    return new ProjectJsonFileSet(_projectFile);
+                }
+
+                _logger.LogError($"Error(s) reading project file '{_projectFile}': ");
+                _logger.LogError(errors);
+                _logger.LogInformation("Fix the error to continue.");
+
+                var fileSet = new FileSet(new[] { _projectFile });
+
+                using (var watcher = new FileSetWatcher(fileSet))
+                {
+                    await watcher.GetChangedFileAsync(cancellationToken);
+
+                    _logger.LogInformation($"File changed: {_projectFile}");
+                }
+            }
+        }
+    }
+}

src/Microsoft.DotNet.Watcher.Tools/Internal/ProjectReaderUtils.cs

@@ -2,16 +2,14 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Collections.Generic;
 using System.Linq;
 using System.Text;
-using Microsoft.DotNet.ProjectModel;
 
 namespace Microsoft.DotNet.Watcher.Internal
 {
-    public class ProjectProvider : IProjectProvider
+    public class ProjectReader
     {
-        public bool TryReadProject(string projectFile, out IProject project, out string errors)
+        public static bool TryReadProject(string projectFile, out Project project, out string errors)
         {
             errors = null;
             project = null;
@@ -35,12 +33,11 @@ namespace Microsoft.DotNet.Watcher.Internal
             return true;
         }
 
-        // Same as TryGetProject but it doesn't throw
+        private static bool TryGetProject(string projectFile, out ProjectModel.Project project, out string errorMessage)
-        private bool TryGetProject(string projectFile, out ProjectModel.Project project, out string errorMessage)
         {
             try
             {
-                if (!ProjectReader.TryGetProject(projectFile, out project))
+                if (!ProjectModel.ProjectReader.TryGetProject(projectFile, out project))
                 {
                     if (project?.Diagnostics != null && project.Diagnostics.Any())
                     {
@@ -66,7 +63,7 @@ namespace Microsoft.DotNet.Watcher.Internal
             return false;
         }
 
-        private string CollectMessages(Exception exception)
+        private static string CollectMessages(Exception exception)
         {
             var builder = new StringBuilder();
             builder.AppendLine(exception.Message);

src/Microsoft.DotNet.Watcher.Tools/Internal/ProjectWatcher.cs

@@ -1,119 +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 System.Collections.Generic;
-using System.IO;
-using System.Threading;
-using System.Threading.Tasks;
-
-namespace Microsoft.DotNet.Watcher.Internal
-{
-    public class ProjectWatcher : IDisposable
-    {
-        private readonly IProjectProvider _projectProvider;
-        private readonly IFileWatcher _fileWatcher;
-
-        private readonly string _rootProject;
-        private readonly bool _watchProjectJsonOnly;
-
-        private ISet<string> _watchedFiles;
-
-        public ProjectWatcher(
-            string projectToWatch,
-            bool watchProjectJsonOnly,
-            Func<IFileWatcher> fileWatcherFactory,
-            IProjectProvider projectProvider)
-        {
-            _projectProvider = projectProvider;
-            _fileWatcher = fileWatcherFactory();
-
-            _rootProject = projectToWatch;
-            _watchProjectJsonOnly = watchProjectJsonOnly;
-        }
-
-        public async Task<string> WaitForChangeAsync(CancellationToken cancellationToken)
-        {
-            _watchedFiles = GetProjectFilesClosure(_rootProject);
-
-            foreach (var file in _watchedFiles)
-            {
-                _fileWatcher.WatchDirectory(Path.GetDirectoryName(file));
-            }
-
-            var tcs = new TaskCompletionSource<string>();
-            cancellationToken.Register(() => tcs.TrySetResult(null));
-
-            Action<string> callback = path =>
-            {
-                // If perf becomes a problem, this could be a good starting point
-                // because it reparses the project on every change
-                // Maybe it could time-buffer the changes in case there are a lot
-                // of files changed at the same time
-                if (IsFileInTheWatchedSet(path))
-                {
-                    tcs.TrySetResult(path);
-                }
-            };
-
-            _fileWatcher.OnFileChange += callback;
-            var changedFile = await tcs.Task;
-            _fileWatcher.OnFileChange -= callback;
-
-            return changedFile;
-        }
-
-        public void Dispose()
-        {
-            _fileWatcher?.Dispose();
-        }
-
-        private bool IsFileInTheWatchedSet(string file)
-        {
-            // If the file was already watched
-            // or if the new project file closure determined
-            // by file globbing patterns contains the new file
-            // Note, we cannot simply rebuild the closure every time because it wouldn't
-            // detect renamed files that have the new name outside of the closure
-            return
-                _watchedFiles.Contains(file) ||
-                GetProjectFilesClosure(_rootProject).Contains(file);
-        }
-
-        private ISet<string> GetProjectFilesClosure(string projectFile)
-        {
-            var closure = new HashSet<string>();
-
-            if (_watchProjectJsonOnly)
-            {
-                closure.Add(projectFile);
-            }
-            else
-            {
-                GetProjectFilesClosure(projectFile, closure);
-            }
-            return closure;
-        }
-
-        private void GetProjectFilesClosure(string projectFile, ISet<string> closure)
-        {
-            closure.Add(projectFile);
-
-            IProject project;
-            string errors;
-
-            if (_projectProvider.TryReadProject(projectFile, out project, out errors))
-            {
-                foreach (var file in project.Files)
-                {
-                    closure.Add(file);
-                }
-
-                foreach (var dependency in project.ProjectDependencies)
-                {
-                    GetProjectFilesClosure(dependency, closure);
-                }
-            }
-        }
-    }
-}

src/Microsoft.DotNet.Watcher.Tools/Microsoft.DotNet.Watcher.Tools.xproj

@@ -4,7 +4,7 @@
     <VisualStudioVersion Condition="'$(VisualStudioVersion)' == ''">14.0</VisualStudioVersion>
     <VSToolsPath Condition="'$(VSToolsPath)' == ''">$(MSBuildExtensionsPath32)\Microsoft\VisualStudio\v$(VisualStudioVersion)</VSToolsPath>
   </PropertyGroup>
-  <Import Project="$(VSToolsPath)\DNX\Microsoft.DNX.Props" Condition="'$(VSToolsPath)' != ''" />
+  <Import Project="$(VSToolsPath)\DotNet\Microsoft.DotNet.Props" Condition="'$(VSToolsPath)' != ''" />
   <PropertyGroup Label="Globals">
     <ProjectGuid>8a8ceabc-ac47-43ff-a5df-69224f7e1f46</ProjectGuid>
     <BaseIntermediateOutputPath Condition="'$(BaseIntermediateOutputPath)'=='' ">.\obj</BaseIntermediateOutputPath>
@@ -16,5 +16,5 @@
   <PropertyGroup>
     <SchemaVersion>2.0</SchemaVersion>
   </PropertyGroup>
-  <Import Project="$(VSToolsPath)\DNX\Microsoft.DNX.targets" Condition="'$(VSToolsPath)' != ''" />
+  <Import Project="$(VSToolsPath)\DotNet\Microsoft.DotNet.targets" Condition="'$(VSToolsPath)' != ''" />
 </Project>

src/Microsoft.DotNet.Watcher.Tools/ProcessSpec.cs

@@ -0,0 +1,18 @@
+// 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;
+using System.IO;
+
+namespace Microsoft.DotNet.Watcher
+{
+    public class ProcessSpec
+    {
+        public string Executable { get; set; }
+        public string WorkingDirectory { get; set; }
+        public IEnumerable<string> Arguments { get; set; }
+
+        public string ShortDisplayName() 
+            => Path.GetFileNameWithoutExtension(Executable);
+    }
+}

src/Microsoft.DotNet.Watcher.Tools/Program.cs

@@ -5,29 +5,23 @@ using System;
 using System.IO;
 using System.Threading;
 using System.Threading.Tasks;
-using Microsoft.Extensions.Logging;
 using Microsoft.DotNet.Cli.Utils;
+using Microsoft.DotNet.Watcher.Internal;
+using Microsoft.Extensions.Logging;
 
 namespace Microsoft.DotNet.Watcher
 {
     public class Program
     {
-        private readonly ILoggerFactory _loggerFactory = new LoggerFactory();
+        private const string LoggerName = "DotNetWatcher";
         private readonly CancellationToken _cancellationToken;
         private readonly TextWriter _stdout;
         private readonly TextWriter _stderr;
 
         public Program(TextWriter consoleOutput, TextWriter consoleError, CancellationToken cancellationToken)
         {
-            if (consoleOutput == null)
+            Ensure.NotNull(consoleOutput, nameof(consoleOutput));
-            {
+            Ensure.NotNull(consoleError, nameof(consoleError));
-                throw new ArgumentNullException(nameof(consoleOutput));
-            }
-
-            if (cancellationToken == null)
-            {
-                throw new ArgumentNullException(nameof(cancellationToken));
-            }
 
             _cancellationToken = cancellationToken;
             _stdout = consoleOutput;
@@ -36,28 +30,43 @@ namespace Microsoft.DotNet.Watcher
 
         public static int Main(string[] args)
         {
+            DebugHelper.HandleDebugSwitch(ref args);
+
             using (CancellationTokenSource ctrlCTokenSource = new CancellationTokenSource())
             {
                 Console.CancelKeyPress += (sender, ev) =>
                 {
+                    if (!ctrlCTokenSource.IsCancellationRequested)
+                    {
+                        Console.WriteLine($"[{LoggerName}] Shutdown requested. Press CTRL+C again to force exit.");
+                        ev.Cancel = true;
+                    }
+                    else
+                    {
+                        ev.Cancel = false;
+                    }
                     ctrlCTokenSource.Cancel();
-                    ev.Cancel = false;
                 };
 
-                int exitCode;
                 try
                 {
-                    exitCode = new Program(Console.Out, Console.Error, ctrlCTokenSource.Token)
+                    return new Program(Console.Out, Console.Error, ctrlCTokenSource.Token)
                         .MainInternalAsync(args)
                         .GetAwaiter()
                         .GetResult();
                 }
-                catch (TaskCanceledException)
+                catch (Exception ex)
                 {
-                    // swallow when only exception is the CTRL+C exit cancellation task
+                    if (ex is TaskCanceledException || ex is OperationCanceledException)
-                    exitCode = 0;
+                    {
+                        // swallow when only exception is the CTRL+C forced an exit
+                        return 0;
+                    }
+
+                    Console.Error.WriteLine(ex.ToString());
+                    Console.Error.WriteLine($"[{LoggerName}] An unexpected error occurred".Bold().Red());
+                    return 1;
                 }
-                return exitCode;
             }
         }
 
@@ -75,17 +84,25 @@ namespace Microsoft.DotNet.Watcher
                 return 2;
             }
 
+            var loggerFactory = new LoggerFactory();
             var commandProvider = new CommandOutputProvider
             {
                 LogLevel = ResolveLogLevel(options)
             };
-            _loggerFactory.AddProvider(commandProvider);
+            loggerFactory.AddProvider(commandProvider);
+            var logger = loggerFactory.CreateLogger(LoggerName);
 
-            var projectToWatch = Path.Combine(Directory.GetCurrentDirectory(), ProjectModel.Project.FileName);
+            var projectFile = Path.Combine(Directory.GetCurrentDirectory(), ProjectModel.Project.FileName);
+            var projectFileSetFactory = new ProjectJsonFileSetFactory(logger, projectFile);
+            var processInfo = new ProcessSpec
+            {
+                Executable = new Muxer().MuxerPath,
+                WorkingDirectory = Path.GetDirectoryName(projectFile),
+                Arguments = options.RemainingArguments
+            };
 
-            await DotNetWatcher
+            await new DotNetWatcher(logger)
-                    .CreateDefault(_loggerFactory)
+                    .WatchAsync(processInfo, projectFileSetFactory, _cancellationToken);
-                    .WatchAsync(projectToWatch, options.RemainingArguments, _cancellationToken);
 
             return 0;
         }
@@ -97,7 +114,7 @@ namespace Microsoft.DotNet.Watcher
                 return LogLevel.Warning;
             }
 
-            bool globalVerbose; 
+            bool globalVerbose;
             bool.TryParse(Environment.GetEnvironmentVariable(CommandContext.Variables.Verbose), out globalVerbose);
 
             if (options.IsVerbose // dotnet watch --verbose

src/Microsoft.DotNet.Watcher.Tools/Properties/Resources.Designer.cs

@@ -26,6 +26,22 @@ namespace Microsoft.DotNet.Watcher.Tools
             return GetString("Error_QuietAndVerboseSpecified");
         }
 
+        /// <summary>
+        /// Value cannot be null or an empty string.
+        /// </summary>
+        internal static string Error_StringNullOrEmpty
+        {
+            get { return GetString("Error_StringNullOrEmpty"); }
+        }
+
+        /// <summary>
+        /// Value cannot be null or an empty string.
+        /// </summary>
+        internal static string FormatError_StringNullOrEmpty()
+        {
+            return GetString("Error_StringNullOrEmpty");
+        }
+
         private static string GetString(string name, params string[] formatterNames)
         {
             var value = _resourceManager.GetString(name);

src/Microsoft.DotNet.Watcher.Tools/Resources.resx

@@ -120,4 +120,7 @@
   <data name="Error_QuietAndVerboseSpecified" xml:space="preserve">
     <value>Cannot specify both '--quiet' and '--verbose' options.</value>
   </data>
+  <data name="Error_StringNullOrEmpty" xml:space="preserve">
+    <value>Value cannot be null or an empty string.</value>
+  </data>
 </root>

test/Microsoft.DotNet.Watcher.Tools.FunctionalTests/Scenario/ProjectToolScenario.cs

@@ -5,14 +5,11 @@ using System;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.IO;
-using System.Threading;
-using System.Xml.Linq;
-using Newtonsoft.Json.Linq;
-using Microsoft.DotNet.Cli.Utils;
-using Microsoft.Extensions.DependencyModel;
-using Microsoft.DotNet.ProjectModel;
-using System.Reflection;
 using System.Linq;
+using System.Reflection;
+using System.Threading;
+using Microsoft.DotNet.Cli.Utils;
+using Microsoft.DotNet.ProjectModel;
 
 namespace Microsoft.DotNet.Watcher.Tools.FunctionalTests
 {