Don't write files in CompilerPackage if not needed

CompilerPackage was previously being lazy and would just delete and
rewrite files as needed when the package was loaded, even if the
machine would ultimately be left in the same state at the end.
For the old project system (which didn't monitor such file changes)
this wasn't bad, but with the new project system it now reloads projects
in response to changes which can be quite expensive.

Fixes #21838.

src/Compilers/Extension/CompilerPackage.cs

@@ -1,11 +1,12 @@
 // Copyright (c) Microsoft.  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.VisualStudio.Shell.Interop;
-using Microsoft.VisualStudio.Shell;
-using System.Reflection;
+using System.Collections.Generic;
 using System.IO;
+using System.Reflection;
 using EnvDTE;
+using Microsoft.VisualStudio.Shell;
+using Microsoft.VisualStudio.Shell.Interop;
 
 namespace Roslyn.Compilers.Extension
 {
@@ -47,23 +48,13 @@ protected override void Initialize()
 
         private void WriteMSBuildFiles(string packagePath, string hiveName)
         {
-            // First we want to ensure any existing Roslyn files are deleted so we don't have old stuff floating
-            // aroud and causing troubles
-            var msbuildDirectory = new DirectoryInfo(GetMSBuildPath());
-            if (msbuildDirectory.Exists)
-            {
-                foreach (var file in msbuildDirectory.EnumerateFiles($"*Roslyn*{hiveName}*", SearchOption.AllDirectories))
-                {
-                    file.Delete();
-                }
-            }
+            // A map of the file name to the content we need to ensure exists in the file
+            var filesToWrite = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
 
-            try
-            {
-                // The props we want to be included as early as possible since we want our tasks to be used and
-                // to ensure our setting of targets path happens early enough
-                var propsContent =
-                    $@"<?xml version=""1.0"" encoding=""utf-8""?>
+            // The props we want to be included as early as possible since we want our tasks to be used and
+            // to ensure our setting of targets path happens early enough
+            filesToWrite.Add(GetMSBuildRelativePath($@"Imports\Microsoft.Common.props\ImportBefore\Roslyn.Compilers.Extension.{hiveName}.props"),
+                $@"<?xml version=""1.0"" encoding=""utf-8""?>
 <Project xmlns=""http://schemas.microsoft.com/developer/msbuild/2003"">
   <PropertyGroup Condition=""'$(RoslynHive)' == '{hiveName}'"">
     <CSharpCoreTargetsPath>{packagePath}\Microsoft.CSharp.Core.targets</CSharpCoreTargetsPath>
@@ -72,12 +63,10 @@ private void WriteMSBuildFiles(string packagePath, string hiveName)
 
   <UsingTask TaskName=""Microsoft.CodeAnalysis.BuildTasks.Csc"" AssemblyFile=""{packagePath}\Microsoft.Build.Tasks.CodeAnalysis.dll"" Condition=""'$(RoslynHive)' == '{hiveName}'"" />
   <UsingTask TaskName=""Microsoft.CodeAnalysis.BuildTasks.Vbc"" AssemblyFile=""{packagePath}\Microsoft.Build.Tasks.CodeAnalysis.dll"" Condition=""'$(RoslynHive)' == '{hiveName}'"" />
-</Project>";
+</Project>");
 
-                WriteMSBuildFile(propsContent, $@"Imports\Microsoft.Common.props\ImportBefore\Roslyn.Compilers.Extension.{hiveName}.props");
-
-                // This targets content we want to be included later since the project flie might touch UseSharedCompilation
-                var targetsContent =
+            // This targets content we want to be included later since the project file might touch UseSharedCompilation
+            var targetsContent =
                     $@"<?xml version=""1.0"" encoding=""utf-8""?>
 <Project xmlns=""http://schemas.microsoft.com/developer/msbuild/2003"">
   <!-- If we're not using the compiler server, set ToolPath/Exe to direct to the exes in this package -->
@@ -90,8 +79,38 @@ private void WriteMSBuildFiles(string packagePath, string hiveName)
   </PropertyGroup>
 </Project>";
 
-                WriteMSBuildFile(targetsContent, $@"Microsoft.CSharp.targets\ImportBefore\Roslyn.Compilers.Extension.{hiveName}.targets");
-                WriteMSBuildFile(targetsContent, $@"Microsoft.VisualBasic.targets\ImportBefore\Roslyn.Compilers.Extension.{hiveName}.targets");
+            filesToWrite.Add(GetMSBuildRelativePath($@"Microsoft.CSharp.targets\ImportBefore\Roslyn.Compilers.Extension.{hiveName}.targets"), targetsContent);
+            filesToWrite.Add(GetMSBuildRelativePath($@"Microsoft.VisualBasic.targets\ImportBefore\Roslyn.Compilers.Extension.{hiveName}.targets"), targetsContent);
+
+            // First we want to ensure any Roslyn files with our hive name that we aren't writing -- this is probably
+            // leftovers from older extensions
+            var msbuildDirectory = new DirectoryInfo(GetMSBuildPath());
+            if (msbuildDirectory.Exists)
+            {
+                foreach (var file in msbuildDirectory.EnumerateFiles($"*Roslyn*{hiveName}*", SearchOption.AllDirectories))
+                {
+                    if (!filesToWrite.ContainsKey(file.FullName))
+                    {
+                        file.Delete();
+                    }
+                }
+            }
+
+            try
+            {
+                foreach (var fileAndContents in filesToWrite)
+                {
+                    var parentDirectory = new DirectoryInfo(Path.GetDirectoryName(fileAndContents.Key));
+                    parentDirectory.Create();
+
+                    // If we already know the file has the same contents, then we can skip
+                    if (File.Exists(fileAndContents.Key) && File.ReadAllText(fileAndContents.Key) == fileAndContents.Value)
+                    {
+                        continue;
+                    }
+
+                    File.WriteAllText(fileAndContents.Key, fileAndContents.Value);
+                }
             }
             catch (Exception e)
             {
@@ -110,6 +129,7 @@ private void WriteMSBuildFiles(string packagePath, string hiveName)
             }
         }
 
+
         private string GetMSBuildVersionString()
         {
             var dte = (DTE)GetService(typeof(SDTE));
@@ -135,23 +155,16 @@ private static Exception GetBadVisualStudioVersionException(string version)
             return new Exception($"Unrecoginzed Visual Studio Version: {version}");
         }
 
-        private void WriteMSBuildFile(string content, string relativeFilePath)
-        {
-            var fileFullPath = Path.Combine(GetMSBuildPath(), relativeFilePath);
-            var directory = new DirectoryInfo(Path.GetDirectoryName(fileFullPath));
-            if (!directory.Exists)
-            {
-                directory.Create();
-            }
-
-            File.WriteAllText(fileFullPath, content);
-        }
-
         private string GetMSBuildPath()
         {
             var version = GetMSBuildVersionString();
             var localAppData = Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData);
             return Path.Combine(localAppData, $@"Microsoft\MSBuild\{version}");
         }
+
+        private string GetMSBuildRelativePath(string relativePath)
+        {
+            return Path.Combine(GetMSBuildPath(), relativePath);
+        }
     }
 }