dotnet · YuliiaKovalova · Oct 7, 2025 · Oct 3, 2025 · Oct 3, 2025 · Oct 6, 2025
diff --git a/src/Build/BackEnd/BuildManager/BuildManager.cs b/src/Build/BackEnd/BuildManager/BuildManager.cs
@@ -35,6 +35,7 @@
 using Microsoft.Build.Logging;
 using Microsoft.Build.Shared;
 using Microsoft.Build.Shared.Debugging;
+using Microsoft.Build.Shared.FileSystem;
 using Microsoft.Build.TelemetryInfra;
 using Microsoft.NET.StringTools;
 using ExceptionHandling = Microsoft.Build.Shared.ExceptionHandling;
@@ -3287,9 +3288,9 @@ private bool ReuseOldCaches(string[] inputCacheFiles)
                     return false;
                 }
 
-                if (inputCacheFiles.Any(f => !File.Exists(f)))
+                if (inputCacheFiles.Any(f => !FileSystems.Default.FileExists(f)))
                 {
-                    LogErrorAndShutdown(ResourceUtilities.FormatResourceStringIgnoreCodeAndKeyword("InputCacheFilesDoNotExist", string.Join(";", inputCacheFiles.Where(f => !File.Exists(f)))));
+                    LogErrorAndShutdown(ResourceUtilities.FormatResourceStringIgnoreCodeAndKeyword("InputCacheFilesDoNotExist", string.Join(";", inputCacheFiles.Where(f => !FileSystems.Default.FileExists(f)))));
                     return false;
                 }
 

diff --git a/src/Build/BackEnd/Components/Communications/CurrentHost.cs b/src/Build/BackEnd/Components/Communications/CurrentHost.cs
@@ -5,6 +5,7 @@
 using System.IO;
 using Microsoft.Build.Internal;
 using Microsoft.Build.Shared;
+using Microsoft.Build.Shared.FileSystem;
 #endif
 
 namespace Microsoft.Build.BackEnd;
@@ -28,7 +29,7 @@ internal static class CurrentHost
             string dotnetExe = Path.Combine(
                 FileUtilities.GetFolderAbove(BuildEnvironmentHelper.Instance.CurrentMSBuildToolsDirectory, 2),
                 Constants.DotnetProcessName);
-            if (File.Exists(dotnetExe))
+            if (FileSystems.Default.FileExists(dotnetExe))
             {
                 s_currentHost = dotnetExe;
             }
@@ -48,7 +49,7 @@ internal static class CurrentHost
                     dotnetExe = Path.Combine(
                         FileUtilities.GetFolderAbove(System.Runtime.InteropServices.RuntimeEnvironment.GetRuntimeDirectory(), 4),
                         Constants.DotnetProcessName);
-                    if (File.Exists(dotnetExe))
+                    if (FileSystems.Default.FileExists(dotnetExe))
                     {
                         s_currentHost = dotnetExe;
                     }

diff --git a/src/Build/BackEnd/Components/FileAccesses/FileAccessManager.cs b/src/Build/BackEnd/Components/FileAccesses/FileAccessManager.cs
@@ -4,13 +4,13 @@
 #if FEATURE_REPORTFILEACCESSES
 using System;
 using System.Collections.Concurrent;
-using System.IO;
 using System.Runtime.Versioning;
 using System.Threading;
 using Microsoft.Build.BackEnd;
 using Microsoft.Build.Execution;
 using Microsoft.Build.Experimental.FileAccess;
 using Microsoft.Build.Shared;
+using Microsoft.Build.Shared.FileSystem;
 
 namespace Microsoft.Build.FileAccesses
 {
@@ -144,7 +144,7 @@ public static void NotifyFileAccessCompletion(int globalRequestId)
         {
             // Make a dummy file access to use as a notification that the file accesses should be completed for a project.
             string filePath = FileAccessCompletionPrefix + globalRequestId.ToString();
-            _ = File.Exists(filePath);
+            _ = FileSystems.Default.FileExists(filePath);
         }
 
         public void WaitForFileAccessReportCompletion(int globalRequestId, CancellationToken cancellationToken)

diff --git a/src/Build/BackEnd/Components/Scheduler/Scheduler.cs b/src/Build/BackEnd/Components/Scheduler/Scheduler.cs
@@ -15,6 +15,7 @@
 using Microsoft.Build.ProjectCache;
 using Microsoft.Build.Shared;
 using Microsoft.Build.Shared.Debugging;
+using Microsoft.Build.Shared.FileSystem;
 using BuildAbortedException = Microsoft.Build.Exceptions.BuildAbortedException;
 using ILoggingService = Microsoft.Build.BackEnd.Logging.ILoggingService;
 using NodeLoggingContext = Microsoft.Build.BackEnd.Logging.NodeLoggingContext;
@@ -2703,7 +2704,7 @@ private void DumpSchedulerState()
                         bool shouldWriteHeader = _debugDumpIsFirstWrite;
                         if (shouldWriteHeader)
                         {
-                            shouldWriteHeader = !File.Exists(string.Format(CultureInfo.CurrentCulture, Path.Combine(_debugDumpPath, "SchedulerState_{0}.txt"), EnvironmentUtilities.CurrentProcessId));
+                            shouldWriteHeader = !FileSystems.Default.FileExists(string.Format(CultureInfo.CurrentCulture, Path.Combine(_debugDumpPath, "SchedulerState_{0}.txt"), EnvironmentUtilities.CurrentProcessId));
                             _debugDumpIsFirstWrite = false;
                         }
                         using StreamWriter file = FileUtilities.OpenWrite(string.Format(CultureInfo.CurrentCulture, Path.Combine(_debugDumpPath, "SchedulerState_{0}.txt"), EnvironmentUtilities.CurrentProcessId), append: true);

diff --git a/src/Build/BuildCheck/Checks/UntrustedLocationCheck.cs b/src/Build/BuildCheck/Checks/UntrustedLocationCheck.cs
@@ -7,6 +7,7 @@
 using System.Runtime.InteropServices;
 using Microsoft.Build.Construction;
 using Microsoft.Build.Shared;
+using Microsoft.Build.Shared.FileSystem;
 
 namespace Microsoft.Build.Experimental.BuildCheck.Checks;
 internal sealed class UntrustedLocationCheck : Check
@@ -79,7 +80,7 @@ private static string GetDownloadsPath()
             else if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
             {
                 string? locationFromEnv = Environment.GetEnvironmentVariable("XDG_DOWNLOAD_DIR");
-                if (locationFromEnv != null && Directory.Exists(locationFromEnv))
+                if (locationFromEnv != null && FileSystems.Default.DirectoryExists(locationFromEnv))
                 {
                     return locationFromEnv.TrimEnd(['\\','/']);
                 }

diff --git a/src/Build/BuildCheck/Infrastructure/EditorConfig/EditorConfigParser.cs b/src/Build/BuildCheck/Infrastructure/EditorConfig/EditorConfigParser.cs
@@ -6,6 +6,7 @@
 using System.Collections.Generic;
 using System.IO;
 using Microsoft.Build.Shared;
+using Microsoft.Build.Shared.FileSystem;
 using static Microsoft.Build.Experimental.BuildCheck.Infrastructure.EditorConfig.EditorConfigGlobsMatcher;
 
 namespace Microsoft.Build.Experimental.BuildCheck.Infrastructure.EditorConfig;
@@ -51,7 +52,7 @@ internal List<EditorConfigFile> DiscoverEditorConfigFiles(string filePath)
         {
             var editorConfig = _editorConfigFileCache.GetOrAdd(editorConfigFilePath, (key) =>
             {
-                return EditorConfigFile.Parse(File.ReadAllText(editorConfigFilePath));
+                return EditorConfigFile.Parse(FileSystems.Default.ReadFileAllText(editorConfigFilePath));
             });
             editorConfigFilePaths.Add(editorConfigFilePath);
             editorConfigDataFromFilesList.Add(editorConfig);

diff --git a/src/Build/Construction/ProjectRootElement.cs b/src/Build/Construction/ProjectRootElement.cs
@@ -1994,7 +1994,7 @@ internal static bool IsEmptyXmlFile(string path)
                     return false;
                 }
 
-                string contents = File.ReadAllText(path);
+                string contents = FileSystems.Default.ReadFileAllText(path);
 
                 // If the file is only whitespace or the XML declaration then it is empty
                 //

diff --git a/src/Build/Construction/Solution/SolutionFile.cs b/src/Build/Construction/Solution/SolutionFile.cs
@@ -669,7 +669,7 @@ internal static string ParseSolutionFromSolutionFilter(string solutionFilterFile
             {
                 // This is to align MSBuild with what VS permits in loading solution filter files. These are not in them by default but can be added manually.
                 JsonDocumentOptions options = new JsonDocumentOptions() { AllowTrailingCommas = true, CommentHandling = JsonCommentHandling.Skip };
-                JsonDocument text = JsonDocument.Parse(File.ReadAllText(solutionFilterFile), options);
+                JsonDocument text = JsonDocument.Parse(FileSystems.Default.ReadFileAllText(solutionFilterFile), options);
                 solution = text.RootElement.GetProperty("solution");
                 // We do NOT want to escape in order to preserve symbols like @, %, $ etc.
                 return FileUtilities.GetFullPath(solution.GetProperty("path").GetString(), Path.GetDirectoryName(solutionFilterFile), escape: false);

diff --git a/src/Build/Evaluation/Evaluator.cs b/src/Build/Evaluation/Evaluator.cs
@@ -1902,7 +1902,7 @@ static string EvaluateProperty(string value, IElementLocation location,
                     // "S:\sdk\.dotnet\sdk\10.0.100-preview.6.25315.102\Sdks\Microsoft.NET.Sdk\Sdk"
                     //                  ^5              ^4               ^3          ^2        ^1
                     string dotnetExe = Path.Combine(FileUtilities.GetFolderAbove(sdkResult.Path, 5), Constants.DotnetProcessName);
-                    if (File.Exists(dotnetExe))
+                    if (FileSystems.Default.FileExists(dotnetExe))
                     {
                         _data.AddSdkResolvedEnvironmentVariable(Constants.DotnetHostPathEnvVarName, dotnetExe);
                     }

diff --git a/src/Build/Evaluation/Expander.cs b/src/Build/Evaluation/Expander.cs
@@ -2611,7 +2611,7 @@ internal static void Exists(IElementLocation elementLocation, string functionNam
                             ProjectErrorUtilities.ThrowInvalidProject(elementLocation, "InvalidItemFunctionExpression", functionName, item.Key, e.Message);
                         }
 
-                        if (File.Exists(rootedPath) || Directory.Exists(rootedPath))
+                        if (FileSystems.Default.FileOrDirectoryExists(rootedPath))
                         {
                             transformedItems.Add(item);
                         }

diff --git a/src/Build/Evaluation/IntrinsicFunctions.cs b/src/Build/Evaluation/IntrinsicFunctions.cs
@@ -739,7 +739,7 @@ public static string GetMSBuildExtensionsPath()
         public static bool RegisterBuildCheck(string projectPath, string pathToAssembly, LoggingContext loggingContext)
         {
             pathToAssembly = FileUtilities.GetFullPathNoThrow(pathToAssembly);
-            if (File.Exists(pathToAssembly))
+            if (FileSystems.Default.FileExists(pathToAssembly))
             {
                 loggingContext.LogBuildEvent(new BuildCheckAcquisitionEventArgs(pathToAssembly, projectPath));
 

diff --git a/src/Build/Logging/BinaryLogger/ProjectImportsCollector.cs b/src/Build/Logging/BinaryLogger/ProjectImportsCollector.cs
@@ -64,7 +64,7 @@ public ProjectImportsCollector(
             else
             {
                 string cacheDirectory = FileUtilities.GetCacheDirectory();
-                if (!Directory.Exists(cacheDirectory))
+                if (!FileSystems.Default.DirectoryExists(cacheDirectory))
                 {
                     Directory.CreateDirectory(cacheDirectory);
                 }
@@ -222,7 +222,7 @@ private bool ShouldAddFile(ref string filePath, bool checkFileExistence, bool ma
                 return false;
             }
 
-            if (checkFileExistence && !File.Exists(filePath))
+            if (checkFileExistence && !FileSystems.Default.FileExists(filePath))
             {
                 _processedFiles.Add(filePath);
                 return false;

diff --git a/src/Build/Utilities/EngineFileUtilities.cs b/src/Build/Utilities/EngineFileUtilities.cs
@@ -5,13 +5,13 @@
 using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Diagnostics;
-using System.IO;
 using System.Linq;
 using System.Text.RegularExpressions;
 using Microsoft.Build.BackEnd.Components.Logging;
 using Microsoft.Build.BackEnd.Logging;
 using Microsoft.Build.Framework;
 using Microsoft.Build.Shared;
+using Microsoft.Build.Shared.FileSystem;
 
 namespace Microsoft.Build.Internal
 {
@@ -600,7 +600,7 @@ internal sealed class IOCache
 
             public bool DirectoryExists(string directory)
             {
-                return existenceCache.Value.GetOrAdd(directory, directory => Directory.Exists(directory));
+                return existenceCache.Value.GetOrAdd(directory, directory => FileSystems.Default.DirectoryExists(directory));
             }
         }
     }

diff --git a/src/Shared/BuildEnvironmentHelper.cs b/src/Shared/BuildEnvironmentHelper.cs
@@ -606,7 +606,7 @@ NativeMethodsShared.ProcessorArchitectures.X64 or NativeMethodsShared.ProcessorA
 
                 // Check for existence of an MSBuild file. Note this is not necessary in a VS installation where we always want to
                 // assume the correct layout.
-                var existsCheck = mode == BuildEnvironmentMode.VisualStudio ? new Func<string, bool>(_ => true) : File.Exists;
+                var existsCheck = mode == BuildEnvironmentMode.VisualStudio ? new Func<string, bool>(_ => true) : FileSystems.Default.FileExists;
 
                 MSBuildToolsDirectory32 = MSBuildToolsDirectoryRoot;
                 MSBuildToolsDirectory64 = existsCheck(potentialAmd64FromX86) ? Path.Combine(MSBuildToolsDirectoryRoot, "amd64") : CurrentMSBuildToolsDirectory;

diff --git a/src/Shared/Debugging/DebugUtils.cs b/src/Shared/Debugging/DebugUtils.cs
@@ -6,6 +6,7 @@
 using System.IO;
 using System.Text.RegularExpressions;
 using Microsoft.Build.Framework;
+using Microsoft.Build.Shared.FileSystem;
 
 #nullable disable
 
@@ -112,7 +113,7 @@ public static string FindNextAvailableDebugFilePath(string fileName)
             var fullPath = Path.Combine(DebugPath, fileName);
 
             var counter = 0;
-            while (File.Exists(fullPath))
+            while (FileSystems.Default.FileExists(fullPath))
             {
                 fileName = $"{fileNameWithoutExtension}_{counter++}{extension}";
                 fullPath = Path.Combine(DebugPath, fileName);

diff --git a/src/Shared/ExceptionHandling.cs b/src/Shared/ExceptionHandling.cs
@@ -391,13 +391,13 @@ internal static string ReadAnyExceptionFromFile(DateTime fromTimeUtc)
 
             foreach (string file in files)
             {
-                if (File.GetLastWriteTimeUtc(file) >= fromTimeUtc)
+                if (FileSystems.Default.GetLastWriteTimeUtc(file) >= fromTimeUtc)
                 {
                     builder.Append(Environment.NewLine);
                     builder.Append(file);
                     builder.Append(':');
                     builder.Append(Environment.NewLine);
-                    builder.Append(File.ReadAllText(file));
+                    builder.Append(FileSystems.Default.ReadFileAllText(file));
                     builder.Append(Environment.NewLine);
                 }
             }

diff --git a/src/Shared/FileUtilities.cs b/src/Shared/FileUtilities.cs
@@ -78,7 +78,7 @@ public static bool GetIsFileSystemCaseSensitive()
                 using (new FileStream(pathWithUpperCase, FileMode.CreateNew, FileAccess.ReadWrite, FileShare.None, 0x1000, FileOptions.DeleteOnClose))
                 {
                     string lowerCased = pathWithUpperCase.ToLowerInvariant();
-                    return !File.Exists(lowerCased);
+                    return !FileSystems.Default.FileExists(lowerCased);
                 }
             }
             catch (Exception exc)
@@ -748,7 +748,7 @@ internal static void DeleteSubdirectoriesNoThrow(string directory)
         {
             try
             {
-                foreach (string dir in Directory.EnumerateDirectories(directory))
+                foreach (string dir in FileSystems.Default.EnumerateDirectories(directory))
                 {
                     DeleteDirectoryNoThrow(dir, recursive: true, retryCount: 1);
                 }

diff --git a/src/Shared/FrameworkLocationHelper.cs b/src/Shared/FrameworkLocationHelper.cs
@@ -1422,7 +1422,7 @@ public virtual string GetPathToDotNetFramework(DotNetFrameworkArchitecture archi
                                 FindDotNetFrameworkPath(
                                     Path.GetDirectoryName(typeof(object).Module.FullyQualifiedName),
                                     this.DotNetFrameworkFolderPrefix,
-                                    Directory.Exists,
+                                    FileSystems.Default.DirectoryExists,
                                     Directory.GetDirectories,
                                     architecture);
 
@@ -1432,8 +1432,8 @@ public virtual string GetPathToDotNetFramework(DotNetFrameworkArchitecture archi
                 // Rollback see https://developercommunity.visualstudio.com/t/Unable-to-locate-MSBuild-path-with-Lates/10824132 
                 if (this._hasMsBuild &&
                     generatedPathToDotNetFramework != null &&
-                    (!File.Exists(Path.Combine(generatedPathToDotNetFramework, NativeMethodsShared.IsWindows ? "MSBuild.exe" : "mcs.exe")) &&
-                     !File.Exists(Path.Combine(generatedPathToDotNetFramework, "Microsoft.Build.dll"))))
+                    (!FileSystems.Default.FileExists(Path.Combine(generatedPathToDotNetFramework, NativeMethodsShared.IsWindows ? "MSBuild.exe" : "mcs.exe")) &&
+                     !FileSystems.Default.FileExists(Path.Combine(generatedPathToDotNetFramework, "Microsoft.Build.dll"))))
                 {
                     return null;
                 }

diff --git a/src/Shared/MSBuildLoadContext.cs b/src/Shared/MSBuildLoadContext.cs
@@ -40,7 +40,7 @@ public MSBuildLoadContext(string assemblyPath)
             // We should maintain previous behavior in the absence of new data (a .deps.json file) indicating that we
             // should do something different.
             // Setting the _resolver to null essentially just opts out of the new behavior.
-            _resolver = File.Exists(assemblyPath) && File.Exists(Path.ChangeExtension(assemblyPath, ".deps.json"))
+            _resolver = FileSystems.Default.FileExists(assemblyPath) && FileSystems.Default.FileExists(Path.ChangeExtension(assemblyPath, ".deps.json"))
                 ? new AssemblyDependencyResolver(assemblyPath) :
                 null;
         }

diff --git a/src/Shared/TaskFactoryUtilities.cs b/src/Shared/TaskFactoryUtilities.cs
@@ -5,6 +5,7 @@
 using System.Collections.Generic;
 using System.IO;
 using System.Reflection;
+using Microsoft.Build.Shared.FileSystem;
 
 namespace Microsoft.Build.Shared
 {
@@ -152,7 +153,7 @@ public static List<string> ExtractUniqueDirectoriesFromAssemblyPaths(List<string
 
             foreach (string assemblyPath in assemblyPaths)
             {
-                if (!string.IsNullOrEmpty(assemblyPath) && File.Exists(assemblyPath))
+                if (!string.IsNullOrEmpty(assemblyPath) && FileSystems.Default.FileExists(assemblyPath))
                 {
                     string? directory = Path.GetDirectoryName(assemblyPath);
                     if (!string.IsNullOrEmpty(directory) && seenDirectories.Add(directory))
@@ -178,7 +179,7 @@ public static Assembly LoadTaskAssembly(string assemblyPath)
             }
 
             // Load the assembly from bytes so we don't lock the file and record its original path for out-of-proc hosts
-            Assembly assembly = Assembly.Load(File.ReadAllBytes(assemblyPath));
+            Assembly assembly = Assembly.Load(FileSystems.Default.ReadFileAllBytes(assemblyPath));
             return assembly;
         }
 
@@ -202,7 +203,7 @@ public static void RegisterAssemblyResolveHandlersFromManifest(string taskLocati
             }
 
             string manifestPath = taskLocation + InlineTaskLoadManifestSuffix;
-            if (!File.Exists(manifestPath))
+            if (!FileSystems.Default.FileExists(manifestPath))
             {
                 return;
             }
@@ -247,7 +248,7 @@ public static void CleanCurrentProcessInlineTaskDirectory()
                 InlineTaskTempDllSubPath,
                 $"pid_{EnvironmentUtilities.CurrentProcessId}");
 
-            if (Directory.Exists(processSpecificInlineTaskDir))
+            if (FileSystems.Default.DirectoryExists(processSpecificInlineTaskDir))
             {
                 FileUtilities.DeleteDirectoryNoThrow(processSpecificInlineTaskDir, recursive: true);
             }
@@ -269,17 +270,17 @@ public static void CleanCurrentProcessInlineTaskDirectory()
                 if (!string.IsNullOrEmpty(assemblyName.CultureName))
                 {
                     path = Path.Combine(directory, assemblyName.CultureName, assemblyName.Name + ".dll");
-                    if (File.Exists(path))
+                    if (FileSystems.Default.FileExists(path))
                     {
-                        return Assembly.Load(File.ReadAllBytes(path));
+                        return Assembly.Load(FileSystems.Default.ReadFileAllBytes(path));
                     }
                 }
 
                 // Try the standard path
                 path = Path.Combine(directory, assemblyName.Name + ".dll");
-                if (File.Exists(path))
+                if (FileSystems.Default.FileExists(path))
                 {
-                    return Assembly.Load(File.ReadAllBytes(path));
+                    return Assembly.Load(FileSystems.Default.ReadFileAllBytes(path));
                 }
             }
 

diff --git a/src/Tasks/AddToWin32Manifest.cs b/src/Tasks/AddToWin32Manifest.cs
@@ -8,6 +8,7 @@
 
 using Microsoft.Build.Framework;
 using Microsoft.Build.Shared;
+using Microsoft.Build.Shared.FileSystem;
 using Microsoft.Build.Tasks.Deployment.ManifestUtilities;
 using Microsoft.Build.Utilities;
 
@@ -89,7 +90,7 @@ public string ManifestPath
         {
             if (ApplicationManifest != null)
             {
-                if (string.IsNullOrEmpty(ApplicationManifest.ItemSpec) || !File.Exists(ApplicationManifest?.ItemSpec))
+                if (string.IsNullOrEmpty(ApplicationManifest.ItemSpec) || !FileSystems.Default.FileExists(ApplicationManifest?.ItemSpec))
                 {
                     Log.LogErrorWithCodeFromResources(null, ApplicationManifest?.ItemSpec, 0, 0, 0, 0, "AddToWin32Manifest.SpecifiedApplicationManifestCanNotBeFound");
                     return null;