Make GenerateDepsFile and GenerateRuntimeConfigurationFiles tasks internally-incremental

src/Tasks/Microsoft.NET.Build.Tasks.UnitTests/GivenAGenerateDepsFile.cs

@@ -0,0 +1,72 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using FluentAssertions;
+using Microsoft.NET.TestFramework;
+using Xunit;
+
+namespace Microsoft.NET.Build.Tasks.UnitTests
+{
+    public class GivenAGenerateDepsFile
+    {
+        private readonly string _depsFilePath;
+
+        public GivenAGenerateDepsFile()
+        {
+            string testTempDir = Path.Combine(Path.GetTempPath(), "dotnetSdkTests");
+            Directory.CreateDirectory(testTempDir);
+            _depsFilePath = Path.Combine(testTempDir, nameof(GivenAGenerateDepsFile) + ".deps.json");
+            if (File.Exists(_depsFilePath))
+            {
+                File.Delete(_depsFilePath);
+            }
+        }
+
+        [Fact]
+        public void ItDoesNotOverwriteFileWithSameContent()
+        {
+            // Execute task first time
+            var task = CreateTestTask();
+            task.PublicExecuteCore();
+            var firstWriteTime = File.GetLastWriteTimeUtc(_depsFilePath);
+
+            // Wait a bit to ensure timestamp would change if file is rewritten
+            Thread.Sleep(100);
+
+            // Execute task again with same configuration
+            var task2 = CreateTestTask();
+            task2.PublicExecuteCore();
+            var secondWriteTime = File.GetLastWriteTimeUtc(_depsFilePath);
+
+            // File should not have been rewritten when content is the same
+            secondWriteTime.Should().Be(firstWriteTime, "file should not be rewritten when content is unchanged");
+        }
+
+        private TestableGenerateDepsFile CreateTestTask()
+        {
+            return new TestableGenerateDepsFile
+            {
+                BuildEngine = new MockNeverCacheBuildEngine4(),
+                ProjectPath = "TestProject.csproj",
+                DepsFilePath = _depsFilePath,
+                TargetFramework = "net8.0",
+                AssemblyName = "TestProject",
+                AssemblyExtension = ".dll",
+                AssemblyVersion = "1.0.0.0",
+                IncludeMainProject = true,
+                CompileReferences = new MockTaskItem[0],
+                ResolvedNuGetFiles = new MockTaskItem[0],
+                ResolvedRuntimeTargetsFiles = new MockTaskItem[0],
+                RuntimeGraphPath = ""
+            };
+        }
+
+        private class TestableGenerateDepsFile : GenerateDepsFile
+        {
+            public void PublicExecuteCore()
+            {
+                base.ExecuteCore();
+            }
+        }
+    }
+}

src/Tasks/Microsoft.NET.Build.Tasks.UnitTests/GivenAGenerateRuntimeConfigurationFiles.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using FluentAssertions;
+using Microsoft.Build.Utilities;
 using Microsoft.NET.TestFramework;
 using Xunit;
 
@@ -218,6 +219,70 @@ public void GivenTargetMonikerItGeneratesShortName()
 }}");
         }
 
+        [Fact]
+        public void ItDoesNotOverwriteFileWithSameContent()
+        {
+            // Execute task first time
+            var task = CreateBasicTestTask();
+            task.PublicExecuteCore();
+            var firstWriteTime = File.GetLastWriteTimeUtc(_runtimeConfigPath);
+
+            // Wait a bit to ensure timestamp would change if file is rewritten
+            Thread.Sleep(100);
+
+            // Execute task again with same configuration
+            var task2 = CreateBasicTestTask();
+            task2.PublicExecuteCore();
+            var secondWriteTime = File.GetLastWriteTimeUtc(_runtimeConfigPath);
+
+            // File should not have been rewritten when content is the same
+            secondWriteTime.Should().Be(firstWriteTime, "file should not be rewritten when content is unchanged");
+        }
+
+        [Fact]
+        public void GivenDifferentRuntimeHostOptionsItWritesNewConfig()
+        {
+            // Execute task first time
+            var task = CreateBasicTestTask();
+            task.PublicExecuteCore();
+            var firstWriteTime = File.GetLastWriteTimeUtc(_runtimeConfigPath);
+
+            // Wait a bit to ensure timestamp would change if file is rewritten
+            Thread.Sleep(100);
+
+            // Execute task again with different host options
+            var task2 = CreateBasicTestTask();
+            task2.HostConfigurationOptions = [
+                new TaskItem("System.Runtime.TieredCompilation", new Dictionary<string, string>{{"Value", "false"}}),
+                new TaskItem("System.GC.Concurrent", new Dictionary<string, string>{{"Value", "false"}}),
+            ];
+            task2.PublicExecuteCore();
+            var secondWriteTime = File.GetLastWriteTimeUtc(_runtimeConfigPath);
+            // File should have been rewritten when content is different
+            secondWriteTime.Should().BeAfter(firstWriteTime, "file should be rewritten when content is different");
+        }
+
+        private TestableGenerateRuntimeConfigurationFiles CreateBasicTestTask()
+        {
+            return new TestableGenerateRuntimeConfigurationFiles
+            {
+                BuildEngine = new MockNeverCacheBuildEngine4(),
+                TargetFrameworkMoniker = $".NETCoreApp,Version=v{ToolsetInfo.CurrentTargetFrameworkVersion}",
+                RuntimeConfigPath = _runtimeConfigPath,
+                RuntimeFrameworks = new[]
+                {
+                    new MockTaskItem(
+                        "Microsoft.NETCore.App",
+                        new Dictionary<string, string>
+                        {
+                            {"FrameworkName", "Microsoft.NETCore.App"}, {"Version", $"{ToolsetInfo.CurrentTargetFrameworkVersion}.0"}
+                        }
+                    )
+                },
+                RollForward = "LatestMinor"
+            };
+        }
+
         private class TestableGenerateRuntimeConfigurationFiles : GenerateRuntimeConfigurationFiles
         {
             public void PublicExecuteCore()

src/Tasks/Microsoft.NET.Build.Tasks/GenerateDepsFile.cs

@@ -254,10 +254,54 @@ bool ShouldIncludeRuntimeAsset(ITaskItem item)
             DependencyContext dependencyContext = builder.Build(UserRuntimeAssemblies);
 
             var writer = new DependencyContextWriter();
-            using (var fileStream = File.Create(depsFilePath))
+
+            bool shouldWriteFile = true;
+            var tempDepsFilePath = depsFilePath + ".tmp";
+
+            // Generate new content
+            using (var fileStream = File.Create(tempDepsFilePath))
             {
                 writer.Write(dependencyContext, fileStream);
             }
+
+            // If file exists, check if content is different using streaming hash comparison
+            if (File.Exists(depsFilePath))
+            {
+                Log.LogMessage("File {0} already exists, checking hash.", depsFilePath);
+                using var existingFileContentStream = File.OpenRead(depsFilePath);
+                var existingContentHash = HashingUtils.ComputeXXHash64(existingFileContentStream);
+                var existingContentHashRendered = BitConverter.ToString(existingContentHash).Replace("-", "");
+                Log.LogMessage("Existing file hash: {0}", existingContentHashRendered);
+                using var newContentStream = File.OpenRead(tempDepsFilePath);
+                var newContentHash = HashingUtils.ComputeXXHash64(newContentStream);
+                var newContentHashRendered = BitConverter.ToString(newContentHash).Replace("-", "");
+                Log.LogMessage("New content hash: {0}", newContentHashRendered);
+                // If hashes are equal, content is the same - don't write
+                if (existingContentHash.SequenceEqual(newContentHash))
+                {
+                    Log.LogMessage("File {0} is unchanged, skipping write.", depsFilePath);
+                    shouldWriteFile = false;
+                }
+            }
+
+            if (shouldWriteFile)
+            {
+                Log.LogMessage("Writing file {0}.", depsFilePath);
+#if NET
+                File.Move(tempDepsFilePath, depsFilePath, overwrite: true);
+#else
+                // For .NET Framework, we can't use File.Move because it doesn't overwrite the existing file
+                // so we delete the existing file first.
+                File.Delete(depsFilePath);
+                File.Move(tempDepsFilePath, depsFilePath);
+#endif
+            }
+            else
+            {
+                // If we didn't write the file, delete the temporary file
+                Log.LogMessage("Deleting temporary file {0}.", tempDepsFilePath);
+                File.Delete(tempDepsFilePath);
+            }
             _filesWritten.Add(new TaskItem(depsFilePath));
 
             if (ValidRuntimeIdentifierPlatformsForAssets != null)

src/Tasks/Microsoft.NET.Build.Tasks/GenerateRuntimeConfigurationFiles.cs

@@ -176,7 +176,7 @@ private void WriteRuntimeConfig(
                 AddAdditionalProbingPaths(config.RuntimeOptions, packageFolders);
             }
 
-            WriteToJsonFile(RuntimeConfigPath, config);
+            WriteToJsonFile(Log, RuntimeConfigPath, config);
             _filesWritten.Add(new TaskItem(RuntimeConfigPath));
         }
 
@@ -340,7 +340,7 @@ private void WriteDevRuntimeConfig(IList<LockFileItem> packageFolders)
 
             AddAdditionalProbingPaths(devConfig.RuntimeOptions, packageFolders);
 
-            WriteToJsonFile(RuntimeConfigDevPath, devConfig);
+            WriteToJsonFile(Log, RuntimeConfigDevPath, devConfig);
             _filesWritten.Add(new TaskItem(RuntimeConfigDevPath));
         }
 
@@ -381,7 +381,7 @@ private static string EnsureNoTrailingDirectorySeparator(string path)
             return path;
         }
 
-        private static void WriteToJsonFile(string fileName, object value)
+        private static void WriteToJsonFile(Logger log, string filePath, object value)
         {
             JsonSerializer serializer = new()
             {
@@ -390,10 +390,55 @@ private static void WriteToJsonFile(string fileName, object value)
                 DefaultValueHandling = DefaultValueHandling.Ignore
             };
 
-            using (JsonTextWriter writer = new(new StreamWriter(File.Create(fileName))))
+            bool shouldWriteFile = true;
+            var tempFilePath = filePath + ".tmp";
+
+            // Generate new content
+            using (JsonTextWriter writer = new(new StreamWriter(File.Create(tempFilePath))))
             {
                 serializer.Serialize(writer, value);
             }
+
+            // If file exists, check if content is different using streaming hash comparison
+            if (File.Exists(filePath))
+            {
+                log.LogMessage("File {0} already exists, checking hash.", filePath);
+                // stream positions are reset as part of these utility calls
+                using var existingContentStream = File.OpenRead(filePath);
+                var existingContentHash = HashingUtils.ComputeXXHash64(existingContentStream);
+                var existingContentHashRendered = BitConverter.ToString(existingContentHash).Replace("-", "");
+                log.LogMessage("Existing file hash: {0}", existingContentHashRendered);
+                using var newContentStream = File.OpenRead(tempFilePath);
+                var newContentHash = HashingUtils.ComputeXXHash64(newContentStream);
+                var newContentHashRendered = BitConverter.ToString(newContentHash).Replace("-", "");
+                log.LogMessage("New content hash: {0}", existingContentHashRendered);
+                // If hashes are equal, content is the same - don't write
+                if (existingContentHash.SequenceEqual(newContentHash))
+                {
+                    log.LogMessage("File {0} is unchanged, skipping write.", filePath);
+                    shouldWriteFile = false;
+                }
+
+            }
+
+            if (shouldWriteFile)
+            {
+                log.LogMessage("Writing file {0}.", filePath);
+#if NET
+                File.Move(tempFilePath, filePath, overwrite: true);
+#else
+                // For .NET Framework, we can't use File.Move because it doesn't overwrite the existing file
+                // so we delete the existing file first.
+                File.Delete(filePath);
+                File.Move(tempFilePath, filePath);
+#endif
+            }
+            else
+            {
+                // If we didn't write the file, delete the temporary file
+                log.LogMessage("Deleting temporary file {0}.", tempFilePath);
+                File.Delete(tempFilePath);
+            }
         }
     }
 }

src/Tasks/Microsoft.NET.Build.Tasks/HashingUtils.cs

@@ -0,0 +1,25 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.IO.Hashing;
+
+namespace Microsoft.NET.Build.Tasks;
+
+public static class HashingUtils
+{
+    /// <summary>
+    /// Computes the XxHash64 hash of a file.
+    /// </summary>
+    /// <param name="content">A stream to read for the hash. If the stream is seekable it will be reset to its incoming position.</param>
+    public static byte[] ComputeXXHash64(Stream content)
+    {
+        var initialPosition = content.CanSeek ? content.Position : 0;
+        var hasher = new XxHash64();
+        hasher.Append(content);
+        if (content.CanSeek)
+        {
+            content.Position = initialPosition;
+        }
+        return hasher.GetCurrentHash();
+    }
+}