Refresh copy marker when implementation output changes

src/Tasks.UnitTests/RegressionTests.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.IO;
+using System.Threading;
 using Microsoft.Build.Evaluation;
 using Microsoft.Build.Shared;
 using Microsoft.Build.UnitTests;
@@ -102,5 +103,97 @@ public void IsWellKnownAttributeValuePreserved()
             MockLogger logger = new MockLogger(_output);
             ObjectModelHelpers.BuildTempProjectFileExpectSuccess("Myapp.proj", logger);
         }
+
+        /// <summary>
+        /// Test for https://github.com/dotnet/msbuild/issues/13478.
+        /// </summary>
+        [Fact]
+        public void CopyUpToDateMarkerTracksImplementationAssemblyWrites()
+        {
+            ObjectModelHelpers.DeleteTempProjectDirectory();
+            CreateCopyMarkerTestProject(produceReferenceAssembly: true);
+
+            MockLogger logger = new MockLogger(_output);
+
+            ObjectModelHelpers.BuildTempProjectFileExpectSuccess("MarkerTest.csproj", logger);
+
+            string markerPath = Path.Combine(ObjectModelHelpers.TempProjectDir, "obj", "Debug", "MarkerTest.csproj.Up2Date");
+            Assert.True(File.Exists(markerPath), $"Expected marker to exist at {markerPath}");
+            DateTime markerAfterFirstBuild = File.GetLastWriteTimeUtc(markerPath);
+
+            ObjectModelHelpers.BuildTempProjectFileExpectSuccess("MarkerTest.csproj", logger);
+
+            DateTime markerAfterNoOpBuild = File.GetLastWriteTimeUtc(markerPath);
+            Assert.Equal(markerAfterFirstBuild, markerAfterNoOpBuild);
+
+            string intermediateRefAssemblyPath = Path.Combine(ObjectModelHelpers.TempProjectDir, "obj", "Debug", "refint", "MarkerTest.dll");
+            Assert.True(File.Exists(intermediateRefAssemblyPath), $"Expected intermediate reference assembly to exist at {intermediateRefAssemblyPath}");
+
+            Thread.Sleep(TimeSpan.FromSeconds(2));
+            File.WriteAllText(intermediateRefAssemblyPath, "Reference output changed");
+
+            ObjectModelHelpers.BuildTempProjectFileExpectSuccess("MarkerTest.csproj", logger);
+
+            DateTime markerAfterReferenceAssemblyOnlyChange = File.GetLastWriteTimeUtc(markerPath);
+            Assert.Equal(markerAfterNoOpBuild, markerAfterReferenceAssemblyOnlyChange);
+
+            Thread.Sleep(TimeSpan.FromSeconds(2));
+            File.WriteAllText(Path.Combine(ObjectModelHelpers.TempProjectDir, "input.txt"), "changed");
+
+            ObjectModelHelpers.BuildTempProjectFileExpectSuccess("MarkerTest.csproj", logger);
+
+            DateTime markerAfterImplementationChange = File.GetLastWriteTimeUtc(markerPath);
+            Assert.True(
+                markerAfterImplementationChange > markerAfterReferenceAssemblyOnlyChange,
+                $"Expected marker to advance from {markerAfterReferenceAssemblyOnlyChange:O}, but it was {markerAfterImplementationChange:O}.");
+        }
+
+        /// <summary>
+        /// Test for https://github.com/dotnet/msbuild/issues/13478.
+        /// </summary>
+        [Fact]
+        public void CopyUpToDateMarkerIsNotCreatedForMainAssemblyWritesWhenReferenceAssembliesAreNotProduced()
+        {
+            ObjectModelHelpers.DeleteTempProjectDirectory();
+            CreateCopyMarkerTestProject(produceReferenceAssembly: false);
+
+            MockLogger logger = new MockLogger(_output);
+
+            ObjectModelHelpers.BuildTempProjectFileExpectSuccess("MarkerTest.csproj", logger);
+
+            string markerPath = Path.Combine(ObjectModelHelpers.TempProjectDir, "obj", "Debug", "MarkerTest.csproj.Up2Date");
+            Assert.False(File.Exists(markerPath), $"Did not expect marker to exist at {markerPath}");
+        }
+
+        private static void CreateCopyMarkerTestProject(bool produceReferenceAssembly)
+        {
+            ObjectModelHelpers.CreateFileInTempProjectDirectory("input.txt", "initial");
+            ObjectModelHelpers.CreateFileInTempProjectDirectory("MarkerTest.csproj", $@"
+<Project DefaultTargets=""Build"" xmlns=""msbuildnamespace"" ToolsVersion=""msbuilddefaulttoolsversion"">
+  <Import Project=""$(MSBuildToolsPath)\Microsoft.Common.props"" />
+
+  <PropertyGroup>
+    <AssemblyName>MarkerTest</AssemblyName>
+    <OutputType>Library</OutputType>
+    <TargetFrameworkVersion>{MSBuildConstants.StandardTestTargetFrameworkVersion}</TargetFrameworkVersion>
+    <ProduceReferenceAssembly>{produceReferenceAssembly.ToString().ToLowerInvariant()}</ProduceReferenceAssembly>
+  </PropertyGroup>
+
+  <Import Project=""$(MSBuildToolsPath)\Microsoft.CSharp.targets"" />
+
+  <Target Name=""CoreCompile""
+          Inputs=""input.txt""
+          Outputs=""@(IntermediateAssembly)"">
+    <MakeDir Directories=""@(IntermediateAssembly->'%(RootDir)%(Directory)');@(IntermediateRefAssembly->'%(RootDir)%(Directory)')"" />
+    <WriteLinesToFile File=""@(IntermediateAssembly)""
+                      Lines=""Implementation output""
+                      Overwrite=""true"" />
+    <WriteLinesToFile File=""@(IntermediateRefAssembly)""
+                      Lines=""Reference output""
+                      Overwrite=""true""
+                      Condition=""'@(IntermediateRefAssembly)' != '' and !Exists('@(IntermediateRefAssembly)')"" />
+  </Target>
+</Project>");
+        }
     }
 }

src/Tasks/Microsoft.Common.CurrentVersion.targets

@@ -4913,6 +4913,7 @@ Copyright (C) Microsoft Corporation. All rights reserved.
       <CopyBuildOutputToOutputDirectory Condition="'$(CopyBuildOutputToOutputDirectory)'==''">true</CopyBuildOutputToOutputDirectory>
       <CopyOutputSymbolsToOutputDirectory Condition="'$(CopyOutputSymbolsToOutputDirectory)'==''">true</CopyOutputSymbolsToOutputDirectory>
       <CopyDocumentationFileToOutputDirectory Condition="'$(CopyDocumentationFileToOutputDirectory)'==''">true</CopyDocumentationFileToOutputDirectory>
+      <_WroteMainAssemblyToOutputDirectory>false</_WroteMainAssemblyToOutputDirectory>
     </PropertyGroup>
 
     <!-- Copy the build product (.dll or .exe). -->
@@ -4931,6 +4932,7 @@ Copyright (C) Microsoft Corporation. All rights reserved.
 
       <Output TaskParameter="DestinationFiles" ItemName="MainAssembly"/>
       <Output TaskParameter="DestinationFiles" ItemName="FileWrites"/>
+      <Output TaskParameter="WroteAtLeastOneFile" PropertyName="_WroteMainAssemblyToOutputDirectory"/>
 
     </Copy>
 
@@ -4948,6 +4950,21 @@ Copyright (C) Microsoft Corporation. All rights reserved.
 
     <Message Importance="High" Text="$(MSBuildProjectName) -&gt; @(MainAssembly->'%(FullPath)')" Condition="'$(CopyBuildOutputToOutputDirectory)' == 'true' and '$(SkipCopyBuildProduct)'!='true'" />
 
+    <!--
+      If this project produces reference assemblies and its implementation assembly changed,
+      subsequent builds of projects that depend on it may need to copy the updated implementation.
+      Touch the marker considered by those projects' up-to-date checks. This is separate from
+      _CopyFilesMarkedCopyLocal so implementation-only changes can advance the marker even when
+      no copy-local references were copied.
+    -->
+    <Touch Files="@(CopyUpToDateMarker)"
+      AlwaysCreate="true"
+      Condition="'$(ProduceReferenceAssembly)' == 'true' and '$(_WroteMainAssemblyToOutputDirectory)' == 'true'" />
+
+    <ItemGroup Condition="'$(ProduceReferenceAssembly)' == 'true'">
+      <FileWrites Include="@(CopyUpToDateMarker)" />
+    </ItemGroup>
+
     <!-- Copy the additional modules. -->
     <Copy
         SourceFiles="@(AddModules)"