Delete stale EmptyFiles marker when output missing

buildTransitive/EmptyFileTargets.md

@@ -1,18 +1,21 @@
 How it works:
 
  1. Inputs="$(MSBuildThisFileFile)" - Tracks the package file timestamp
- 2. Outputs="$(EmptyFilesMarker)" - Tracks a marker file in the output directory
+ 2. Outputs="$(EmptyFilesMarker)" - Tracks a marker file in the intermediate output directory
  3. MSBuild automatically skips the target if all outputs are newer than all inputs
  4. SkipUnchangedFiles="true" - Additional optimization to skip individual unchanged files
  5. Touch - Updates the marker file timestamp after successful copy
+ 6. DeleteEmptyFilesMarkerIfTargetMissing - If the EmptyFiles directory is missing from the output, deletes the marker file so the copy re-runs
 
 This will only copy files when:
 
  1. The targets is newer than the marker file, OR
- 2. The marker file doesn't exist (first build/clean build)
+ 2. The marker file doesn't exist (first build/clean build), OR
+ 3. The EmptyFiles directory doesn't exist in the output (marker is deleted to force re-copy)
 
 Benefits:
 
  * Dramatically reduces IO on incremental builds
  * Works with dotnet clean (removes marker file)
+ * Recovers when the output directory is cleaned without cleaning the intermediate directory
  * Still respects individual file changes via SkipUnchangedFiles

buildTransitive/EmptyFiles.targets

@@ -4,6 +4,12 @@
     <EmptyFilesSourcePath>$(MSBuildThisFileDirectory)..\files</EmptyFilesSourcePath>
   </PropertyGroup>
 
+  <Target Name="DeleteEmptyFilesMarkerIfTargetMissing"
+          BeforeTargets="CopyEmptyFilesIncremental"
+          Condition="$(DesignTimeBuild) != true AND !Exists('$(TargetDir)EmptyFiles')">
+    <Delete Files="$(IntermediateOutputPath)EmptyFiles.copied" />
+  </Target>
+
   <Target Name="CopyEmptyFilesIncremental"
           AfterTargets="Build"
           Condition="$(DesignTimeBuild) != true"
@@ -29,4 +35,4 @@
 
     <Touch Files="$(EmptyFilesMarker)" AlwaysCreate="true" />
   </Target>
-</Project>
+</Project>

src/Directory.Packages.props

@@ -10,10 +10,12 @@
     <PackageVersion Include="NUnit3TestAdapter" Version="5.2.0" Pinned="true" />
     <PackageVersion Include="ProjectDefaults" Version="1.0.171" />
     <PackageVersion Include="Polyfill" Version="9.8.1" />
+    <PackageVersion Include="ProjectFiles" Version="0.5.0" />
     <PackageVersion Include="System.Memory" Version="4.6.3" />
     <PackageVersion Include="Microsoft.Sbom.Targets" Version="4.1.5" />
     <!-- Keep at 8 to support old frameworks -->
     <PackageVersion Include="System.Collections.Immutable" Version="8.0.0" Pinned="true" />
     <PackageVersion Include="System.ValueTuple" Version="4.5.0" Pinned="true" />
+    <PackageVersion Include="Verify" Version="31.11.0" />
   </ItemGroup>
 </Project>

src/Tests/BuildTargetsTests.cs

@@ -0,0 +1,130 @@
+public class BuildTargetsTests
+{
+    [Test]
+    public async Task BuildCopiesEmptyFiles()
+    {
+        using var temp = new TempDirectory();
+
+        var (nugetSource, packageVersion) = FindPackageInfo();
+        WriteCsproj(temp, packageVersion);
+        WriteNugetConfig(temp, nugetSource);
+
+        var exitCode = await DotnetBuild(temp);
+        That(exitCode, Is.EqualTo(0));
+
+        var emptyFilesDir = Path.Combine(temp.Path, "bin", "Release", "net10.0", "EmptyFiles");
+        That(Directory.Exists(emptyFilesDir), Is.True, "EmptyFiles directory should exist after build");
+        That(Directory.GetFiles(emptyFilesDir, "*", SearchOption.AllDirectories), Is.Not.Empty, "EmptyFiles directory should contain files");
+    }
+
+    [Test]
+    public async Task RecoverFromDeletedEmptyFilesDirectory()
+    {
+        using var temp = new TempDirectory();
+
+        var (nugetSource, packageVersion) = FindPackageInfo();
+        WriteCsproj(temp, packageVersion);
+        WriteNugetConfig(temp, nugetSource);
+
+        // First build
+        var exitCode = await DotnetBuild(temp);
+        That(exitCode, Is.EqualTo(0));
+
+        var emptyFilesDir = Path.Combine(temp.Path, "bin", "Release", "net10.0", "EmptyFiles");
+        That(Directory.Exists(emptyFilesDir), Is.True, "EmptyFiles directory should exist after first build");
+
+        // Delete EmptyFiles directory from output (leave obj/ intact so marker file survives)
+        Directory.Delete(emptyFilesDir, true);
+        That(Directory.Exists(emptyFilesDir), Is.False);
+
+        // Second build — should recover
+        exitCode = await DotnetBuild(temp);
+        That(exitCode, Is.EqualTo(0));
+
+        That(Directory.Exists(emptyFilesDir), Is.True, "EmptyFiles directory should exist after second build");
+        That(Directory.GetFiles(emptyFilesDir, "*", SearchOption.AllDirectories), Is.Not.Empty, "EmptyFiles directory should contain files after recovery");
+    }
+
+    static void WriteCsproj(TempDirectory temp, string version)
+    {
+        var csproj = $"""
+            <Project Sdk="Microsoft.NET.Sdk">
+              <PropertyGroup>
+                <TargetFramework>net10.0</TargetFramework>
+                <RestorePackagesPath>packages</RestorePackagesPath>
+              </PropertyGroup>
+              <ItemGroup>
+                <PackageReference Include="EmptyFiles" Version="{version}" />
+              </ItemGroup>
+            </Project>
+            """;
+        File.WriteAllText(Path.Combine(temp.Path, "Project.csproj"), csproj);
+    }
+
+    static void WriteNugetConfig(TempDirectory temp, string nugetSource)
+    {
+        var config = $"""
+            <?xml version="1.0" encoding="utf-8"?>
+            <configuration>
+              <packageSources>
+                <clear />
+                <add key="local" value="{nugetSource}" />
+              </packageSources>
+            </configuration>
+            """;
+        File.WriteAllText(Path.Combine(temp.Path, "nuget.config"), config);
+    }
+
+    static async Task<int> DotnetBuild(TempDirectory temp)
+    {
+        var startInfo = new ProcessStartInfo("dotnet", "build --configuration Release --disable-build-servers -nodeReuse:false /p:UseSharedCompilation=false")
+        {
+            WorkingDirectory = temp.Path,
+            RedirectStandardOutput = true,
+            RedirectStandardError = true,
+            UseShellExecute = false,
+            CreateNoWindow = true,
+        };
+
+        using var process = Process.Start(startInfo)!;
+        var stdout = await process.StandardOutput.ReadToEndAsync();
+        var stderr = await process.StandardError.ReadToEndAsync();
+        await process.WaitForExitAsync();
+
+        await TestContext.Out.WriteLineAsync("STDOUT:");
+        await TestContext.Out.WriteLineAsync(stdout);
+        await TestContext.Out.WriteLineAsync("STDERR:");
+        await TestContext.Out.WriteLineAsync(stderr);
+
+        return process.ExitCode;
+    }
+
+    static (string nugetSource, string packageVersion) FindPackageInfo()
+    {
+        var nugetSource = FindNugetSource();
+        var packageVersion = FindPackageVersion(nugetSource);
+        return (nugetSource, packageVersion);
+    }
+
+    static string FindNugetSource()
+    {
+        var nugetsDir = Path.GetFullPath(Path.Combine(ProjectFiles.SolutionDirectory, "..", "nugets"));
+        if (Directory.Exists(nugetsDir))
+        {
+            return nugetsDir;
+        }
+
+        throw new InvalidOperationException($"Cannot find nugets directory at {nugetsDir}");
+    }
+
+    static string FindPackageVersion(string nugetSource)
+    {
+        var nupkg = Directory
+            .GetFiles(nugetSource, "EmptyFiles.*.nupkg")
+            .FirstOrDefault(_ => !Path.GetFileName(_).StartsWith("EmptyFiles.Tool")) ??
+                    throw new InvalidOperationException($"Cannot find EmptyFiles nupkg in {nugetSource}");
+
+        var fileName = Path.GetFileNameWithoutExtension(nupkg);
+        return fileName["EmptyFiles.".Length..];
+    }
+}

src/Tests/GlobalUsings.cs

@@ -1,3 +1,5 @@
 global using EmptyFiles;
 global using NUnit.Framework;
-global using System.Collections.Immutable;
+global using System.Collections.Immutable;
+global using System.Diagnostics;
+global using System.Runtime.InteropServices;

src/Tests/Tests.cs

@@ -213,7 +213,7 @@ public void UseFile()
     [Test]
     public async Task WriteExtensions()
     {
-        var md = Path.Combine(SolutionDirectoryFinder.Find(), "extensions.include.md");
+        var md = Path.Combine(ProjectFiles.SolutionDirectory, "extensions.include.md");
         File.Delete(md);
         await using var writer = File.CreateText(md);
         await WriteCategory(writer, "Archive", AllFiles.Archives);

src/Tests/Tests.csproj

@@ -12,6 +12,8 @@
     <PackageReference Include="NUnit" />
     <PackageReference Include="NUnit3TestAdapter" />
     <PackageReference Include="ProjectDefaults" PrivateAssets="all" />
+    <PackageReference Include="ProjectFiles" />
+    <PackageReference Include="Verify" />
     <ProjectReference Include="..\EmptyFiles\EmptyFiles.csproj" />
     <Using Include="NUnit.Framework.Legacy.ClassicAssert" Static="True" />
     <Using Include="NUnit.Framework.Assert" Static="True" />