.

Author: SimonCropp

buildTransitive/EmptyFiles.targets

@@ -1,9 +1,25 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Project>
-  <ItemGroup Condition="$(DesignTimeBuild) != true">
-    <ContentWithTargetPath
-       Include="$(MSBuildThisFileDirectory)..\files\**\*.*"
-       CopyToOutputDirectory="PreserveNewest"
-       TargetPath="EmptyFiles\%(RecursiveDir)%(Filename)%(Extension)" />
-  </ItemGroup>
+  <PropertyGroup>
+    <EmptyFilesSourcePath>$(MSBuildThisFileDirectory)..\files</EmptyFilesSourcePath>
+    <EmptyFilesTargetPath>$(OutDir)EmptyFiles</EmptyFilesTargetPath>
+    <EmptyFilesMarker>$(EmptyFilesTargetPath)\.copied</EmptyFilesMarker>
+  </PropertyGroup>
+
+  <Target Name="CopyEmptyFilesIncremental"
+          BeforeTargets="Build"
+          Condition="$(DesignTimeBuild) != true"
+          Inputs="$(MSBuildThisFileFile)"
+          Outputs="$(EmptyFilesMarker)">
+
+    <ItemGroup>
+      <EmptyFilesToCopy Include="$(EmptyFilesSourcePath)\**\*.*" />
+    </ItemGroup>
+
+    <Copy SourceFiles="@(EmptyFilesToCopy)"
+          DestinationFiles="@(EmptyFilesToCopy->'$(EmptyFilesTargetPath)\%(RecursiveDir)%(Filename)%(Extension)')"
+          SkipUnchangedFiles="true" />
+
+    <Touch Files="$(EmptyFilesMarker)" AlwaysCreate="true" />
+  </Target>
 </Project>

src/EmptyFiles/EmptyFileTargets.md

@@ -0,0 +1,18 @@
+How it works:
+
+ 1. Inputs="$(MSBuildThisFileFile)" - Tracks the package file timestamp
+ 2. Outputs="$(EmptyFilesMarker)" - Tracks a marker file in the 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
+
+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)
+
+Benefits:
+
+ * Dramatically reduces IO on incremental builds
+ * Works with dotnet clean (removes marker file)
+ * Still respects individual file changes via SkipUnchangedFiles