Avoid file io (#199)

Author: SimonCropp

buildTransitive/EmptyFiles.targets

@@ -0,0 +1,32 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project>
+  <PropertyGroup>
+    <EmptyFilesSourcePath>$(MSBuildThisFileDirectory)..\files</EmptyFilesSourcePath>
+  </PropertyGroup>
+
+  <Target Name="CopyEmptyFilesIncremental"
+          AfterTargets="Build"
+          Condition="$(DesignTimeBuild) != true"
+          Inputs="$(MSBuildThisFileFullPath)"
+          Outputs="$(IntermediateOutputPath)EmptyFiles.copied">
+
+    <PropertyGroup>
+      <EmptyFilesTargetPath>$(TargetDir)EmptyFiles</EmptyFilesTargetPath>
+      <EmptyFilesMarker>$(IntermediateOutputPath)EmptyFiles.copied</EmptyFilesMarker>
+    </PropertyGroup>
+
+    <ItemGroup>
+      <EmptyFilesToCopy Include="$(EmptyFilesSourcePath)\**\*.*" />
+    </ItemGroup>
+
+    <Message Text="Copying EmptyFiles to $(EmptyFilesTargetPath)" Importance="high" />
+
+    <MakeDir Directories="$(EmptyFilesTargetPath)" />
+
+    <Copy SourceFiles="@(EmptyFilesToCopy)"
+          DestinationFiles="@(EmptyFilesToCopy->'$(EmptyFilesTargetPath)\%(RecursiveDir)%(Filename)%(Extension)')"
+          SkipUnchangedFiles="true" />
+
+    <Touch Files="$(EmptyFilesMarker)" AlwaysCreate="true" />
+  </Target>
+</Project>

src/Directory.Build.props

@@ -2,7 +2,7 @@
 <Project>
   <PropertyGroup>
     <NoWarn>CS1591;CS0649;NU5119;NU1608;NU1109</NoWarn>
-    <Version>8.17.0</Version>
+    <Version>8.17.1</Version>
     <LangVersion>preview</LangVersion>
     <AssemblyVersion>1.0.0</AssemblyVersion>
     <Description>A collection of minimal binary files.</Description>

src/EmptyFiles.slnx

@@ -1,6 +1,7 @@
 <Solution>
   <Folder Name="/Solution Items/">
     <File Path="../.gitattributes" />
+    <File Path="../buildTransitive/EmptyFiles.targets" />
     <File Path="../readme.md" />
     <File Path=".editorconfig" />
     <File Path="appveyor.yml" />

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

src/EmptyFiles/EmptyFiles.csproj

@@ -12,9 +12,9 @@
     <PackageReference Include="System.ValueTuple" Condition="'$(TargetFramework)' == 'net462'"  />
     <PackageReference Include="Polyfill" PrivateAssets="all" />
     <PackageReference Include="Microsoft.Sbom.Targets" PrivateAssets="all" />
-    <None Include="..\EmptyFiles.targets" Pack="True" PackagePath="build\EmptyFiles.targets" CopyToOutputDirectory="PreserveNewest" />
-    <None Include="..\EmptyFiles.targets" Pack="True" PackagePath="buildTransitive\EmptyFiles.targets" CopyToOutputDirectory="PreserveNewest" />
-    <None Include="$(ProjectDir)..\..\files\**\empty.*">
+    <None Include="$(SolutionDir)..\buildTransitive\EmptyFiles.targets" Pack="True" PackagePath="build\EmptyFiles.targets" CopyToOutputDirectory="PreserveNewest" />
+    <None Include="$(SolutionDir)..\buildTransitive\EmptyFiles.targets" Pack="True" PackagePath="buildTransitive\EmptyFiles.targets" CopyToOutputDirectory="PreserveNewest" />
+    <None Include="$(SolutionDir)..\files\**\empty.*">
       <Pack>true</Pack>
       <PackagePath>files</PackagePath>
     </None>

src/Tests/Tests.csproj

@@ -16,5 +16,5 @@
     <Using Include="NUnit.Framework.Legacy.ClassicAssert" Static="True" />
     <Using Include="NUnit.Framework.Assert" Static="True" />
   </ItemGroup>
-  <Import Project="$(ProjectDir)..\EmptyFiles.targets" />
+  <Import Project="$(SolutionDir)..\buildTransitive\EmptyFiles.targets" />
 </Project>