including-generated-files

name	including-generated-files
description	Fix MSBuild targets that generate files during the build but those files are missing from compilation or output. USE FOR: generated source files not compiling (CS0246 for a type that should exist), custom build tasks that create files but they are invisible to subsequent targets, globs not capturing build-generated files because they expand at evaluation time before execution creates them, ensuring generated files are cleaned by the Clean target. Covers correct BeforeTargets timing (CoreCompile, BeforeBuild, AssignTargetPaths), adding to Compile/FileWrites item groups, using $(IntermediateOutputPath) instead of hardcoded obj/ paths. DO NOT USE FOR: C# source generators that already work via the Roslyn pipeline, T4 design-time generation that runs in Visual Studio, non-MSBuild build systems.
license	MIT

Including Generated Files Into Your Build

Overview

Files generated during the build are generally ignored by the build process. This leads to confusing results such as:

• Generated files not being included in the output directory
• Generated source files not being compiled
• Globs not capturing files created during the build

This happens because of how MSBuild's build phases work.

Quick Takeaway

For code files generated during the build - we need to add those to Compile and FileWrites item groups within the target generating the file(s):

  <ItemGroup>
    <Compile Include="$(GeneratedFilePath)" />
    <FileWrites Include="$(GeneratedFilePath)" />
  </ItemGroup>

The target generating the file(s) should be hooked before CoreCompile and BeforeCompile targets - BeforeTargets="CoreCompile;BeforeCompile"

Why Generated Files Are Ignored

For detailed explanation, see How MSBuild Builds Projects.

Evaluation Phase

MSBuild reads your project, imports everything, creates Properties, expands globs for Items outside of Targets, and sets up the build process.

Execution Phase

MSBuild runs Targets & Tasks with the provided Properties & Items to perform the build.

Key Takeaway: Files generated during execution don't exist during evaluation, therefore they aren't found. This particularly affects files that are globbed by default, such as source files (.cs).

Solution: Manually Add Generated Files

When files are generated during the build, manually add them into the build process. The approach depends on the type of file being generated.

Use $(IntermediateOutputPath) for Generated File Location

Always use $(IntermediateOutputPath) as the base directory for generated files. Do not hardcode obj\ or construct the intermediary path manually (e.g., obj\$(Configuration)\$(TargetFramework)\). The intermediate output path can be redirected to a different location in some build configurations (e.g., shared output directories, CI environments). Using $(IntermediateOutputPath) ensures your target works correctly regardless of the actual path.

Always Add Generated Files to FileWrites

Every generated file should be added to the FileWrites item group. This ensures that MSBuild's Clean target properly removes your generated files. Without this, generated files will accumulate as stale artifacts across builds.

<ItemGroup>
  <FileWrites Include="$(IntermediateOutputPath)my-generated-file.xyz" />
</ItemGroup>

Basic Pattern (Non-Code Files)

For generated files that need to be copied to output (config files, data files, etc.), add them to Content or None items before BeforeBuild:

<Target Name="IncludeGeneratedFiles" BeforeTargets="BeforeBuild">
  
  <!-- Your logic that generates files goes here -->

  <ItemGroup>
    <None Include="$(IntermediateOutputPath)my-generated-file.xyz" CopyToOutputDirectory="PreserveNewest"/>
    
    <!-- Capture all files of a certain type with a glob -->
    <None Include="$(IntermediateOutputPath)generated\*.xyz" CopyToOutputDirectory="PreserveNewest"/>

    <!-- Register generated files for proper cleanup -->
    <FileWrites Include="$(IntermediateOutputPath)my-generated-file.xyz" />
    <FileWrites Include="$(IntermediateOutputPath)generated\*.xyz" />
  </ItemGroup>
</Target>

For Generated Source Files (Code That Needs Compilation)

If you're generating .cs files that need to be compiled, use BeforeTargets="CoreCompile;BeforeCompile". This is the correct timing for adding Compile items — it runs late enough that the file generation has occurred, but before the compiler runs. Using BeforeBuild is too early for some scenarios and may not work reliably with all SDK features.

<Target Name="IncludeGeneratedSourceFiles" BeforeTargets="CoreCompile;BeforeCompile">
  <PropertyGroup>
    <GeneratedCodeDir>$(IntermediateOutputPath)Generated\</GeneratedCodeDir>
    <GeneratedFilePath>$(GeneratedCodeDir)MyGeneratedFile.cs</GeneratedFilePath>
  </PropertyGroup>

  <MakeDir Directories="$(GeneratedCodeDir)" />

  <!-- Your logic that generates the .cs file goes here -->

  <ItemGroup>
    <Compile Include="$(GeneratedFilePath)" />
    <FileWrites Include="$(GeneratedFilePath)" />
  </ItemGroup>
</Target>

Note: Specifying both CoreCompile and BeforeCompile ensures the target runs before whichever target comes first, providing robust ordering regardless of customizations in the build.

Target Timing

Choose the BeforeTargets value based on the type of file being generated:

• BeforeTargets="BeforeBuild" — For non-code files added to None or Content. Runs early enough for copy-to-output scenarios.
• BeforeTargets="CoreCompile;BeforeCompile" — For generated source files added to Compile. Ensures the file is included before the compiler runs.
• BeforeTargets="AssignTargetPaths" — The "final stop" before None and Content items (among others) are transformed into new items. Use as a fallback if BeforeBuild is too early.

Globbing Behavior

Globs behave according to when the glob took place:

Glob Location	Files Captured
Outside of a target	Only files visible during Evaluation phase (before build starts)
Inside of a target	Files visible when the target runs (can capture generated files if timed correctly)

This is why the solution places the <ItemGroup> inside a <Target> - the glob runs during execution when the generated files exist.

Relevant Links

• How MSBuild Builds Projects
• Evaluation Phase
• Execution Phase
• Common Item Types
• How the SDK imports items by default
• Official docs: Handle generated files