why do we put .targets file inside a NuGet package

Including a .targets file inside a NuGet package allows the package to define custom build actions that are automatically integrated into the build process of any project that references the package. This is particularly useful for packages that need to perform specific tasks or configurations when the project is built, such as copying files, running scripts, or setting properties.

Here’s how it works and why it’s beneficial:

How .targets Files in NuGet Packages Work

1. Packaging the .targets File:

   • The .targets file is included in the NuGet package under a specific directory (build or buildTransitive). This file contains MSBuild tasks, properties, and targets that the package author wants to be executed as part of the build process.

2. Installation:

   • When the NuGet package is installed in a project, the .targets file is automatically imported into the project’s build process. This happens because of conventions and mechanisms in the NuGet and MSBuild systems that look for and import these files.

3. Integration:

   • MSBuild automatically imports the .targets files from the build directory of the installed packages. This means any targets, properties, or tasks defined in the .targets file are incorporated into the project’s build process.

Why Pack .targets Files Inside NuGet Packages

1. Automation:

   • It allows package authors to automate repetitive tasks or necessary steps without requiring users to manually configure their projects. For instance, setting up configuration files, copying dependencies, or generating code.

2. Consistency:

   • Ensures that any necessary build steps are consistently applied across all projects that use the package, reducing the chance of errors or omissions.

3. Flexibility:

   • Package authors can include sophisticated build logic that can adapt based on the project’s configuration, making the package more powerful and versatile.

4. Ease of Use:

   • Simplifies the end user’s experience by reducing the need for them to understand or manually implement complex build steps. The users simply install the package, and the necessary build actions are automatically wired up.

Example

Consider a NuGet package that provides a custom tool which needs to be invoked during the build process. The package might include a .targets file to ensure the tool is run as part of the build.

MyTool.targets:

<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <PropertyGroup>
    <MyToolPath>$(MSBuildThisFileDirectory)tools\mytool.exe</MyToolPath>
  </PropertyGroup>
  
  <Target Name="RunMyTool" BeforeTargets="AfterBuild">
    <Exec Command="&quot;$(MyToolPath)&quot; &quot;$(TargetDir)&quot;" />
  </Target>
</Project>

Packing the NuGet Package:

The .targets file is placed in the build directory within the NuGet package:

MyNuGetPackage.nupkg
│
└───build
    └───MyTool.targets
    └───tools
        └───mytool.exe

Using the Package:

When a project installs this NuGet package, the MyTool.targets file is automatically imported, and the RunMyTool target runs after the build completes, executing the mytool.exe with the target directory as a parameter.