Understanding VS_DOTNET_REFERENCES_COPY_LOCAL in CMake: Streamlining .NET Reference Deployment

Purpose

• Applies to assemblies specified as .NET hint references.
• Controls whether .NET assemblies referenced by your project are copied alongside your executable during the build process.

Functionality

• When set to OFF:

  • CMake doesn't copy the assemblies.
  • Your application needs to locate the assemblies elsewhere at runtime, typically in the GAC or a specific directory you've configured.

• When set to ON (default behavior):

  • CMake instructs Visual Studio to copy the referenced assemblies to the output directory where your executable is placed.
  • This ensures that the assemblies are readily available at runtime, even if they are not installed in the Global Assembly Cache (GAC).

Usage

1. CMake version requirement
   This property is available in CMake versions 3.8 and later.
2. Target configuration
   
   • Use the set_target_properties command:

     set_target_properties(your_target_name PROPERTIES VS_DOTNET_REFERENCES_COPY_LOCAL OFF)
     

     • Replace your_target_name with the actual name of your target.
     • Set the value to ON or OFF as needed.

Considerations

• If you're unsure, keeping it ON (default) is generally safe.
• Be aware of potential runtime issues if assemblies are not readily accessible.
• Disabling copying (setting to OFF) might be suitable if:
  • Assemblies are already part of a shared framework or globally available.
  • You want more control over assembly deployment.

find_package(DotNet REQUIRED)  # Assuming you've configured DotNet usage

add_executable(my_app main.cpp)
target_link_libraries(my_app PRIVATE MyLibrary.dll)  # Example .NET reference

# Set to OFF to avoid copying MyLibrary.dll during build
set_target_properties(my_app PROPERTIES VS_DOTNET_REFERENCES_COPY_LOCAL OFF)

---

Scenario 1: Copying Assemblies by Default (ON)

This is the most common scenario where you want CMake to handle copying assemblies during the build process. No additional configuration is needed:

find_package(DotNet REQUIRED)

add_executable(my_app main.cpp)
target_link_libraries(my_app PRIVATE MyLibrary.dll AnotherAssembly.dll)

# VS_DOTNET_REFERENCES_COPY_LOCAL is implicitly ON by default
# Assemblies (MyLibrary.dll and AnotherAssembly.dll) will be copied
# to the output directory along with your executable (my_app.exe).

Scenario 2: Explicitly Disabling Copying (OFF)

If you know the assemblies are already available in the GAC or a specific location, you can disable copying:

find_package(DotNet REQUIRED)

add_executable(my_app main.cpp)
target_link_libraries(my_app PRIVATE MyLibrary.dll AnotherAssembly.dll)

set_target_properties(my_app PROPERTIES VS_DOTNET_REFERENCES_COPY_LOCAL OFF)

# Assemblies won't be copied. Ensure they are accessible at runtime
# through the GAC or a configured path.

Scenario 3: Conditional Copying Based on Configuration

You might want to control copying behavior based on your build configuration (e.g., Debug vs. Release):

find_package(DotNet REQUIRED)

add_executable(my_app main.cpp)
target_link_libraries(my_app PRIVATE MyLibrary.dll AnotherAssembly.dll)

if(CMAKE_BUILD_TYPE STREQUAL "Debug")
  set_target_properties(my_app PROPERTIES VS_DOTNET_REFERENCES_COPY_LOCAL ON)
else()
  set_target_properties(my_app PROPERTIES VS_DOTNET_REFERENCES_COPY_LOCAL OFF)
endif()

# In Debug configuration, assemblies will be copied.
# In Release configuration, they won't be copied.

---

1. • Instead of relying on CMake to copy the assemblies during the build process, you can manage their deployment manually. This involves:
     • Copying the required .NET assemblies to a specific directory within your project or a designated deployment location.
     • Configuring your application to locate the assemblies at runtime. This might involve setting environment variables or using configuration files that specify the assembly paths.

2. Packaging Tools
   

   • Utilize packaging tools like NuGet to manage dependencies.
     • Create a .nuspec file that specifies your project's dependencies on the .NET assemblies.
     • During the build process, use tools like nuget.exe to create a NuGet package that includes your executable and the referenced assemblies.
     • Deploy the NuGet package, which can be installed on target machines to ensure all necessary components are present.

3. GAC (Global Assembly Cache)
   

   • If your application's .NET references are intended to be shared by multiple applications on the same machine, consider installing them in the Global Assembly Cache (GAC).
     • This requires administrative privileges during the installation process.
     • Be mindful that over-reliance on the GAC can lead to dependency conflicts between different applications.

Choosing the Right Approach

The best approach depends on your project's specific requirements and deployment strategy. Here are some general considerations:

• Control and Customization
  Manual deployment provides the most control over where assemblies are placed and how your application locates them. However, it requires more manual effort during the deployment process.
• Target Environment
  If your application is meant to be deployed on various environments with varying levels of access control, managing NuGet packages might be more suitable than relying on the GAC.
• Project Size and Complexity
  For smaller projects with few dependencies, manual deployment might be sufficient. However, for larger projects or those with complex dependency management, packaging tools like NuGet offer a more scalable and maintainable solution.