Optimizing CMake Projects: Controlling Library Search Paths with CMP0142

What is CMP0142?

CMP0142 is a policy that affects how the Xcode generator in CMake handles library search paths. It controls whether the generator appends per-configuration suffixes to these paths.

What does it do?

• New Behavior (CMake 3.25 and above)
  

  • CMP0142 introduces the new behavior where the Xcode generator no longer appends these suffixes.
  • This aligns with modern CMake's handling of per-configuration directories and avoids unnecessary warnings.
• • The Xcode generator would prepend each library search path entry with a copy of itself, modified with $(CONFIGURATION) (build configuration) and $(EFFECTIVE_PLATFORM_NAME) (platform name) variables.
  • This behavior originated from earlier CMake versions where per-configuration directories weren't well-represented.
  • The resulting paths often didn't exist, leading to warnings from the toolchain.

Why was this policy introduced?

• The new behavior is more streamlined and avoids these issues, reflecting the improved handling of per-configuration directories in CMake.
• The old behavior could lead to warnings from the toolchain due to non-existent paths.

How to control CMP0142

• Alternatively, you can use cmake_minimum_required with a version that's at least 3.25. This will implicitly enable the new behavior for CMP0142 if it's not explicitly set.
• You can use the cmake_policy command to explicitly set CMP0142 to either OLD or NEW behavior.

Recommendation

• It's generally recommended to use the new behavior (CMP0142:NEW) for projects targeting CMake 3.25 and above to avoid unnecessary warnings and benefit from the improved handling of per-configuration directories.

In summary,

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Explicitly setting CMP0142 with cmake_policy

# Use the new behavior (recommended for CMake 3.25+)
cmake_policy(SET CMP0142 NEW)

project(MyProject)
# ... rest of your project code

Implicitly enabling new behavior with cmake_minimum_required

cmake_minimum_required(VERSION 3.25)  # Requires CMake 3.25 or later

project(MyProject)
# ... rest of your project code

This approach utilizes the fact that cmake_minimum_required with a version at least 3.25 will implicitly enable the new behavior for CMP0142 unless explicitly set otherwise.

Using the old behavior (not recommended)

# Only use this if you have a specific reason to maintain compatibility with older CMake versions
cmake_policy(SET CMP0142 OLD)

project(MyProject)
# ... rest of your project code

• While the old behavior might be necessary for compatibility with very old CMake versions, it's generally recommended to use the new behavior (CMP0142:NEW) to avoid potential warnings and benefit from the improved handling of per-configuration directories.

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1. • If you need to control library search paths for specific targets, the target_link_directories command offers a more targeted approach than relying on CMP0142.
   • This allows you to define search paths specific to a target, potentially with different paths depending on the build configuration.

2. Setting Library Search Paths Manually
   

   • If you have complete control over the build environment and libraries, you might consider setting the library search paths directly using environment variables or command-line arguments specific to your build system.
   • However, this approach can lead to less portable CMakeLists.txt files.

Remember

• The recommended approach is to leverage the new behavior of CMP0142 (not appending suffixes) for CMake 3.25 and above to avoid unnecessary warnings and maintain alignment with modern CMake practices.
• CMP0142 is primarily about the Xcode generator's behavior. It doesn't necessarily control how other generators (e.g., Makefiles) handle library search paths.

Additional Considerations

• Consulting CMake documentation on target_link_directories, finding libraries, and custom build rules might provide more insights into managing library search paths effectively.
• If you're working with a complex build system or need very specific control over library search paths, exploring advanced CMake techniques like using custom build rules or finding libraries might be necessary.