Problem

The cpp-libp2p repository was failing to build on modern systems due to CMake compatibility issues with several Hunter package dependencies. These packages had outdated CMake configurations that required CMake < 3.5, but modern CMake versions have removed support for that compatibility level.

Root Cause

Multiple Hunter packages were using outdated CMake configurations:

• Protobuf (3.19.4-p0)
• c-ares (1.14.0-p0)
• yaml-cpp (0.6.2-0f9a586-p1)
• Boost.DI (1.1.0-p1)

These packages contained cmake_minimum_required(VERSION < 3.5) statements that are incompatible with modern CMake versions.

Solution

Updated the Hunter configuration in cmake/Hunter/config.cmake to add custom configurations for each problematic dependency with the CMAKE_POLICY_VERSION_MINIMUM=3.5 flag. This ensures compatibility with modern CMake versions while maintaining the existing package versions.

Changes Made

cmake/Hunter/config.cmake

• Added custom hunter_config for Protobuf with CMake compatibility flags
• Added custom hunter_config for c-ares with CMake compatibility flags
• Added custom hunter_config for yaml-cpp with CMake compatibility flags
• Added custom hunter_config for Boost.DI with CMake compatibility flags

CMakeLists.txt

• Added CMake policy settings to handle compatibility with older dependencies
• Set CMP0144 and CMP0000 policies for better compatibility

Testing

• Clean build from scratch successful
• All dependencies resolved successfully
• Project compiles without errors
• All test targets build successfully
• Examples build successfully

Before/After

Before: Build failed with errors like:

CMake Error at CMakeLists.txt:1 (cmake_minimum_required):
  Compatibility with CMake < 3.5 has been removed from CMake.

After: Build completes successfully with all targets compiled.

Impact

• Build Success: Repository now builds successfully on modern systems
• Developer Experience: Developers can clone and build the project without CMake errors
• CI/CD Compatibility: Build systems with modern CMake versions will work correctly
• No Breaking Changes: Maintains existing functionality while fixing compatibility

Related Issues

This fix addresses build failures that were preventing users from compiling the cpp-libp2p library on systems with current CMake versions.

Notes

• No changes to the actual library code or functionality
• Only affects the build system configuration
• Maintains backward compatibility with existing Hunter package versions
• Follows Hunter package manager best practices for custom configurations