Resolving Dependency Conflicts in Conan 2.0: libcurl Version Override Guide

Resolving dependency version conflicts in Conan 2.0 requires using the override feature to force a single package reference across the dependency graph. When libraries like cpr/1.14.1 and prometheus-cpp/1.3.0 require different versions of libcurl, you can explicitly resolve the conflict by overriding libcurl with a compatible version using the --override attribute in your conan install command, allowing both pre-compiled libraries to work without rebuilding.

Contents

• Understanding Dependency Version Conflicts in Conan 2.0
• The Override Solution for libcurl Conflicts
• Step-by-Step Implementation
• Alternative Resolution Strategies
• Best Practices for Managing Dependencies
• Conclusion

Understanding Dependency Version Conflicts in Conan 2.0

Dependency version conflicts in Conan 2.0 occur when two packages in a dependency graph require different versions of the same dependency. This is a common scenario in C++ projects where libraries may have been developed with different versions of shared dependencies. The specific case mentioned involves cpr/1.14.1 requiring libcurl/8.12.Z while prometheus-cpp/1.3.0 requires libcurl/8.10.Z.

When Conan encounters this situation, it reports a version conflict and refuses to install the packages. The official Conan documentation explains that “When two packages in a dependency graph require different versions of the same dependency, Conan reports a version conflict and refuses to install.” This is because Conan cannot automatically determine which version to use without causing potential compatibility issues.

The Override Solution for libcurl Conflicts

The most effective way to resolve this specific libcurl conflict in Conan 2.0 is by using the override feature. This approach allows you to force a single package reference for the entire dependency graph, telling Conan to use the same binary for every consumer regardless of the version requested by individual recipes.

The official Conan FAQ recommends “Use Conan’s override feature to force a single package reference for the entire dependency graph. By overriding libcurl you tell Conan to use the same binary for every consumer, regardless of the version requested by the individual recipes.” This solution is particularly effective when the two libraries are binary-compatible with the chosen libcurl version, allowing the install to succeed without rebuilding anything.

Step-by-Step Implementation

To implement the override solution for resolving dependency version conflicts between cpr/1.14.1 and prometheus-cpp/1.3.0, follow these steps:

1. First, identify the available libcurl versions in your Conan remotes:

conan list "libcurl/*" -r=your-remote-name

2. Determine which libcurl version is compatible with both libraries. In many cases, a newer version (like 8.12.Z) will be backward compatible with requirements for older versions (like 8.10.Z).

3. Use the override option in your conan install command:

conan install . --override=libcurl/8.12.Z

4. If the default remote doesn’t have the required version, specify the remote explicitly:

conan install . --override=libcurl/8.12.Z@user/channel --remote=your-remote

5. Verify that the installation succeeded without conflicts:

conan graph info .

The Stack Overflow discussion provides additional context for troubleshooting if you encounter errors like “Missing prebuilt package for ‘cpr/1.14.1’”.

Alternative Resolution Strategies

While the override approach is often the simplest solution, there are alternative strategies for resolving dependency version conflicts in Conan 2.0:

Using Version Ranges

Modify your recipes to use version ranges for dependencies when possible. As mentioned in a Reddit discussion, “If you’re writing a recipe for conan or any other packaging system you should consider using version ranges for dependencies to avoid conflicts with other libraries.” This approach requires modifying the recipe files for cpr or prometheus-cpp if you have control over them.

System Requirements

For advanced scenarios, Conan 2.0 offers the platform_requires feature that allows you to completely replace dependencies with system-installed packages. The Conan blog post explains that “The ability to completely drop requires defined in any Conan recipe in the dependency graph, and use system installed ones, with the [platform_requires] feature” can be useful in different scenarios, though it requires more configuration.

Rebuilding with a Compatible Version

If you cannot find a compatible libcurl version or prefer not to use overrides, you may need to rebuild one of the libraries with a compatible libcurl version. This approach defeats the purpose of using pre-compiled packages but may be necessary in some cases.

Best Practices for Managing Dependencies

To prevent dependency version conflicts in your Conan 2.0 projects, consider these best practices:

1. Use Virtual Packages: Define virtual packages in your Conan recipes to allow different implementations of the same functionality without version conflicts.

2. Semantic Versioning: Ensure your dependencies follow semantic versioning practices to make version compatibility more predictable.

3. Dependency Scanning: Regularly scan your dependency graph for potential conflicts using conan graph info and conan graph export.

4. Centralized Configuration: Use conanfile.py or conanfile.txt to define dependency versions centrally rather than hardcoding them in multiple places.

5. Version Range Support: Whenever possible, use version ranges in your requirements to be more flexible with dependency versions.

6. Regular Updates: Keep your dependencies updated to the latest compatible versions to benefit from bug fixes and security patches.

Conclusion

Resolving dependency version conflicts in Conan 2.0, particularly when dealing with pre-compiled libraries like cpr/1.14.1 and prometheus-cpp/1.3.0 that require different versions of libcurl, is straightforward using the override feature. By explicitly specifying a compatible libcurl version with the --override option, you can tell Conan to use the same binary across your entire dependency graph without rebuilding anything. This approach maintains the efficiency of pre-compiled packages while resolving version conflicts that would otherwise prevent installation.

For ongoing dependency management, adopting best practices like using version ranges, semantic versioning, and regular dependency scanning can help prevent such conflicts from occurring in the first place. The official Conan documentation provides comprehensive guidance on these topics, and the community offers additional insights through forums and discussions.

Sources

• Dependencies conflicts — conan 2.24.0 documentation
• FAQ — conan 2.24.0 documentation
• c++ - How to resolve conflicting versions of the same library required by two dependencies in Conan 2.0? - Stack Overflow
• r/cpp on Reddit: Conan conflict resolution best practices
• Conan 2 new graph features: replacing dependencies with system requirements and API compatible dependencies