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Consuming recipes

Recipes in this repository are evolving continuously, contributors are creating pull-requests fixing issues and adding new features every day. It is expected that from time to time these new recipe revisions stop to work in your project.

Contents

Breaking changes

There can be several root causes if a recipe (a new revision) stopped to work in your project:

  • Fixes in recipes that modify the libraries they are creating: exported symbols, compiler flags, generated files for your build system, CMake target names,...

    Every contributor tries to do their best and reviewers do an amazing work checking that the changes are really improving recipes.

  • New Conan features (breaking syntax): sometimes Conan introduces a new feature that requires new attributes or statements in recipes. If your Conan client is not new enough, Conan will fail to parse the recipe and will raise a cryptic Python syntax error.

    This use case is covered by the required_conan_version feature. It will substitute the syntax error by one nicer error provided by Conan client.

  • New Conan features: Conan keeps evolving and adding new features in its road to Conan v2, and ConanCenter is committed in this roadmap as well, and tries to push the user base to these new features in order to ease the migration to new versions.

    New recipe revisions can take into account changes that are introduced in new Conan client version, sometimes these changes modify some experimental behavior without modifying recipe syntax.

    When these changes are in the critical path to Conan v2 we can introduce the required_conan_version statement to be sure that people using these new experimental features are using the required Conan version and testing the actual behavior of those features (feedback about them is very important to Conan).

Isolate your project from upstream changes

There are two main ways you can isolate your project from changes in recipes:

  • Cache recipes in your own Artifactory: your project should use only this remote and new recipe revisions are only pushed to your Artifactory after they have been validated in your project.
  • Pin the version of every reference you consume in your project using recipe revisions and lockfiles.

Use your own Artifactory instance

Using your own Artifactory instance is not as complicated as it sounds. You can deploy it on-premise or use a cloud provided solution for free.

Once you have configured your Artifactory instance, you should ensure that your project is using only that remote (conan remote list). Conan makes it easy to use different configurations per project (check CONAN_USER_HOME env variable) or to store the configuration in some external file or repository so you can shared and install it using one command (conan config install ...).

Use recipe revisions and lockfiles

If you don't want to deploy and maintain your own Artifactory instance, you can isolate from changes in upstream recipes in ConanCenter using recipe revisions and lockfiles (please, read linked Conan documentation for more detailed explanation).

Recipe revisions and lockfiles can be used to define exactly the binary you want to use in your project. Nothing is removed from ConanCenter, even if the recipe is modified and new binaries are generated for the same configurations, existing binaries are still there, you just need to instruct Conan to use them even if new ones are available.

Recipe revisions are the way to tell Conan to use a specific snapshot of the recipe. It is a hash added to the reference and can be used in Conan at the same place as regular revisions:

  • In the command line:

    conan install openssl/3.0.1@#1955937e88f13a02aa4fdae98c3f9fb8

  • In a conanfile.txt file:

    [requires]
openssl/3.0.1@#1955937e88f13a02aa4fdae98c3f9fb8

If you use explicit recipe revisions in your project you can be sure that Conan will always use the same recipe revision of those references. You might get new binaries if the same configuration (same packageID) is built again for the same recipe revision, but that is not going to be a compatibility problem.

This might not be enough for some projects, where you want to be sure nothing is modified, not just the revisions you are listing explicitly but also any other transitive dependency, this is what lockfiles are for.

Lockfiles are files where all the information about requirements is written: recipe revisions, package IDs and package revisions. You can create a lockfile with all the dependencies for your project once you are happy with them, and use that same lockfile with every Conan command. Conan will always build the same graph (the locked one) and will always retrieve the same recipes and binaries.

Then, it would be up to you to generate a new lockfile if you want to introduce new revisions for existing references.

The two basic commands you need to know (full docs here):

  • Create lockfile from conanfile.txt file:

    conan lock create conanfile.txt --lockfile-out=locks/project.lock

  • Consume a lockfile:

    conan install conanfile.txt --lockfile=locks/project.lock

If your project is managing several configurations, you would probably like to have a look to base lockfiles and lockfile bundles in the documentation.

This repository will keep evolving, and Conan will release new features. Even if these breaking changes can cause some disruption, we think that they are needed and they contribute to improve the overall experience in the C++ ecosystem.