Conan migration guide to 2.0

Conan team is working hard on the next major release. We’ve been gathering feedback from the community about our features and we think it’s time to break some default behaviors, clean the codebase and add space for new developments. Development is ongoing and the Conan 2.0 Tribe is having discussions about it.

Conan 2.0-alpha is already released and can be installed from PyPI doing:

$ pip install conan==2.0.0-alpha1

The documentation for 2.0 is still far from being complete, but we are working on it and you can access it with the right version label.

This section summarizes some of the necessary changes during Conan 1.X to be ready to upgrade to Conan 2.0:

Update the syntax of your Conanfile

Use the from conan import ConanFile import instead of the legacy from conans ... (note the plural)
Do not use dictionary expressions in your recipe settings definition (like settings = {"os": ["Windows", "Linux"]}. This way of limiting supported configurations by one recipe will be removed. Use the validate() method instead to raise ConanInvalidConfiguration if strictly necessary to fail fast for unsupported configurations.
Use self.test_requires() to define test requirements instead of the legacy self.build_requires(..., force_host_context).
Move all your packages to lowercase. Uppercase package names (or versions/user/channel) will not be possible in 2.0.

New namespace conan.tools.xxxxx

Use generators and helpers only from conan.tools.xxxx space. All the other ones are going to be removed. Please check the tools section to learn more about the new tools available for Conan 2.0.

Host and build profiles and new cross-building model

Use always build and host profiles. You can enable it by passing -pr:b=default in the command line to most commands. Do not use os_build, arch_build anywhere in your recipes or code.

Conan uses revisions by default in Conan 2.0

Conan 2.0 uses revisions by default and the local cache 2.0 will store multiple recipe and package revisions for your Conan packages (Conan 1.X supports only one revision). To start working with revisions enabled in Conan 1.X, please enable them in your Conan configuration:

$ conan config set general.revisions_enabled=True

self.dependencies to access information about dependencies

Do not use self.deps_cpp_info, self.deps_env_info or self.deps_user_info. Use the self.dependencies access to get information about dependencies.

Commands that disappear in 2.0: copy

Do not use the conan copy command to change user/channel. Packages will be immutable, and this command will dissapear in 2.0. Package promotions are generally done in the server side, copying packages from one server repository to another repository.

Editables don’t use external templates any more. New layout model

If you are using editables, the external template files are going to be removed. Use the layout() method definition instead. Please check the documentation for more information about layouts.

New properties model for the cpp_info in Conan 2.0 generators

Using .names, .filenames and .build_modules will not work any more for new generators, like CMakeDeps and PkgConfigDeps. They have a new way of setting this information using set_property and get_property methods of the cpp_info object (available since Conan 1.36).

def set_property(self, property_name, value)
def get_property(self, property_name):

New properties cmake_target_name, cmake_file_name, cmake_module_target_name, cmake_module_file_name, pkg_config_name and cmake_build_modules are defined to allow migrating names, filenames and build_modules properties to this model. In Conan 2.0 this will be the default way of setting these properties for all generators and also passing custom properties to generators.

Important

The 2 mechanisms are completely independent:

Old way using .names, .filenames will work exclusively for legacy generators like cmake_find_package
New properties, like set_property("cmake_target_name") will work exclusively for new generators like CMakeDeps. They have changed to be absolute, and that would break legacy generators.
Recipes that want to provide support for both generators need to provide the 2 definitions in their package_info()

New properties defined for CMake generators family, used by CMakeDeps generator:

cmake_file_name property will define in CMakeDeps the name of the generated config file (xxx-config.cmake)
cmake_target_name property will define the absolute target name in CMakeDeps
cmake_module_file_name property defines the generated filename for modules (Findxxxx.cmake)
cmake_module_target_name defines the absolute target name for find modules.
cmake_build_modules property replaces the build_modules property.
cmake_find_mode will tell CMakeDeps to generate config files, modules files, both or none of them, depending on the value set (config, module, both or none)

Properties related to pkg_config, supported by both legacy pkg_config and new PkgConfigDeps:

pkg_config_name property equivalent to the names attribute.
pkg_config_custom_content property supported by both generators that will add user defined content to the .pc files created by the generator

Properties related to pkg_config, only supported by new PkgConfigDeps:

pkg_config_aliases property sets some aliases of any package/component name for the PkgConfigDeps generator only, it doesn’t work in pkg_config. This property only accepts list-like Python objects.

All of these properties, but cmake_file_name and cmake_module_file_name can be defined at global cpp_info level or at component level.

The set/get_property model is very useful if you are creating a custom generator. Using set_property() you can pass the parameters of your choice and read them using the get_property() method inside the generator.

def package_info(self):
    ...
    # you have created a custom generator that reads the 'custom_property' property and you set here
    # the value to 'prop_value'
    self.cpp_info.components["mycomponent"].set_property("custom_property", "prop_value")
    ...

Please check a detailed migration guide in the dedicated section.