Migrating the recipes

We introduced changes to Conan 1.X versions so you can start migrating your recipes to do a smooth transition to Conan 2.0.

Python import statements

• All the imports from the conans package have to be replaced. The Conan 2.0 ones are in the conan package. Note the plural.

• The “tools” functions are now organized in different packages, you can check the complete reference here.

From:

 from conans import ConanFile, tools

To:

 from conan import ConanFile
 from conan.tools.files import save, load
 from conan.tools.gnu import AutotoolsToolchain, AutotoolsDeps
 from conan.tools.microsoft import unix_path, VCVars, is_msvc
 from conan.errors import ConanInvalidConfiguration
 from conan.errors import ConanException
 ...

Requirements

• Use self.test_requires() to define test requirements instead of the legacy self.build_requires(..., force_host_context).

• Use self.tool_requires() to define the legacy build_requires.

From:

 from conans import ConanFile

 class Pkg(Conanfile):

       ...

       def build_requirements(self):
           self.build_requires("nasm/2.15.05")
           self.build_requires("gtest/0.1", force_host_context=True)

To:

 from conan import ConanFile

 class Pkg(Conanfile):

       ...

       def build_requirements(self):
           self.tool_requires("nasm/2.15.05")
           self.test_requires("gtest/0.1")

Settings

• 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.

  from conan import ConanFile
  
  class Pkg(Conanfile):
  
        settings = "os", "arch", "compiler"
  
        ...
  
        def validate(self):
            if self.info.settings.os == "Macos":
                raise ConanInvalidConfiguration("Macos not supported")
  

• In Conan 2, removing a setting, for example, del self.settings.compiler.libcxx in the configure() method, will raise an exception if the setting doesn’t exist. It has to be protected with try/except:

  def configure(self):
      try:
         # In windows, with msvc, the compiler.libcxx doesn't exist, so it will raise.
         del self.settings.compiler.libcxx
      except Exception:
         pass
  

Options

default_options

The definition of the default_options attribute has changed when referring to a dependency. It is related to the unified patterns in the command line.

From:

 from conans import ConanFile

 class Pkg(Conanfile):
     default_options = {"pkg:some_option": "value"}

To:

 from conan import ConanFile

 class Pkg(Conanfile):
     # "pkg/*:some_option" or ""pkg/1.0:some_option" or "pkg*:some_option" would be valid
     default_options = {"pkg/*:some_option": "value"}

ANY special value

The special value ANY has to be declared in a list:

From:

 from conans import ConanFile

 class Pkg(Conanfile):
     options = {"opt": "ANY"}

To:

 from conan import ConanFile

 class Pkg(Conanfile):
     options = {"opt": ["ANY"]}

The validate() method

Use always the self.info.settings instead of self.settings and self.info.options instead of self.options. Otherwise, the compatibility mechanism won’t be able to verify if the configurations of potential compatible packages are valid.

From:

class Pkg(Conanfile):

    def validate(self):
        if self.settings.os == "Windows":
            raise ConanInvalidConfiguration("This package is not compatible with Windows")

To:

class Pkg(Conanfile):

    def validate(self):
        if self.info.settings.os == "Windows":
            raise ConanInvalidConfiguration("This package is not compatible with Windows")

If you are not checking if the resulting binary is valid for the current configuration but need to check if a package can be built or not for a specific configuration you must use the validate_build() method instead using self.settings and self.options to perform the checks:

from conan import ConanFile
from conan.errors import ConanInvalidConfiguration

class myConan(ConanFile):
    name = "foo"
    version = "1.0"
    settings = "os", "arch", "compiler"

    def package_id(self):
        # For this package, it doesn't matter the compiler used for the binary package
        del self.info.settings.compiler

    def validate_build(self):
        # But we know this cannot be build with "gcc"
        if self.settings.compiler == "gcc":
            raise ConanInvalidConfiguration("This doesn't build in GCC")

    def validate(self):
        # We shouldn't check here if the self.info.settings.compiler because it has been removed in the package_id()
        # so it doesn't make sense to check if the binary is compatible with gcc because the compiler doesn't matter
        pass

The layout() method

The layout method is not mandatory but very recommended to:

• Give better support for editable packages.

• Work with local commands, conan install + conan source + conan build.

If your recipe is using CMake, you might want to use the cmake_layout(self):

from conan import ConanFile
from conan.tools.cmake import cmake_layout

class Pkg(Conanfile):

    def layout(self):
        cmake_layout(self)

A typical anti-pattern in the recipes that can be solved with a layout() declaration would be:

From:

from conans import ConanFile, tools

class Pkg(Conanfile):

   @property
   def _source_subfolder(self):
       return "source_subfolder"

   def source(self):
       tools.get(**self.conan_data["sources"][self.version],
                 destination=self._source_subfolder, strip_root=True)

To:

from conan import ConanFile
from conan.tools.layout import basic_layout
from conan.tools.files import get

class Pkg(Conanfile):

   def layout(self):
       basic_layout(self, src_folder="source")

   def source(self):
       get(self, **self.conan_data["sources"][self.version], strip_root=True)

Declaring the layout, the variables self.source_folder, self.build_folder will point to the correct folder, both in the cache or locally when using local methods, it is always recommended to use these when performing disk operations (read, write, copy, etc).

If you are using editables, the external template files are going to be removed. Use the layout() method definition instead.

Read more about the layout feature and the reference of the layout() method.

Adjusting the cpp_info objects

You can adjust the cpp_info in the layout method too, not only for a package in the cache, that was typically done in the package_info() method using the self.cpp_info, but for editable packages (to reuse a conan package that is being developed in a local directory):

def layout(self):

    # This will be automatically copied to self.cpp_info
    # This information is relative to the self.package_folder
    self.cpp.package.includedirs.append("other_includes")

    # This information is relative to the self.build_folder
    self.cpp.build.libdirs = ["."]
    self.cpp.build.bindirs = ["bin"]

    # This information is relative to the self.source_folder
    self.cpp.source.includedirs = ["."]

The scm attribute

The scm attribute won’t exist in Conan 2.0. You have to start using the export() and source() methods to mimic the same behavior:

• The export() method is responsible for capturing the “coordinates” of the current URL and commit. The new conan.tools.scm.Git can be used for this (do not use the legacy Git helper but this one)

• The export() method, after capturing the coordinates, can store them in the conandata.yml using the update_conandata() helper function

• The source() method can use the information in self.conan_data coming from exported conandata.yml file to do a clone and checkout of the matching code. The new conan.tools.scm.Git can be used for this purpose.

From:

from conans import ConanFile, tools

class Pkg(Conanfile):

    scm = {
         "type": "git",
         "url": "auto",
         "revision": "auto",
    }

To:

from conan import ConanFile
from conan.tools.scm import Git
from conan.tools.files import load, update_conandata

class Pkg(Conanfile):

   def export(self):
       git = Git(self, self.recipe_folder)
       scm_url, scm_commit = git.get_url_and_commit()
       update_conandata(self, {"sources": {"commit": scm_commit, "url": scm_url}})

   def source(self):
       git = Git(self)
       sources = self.conan_data["sources"]
       git.clone(url=sources["url"], target=".")
       git.checkout(commit=sources["commit"])

Please check the full example on the conan.tools.scm.Git section.

The generate() method

This is a key method to understand how Conan 2.0 works. This method is called during the “install” process, before calling the “build()” method. All information needed to build the current package has to be calculated and written in disk (in the self.generators_folder) by the generate() method. That information is about:

• The dependencies of the recipe: Typically called “generators”.

• The configuration (settings, options…): Typically called “toolchains”.

The goal of the generate() method is to have a very simple build process (the more dummy, the better), calling the build system passing some files or arguments and activating some environment launchers.

This improves a lot the local development, a simple conan install will generate everything we need to build our project in the IDE or just call the build system. This example is using the CMake integration, but if you use other build systems, even a custom one, remember you should generate everything needed in the generate() method:

from conan import ConanFile
from conan.tools.cmake import CMakeToolchain, CMakeDeps, CMake, cmake_layout


class Pkg(ConanFile):
    ...
    requires = "foo/1.0", "bar/1.0"

    def layout(self):
        cmake_layout(self)

    def generate(self):
        # This generates "conan_toolchain.cmake" in self.generators_folder
        tc = CMakeToolchain(self)
        tc.variables["MYVAR"] = "1"
        tc.preprocessor_definitions["MYDEFINE"] = "2"
        tc.generate()

        # This generates "foo-config.cmake" and "bar-config.cmake" in self.generators_folder
        deps = CMakeDeps(self)
        deps.generate()

    ...

If we are using that recipe for our project we can build it by typing:

$ conan install .
# This will generate the config files from the dependencies and the toolchain
$ cmake . -DCMAKE_TOOLCHAIN_FILE=./cmake-build-release/conan/conan_toolchain.cmake
$ cmake --build .

You can check all the generators and toolchains for different build systems in the tools reference page.

It is also very important to know that every access to the information from the dependencies must be done in the generate() method using the self.dependencies access. Do not use self.deps_cpp_info, self.deps_env_info or self.deps_user_info, these have been removed in 2.0.

Note

If you don’t need to customize anything in a generator you can specify it in the generators attribute and skip using the generate() method for that:

from conan import ConanFile
from conan.tools.cmake import CMake, cmake_layout


class Pkg(ConanFile):
    ...
    requires = "foo/1.0", "bar/1.0"
    generators = "CMakeToolchain", "CMakeDeps"
    ...

The build() method

There is nothing special in the build() method, just emphasize the concept of dummy build explained before.

The package() method

The self.copy has been replaced by the explicit tool copy.

From:

def package(self):
    ...
    self.copy("*.h", dst="include", src="src")
    self.copy("*.lib", dst="lib", keep_path=False)
    self.copy("*.dll", dst="bin", keep_path=False)

To:

from conan.tools.files import copy

def package(self):
    ...
    copy(self, "*.h", self.source_folder, join(self.package_folder, "include"), keep_path=False)
    copy(self, "*.lib", self.build_folder, join(self.package_folder, "lib"), keep_path=False)
    copy(self, "*.dll", self.build_folder, join(self.package_folder, "bin"), keep_path=False)

The package_info() method

Changed cpp_info default values

There are some defaults in self.cpp_info object that are not the same in Conan 2.X than in Conan 1.X (except for Conan >= 1.50 if the layout() method is declared):

self.cpp_info.includedirs => ["include"]
self.cpp_info.libdirs => ["lib"]
self.cpp_info.resdirs => []
self.cpp_info.bindirs => ["bin"]
self.cpp_info.builddirs => []
self.cpp_info.frameworkdirs => []

If you declare components, the defaults are the same, so you only need to change the defaults if they are not correct.

Note

Remember that now is possible to declare the cpp_info in the layout() method using the self.cpp.package instead of using self.cpp_info in the package_info().

Removed self.user_info

Replaced by the self.conf_info object, much more versatile than the previous self.user_info. Check the complete usage of self.conf_info.

Example:

From:

 import os
 from conans import ConanFile

 class Pkg(ConanFile):
     name = "pkg"
     version = "1.0"

     def package_info(self):
         self.user_info.FOO = "bar"

To:

 import os
 from conans import ConanFile

 class Pkg(ConanFile):
     name = "pkg"
     version = "1.0"

     def package_info(self):
         self.conf_info.define("user.myconf:foo", "bar")

In a consumer recipe:

import os
from conans import ConanFile

class Pkg(ConanFile):
    requires = "pkg/1.0"

    def generate(self):
       my_value = self.dependencies[pkg].conf_info.get("user.myconf:foo")
       ...

Note

The consumer recipes will have a self.conf object available with the aggregated configuration from all the recipes in the build context:

from conan import ConanFile

class Pkg(ConanFile):
    settings = "os", "compiler", "build_type", "arch"
    generators = "CMakeToolchain"
    build_requires = "android_ndk/1.0"

    def generate(self):
        self.output.info("NDK: %s" % self.conf.get("tools.android:ndk_path"))

Removed self.env_info

The attribute self.env_info has been replaced by:

• self.buildenv_info: For the dependant recipes, the environment variables will be present during the build process.

• self.runenv_info: For the dependant recipes, environment variables will be present during the runtime.

Read more about how to use them in the environment management of Conan 2.0.

Remember that if you want to pass general information to the dependant recipes, you should use the self.conf_info and not environment variables if they are not supposed to be reused as environment variables in the dependent recipes.

Removed self.cpp_info.builddirs

The default value (pointing to the package root folder) form self.cpp_info.builddirs has been removed. Also assigning it will be discouraged because it affects how CMakeToolchain and CMakeDeps locate executables, libraries, headers… from the right context (host vs build).

To be prepared for Conan 2.0:

• If you have cmake modules or cmake config files at the root of the package, it is strongly recommended to move them to a subfolder cmake and assing it: self.cpp_info.builddirs = ["cmake"]

• If you are not assigning any self.cpp_info.builddirs assign an empty list: self.cpp_info.builddirs = [].

• Instead of appending new values to the default list, assign it: self.cpp_info.builddirs = ["cmake"]

The package_id() method

The self.info.header_only() method has been replaced with self.info.clear()

From:

     def package_id(self):
         self.info.header_only()

To:

     def package_id(self):
         self.info.clear()

New properties model

Using .names, .filenames and .build_modules will not work anymore 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. It can’t be declared in a component, do it in self.cpp_info.

• 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

• component_version property supported by both generators that set a custom version to be used in the Version field belonging to the created *.pc file for that component.

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 the global cpp_info level or at the 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.

Removed imports() method

The def imports(self) method from the conanfile has been removed. If you need to import files from your dependencies you can do it in the generate(self) method with the new copy tool:

from conan.tools.files import copy

def generate(self):
    for dep in self.dependencies.values():
        copy(self, "*.dylib", dep.cpp_info.libdirs[0], self.build_folder)
        copy(self, "*.dll", dep.cpp_info.libdirs[0], self.build_folder)

Changes in the test_package recipe

In Conan 2.0, the test_package/conanfile.py needs to declare the requirement being tested explicitly. To be prepared you have to set the attribute test_type="explicit" (this will be ignored in 2.0) to make Conan activate the explicit mode, then declaring the requirement using the self.tested_reference_str that contains the reference being tested.

from conan import ConanFile

class MyTestPkg(ConanFile):
    test_type = "explicit"

    def requirements(self):
        # A regular requirement
        self.requires(self.tested_reference_str)

    def build_requirements(self):
        # If we want to test the package as a tool_require (formerly `test_type = "build_requires"`)
        # Keep both "requires()" and "tool_requires()" if you want to test the same package both as a regular
        # require and a tool_require (formerly `test_type = "build_requires", "requires"`)
        self.tool_requires(self.tested_reference_str)

Other recipe changes

The environment management

The environment management has changed quite a bit. In Conan 1.X the environment was managed by modifying the environment of Python (of the running process), often using the environment_append tool, which is not available in 2.0 anymore. In Conan 2.0, all the applied environment variables are managed by script files (sh, bat) that will be run just before calling the command specified in every self.run("mycommand").

These “environment launchers” can be organized by scopes. Conan will aggregate all the launchers of the same scope in a single launcher called conan<scope_name>.bat/sh.

For example, if you need to call your build system, passing some environment variables:

from conan import ConanFile
from conan.tools.env import Environment

class MyTestPkg(ConanFile):
    ...
    def generate(self):
        env = Environment()
        env.define("foo", "var")
        # scope="build" is the default
        envvars = env.vars(self, scope="build")
        # This will generate a my_launcher.sh but also will create a "conan_build.sh" calling "my_launcher.sh"
        envvars.save_script("my_launcher")


    def build(self):
        # by default env="conanbuild"
        self.run("my_build_system.exe", env="conanbuild")

The resulting command executed in the build() method would be something like:

$ conan_build.sh && my_build_system.exe

So the environment variable foo declared in the generate() method will be automatically passed to the my_build_system.exe.

There are two generators managing the environment, the VirtualBuildEnv and the VirtualRunEnv. By default, these generators are automatically declared in Conan 2.0 but you have to explicitly declare them in Conan 1.X otherwise you can set tools.env.virtualenv:auto_use=True in the global.conf.

• VirtualBuildEnv: It will generate a conanbuildenv .bat or .sh script containing environment variables of the build time environment. That information is collected from the direct tool_requires in “build” context recipes from the self.buildenv_info definition plus the self.runenv_info of the transitive dependencies of those tool_requires.

  The scope used by the VirtualBuildEnv is build so, as explained before, it will be applied by default before calling any command.

  Check more details here.

• VirtualRunEnv: It will generate a conanrunenv .bat or .sh script containing environment variables of the run time environment. The launcher contains the runtime environment information, anything that is necessary for the environment to actually run the compiled executables and applications. The information is obtained from the self.runenv_info and also automatically deducted from the self.cpp_info definition of the package, to define PATH, LD_LIBRARY_PATH, DYLD_LIBRARY_PATH, and DYLD_FRAMEWORK_PATH environment variables.

  The scope used by the VirtualRunEnv is run so if you need that environment applied you need to specify it in the self.run command.

  An example of usage of the conanrun is the test_package of a recipe that builds a shared library:

  import os
  from conan import ConanFile
  from conan.tools.env import Environment
  
  class MyTestPkg(ConanFile):
      generators = "VirtualRunEnv"
  
      ...
  
      def test(self):
          my_app_path = os.path.join(self.cpp.build.bindirs[0], "my_app")
          # The default env is "conanbuild" but we want the runtime here to locate the shared library
          self.run(my_app_path, env="conanrun")
  

  Check more details here.

Windows Subsystems

If you want to run commands inside a Windows subsystem (e.g bash from msys2) you have to set the self.win_bash=True in your recipe, instead of using the deprecated self.run(..., win_bash=True) from 1.X.

You need to configure how to run the commands with two config variables:

• tools.microsoft.bash:subsystem: Possible values: ‘msys2’, ‘msys’, ‘cygwin’, ‘wsl’ and ‘sfu’

• tools.microsoft.bash:path (Default “bash”): Path to the shell executable.

Any command run with self.run, if self.win_bash == True will run the command inside the specified shell.

Symlinks

Conan won’t alter any symlink while exporting or packaging files. If any manipulation to the symlinks is required, the package conan.tools.files.symlinks contains some tools to help with that.

New tools for managing system package managers

There are some changes you should be aware of if you are migrating from SystemPackageTool to the new conan.tools.system.package_manager to prepare the recipe for Conan 2.0:

• Unlike in SystemPackageTool that uses CONAN_SYSREQUIRES_SUDO and is set to True as default, the tools.system.package_manager:sudo configuration is False by default.

• SystemPackageTool is initialized with default_mode='enabled' but for these new tools tools.system.package_manager:mode='check' by default.