Dependencies

Introduced in Conan 1.38.

Warning

These tools are very experimental and subject to breaking changes. It also contains some known bugs regarding build_requires, to be addressed in next Conan 1.39

Note

This is an advanced feature. Most users will not need to use it, it is intended for developing new build system integrations and similar purposes. For defining dependencies between packages, check the requires, build_requires and other attributes

Conan recipes provide access to their dependencies via the self.dependencies attribute. This attribute is extensively used by generators like CMakeDeps or MSBuildDeps to generate the necessary files for the build.

This section documents the self.dependencies attribute, as it might be used by users both directly in recipe or indirectly to create custom build integrations and generators.

Dependencies interface

It is possible to access each one of the individual dependencies of the current recipe, with the following syntax:

class Pkg(ConanFile):
    requires = "openssl/0.1"

    def generate(self):
        openssl = self.dependencies["openssl"]
        # access to members
        openssl.ref.version
        openssl.ref.revision # recipe revision
        openssl.options
        openssl.settings

Some important points:

All the information is read only. Any attempt to modify dependencies information is an error and can raise at any time, even if it doesn’t raise yet.
It is not possible either to call any methods or any attempt to reuse code from the dependencies via this mechanism.
This information does not exist in some recipe methods, only in those methods that evaluate after the full dependency graph has been computed. It will not exist in configure(), config_options, export(), export_source(), set_name(), set_version(), requirements(), build_requirements(), system_requirements(), source(), init(), layout(). Any attempt to use it in these methods can raise an error at any time.
At the moment, this information should only be used in generate() and validate() methods. Any other use, please submit a Github issue.

Not all fields of the dependency conanfile are exposed, the current fields are:

package_folder: The folder location of the dependency package binary
ref: an object that contains name, version, user, channel and revision (recipe revision)
pref: an object that contains ref, package_id and revision (package revision)
buildenv_info: Environment object with the information of the environment necessary to build
runenv_info: Environment object with the information of the environment necessary to run the app
cpp_info: includedirs, libdirs, etc for the dependency.
settings: The actual settings values of this dependency
settings_build: The actual build settings values of this dependency
options: The actual options values of this dependency
context: The context (build, host) of this dependency
conf_info: Configuration information of this dependency, intended to be applied to consumers.
dependencies: The transitive dependencies of this dependency
is_build_context: Return True if context == "build".

Iterating dependencies

It is possible to iterate in a dict-like fashion all dependencies of a recipe. Take into account that self.dependencies contains all the current dependencies, both direct and transitive. Every upstream dependency of the current one that has some effect on it, will have an entry in this self.dependencies.

Iterating the dependencies can be done as:

requires = "zlib/1.2.11", "poco/1.9.4"

def generate(self):
    for require, dependency in self.dependencies.items():
        self.output.info("Dependency is direct={}: {}".format(require.direct, dependency.ref))

will output:

conanfile.py (hello/0.1): Dependency is direct=True: zlib/1.2.11
conanfile.py (hello/0.1): Dependency is direct=True: poco/1.9.4
conanfile.py (hello/0.1): Dependency is direct=False: pcre/8.44
conanfile.py (hello/0.1): Dependency is direct=False: expat/2.4.1
conanfile.py (hello/0.1): Dependency is direct=False: sqlite3/3.35.5
conanfile.py (hello/0.1): Dependency is direct=False: openssl/1.1.1k
conanfile.py (hello/0.1): Dependency is direct=False: bzip2/1.0.8

Where the require dictionary key is a “requirement”, and can contain specifiers of the relation between the current recipe and the dependency. At the moment they can be:

require.direct: boolean, True if it is direct dependency or False if it is a transitive one.
require.build: boolean, True if it is a build_require in the build context, as cmake.
require.test: boolean, True if its a build_require in the host context (defined with self.test_requires()), as gtest.

The dependency dictionary value is the read-only object described above that access the dependency attributes.

The self.dependencies contains some helpers to filter based on some criteria:

self.dependencies.host: Will filter out requires with build=True, leaving regular dependencies like zlib or poco.
self.dependencies.direct_host: Will filter out requires with build=True or direct=False
self.dependencies.build: Will filter out requires with build=False, leaving only build_requires in the build context, as cmake.
self.dependencies.direct_build: Will filter out requires with build=False or direct=False
self.dependencies.test: Will filter out requires with build=True or with test=False, leaving only test requirements as gtest in the host context.

They can be used in the same way:

requires = "zlib/1.2.11", "poco/1.9.4"

def generate(self):
    cmake = self.dependencies.direct_build["cmake"]
    for require, dependency in self.dependencies.build.items():
        # do something, only build deps here

Dependencies `cpp_info` interface

The cpp_info interface is heavily used by build systems to access the data. This object defines global and per-component attributes to access information like the include folders:

def generate(self):
    cpp_info = self.dependencies["mydep"].cpp_info
    cpp_info.includedirs
    cpp_info.libdirs

    cpp_info.components["mycomp"].includedirs
    cpp_info.components["mycomp"].libdirs

These are the defined attributes in cpp_info. All the paths are typically relative paths to the root of the package folder that contains the dependency artifacts:

# ###### DIRECTORIES
self.includedirs = None  # Ordered list of include paths
self.srcdirs = None  # Ordered list of source paths
self.libdirs = None  # Directories to find libraries
self.resdirs = None  # Directories to find resources, data, etc
self.bindirs = None  # Directories to find executables and shared libs
self.builddirs = None
self.frameworkdirs = None

# ##### FIELDS
self.system_libs = None  # Ordered list of system libraries
self.frameworks = None  # Macos .framework
self.libs = None  # The libs to link against
self.defines = None  # preprocessor definitions
self.cflags = None  # pure C flags
self.cxxflags = None  # C++ compilation flags
self.sharedlinkflags = None  # linker flags
self.exelinkflags = None  # linker flags
self.objects = None  # objects to link

Dependencies

Dependencies interface

Iterating dependencies

Dependencies cpp_info interface

Dependencies `cpp_info` interface