Define information for consumers: the package_info() method

In the previous tutorial section, we explained how to store the headers and binaries of a library in a Conan package using the package method. Consumers that depend on that package will reuse those files, but we have to provide some additional information so that Conan can pass that to the build system and consumers can use the package.

For instance, in our example, we are building a static library named hello that will result in a libhello.a file in Linux and macOS or a hello.lib file in Windows. Also, we are packaging a header file hello.h with the declaration of the library functions. The Conan package ends up with the following structure in the Conan local cache:

.
├── include
│   └── hello.h
└── lib
    └── libhello.a

Then, consumers that want to link against this library will need some information:

  • The location of the include folder in the Conan local cache to search for the hello.h file.

  • The name of the library file to link against it (libhello.a or hello.lib)

  • The location of the lib folder in the Conan local cache to search for the library file.

Conan provides an abstraction over all the information consumers may need in the cpp_info attribute of the ConanFile. The information for this attribute must be set in the package_info() method. Let’s have a look at the package_info() method of our hello/1.0 Conan package:

conanfile.py
...

class helloRecipe(ConanFile):
    name = "hello"
    version = "1.0"

    ...

    def package_info(self):
        self.cpp_info.libs = ["hello"]

We can see a couple of things:

  • We are adding a hello library to the libs property of the cpp_info to tell consumers that they should link the libraries from that list.

  • We are not adding information about the lib or include folders where the library and headers files are packaged. The cpp_info object provides the .includedirs and .libdirs properties to define those locations but Conan sets their value as lib and include by default so it’s not needed to add those in this case. If you were copying the package files to a different location then you have to set those explicitly. The declaration of the package_info method in our Conan package would be equivalent to this one:

conanfile.py
...

class helloRecipe(ConanFile):
    name = "hello"
    version = "1.0"

    ...

    def package_info(self):
        self.cpp_info.libs = ["hello"]
        # conan sets libdirs = ["lib"] and includedirs = ["include"] by default
        self.cpp_info.libdirs = ["lib"]
        self.cpp_info.includedirs = ["include"]

Setting information in the package_info() method

Besides what we explained above about the information you can set in the package_info() method, there are some typical use cases:

  • Define information for consumers depending on settings or options

  • Customizing certain information that generators provide to consumers, like the target names for CMake or the generated files names for pkg-config for example

  • Propagating configuration values to consumers

  • Propagating environment information to consumers

  • Define components for Conan packages that provide multiple libraries

Let’s see some of those in action. First, clone the project sources if you haven’t done so yet. You can find them in the examples2 repository on GitHub:

$ git clone https://github.com/conan-io/examples2.git
$ cd examples2/tutorial/creating_packages/package_information

Define information for consumers depending on settings or options

For this section of the tutorial we introduced some changes in the library and recipe. Let’s check the relevant parts:

Changes introduced in the library sources

First, please note that we are using another branch from the libhello library. Let’s check the library’s CMakeLists.txt:

CMakeLists.txt
cmake_minimum_required(VERSION 3.15)
project(hello CXX)

...

add_library(hello src/hello.cpp)

if (BUILD_SHARED_LIBS)
    set_target_properties(hello PROPERTIES OUTPUT_NAME hello-shared)
else()
    set_target_properties(hello PROPERTIES OUTPUT_NAME hello-static)
endif()

...

As you can see, we are setting the output name for the library depending on whether we are building the library as static (hello-static) or as shared (hello-shared). Now let’s see how to translate these changes to the Conan recipe.

Changes introduced in the recipe

To update our recipe according to the changes in the library’s CMakeLists.txt we have to conditionally set the library name depending on the self.options.shared option in the package_info() method:

conanfile.py
class helloRecipe(ConanFile):
    ...

    def source(self):
        git = Git(self)
        git.clone(url="https://github.com/conan-io/libhello.git", target=".")
        # Please, be aware that using the head of the branch instead of an immutable tag
        # or commit is not a good practice in general
        git.checkout("package_info")

    ...

    def package_info(self):
        if self.options.shared:
            self.cpp_info.libs = ["hello-shared"]
        else:
            self.cpp_info.libs = ["hello-static"]

Now, let’s create the Conan package with shared=False (that’s the default so no need to set it explicitly) and check that we are packaging the correct library (libhello-static.a or hello-static.lib) and that we are linking the correct library in the test_package.

$ conan create . --build=missing
...
-- Install configuration: "Release"
-- Installing: /Users/user/.conan2/p/tmp/a311fcf8a63f3206/p/lib/libhello-static.a
-- Installing: /Users/user/.conan2/p/tmp/a311fcf8a63f3206/p/include/hello.h
hello/1.0 package(): Packaged 1 '.h' file: hello.h
hello/1.0 package(): Packaged 1 '.a' file: libhello-static.a
hello/1.0: Package 'fd7c4113dad406f7d8211b3470c16627b54ff3af' created
...
-- Build files have been written to: /Users/user/.conan2/p/tmp/a311fcf8a63f3206/b/build/Release
hello/1.0: CMake command: cmake --build "/Users/user/.conan2/p/tmp/a311fcf8a63f3206/b/build/Release" -- -j16
hello/1.0: RUN: cmake --build "/Users/user/.conan2/p/tmp/a311fcf8a63f3206/b/build/Release" -- -j16
[ 25%] Building CXX object CMakeFiles/hello.dir/src/hello.cpp.o
[ 50%] Linking CXX static library libhello-static.a
[ 50%] Built target hello
[ 75%] Building CXX object tests/CMakeFiles/test_hello.dir/test.cpp.o
[100%] Linking CXX executable test_hello
[100%] Built target test_hello
hello/1.0: RUN: tests/test_hello
...
[ 50%] Building CXX object CMakeFiles/example.dir/src/example.cpp.o
[100%] Linking CXX executable example
[100%] Built target example

-------- Testing the package: Running test() --------
hello/1.0 (test package): Running test()
hello/1.0 (test package): RUN: ./example
hello/1.0: Hello World Release! (with color!)

As you can see both the tests for the library and the Conan test_package linked against the libhello-static.a library successfully.

Properties model: setting information for specific generators

The CppInfo object provides the set_property method to set information specific to each generator. For example, in this tutorial, we use the CMakeDeps generator to generate the information that CMake needs to build a project that requires our library. CMakeDeps, by default, will set a target name for the library using the same name as the Conan package. If you have a look at that CMakeLists.txt from the test_package:

test_package CMakeLists.txt
cmake_minimum_required(VERSION 3.15)
project(PackageTest CXX)

find_package(hello CONFIG REQUIRED)

add_executable(example src/example.cpp)
target_link_libraries(example hello::hello)

You can see that we are linking with the target name hello::hello. Conan sets this target name by default, but we can change it using the properties model. Let’s try to change it to the name hello::myhello. To do this, we have to set the property cmake_target_name in the package_info method of our hello/1.0 Conan package:

conanfile.py
class helloRecipe(ConanFile):
    ...

    def package_info(self):
        if self.options.shared:
            self.cpp_info.libs = ["hello-shared"]
        else:
            self.cpp_info.libs = ["hello-static"]

        self.cpp_info.set_property("cmake_target_name", "hello::myhello")

Then, change the target name we are using in the CMakeLists.txt in the test_package folder to hello::myhello:

test_package CMakeLists.txt
cmake_minimum_required(VERSION 3.15)
project(PackageTest CXX)
# ...
target_link_libraries(example hello::myhello)

And re-create the package:

$ conan create . --build=missing
Exporting the recipe
hello/1.0: Exporting package recipe
hello/1.0: Using the exported files summary hash as the recipe revision: 44d78a68b16b25c5e6d7e8884b8f58b8
hello/1.0: A new conanfile.py version was exported
hello/1.0: Folder: /Users/user/.conan2/p/a8cb81b31dc10d96/e
hello/1.0: Exported revision: 44d78a68b16b25c5e6d7e8884b8f58b8
...
-------- Testing the package: Building --------
hello/1.0 (test package): Calling build()
...
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Conan: Target declared 'hello::myhello'
...
[100%] Linking CXX executable example
[100%] Built target example

-------- Testing the package: Running test() --------
hello/1.0 (test package): Running test()
hello/1.0 (test package): RUN: ./example
hello/1.0: Hello World Release! (with color!)

You can see how Conan now declares the hello::myhello instead of the default hello::hello and the test_package builds successfully.

The target name is not the only property you can set in the CMakeDeps generator. For a complete list of properties that affect the CMakeDeps generator behaviour, please check the reference.

Propagating environment or configuration information to consumers

You can provide environment information to consumers in the package_info(). To do so, you can use the ConanFile’s runenv_info and buildenv_info properties:

  • runenv_info Environment object that defines environment information that consumers that use the package may need when running.

  • buildenv_info Environment object that defines environment information that consumers that use the package may need when building.

Please note that it’s not necessary to add cpp_info.bindirs to PATH or cpp_info.libdirs to LD_LIBRARY_PATH, those are automatically added by the VirtualBuildEnv and VirtualRunEnv.

You can also define configuration values in the package_info() so that consumers can use that information. To do this, set the conf_info property of the ConanFile.

To know more about this use case, please check the corresponding example.

Define components for Conan packages that provide multiple libraries

There are cases in which a Conan package may provide multiple libraries, for these cases you can set the separate information for each of those libraries using the components attribute from the CppInfo object.

To know more about this use case, please check the components example in the examples section.

Read more

See also