Understanding packaging

Manual package creation and testing

The previous create approach using test_package subfolder, is not strictly necessary, though very strongly recommended. If we didn’t want to use the test_package functionality, we could just write our recipe ourselves or use the conan new command without the -t. command line argument.

$ mkdir mypkg && cd mypkg
$ conan new Hello/0.1

This will create just the conanfile.py recipe file. Now we could create our package:

$ conan create demo/testing

This would be equivalent to:

$ conan export . demo/testing
$ conan install Hello/0.1@demo/testing --build=Hello

Once the package is there, it can be consumed like any other package, just add Hello/0.1@demo/testing to some project conanfile.txt or conanfile.py requirements and run:

$ conan install .
# build and run your project to ensure the package works

The package creation process

It is very useful for package creators and conan users in general to understand the flow of package creation inside the conan local cache, and its layout.

For every package recipe, there are 5 important folders in the local cache:

  • export: The folder where the package recipe is stored.

  • export_source: The folder where code copied with the recipe exports_sources attribute is stored.

  • source: Where the source code for building from sources is stored.

  • build: Where the actual compilation of sources is done. There will typically be one subfolder for each different binary configuration

  • package: Where the final package artifacts are stored. There will be one subfolder for each different binary configuration

The source and build folders only exist when the packages have been built from sources.

../_images/package_create_flow.png

The process starts when a package is “exported”, via the conan export command or more typically, with the conan create command. The conanfile.py and files specified by the exports_sources field are copied from the user space into the local cache.

The export and export_source files are copied to the source folder, and then the source() method is executed (if existing). Note that there is only one source folder for all the binary packages. If some source code is to be generated that will be different for different configurations, it cannot be generated in the source() method, it has to be done in the build() method.

Then, for each different configuration of settings and options, a package ID will be computed in the form of a SHA-1 hash of such configuration. Sources will be copied to the build/hashXXX folder, and the build() method will be triggered.

After that, the package() method will be called to copy artifacts from the build/hashXXX folder to the package/hashXXX folder.

Finally, the package_info() methods of all dependencies will be called and gathered to be able to generate files for the consumer build system, as the conanbuildinfo.cmake for the cmake generator. Also the imports feature will copy artifacts from the local cache into user space if specified.

Any doubts? Please check out our FAQ section or write us.