Declaring the layout when creating packages for third-party libraries¶

Please, first clone the sources to recreate this project. You can find them in the examples2 repository in GitHub:

$ git clone https://github.com/conan-io/examples2.git
$ cd examples2/examples/conanfile/layout/third_party_libraries

If we have this project, intended to create a package for a third-party library whose code is located externally:

.
├── conanfile.py
└── patches
    └── mypatch

The conanfile.py would look like this:

...

class Pkg(ConanFile):
    name = "hello"
    version = "1.0"
    exports_sources = "patches*"

    ...

    def layout(self):
        cmake_layout(self, src_folder="src")
        # if you are declaring your own layout, just declare:
        # self.folders.source = "src"

    def source(self):
        # we are inside a "src" subfolder, as defined by layout
        # the downloaded soures will be inside the "src" subfolder
        get(self, "https://github.com/conan-io/libhello/archive/refs/heads/main.zip",
            strip_root=True)
        # Please, be aware that using the head of the branch instead of an immutable tag
        # or commit is not a good practice in general as the branch may change the contents

        # patching, replacing, happens here
        patch(self, patch_file=os.path.join(self.export_sources_folder, "patches/mypatch"))

    def build(self):
        # If necessary, the build() method also has access to the export_sources_folder
        # for example if patching happens in build() instead of source()
        #patch(self, patch_file=os.path.join(self.export_sources_folder, "patches/mypatch"))
        cmake = CMake(self)
        cmake.configure()
        cmake.build()
        ...

We can see that the ConanFile.export_sources_folder attribute can provide access to the root folder of the sources:

Locally it will be the folder where the conanfile.py lives
In the cache it will be the “source” folder, that will contain a copy of CMakeLists.txt and patches, while the “source/src” folder will contain the actual downloaded sources.

We can check that everything runs fine now:

$ conan create .
...
Downloading main.zip
hello/1.0: Unzipping 3.7KB
Unzipping 100 %
...
[ 50%] Building CXX object CMakeFiles/hello.dir/src/hello.cpp.o
[100%] Linking CXX static library libhello.a
[100%] Built target hello
...
$ conan list hello/1.0
Local Cache
hello
    hello/1.0