Packages in editable mode

Important

This is a tutorial section. You are encouraged to execute these commands. Some of the features used in this section are experimental, like layout() or CMakeToolchain, and they might change in future releases. Check the reference section for more information.

When working in big projects with several functionalities interconnected it is recommended to avoid the one-and-only huge project approach in favor of several libraries, each one specialized in a set of common tasks, even maintained by dedicated teams. This approach helps to isolate and reusing code helps with compiling times and reduces the likelihood of including files that not correspond to the API of the required library.

Nevertheless, in some case, it is useful to work in several libraries at the same time and see how the changes in one of them are propagated to the others. With the normal flow, for every source change, it is necessary to do conan create or conan export-pkg to put the package in the cache and make it available to consumers.

With the editable packages, you can tell Conan where to find the headers and the artifacts ready for consumption in your local working directory. There is no need to package.

Let’s see this feature over a practical example, the code can be found in the examples repository:

$ git clone https://github.com/conan-io/examples.git
$ cd examples/features/editable/cmake

There are 2 folders inside this project:

• A “say” folder containing a fully fledge package, with its conanfile.py, its source code.

• A “hello” folder containing a simple consumer project with a conanfile.txt and its source code, which depends on the say/0.1@user/testing requirement.

The goal is to be able to build the “hello” project, without actually having the say/0.1@user/testing package in the cache, but directly in this project folder.

Put a package in editable mode

To avoid creating the package say/0.1@user/channel in the cache for every change, we are going to put that package in editable mode, creating a link from the reference in the cache to the local working directory:

$ conan editable add say say/0.1@user/channel
$ conan editable list
say/0.1@user/channel
    Path: ...

That is it. Now, every usage of say/0.1@user/channel, by any other Conan package or project, will be redirected to the examples/features/editable/cmake/say user folder instead of using the package from the conan cache.

Note that the key of editable packages is a correct definition of the layout() of the package. In this example, the say conanfile.py recipe is using the predefined cmake_layout() which defines the typical CMake project layout, which can be different in the different platforms. Take also into account that only using the new build system integrations like CMakeDeps and CMakeToolchain will correctly follow the layout definition.

Now the say/0.1@user/channel package is in editable mode, lets build it locally:

$ cd say

# windows, we will build 2 configurations to show multi-config
$ conan install . -s build_type=Release
$ conan install . -s build_type=Debug
$ cd build
$ cmake .. -DCMAKE_TOOLCHAIN_FILE=generators/conan_toolchain.cmake
$ cmake --build . --config Release
$ cmake --build . --config Debug

# Linux, we will only build 1 configuration
$ conan install .
$ cd build/Release
$ cmake .. -DCMAKE_BUILD_TYPE=Release -DCMAKE_TOOLCHAIN_FILE=generators/conan_toolchain.cmake
$ cmake --build .

Using a package in editable mode

Consuming a package in editable mode is transparent from the consumer perspective. In this case we can build the hello application as usual:

$ cd ../../hello

# windows, we will build 2 configurations to show multi-config
$ conan install . -s build_type=Release
$ conan install . -s build_type=Debug
$ cd build
$ cmake .. -DCMAKE_TOOLCHAIN_FILE=generators/conan_toolchain.cmake
$ cmake --build . --config Release
$ cmake --build . --config Debug
$ Release\hello.exe
say/0.1: Hello World Release!
$ Debug\hello.exe
say/0.1: Hello World Debug!

# Linux, we will only build 1 configuration
$ conan install .
$ cd build/Release
$ cmake .. -DCMAKE_BUILD_TYPE=Release -DCMAKE_TOOLCHAIN_FILE=generators/conan_toolchain.cmake
$ cmake --build .
$ ./hello
say/0.1: Hello World Release!

Working with editable packages

Once the above steps have been done, we can basically work with our build system or IDE, no Conan involved, and do changes in the editable packages and have those changes used by the consumers directly. Lets see it, lets start by doing a change in the say source code:

$ cd ../../say
# Edit src/say.cpp and change the error message from "Hello" to "Bye"

# windows, we will build 2 configurations to show multi-config
$ cd build
$ cmake --build . --config Release
$ cmake --build . --config Debug

# Linux, we will only build 1 configuration
$ cd build/Release
$ cmake --build .

And build and run the “hello” project:

$ cd ../../hello

# windows,
$ cd build
$ cmake --build . --config Release
$ cmake --build . --config Debug
$ Release\hello.exe
say/0.1: Bye World Release!
$ Debug\hello.exe
say/0.1: Bye World Debug!

# Linux
$ cd build/Release
$ cmake --build .
$ ./hello
say/0.1: Bye World Release!

In that way, it is possible to be developing both the say library and the hello application, at the same time, without any Conan command. If you had both open in the IDE, it would be just building one after the other.

Note

When a package is in editable mode, most of the commands will not work. It is not possible to conan upload, conan export or conan create when a package is in editable mode.

Revert the editable mode

In order to revert the editable mode just remove the link using:

$ conan editable remove say/0.1@user/channel

It will remove the link (the local directory won’t be affected) and all the packages consuming this requirement will get it from the cache again.

Warning

Packages that are built consuming an editable package in its graph upstreams can generate binaries and packages incompatible with the released version of the editable package. Avoid uploading these packages without re-creating them with the in-cache version of all the libraries.