Using build tools as Conan packages¶
In the previous example, we built our CMake project and used Conan to install and locate
the Zlib library. We used the CMake already installed in our system to build our
compressor binary. However, what happens if you want to build your project with a specific
CMake version, different from the one already installed system-wide? Conan can also help
you install these tools and use them to compile consumer projects or other Conan
packages. In this case, you can declare this dependency in Conan using a type of
requirement named tool_requires
. Let’s see an example of how to add a
tool_requires
to our project and use a different CMake version to build it.
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/tutorial/consuming_packages/tool_requires
The structure of the project is the same as the one of the previous example:
.
├── conanfile.txt
├── CMakeLists.txt
└── src
└── main.c
The main difference is the addition of the [tool_requires] section in the conanfile.txt file. In this section, we declare that we want to build our application using CMake v3.22.6.
[requires]
zlib/1.2.11
[tool_requires]
cmake/3.22.6
[generators]
CMakeDeps
CMakeToolchain
Important
Please note that this conanfile.txt will install zlib/1.2.11 and cmake/3.22.6
separately. However, if Conan does not find a binary for Zlib in Conan Center and it
needs to be built from sources, a CMake installation must already be present in your
system, because the cmake/3.22.6
declared in your conanfile.txt
only applies to
your current project, not all dependencies.
If you want to use that cmake/3.22.6 to also build Zlib, when installing if
necessary, you may add the [tool_requires]
section to the profile you are using.
Please check the profile doc for more
information.
We also added a message to the CMakeLists.txt to output the CMake version:
cmake_minimum_required(VERSION 3.15)
project(compressor C)
find_package(ZLIB REQUIRED)
message("Building with CMake version: ${CMAKE_VERSION}")
add_executable(${PROJECT_NAME} src/main.c)
target_link_libraries(${PROJECT_NAME} ZLIB::ZLIB)
Now, as in the previous example, we will use Conan to install Zlib and CMake 3.22.6 and generate the files to find both of them. We will generate those files the folder build. To do that, just run:
$ conan install . --output-folder=build --build=missing
Note
Powershell users need to add --conf=tools.env.virtualenv:powershell=True
to the previous command
to generate .ps1
files instead of .bat
files.
To avoid the need to add this line every time, we recommend configuring it in the [conf]
section of your profile. For detailed information, please refer to the profiles section.
You can check the output:
-------- Computing dependency graph ----------
cmake/3.22.6: Not found in local cache, looking in remotes...
cmake/3.22.6: Checking remote: conancenter
cmake/3.22.6: Trying with 'conancenter'...
Downloading conanmanifest.txt
Downloading conanfile.py
cmake/3.22.6: Downloaded recipe revision 3e3d8f3a848b2a60afafbe7a0955085a
Graph root
conanfile.txt: /Users/user/Documents/developer/conan/examples2/tutorial/consuming_packages/tool_requires/conanfile.txt
Requirements
zlib/1.2.11#f1fadf0d3b196dc0332750354ad8ab7b - Cache
Build requirements
cmake/3.22.6#3e3d8f3a848b2a60afafbe7a0955085a - Downloaded (conancenter)
-------- Computing necessary packages ----------
Requirements
zlib/1.2.11#f1fadf0d3b196dc0332750354ad8ab7b:2a823fda5c9d8b4f682cb27c30caf4124c5726c8#48bc7191ec1ee467f1e951033d7d41b2 - Cache
Build requirements
cmake/3.22.6#3e3d8f3a848b2a60afafbe7a0955085a:f2f48d9745706caf77ea883a5855538256e7f2d4#6c519070f013da19afd56b52c465b596 - Download (conancenter)
-------- Installing packages ----------
Installing (downloading, building) binaries...
cmake/3.22.6: Retrieving package f2f48d9745706caf77ea883a5855538256e7f2d4 from remote 'conancenter'
Downloading conanmanifest.txt
Downloading conaninfo.txt
Downloading conan_package.tgz
Decompressing conan_package.tgz
cmake/3.22.6: Package installed f2f48d9745706caf77ea883a5855538256e7f2d4
cmake/3.22.6: Downloaded package revision 6c519070f013da19afd56b52c465b596
zlib/1.2.11: Already installed!
-------- Finalizing install (deploy, generators) ----------
conanfile.txt: Generator 'CMakeToolchain' calling 'generate()'
conanfile.txt: Generator 'CMakeDeps' calling 'generate()'
conanfile.txt: Generating aggregated env files
Now, if you check the folder you will see that Conan generated a new
file called conanbuild.sh/bat
. This is the result of automatically invoking a
VirtualBuildEnv
generator when we declared the tool_requires
in the
conanfile.txt. This file sets some environment variables like a new PATH
that
we can use to inject to our environment the location of CMake v3.22.6.
Activate the virtual environment, and run cmake --version
to check that you
have installed the new CMake version in the path.
$ cd build
$ conanbuild.bat
# conanbuild.ps1 if using Powershell
$ cd build
$ source conanbuild.sh
Capturing current environment in deactivate_conanbuildenv-release-x86_64.sh
Configuring environment variables
Run cmake
and check the version:
$ cmake --version
cmake version 3.22.6
...
As you can see, after activating the environment, the CMake v3.22.6 binary folder was added to the path and is the currently active version now. Now you can build your project as you previously did, but this time Conan will use CMake 3.22.6 to build it:
# assuming Visual Studio 15 2017 is your VS version and that it matches your default profile
$ cmake .. -G "Visual Studio 15 2017" -DCMAKE_TOOLCHAIN_FILE=conan_toolchain.cmake
$ cmake --build . --config Release
...
Building with CMake version: 3.22.6
...
[100%] Built target compressor
$ Release\compressor.exe
Uncompressed size is: 233
Compressed size is: 147
ZLIB VERSION: 1.2.11
$ cmake .. -DCMAKE_TOOLCHAIN_FILE=conan_toolchain.cmake -DCMAKE_BUILD_TYPE=Release
$ cmake --build .
...
Building with CMake version: 3.22.6
...
[100%] Built target compressor
$ ./compressor
Uncompressed size is: 233
Compressed size is: 147
ZLIB VERSION: 1.2.11
Note that when we activated the environment, a new file named
deactivate_conanbuild.sh/bat
was created in the same folder. If you source this file
you can restore the environment as it was before.
$ deactivate_conanbuild.bat
$ source deactivate_conanbuild.sh
Restoring environment
Run cmake
and check the version, it will be the version that was installed previous to
the environment activation:
$ cmake --version
cmake version 3.22.0
...
Note
Best practice
tool_requires
and tool packages are intended for executable applications, like cmake
or ninja
. Do not
use tool_requires
to depend on library or library-like dependencies.
See also
Using the same requirement as a requires and as a tool_requires
Using conf to set a toolchain from a tool requires