MesonToolchain

Warning

This is an experimental feature subject to breaking changes in future releases.

Available since: 1.33.0

The MesonToolchain can be used in the generate() method:

from conan import ConanFile
from conan.tools.meson import MesonToolchain

class App(ConanFile):
    settings = "os", "arch", "compiler", "build_type"
    requires = "hello/0.1"
    options = {"shared": [True, False]}
    default_options = {"shared": False}

    def generate(self):
        tc = MesonToolchain(self)
        tc.preprocessor_definitions["MYDEFINE"] = "MYDEF_VALUE"
        tc.generate()

The MesonToolchain will generate a file: - conan_meson_native.ini: if doing a native build. - conan_meson_cross.ini: if doing a cross-build (tools.cross_building()).

Important

This class will require very soon to define both the “host” and “build” profiles. It is very recommended to start defining both profiles immediately to avoid future breaking. Furthermore, some features, like trying to cross-compile might not work at all if the “build” profile is not provided.

conan_meson_native.ini will contain the definitions of all the Meson properties related to the Conan options and settings for the current package, platform, etc. This includes but is not limited to the following:

  • Detection of default_library from Conan settings
    • Based on existance/value of a option named shared
  • Detection of buildtype from Conan settings
  • Definition of the C++ standard as necessary
  • The Visual Studio runtime (b_vscrt), obtained from Conan input settings

conan_meson_cross.ini contains the same information as conan_meson_native.ini, but with additional information to describe host, target, and build machines (such as the processor architecture).

Check out the meson documentation for more details on native and cross files:

constructor

def __init__(self, conanfile, backend=None):

Most of the arguments are optional and will be deduced from the current settings, and not necessary to define them.

  • conanfile: the current recipe object. Always use self.
  • backend: the meson backend to use. By default, ninja is used. Possible values: ninja, vs, vs2010, vs2015, vs2017, vs2019, xcode.

project_options

This attribute allows defining Meson project options:

def generate(self):
    tc = MesonToolchain(self)
    tc.project_options["MYVAR"] = "MyValue"
    tc.generate()
  • One project options definition for MYVAR in conan_meson_native.init or conan_meson_cross.ini file.

preprocessor_definitions

This attribute allows defining compiler preprocessor definitions, for multiple configurations (Debug, Release, etc).

def generate(self):
    tc = MesonToolchain(self)
    tc.preprocessor_definitions["MYDEF"] = "MyValue"
    tc.generate()

This will be translated to:

  • One preprocessor definition for MYDEF in conan_meson_native.ini or conan_meson_cross.ini file.

Generators

The MesonToolchain only works with the PkgConfigDeps generator. Please, do not use other generators, as they can have overlapping definitions that can conflict.

Default directories

Since Conan 1.51, MesonToolchain manages some of the directories used by Meson. These are variables declared under the [project options] section of the files conan_meson_native.ini and conan_meson_cross.ini (see more information about Meson directories):

bindir: value coming from self.cpp.package.bindirs. Defaulted to None. sbindir: value coming from self.cpp.package.bindirs. Defaulted to None. libexecdir: value coming from self.cpp.package.bindirs. Defaulted to None. datadir: value coming from self.cpp.package.resdirs. Defaulted to None. localedir: value coming from self.cpp.package.resdirs. Defaulted to None. mandir: value coming from self.cpp.package.resdirs. Defaulted to None. infodir: value coming from self.cpp.package.resdirs. Defaulted to None. includedir: value coming from self.cpp.package.includedirs. Defaulted to None. libdir: value coming from self.cpp.package.libdirs. Defaulted to None.

Notice that it needs a layout to be able to initialize those self.cpp.package.xxxxx variables. For instance:

from conan import ConanFile
from conan.tools.meson import MesonToolchain

class App(ConanFile):
    settings = "os", "arch", "compiler", "build_type"

    def layout(self):
        self.folders.build = "build"
        self.cpp.package.resdirs = ["res"]

    def generate(self):
        tc = MesonToolchain(self)
        self.output.info(tc.project_options["datadir"])  # Will print '["res"]'
        tc.generate()

Note

All of them are saved only if they have any value. If the values are``None``, they won’t be mentioned in [project options] section.

Using the toolchain in developer flow

One of the advantages of using Conan toolchains is that they can help to achieve the exact same build with local development flows, than when the package is created in the cache.

With the MesonToolchain it is possible to do:

# Lets start in the folder containing the conanfile.py
$ mkdir build && cd build
# Install both debug and release deps and create the toolchain
$ conan install ..
# the build type Release is encoded in the toolchain already.
# This conan_meson_native.iniis specific for release
$ meson setup --native-file conan_meson_native.ini build .
$ meson compile -C build

conf

MesonToolchain is affected by these [conf] variables:

  • tools.meson.mesontoolchain:backend. the meson backend to use. Possible values: ninja, vs, vs2010, vs2015, vs2017, vs2019, xcode.
  • tools.apple:sdk_path argument for SDK path in case of Apple cross-compilation. It will be used as value of the flag -isysroot.
  • tools.android:ndk_path argument for NDK path in case of Android cross-compilation. It will be used to get some binaries like c, cpp and ar used in [binaries] section from conan_meson_cross.ini.

Apart from that, since Conan 1.47, you can inject extra flags thanks to these ones:

  • tools.build:cxxflags list of extra C++ flags that will be used by cpp_args.
  • tools.build:cflags list of extra of pure C flags that will be used by c_args.
  • tools.build:sharedlinkflags list of extra linker flags that will be used by c_link_args and cpp_link_args.
  • tools.build:exelinkflags list of extra linker flags that will be used by c_link_args and cpp_link_args.

Cross-building for Apple and Android

It deserves a special mention because MesonToolchain is automatically adding all the flags needed to cross-compile for Apple (MacOS M1, iOS, etc.) and Android.

Apple

It’ll add link flags like -arch XXX, -isysroot [SDK_PATH] and the minimum deployment target flag, e.g., -mios-version-min=8.0 into Meson c_args, c_link_args, cpp_args and cpp_link_args built-in options.

Android

It’ll initialize the c, cpp and ar variables which are needed to cross-compile for Android. For instance:

  • c == $TOOLCHAIN/bin/llvm-ar
  • cpp == $TOOLCHAIN/bin/$TARGET$API-clang
  • ar == $TOOLCHAIN/bin/$TARGET$API-clang++

Where:

  • $TOOLCHAIN: [NDK_PATH]/toolchains/llvm/prebuilt/[OS_BUILD]-x86_64/bin.
  • $TARGET: target triple, e.g., for armv8 will be aarch64-linux-android.
  • $API: Android API version.

Besides that, you’ll always be able to change any of these variables before being applied thanks to the MesonToolchain class interface. For instance:

from conan import ConanFile
from conan.tools.meson import MesonToolchain

class App(ConanFile):
    settings = "os", "arch", "compiler", "build_type"
    requires = "hello/0.1"
    options = {"shared": [True, False]}
    default_options = {"shared": False}

    def generate(self):
        tc = MesonToolchain(self)
        tc.cpp = "/path/to/other/compiler"
        tc.generate()

Objective-C arguments

Since Conan 1.51, it’s been introduced some specific Objective-C/Objective-C++ arguments: objc, objcpp, objc_args, objc_link_args, objcpp_args, and objcpp_link_args, as public attributes of the MesonToolchain class, where the variables objc and objcpp are initialized as clang and clang++ respectively by default.

Note

They will be only initialized if the OS used belongs to any of the Apple ones.