--- short-description: Dependencies for external libraries and frameworks ... # Dependencies Very few applications are fully self-contained, but rather they use external libraries and frameworks to do their work. Meson makes it very easy to find and use external dependencies. Here is how one would use the zlib compression library. ```meson zdep = dependency('zlib', version : '>=1.2.8') exe = executable('zlibprog', 'prog.c', dependencies : zdep) ``` First Meson is told to find the external library `zlib` and error out if it is not found. The `version` keyword is optional and specifies a version requirement for the dependency. Then an executable is built using the specified dependency. Note how the user does not need to manually handle compiler or linker flags or deal with any other minutiae. If you have multiple dependencies, pass them as an array: ```meson executable('manydeps', 'file.c', dependencies : [dep1, dep2, dep3, dep4]) ``` If the dependency is optional, you can tell Meson not to error out if the dependency is not found and then do further configuration. ```meson opt_dep = dependency('somedep', required : false) if opt_dep.found() # Do something. else # Do something else. endif ``` You can pass the `opt_dep` variable to target construction functions whether the actual dependency was found or not. Meson will ignore non-found dependencies. Meson also allows to get variables that are defined in the `pkg-config` file. This can be done by using the `get_pkgconfig_variable` function. ```meson zdep_prefix = zdep.get_pkgconfig_variable('prefix') ``` These variables can also be redefined by passing the `define_variable` parameter, which might be useful in certain situations: ```meson zdep_prefix = zdep.get_pkgconfig_variable('libdir', define_variable: ['prefix', '/tmp']) ``` The dependency detector works with all libraries that provide a `pkg-config` file. Unfortunately several packages don't provide pkg-config files. Meson has autodetection support for some of these, and they are described [later in this page](#dependencies-with-custom-lookup-functionality). # Declaring your own You can declare your own dependency objects that can be used interchangeably with dependency objects obtained from the system. The syntax is straightforward: ```meson my_inc = include_directories(...) my_lib = static_library(...) my_dep = declare_dependency(link_with : my_lib, include_directories : my_inc) ``` This declares a dependency that adds the given include directories and static library to any target you use it in. # Building dependencies as subprojects Many platforms do not provide a system package manager. On these systems dependencies must be compiled from source. Meson's subprojects make it simple to use system dependencies when they are available and to build dependencies manually when they are not. To make this work, the dependency must have Meson build definitions and it must declare its own dependency like this: ```meson foo_dep = declare_dependency(...) ``` Then any project that wants to use it can write out the following declaration in their main `meson.build` file. ```meson foo_dep = dependency('foo', fallback : ['foo', 'foo_dep']) ``` What this declaration means is that first Meson tries to look up the dependency from the system (such as by using pkg-config). If it is not available, then it builds subproject named `foo` and from that extracts a variable `foo_dep`. That means that the return value of this function is either an external or an internal dependency object. Since they can be used interchangeably, the rest of the build definitions do not need to care which one it is. Meson will take care of all the work behind the scenes to make this work. # Dependency method You can use the keyword `method` to let meson know what method to use when searching for the dependency. The default value is `auto`. Aditional dependencies methods are `pkg-config`, `config-tool`, `cmake`, `system`, `sysconfig`, `qmake`, `extraframework` and `dub`. ```meson cups_dep = dependency('cups', method : 'pkg-config') ``` The dependency method order for `auto` is: 1. `pkg-config` 2. `cmake` 3. `extraframework` (OSX only) ## CMake Meson can use the CMake `find_package()` function to detect dependencies with the builtin `Find.cmake` modules and exported project configurations (usually in `/usr/lib/cmake`). Meson is able to use both the old-style `_LIBRARIES` variables as well as imported targets. It is possible to manually specify a list of CMake targets that should be used with the `modules` property. Howerver, this step is optional since meson tries to automatically guess the correct target based on the name of the dependency. Depending on the dependency it may be neccessary to explicitly specify a CMake target with the `modules` property if meson is unable to guess it automatically. ```meson cmake_dep = dependency('ZLIB', method : 'cmake', modules : ['ZLIB::ZLIB']) ``` ### Some notes on Dub Please understand that meson is only able to find dependencies that exist in the local Dub repository. You need to manually fetch and build the target dependencies. For `urld`. ``` dub fetch urld dub build urld ``` Other thing you need to keep in mind is that both meson and Dub need to be using the same compiler. This can be achieved using Dub's `-compiler` argument and/or manually setting the `DC` environment variable when running meson. ``` dub build urld --compiler=dmd DC="dmd" meson builddir ``` # Dependencies with custom lookup functionality Some dependencies have specific detection logic. Generic dependency names are case-sensitive[1](#footnote1), but these dependency names are matched case-insensitively. The recommended style is to write them in all lower-case. In some cases, more than one detection method exists, and the `method` keyword may be used to select a detection method to use. The `auto` method uses any checking mechanisms in whatever order meson thinks is best. e.g. libwmf and CUPS provide both pkg-config and config-tool support. You can force one or another via the `method` keyword: ```meson cups_dep = dependency('cups', method : 'pkg-config') wmf_dep = dependency('libwmf', method : 'config-tool') ``` ## Dependencies using config tools [CUPS](#cups), [LLVM](#llvm), [pcap](#pcap), [WxWidgets](#wxwidgets), [libwmf](#libwmf), [GCrypt](#libgcrypt), and GnuStep either do not provide pkg-config modules or additionally can be detected via a config tool (cups-config, llvm-config, libgcrypt-config, etc). Meson has native support for these tools, and they can be found like other dependencies: ```meson pcap_dep = dependency('pcap', version : '>=1.0') cups_dep = dependency('cups', version : '>=1.4') llvm_dep = dependency('llvm', version : '>=4.0') libgcrypt_dep = dependency('libgcrypt', version: '>= 1.8') ``` ## AppleFrameworks Use the `modules` keyword to list frameworks required, e.g. ```meson dep = dependency('appleframeworks', modules : 'foundation') ``` These dependencies can never be found for non-OSX hosts. ## Boost Boost is not a single dependency but rather a group of different libraries. To use Boost headers-only libraries, simply add Boost as a dependency. ```meson boost_dep = dependency('boost') exe = executable('myprog', 'file.cc', dependencies : boost_dep) ``` To link against boost with Meson, simply list which libraries you would like to use. ```meson boost_dep = dependency('boost', modules : ['thread', 'utility']) exe = executable('myprog', 'file.cc', dependencies : boost_dep) ``` You can call `dependency` multiple times with different modules and use those to link against your targets. If your boost headers or libraries are in non-standard locations you can set the BOOST_ROOT, BOOST_INCLUDEDIR, and/or BOOST_LIBRARYDIR environment variables. You can set the argument `threading` to `single` to use boost libraries that have been compiled for single-threaded use instead. ## CUPS `method` may be `auto`, `config-tool`, `pkg-config`, `cmake` or `extraframework`. ## GL This finds the OpenGL library in a way appropriate to the platform. `method` may be `auto`, `pkg-config` or `system`. ## GTest and GMock GTest and GMock come as sources that must be compiled as part of your project. With Meson you don't have to care about the details, just pass `gtest` or `gmock` to `dependency` and it will do everything for you. If you want to use GMock, it is recommended to use GTest as well, as getting it to work standalone is tricky. You can set the `main` keyword argument to `true` to use the `main()` function provided by GTest: ``` gtest_dep = dependency('gtest', main : true, required : false) e = executable('testprog', 'test.cc', dependencies : gtest_dep) test('gtest test', e) ``` ## libwmf *(added 0.44.0)* `method` may be `auto`, `config-tool` or `pkg-config`. ## LLVM Meson has native support for LLVM going back to version LLVM version 3.5. It supports a few additional features compared to other config-tool based dependencies. As of 0.44.0 Meson supports the `static` keyword argument for LLVM. Before this LLVM >= 3.9 would always dynamically link, while older versions would statically link, due to a quirk in `llvm-config`. ### Modules, a.k.a. Components Meson wraps LLVM's concept of components in it's own modules concept. When you need specific components you add them as modules as meson will do the right thing: ```meson llvm_dep = dependency('llvm', version : '>= 4.0', modules : ['amdgpu']) ``` As of 0.44.0 it can also take optional modules (these will affect the arguments generated for a static link): ```meson llvm_dep = dependency( 'llvm', version : '>= 4.0', modules : ['amdgpu'], optional_modules : ['inteljitevents'], ) ``` ## MPI *(added 0.42.0)* MPI is supported for C, C++ and Fortran. Because dependencies are language-specific, you must specify the requested language using the `language` keyword argument, i.e., * `dependency('mpi', language: 'c')` for the C MPI headers and libraries * `dependency('mpi', language: 'cpp')` for the C++ MPI headers and libraries * `dependency('mpi', language: 'fortran')` for the Fortran MPI headers and libraries Meson prefers pkg-config for MPI, but if your MPI implementation does not provide them, it will search for the standard wrapper executables, `mpic`, `mpicxx`, `mpic++`, `mpifort`, `mpif90`, `mpif77`. If these are not in your path, they can be specified by setting the standard environment variables `MPICC`, `MPICXX`, `MPIFC`, `MPIF90`, or `MPIF77`, during configuration. ## OpenMP *(added 0.46.0)* This dependency selects the appropriate compiler flags and/or libraries to use for OpenMP support. The `language` keyword may used. ## pcap *(added 0.42.0)* `method` may be `auto`, `config-tool` or `pkg-config`. ## libgcrypt *(added 0.49.0)* `method` may be `auto`, `config-tool` or `pkg-config`. ## Python3 Python3 is handled specially by meson: 1. Meson tries to use `pkg-config`. 2. If `pkg-config` fails meson uses a fallback: - On Windows the fallback is the current `python3` interpreter. - On OSX the fallback is a framework dependency from `/Library/Frameworks`. Note that `python3` found by this dependency might differ from the one used in `python3` module because modules uses the current interpreter, but dependency tries `pkg-config` first. `method` may be `auto`, `extraframework`, `pkg-config` or `sysconfig` ## Qt4 & Qt5 Meson has native Qt support. Its usage is best demonstrated with an example. ```meson qt5_mod = import('qt5') qt5widgets = dependency('qt5', modules : 'Widgets') processed = qt5_mod.preprocess( moc_headers : 'mainWindow.h', # Only headers that need moc should be put here moc_sources : 'helperFile.cpp', # must have #include"moc_helperFile.cpp" ui_files : 'mainWindow.ui', qresources : 'resources.qrc', ) q5exe = executable('qt5test', sources : ['main.cpp', 'mainWindow.cpp', processed], dependencies: qt5widgets) ``` Here we have an UI file created with Qt Designer and one source and header file each that require preprocessing with the `moc` tool. We also define a resource file to be compiled with `rcc`. We just have to tell Meson which files are which and it will take care of invoking all the necessary tools in the correct order, which is done with the `preprocess` method of the `qt5` module. Its output is simply put in the list of sources for the target. The `modules` keyword of `dependency` works just like it does with Boost. It tells which subparts of Qt the program uses. You can set the `main` keyword argument to `true` to use the `WinMain()` function provided by qtmain static library (this argument does nothing on platforms other than Windows). Setting the optional `private_headers` keyword to true adds the private header include path of the given module(s) to the compiler flags. (since v0.47.0) **Note** using private headers in your project is a bad idea, do so at your own risk. `method` may be `auto`, `pkgconfig` or `qmake`. ## SDL2 SDL2 can be located using `pkg-confg`, the `sdl2-config` config tool, or as an OSX framework. `method` may be `auto`, `config-tool`, `extraframework` or `pkg-config`. ## Threads This dependency selects the appropriate compiler flags and/or libraries to use for thread support. See [threads](Threads.md). ## Valgrind Meson will find valgrind using `pkg-config`, but only uses the compilation flags and avoids trying to link with it's non-PIC static libs. ## Vulkan *(added 0.42.0)* Vulkan can be located using `pkg-config`, or the `VULKAN_SDK` environment variable. `method` may be `auto`, `pkg-config` or `system`. ## WxWidgets Similar to [Boost](#boost), WxWidgets is not a single library but rather a collection of modules. WxWidgets is supported via `wx-config`. Meson substitutes `modules` to `wx-config` invocation, it generates - `compile_args` using `wx-config --cxxflags $modules...` - `link_args` using `wx-config --libs $modules...` ### Example ```meson wx_dep = dependency( 'wxwidgets', version : '>=3.0.0', modules : ['std', 'stc'], ) ``` ```shell # compile_args: $ wx-config --cxxflags std stc # link_args: $ wx-config --libs std stc ```
1: They may appear to be case-insensitive, if the underlying file system happens to be case-insensitive.