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.

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:

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.

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.

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 on this page.

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:

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:

foo_dep = declare_dependency(...)

Then any project that wants to use it can write out the following declaration in their main meson.build file.

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.

Dependencies with custom lookup functionality

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.

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.

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 has been compiled for single-threaded use instead.

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.

MPI

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.

Qt5

Meson has native Qt5 support. Its usage is best demonstrated with an example.

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.

Dependencies using config tools

CUPS, LLVM, PCAP, WxWidgets, libwmf, and GnuStep either do not provide pkg-config modules or additionally can be detected via a config tool (cups-config, llvm-config, etc). Meson has native support for these tools, and then can be found like other dependencies:

pcap_dep = dependency('pcap', version : '>=1.0')
cups_dep = dependency('cups', version : '>=1.4')
llvm_dep = dependency('llvm', version : '>=4.0')

Some of these tools (like wmf and cups) provide both pkg-config and config tools support. You can force one or another via the method keyword:

wmf_dep = dependency('wmf', method : 'config-tool')

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:

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):

llvm_dep = dependency(
  'llvm', version : '>= 4.0', modules : ['amdgpu'], optional_modules : ['inteljitevents'],
)

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