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
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
Meson also allows to get variables that are defined in the
pkg-config file. This can be done by using the
zdep_prefix = zdep.get_pkgconfig_variable('prefix')
These variables can also be redefined by passing the
parameter, which might be useful in certain situations:
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 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
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 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
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
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
function provided by GTest:
gtest_dep = dependency('gtest', main : true, required : false) e = executable('testprog', 'test.cc', dependencies : gtest_dep) test('gtest test', e)
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,
mpif77. If these
are not in your path, they can be specified by setting the standard
MPIF77, during configuration.
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')
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
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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