Built-in options

Meson provides two kinds of options: build options provided by the build files and built-in options that are either universal options, base options, compiler options.

Universal options

All these can be set by passing -Doption=value to meson (aka meson setup), or by setting them inside default_options of project() in your meson.build. Some options can also be set by --option=value, or --option value -- a list is shown by running meson setup --help.

For legacy reasons --warnlevel is the cli argument for the warning_level option.

They can also be edited after setup using meson configure -Doption=value.

Installation options are usually relative to the prefix but it should not be relied on, since they can be absolute paths in the following cases:

• When the prefix is /usr: sysconfdir defaults to /etc, localstatedir defaults to /var, and sharedstatedir defaults to /var/lib
• When the prefix is /usr/local: localstatedir defaults to /var/local, and sharedstatedir defaults to /var/local/lib
• When an absolute path outside of prefix is provided by the user/distributor.

Directories

Option	Default value	Description
prefix	see below	Installation prefix
bindir	bin	Executable directory
datadir	share	Data file directory
includedir	include	Header file directory
infodir	share/info	Info page directory
libdir	see below	Library directory
licensedir	see below	Licenses directory (since 1.1.0)
libexecdir	libexec	Library executable directory
localedir	share/locale	Locale data directory
localstatedir	var	Localstate data directory
mandir	share/man	Manual page directory
sbindir	sbin	System executable directory
sharedstatedir	com	Architecture-independent data directory
sysconfdir	etc	Sysconf data directory

prefix defaults to C:/ on Windows, and /usr/local otherwise. You should always override this value.

libdir is automatically detected based on your platform, it should be correct when doing "native" (build machine == host machine) compilation. For cross compiles Meson will try to guess the correct libdir, but it may not be accurate, especially on Linux where different distributions have different defaults. Using a cross file, particularly the paths section may be necessary.

licensedir is empty by default. If set, it defines the default location to install a dependency manifest and project licenses. For more details, see meson.install_dependency_manifest().

Core options

Options that are labeled "per machine" in the table are set per machine. See the specifying options per machine section for details.

Option	Default value	Description	Is per machine	Per subproject (since)
auto_features {enabled, disabled, auto}	auto	Override value of all 'auto' features	no	no
backend {ninja, vs, vs2010, vs2012, vs2013, vs2015, vs2017, vs2019, vs2022, xcode, none}	ninja	Backend to use	no	no
genvslite {vs2022}	vs2022	Setup multi-buildtype ninja build directories and Visual Studio solution	no	no
buildtype {plain, debug, debugoptimized, release, minsize, custom}	debug	Build type to use	no	1.8.0
debug	true	Enable debug symbols and other information	no	1.8.0
default_both_libraries {shared, static, auto}	shared	Default library type for both_libraries	no	1.8.0
default_library {shared, static, both}	shared	Default library type	no	0.54.0
errorlogs	true	Whether to print the logs from failing tests.	no	no
install_umask {preserve, 0000-0777}	022	Default umask to apply on permissions of installed files	no	no
layout {mirror,flat}	mirror	Build directory layout	no	no
optimization {plain, 0, g, 1, 2, 3, s}	0	Optimization level	no	1.8.0
pkg_config_path {OS separated path}	''	Additional paths for pkg-config to search before builtin paths	yes	no
prefer_static	false	Whether to try static linking before shared linking	no	no
cmake_prefix_path	[]	Additional prefixes for cmake to search before builtin paths	yes	no
stdsplit	true	Split stdout and stderr in test logs	no	no
strip	false	Strip targets on install	no	1.8.0
unity {on, off, subprojects}	off	Unity build	no	1.8.0
unity_size {>=2}	4	Unity file block size	no	1.8.0
warning_level {0, 1, 2, 3, everything}	1	Set the warning level. From 0 = compiler default to everything = highest	no	0.56.0
werror	false	Treat warnings as errors	no	0.54.0
wrap_mode {default, nofallback, nodownload, forcefallback, nopromote}	default	Wrap mode to use	no	no
force_fallback_for	[]	Force fallback for those dependencies	no	no
vsenv	false	Activate Visual Studio environment	no	no

(For the Rust language only, warning_level=0 disables all warnings).

Details for backend

Several build file formats are supported as command runners to build the configured project. Meson prefers ninja by default, but platform-specific backends are also available for better IDE integration with native tooling: Visual Studio for Windows, and xcode for macOS. It is also possible to configure with no backend at all, which is an error if you have targets to build, but for projects that need configuration + testing + installation allows for a lighter automated build pipeline.

Details for genvslite

Setup multiple buildtype-suffixed, ninja-backend build directories (e.g. [builddir]_[debug/release/etc.]) and generate [builddir]_vs containing a Visual Studio solution with multiple configurations that invoke a meson compile of the setup build directories, as appropriate for the current configuration (buildtype).

This has the effect of a simple setup macro of multiple 'meson setup ...' invocations with a set of different buildtype values. E.g. meson setup ... --genvslite vs2022 somebuilddir does the following -

meson setup ... --backend ninja --buildtype debug somebuilddir_debug
meson setup ... --backend ninja --buildtype debugoptimized somebuilddir_debugoptimized
meson setup ... --backend ninja --buildtype release somebuilddir_release

and additionally creates another 'somebuilddir_vs' directory that contains a generated multi-configuration visual studio solution and project(s) that are set to build/compile with the somebuilddir_[...] that's appropriate for the solution's selected buildtype configuration.

Details for buildtype

For setting optimization levels and toggling debug, you can either set the buildtype option, or you can set the optimization and debug options which give finer control over the same. Whichever you decide to use, the other will be deduced from it. For example, -Dbuildtype=debugoptimized is the same as -Ddebug=true -Doptimization=2 and vice-versa. This table documents the two-way mapping:

buildtype	debug	optimization
plain	false	plain
debug	true	0
debugoptimized	true	2
release	false	3
minsize	true	s

All other combinations of debug and optimization set buildtype to 'custom'.

Note that -Ddebug=false does not cause the compiler preprocessor macro NDEBUG to be defined. The macro can be defined using the base option b_ndebug, described below.

Details for warning_level

Exact flags per warning level is compiler specific, but there is an approximate table for most common compilers.

Warning level	GCC/Clang	MSVC
0
1	-Wall	/W2
2	-Wall -Wextra	/W3
3	-Wall -Wextra -Wpedantic	/W4
everything	-Weverything	/Wall

Clang's -Weverything is emulated on GCC by passing all known warning flags.

Details for vsenv

The --vsenv argument is supported since 0.60.0, -Dvsenv=true syntax is supported since 1.1.0.

Since 0.59.0, meson automatically activates a Visual Studio environment on Windows for all its subcommands, but only if no other compilers (e.g. gcc or clang) are found, and silently continues if Visual Studio activation fails.

Setting the vsenv option to true forces Visual Studio activation even when other compilers are found. It also make Meson abort with an error message when activation fails.

vsenv is true by default when using the vs backend.

Details for default_both_libraries

Since 1.6.0, you can specify the default type of library selected when using a both_libraries object with default_both_libraries. Note that, unlike default_library, this option does not affect how the library artifacts are built, but how they are internally linked to the dependent targets within the same project.

The possible values of this option are 'shared' (default value, compatible with previous meson versions), 'static', and 'auto'. With auto, the value from the default_library option is used, unless it is 'both', in which case 'shared' is used instead.

When default_both_libraries is 'auto', passing a both_libs dependency in both_libraries() will link the static dependency with the static lib, and the shared dependency with the shared lib.

Base options

These are set in the same way as universal options, either by -Doption=value, or by setting them inside default_options of project() in your meson.build. However, they cannot be shown in the output of meson setup --help because they depend on both the current platform and the compiler that will be selected. The only way to see them is to setup a builddir and then run meson configure on it with no options.

The following options are available. Note that they may not be available on all platforms or with all compilers:

Option	Default value	Possible values	Description
b_asneeded	true	true, false	Use -Wl,--as-needed when linking
b_bitcode	false	true, false	Embed Apple bitcode, see below
b_colorout	always	auto, always, never	Use colored output
b_coverage	false	true, false	Enable coverage tracking
b_lundef	true	true, false	Don't allow undefined symbols when linking
b_lto	false	true, false	Use link time optimization
b_lto_threads	0	Any integer*	Use multiple threads for lto. (Added in 0.57.0)
b_lto_mode	default	default, thin	Select between lto modes, thin and default. (Added in 0.57.0)
b_thinlto_cache	false	true, false	Enable LLVM's ThinLTO cache for faster incremental builds. (Added in 0.64.0)
b_thinlto_cache_dir	(Internal build dir)	true, false	Specify where to store ThinLTO cache objects. (Added in 0.64.0)
b_ndebug	false	true, false, if-release	Disable asserts
b_pch	true	true, false	Use precompiled headers
b_pgo	off	off, generate, use	Use profile guided optimization
b_sanitize	none	see below	Code sanitizer to use
b_staticpic	true	true, false	Build static libraries as position independent
b_pie	false	true, false	Build position-independent executables (since 0.49.0)
b_vscrt	from_buildtype	none, md, mdd, mt, mtd, from_buildtype, static_from_buildtype	VS runtime library to use (since 0.48.0) (static_from_buildtype since 0.56.0)

The default and possible values of sanitizers changed in 1.8. Before 1.8 they were string values, and restricted to a specific subset of values: none, address, thread, undefined, memory, leak, or address,undefined. In 1.8 it was changed to a free form array of sanitizers, which are checked by a compiler and linker check. For backwards compatibility reasons get_option('b_sanitize') continues to return a string with the array values separated by a comma. Furthermore:

• If the b_sanitize option is empty, the 'none' string is returned.

• If it contains only the values 'address' and 'undefined', they are always returned as the 'address,undefined' string, in this order.

• Otherwise, the array elements are returned in undefined order.

* < 0 means disable, == 0 means automatic selection, > 0 sets a specific number to use

LLVM supports thin lto, for more discussion see LLVM's documentation

The default value of b_vscrt is from_buildtype. The following table is used internally to pick the CRT compiler arguments for from_buildtype or static_from_buildtype (since 0.56) based on the value of the buildtype option:

buildtype	from_buildtype	static_from_buildtype
debug	/MDd	/MTd
debugoptimized	/MD	/MT
release	/MD	/MT
minsize	/MD	/MT
custom	error!	error!

Notes about Apple Bitcode support

b_bitcode will pass -fembed-bitcode while compiling and will pass -Wl,-bitcode_bundle while linking. These options are incompatible with b_asneeded, so that option will be silently disabled.

shared_module()s will not have bitcode embedded because -Wl,-bitcode_bundle is incompatible with -Wl,-undefined,dynamic_lookup which is necessary for shared modules to work.

Compiler options

Same caveats as base options above.

The following options are available. They can be set by passing -Doption=value to meson. Note that both the options themselves and the possible values they can take will depend on the target platform or compiler being used:

Option	Default value	Possible values	Description
c_args		free-form comma-separated list	C compile arguments to use
c_link_args		free-form comma-separated list	C link arguments to use
c_std	none	none, c89, c99, c11, c17, c18, c2x, c23, c2y, gnu89, gnu99, gnu11, gnu17, gnu18, gnu2x, gnu23, gnu2y	C language standard to use
c_winlibs	see below	free-form comma-separated list	Standard Windows libs to link against
c_thread_count	4	integer value ≥ 0	Number of threads to use with emcc when using threads
cpp_args		free-form comma-separated list	C++ compile arguments to use
cpp_link_args		free-form comma-separated list	C++ link arguments to use
cpp_std	none	none, c++98, c++03, c++11, c++14, c++17, c++20 c++2a, c++1z, gnu++03, gnu++11, gnu++14, gnu++17, gnu++1z, gnu++2a, gnu++20, vc++14, vc++17, vc++20, vc++latest	C++ language standard to use
cpp_debugstl	false	true, false	C++ STL debug mode
cpp_eh	default	none, default, a, s, sc	C++ exception handling type
cpp_rtti	true	true, false	Whether to enable RTTI (runtime type identification)
cpp_thread_count	4	integer value ≥ 0	Number of threads to use with emcc when using threads
cpp_winlibs	see below	free-form comma-separated list	Standard Windows libs to link against
fortran_std	none	[none, legacy, f95, f2003, f2008, f2018]	Fortran language standard to use
cuda_ccbindir		filesystem path	CUDA non-default toolchain directory to use (-ccbin) (Added in 0.57.1)

The default values of c_winlibs and cpp_winlibs are in compiler-specific argument forms, but the libraries are: kernel32, user32, gdi32, winspool, shell32, ole32, oleaut32, uuid, comdlg32, advapi32.

All these <lang>_* options are specified per machine. See below in the specifying options per machine section on how to do this in cross builds.

When using MSVC, cpp_eh=[value] will result in /EH[value] being passed. The magic value none translates to s-c- to disable exceptions. Since 0.51.0 default translates to sc. When using gcc-style compilers, nothing is passed (allowing exceptions to work), while cpp_eh=none passes -fno-exceptions.

Since 0.54.0 The <lang>_thread_count option can be used to control the value passed to -s PTHREAD_POOL_SIZE when using emcc. No other c/c++ compiler supports this option.

Since 0.63.0 all compiler options can be set per subproject, see here for details on how the default value is inherited from the main project. This is useful, for example, when the main project requires C++11, but a subproject requires C++14. The cpp_std value from the subproject's default_options is now respected.

Since 1.3.0 c_std and cpp_std options now accept a list of values. Projects that prefer GNU C, but can fallback to ISO C, can now set, for example, default_options: 'c_std=gnu11,c11', and it will use gnu11 when available, but fallback to c11 otherwise. It is an error only if none of the values are supported by the current compiler. Likewise, a project that can take benefit of c++17 but can still build with c++11 can set default_options: 'cpp_std=c++17,c++11'. This allows us to deprecate gnuXX values from the MSVC compiler. That means that default_options: 'c_std=gnu11' will now print a warning with MSVC but fallback to c11. No warning is printed if at least one of the values is valid, i.e. default_options: 'c_std=gnu11,c11'. In the future that deprecation warning will become an hard error because c_std=gnu11 should mean GNU is required, for projects that cannot be built with MSVC for example.

Specifying options per machine

Since 0.51.0, some options are specified per machine rather than globally for all machine configurations. Prefixing the option with build. only affects the build machine configuration, while leaving it unprefixed only affects the host machine configuration. For example:

• build.pkg_config_path controls the paths pkg-config will search for native: true (build machine) dependencies.

• pkg_config_path controls the paths pkg-config will search for native: false (host machine) dependencies.

This is useful for cross builds. In native builds, the build and host machines are the same, and the unprefixed option alone will suffice.

Prior to 0.51.0, these options only affected native builds when specified on the command line as there was no build. prefix. Similarly named fields in the [properties] section of the cross file would affect cross compilers, but the code paths were fairly different, allowing differences in behavior to crop out.

Specifying options per subproject

Several built-in options and all compiler options can be defined per subproject. This is useful, for example, when building shared libraries in the main project and statically linking a subproject, or when the main project must build with no warnings but some subprojects cannot.

Most of the time, this would be used either in the parent project by setting subproject's default_options (e.g. subproject('foo', default_options: 'default_library=static')), or by the user through the command line: -Dfoo:default_library=static.

The value is overridden in this order:

• opt=value from parent project's default_options
• opt=value from subproject's default_options
• subp:opt=value from parent project's default options
• opt=value from subproject() default_options
• opt=value from machine file
• opt=value from command line
• subp:opt=value from machine file
• subp:opt=value from command line

Old behavior

Between 0.54.0 and 1.7.x only a few options could be defined per subproject:

• default_library and werror since 0.54.0;
• warning_level since 0.56.0;
• compiler options since 0.63.0

The value was overridden in this order:

• Value from parent project
• Value from subproject's default_options
• Value from subproject() default_options
• Value from machine file
• Value from command line

Module options

Some Meson modules have built-in options. They can be set by prefixing the option with the module's name: -D<module>.<option>=<value> (e.g. -Dpython.platlibdir=/foo).

Pkgconfig module

Option	Default value	Possible values	Description
relocatable	false	true, false	Generate the pkgconfig files as relocatable (Since 0.63.0)

Since 0.63.0 The pkgconfig.relocatable option is used by the pkgconfig module–namely pkg.generate()–and affects how the prefix (not to be confused with the install prefix) in the generated pkgconfig file is set. When it is true, the prefix will be relative to the install_dir-this allows the pkgconfig file to be moved around and still work, as long as the relative path is not broken. In general, this allows for the whole installed package to be placed anywhere on the system and still work as a dependency. When it is set to false, the prefix will be the same as the install prefix.

An error will be raised if pkgconfig.relocatable is true and the install_dir for a generated pkgconfig file points outside the install prefix. For example: if the install prefix is /usr and the install_dir for a pkgconfig file is /var/lib/pkgconfig.

Python module

Option	Default value	Possible values	Description
bytecompile	0	integer from -1 to 2	What bytecode optimization level to use (Since 1.2.0)
install_env	prefix	{auto,prefix,system,venv}	Which python environment to install to (Since 0.62.0)
platlibdir		Directory path	Directory for site-specific, platform-specific files (Since 0.60.0)
purelibdir		Directory path	Directory for site-specific, non-platform-specific files (Since 0.60.0)
allow_limited_api	true	true, false	Disables project-wide use of the Python Limited API (Since 1.3.0)

Since 0.60.0 The python.platlibdir and python.purelibdir options are used by the python module methods python.install_sources() and python.get_install_dir(); Meson tries to detect the correct installation paths and make them relative to the installation prefix by default which will often result in the interpreter not finding the installed python modules unless prefix is /usr on Linux, or, for instance, C:\Python39 on Windows. These options can be absolute paths outside of prefix.

Since 0.62.0 The python.install_env option is used to detect the correct installation path. Setting to system will avoid making the paths relative to prefix and instead use the global site-packages of the selected python interpreter directly, even if it is a venv. Setting to venv will instead use the paths for the virtualenv the python found installation comes from (or fail if it is not a virtualenv). Setting to auto will check if the found installation is a virtualenv, and use venv or system as appropriate (but never prefix). Note that Conda environments are treated as system. This option is mutually exclusive with the platlibdir/purelibdir.

For backwards compatibility purposes, the default install_env is prefix.

Since 1.2.0 The python.bytecompile option can be used to enable compiling python bytecode. Bytecode has 3 optimization levels:

• 0, bytecode without optimizations
• 1, bytecode with some optimizations
• 2, bytecode with some more optimizations

To this, Meson adds level -1, which is to not attempt to compile bytecode at all.

Since 1.3.0 The python.allow_limited_api option affects whether the limited_api keyword argument of the extension_module method is respected. If set to false, the effect of the limited_api argument is disabled.