New features

Allow early return from a script

Added the function subdir_done(). Its invocation exits the current script at the point of invocation. All previously invoked build targets and commands are build/executed. All following ones are ignored. If the current script was invoked via subdir() the parent script continues normally.

Concatenate string literals returned from get_define()

After obtaining the value of a preprocessor symbol consecutive string literals are merged into a single string literal. For example a preprocessor symbol's value "ab" "cd" is returned as "abcd".

ARM compiler(version 6) for C and CPP

Cross-compilation is now supported for ARM targets using ARM compiler version 6 - ARMCLANG. The required ARMCLANG compiler options for building a shareable library are not included in the current Meson implementation for ARMCLANG support, so it can not build shareable libraries. This current Meson implementation for ARMCLANG support can not build assembly files with arm syntax (we need to use armasm instead of ARMCLANG for the .s files with this syntax) and only supports GNU syntax.

The default extension of the executable output is .axf. The environment path should be set properly for the ARM compiler executables. The --target, -mcpu options with the appropriate values should be mentioned in the cross file as shown in the snippet below.

c_args      = ['--target=arm-arm-none-eabi', '-mcpu=cortex-m0plus']
cpp_args    = ['--target=arm-arm-none-eabi', '-mcpu=cortex-m0plus']


  • The current changes are tested on Windows only.
  • PIC support is not enabled by default for ARM, if users want to use it, they need to add the required arguments explicitly from cross-file(c_args/cpp_args) or some other way.

New base build option for LLVM (Apple) bitcode support

When building with clang on macOS, you can now build your static and shared binaries with embedded bitcode by enabling the b_bitcode base option by passing -Db_bitcode=true to Meson.

This is better than passing the options manually in the environment since Meson will automatically disable conflicting options such as b_asneeded, and will disable bitcode support on targets that don't support it such as shared_module().

Since this requires support in the linker, it is currently only enabled when using Apple ld. In the future it can be extended to clang on other platforms too.

New compiler check: check_header()

The existing compiler check has_header() only checks if the header exists, either with the __has_include C++11 builtin, or by running the pre-processor.

However, sometimes the header you are looking for is unusable on some platforms or with some compilers in a way that is only detectable at compile-time. For such cases, you should use check_header() which will include the header and run a full compile.

Note that has_header() is much faster than check_header(), so it should be used whenever possible.

New action copy: for configure_file()

In addition to the existing actions configuration: and command:, configure_file() now accepts a keyword argument copy: which specifies a new action to copy the file specified with the input: keyword argument to a file in the build directory with the name specified with the output: keyword argument.

These three keyword arguments are, as before, mutually exclusive. You can only do one action at a time.

New keyword argument encoding: for configure_file()

Add a new keyword to configure_file() that allows the developer to specify the input and output file encoding. The default value is the same as before: UTF-8.

In the past, Meson would not handle non-UTF-8/ASCII files correctly, and in the worst case would try to coerce it to UTF-8 and mangle the data. UTF-8 is the standard encoding now, but sometimes it is necessary to process files that use a different encoding.

For additional details see #3135.

New keyword argument output_format: for configure_file()

When called without an input file, configure_file generates a C header file by default. A keyword argument was added to allow specifying the output format, for example for use with nasm or yasm:

conf = configuration_data()
conf.set('FOO', 1)

  configuration: conf,
  output_format: 'nasm')

Substitutions in custom_target(depfile:)

The depfile keyword argument to custom_target now accepts the @BASENAME@ and @PLAINNAME@ substitutions.

Deprecated build_always: for custom targets

Setting build_always to true for a custom target not only marks the target to be always considered out of date, but also adds it to the set of default targets. This option is therefore deprecated and the new option build_always_stale is introduced.

build_always_stale only marks the target to be always considered out of date, but does not add it to the set of default targets. The old behaviour can be achieved by combining build_always_stale with build_by_default.

The documentation has been updated accordingly.

New built-in object type: dictionary

Meson dictionaries use a syntax similar to python's dictionaries, but have a narrower scope: they are immutable, keys can only be string literals, and initializing a dictionary with duplicate keys causes a fatal error.

Example usage:

d = {'foo': 42, 'bar': 'baz'}

foo = d.get('foo')
foobar = d.get('foobar', 'fallback-value')

foreach key, value : d
  Do something with key and value

Array options treat -Dopt= and -Dopt=[] as equivalent

Prior to this change passing -Dopt= to an array opt would be interpreted as [''] (an array with an empty string), now -Dopt= is the same as -Dopt=[], an empty list.

Feature detection based on meson_version: in project()

Meson will now print a WARNING: message during configuration if you use a function or a keyword argument that was added in a meson version that's newer than the version specified inside project(). For example:

project('featurenew', meson_version: '>=0.43')

cdata = configuration_data()
cdata.set('FOO', 'bar')

This will output:

The Meson build system
Version: 0.47.0.dev1
Source dir: C:\path\to\srctree
Build dir: C:\path\to\buildtree
Build type: native build
Project name: featurenew
Project version: undefined
Build machine cpu family: x86_64
Build machine cpu: x86_64
WARNING: Project targetting '>=0.43' but tried to use feature introduced in '0.44.0': configuration_data.get_unquoted()
Message: bar
Build targets in project: 0
WARNING: Project specifies a minimum meson_version '>=0.43' which conflicts with:
 * 0.44.0: {'configuration_data.get_unquoted()'}

New type of build option for features

A new type of option called feature can be defined in meson_options.txt for the traditional enabled / disabled / auto tristate. The value of this option can be passed to the required keyword argument of functions dependency(), find_library(), find_program() and add_languages().

A new global option auto_features has been added to override the value of all auto features. It is intended to be used by packagers to have full control on which feature must be enabled or disabled.

New options to gnome.gdbus_codegen()

You can now pass additional arguments to gdbus-codegen using the extra_args keyword. This is the same for the other gnome function calls.

Meson now automatically adds autocleanup support to the generated code. This can be modified by setting the autocleanup keyword.

For example:

sources += gnome.gdbus_codegen('com.mesonbuild.Test',
  autocleanup : 'none',
  extra_args : ['--pragma-once'])

Made 'install' a top level Meson command

You can now run meson install in your build directory and it will do the install. It has several command line options you can toggle the behaviour that is not in the default ninja install invocation. This is similar to how meson test already works.

For example, to install only the files that have changed, you can do:

$ meson install --only-changed

install_mode: keyword argument extended to all installable targets

It is now possible to pass an install_mode argument to all installable targets, such as executable(), libraries, headers, man pages and custom/generated targets.

The install_mode argument can be used to specify the file mode in symbolic format and optionally the owner/uid and group/gid for the installed files.

New built-in option install_umask with a default value 022

This umask is used to define the default permissions of files and directories created in the install tree. Files will preserve their executable mode, but the exact permissions will obey the install_umask.

The install_umask can be overridden in the meson command-line:

$ meson --install-umask=027 builddir/

A project can also override the default in the project() call:

project('myproject', 'c',
  default_options : ['install_umask=027'])

To disable the install_umask, set it to preserve, in which case permissions are copied from the files in their origin.

Octal and binary string literals

Octal and binary integer literals can now be used in build and option files.

int_493 = 0o755
int_1365 = 0b10101010101

New keyword arguments: 'check' and 'capture' for run_command()

If check: is true, then the configuration will fail if the command returns a non-zero exit status. The default value is false for compatibility reasons.

run_command() used to always capture the output and stored it for use in build files. However, sometimes the stdout is in a binary format which is meant to be discarded. For that case, you can now set the capture: keyword argument to false.

Windows resource files dependencies

The compile_resources() function of the windows module now takes the depend_files: and depends: keywords.

When using binutils's windres, dependencies on files #include'd by the preprocessor are now automatically tracked.

Polkit support for privileged installation

When running install, if installation fails with a permission error and pkexec is available, Meson will attempt to use it to spawn a permission dialog for privileged installation and retry the installation.

If pkexec is not available, the old behaviour is retained and you will need to explicitly run the install step with sudo.

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