New features

Meson 1.1.0 was released on 10 April 2023

clang-cl now accepts cpp_std=c++20

Requires clang-cl 13 or later.

coercing values in the option() function is deprecated

Currently code such as:

option('foo', type : 'boolean', value : 'false')

works, because Meson coerces 'false' to false.

This should be avoided, and will now result in a deprecation warning.

New declare_dependency(objects: ) argument

A new argument to declare_dependency makes it possible to add objects directly to executables that use an internal dependency, without going for example through link_whole.

Dump devenv into file and select format

meson devenv --dump [<filename>] command now takes an optional filename argument to write the environment into a file instead of printing to stdout.

A new --dump-format argument has been added to select which shell format should be used. There are currently 3 formats supported:

• sh: Lines are in the format VAR=/prepend:$VAR:/append.
• export: Same as sh but with extra export VAR lines.
• vscode: Same as sh but without $VAR substitution because they do not seems to be properly supported by vscode.

Feature objects now have an enable_auto_if method

This performs the opposite task of the disable_auto_if method, enabling the feature if the condition is true.

Add a FeatureOption.enable_if and .disable_if

These are useful when features need to be constrained to pass to dependency(), as the behavior of an auto and disabled or enabled feature is markedly different. consider the following case:

opt = get_option('feature').disable_auto_if(not foo)
if opt.enabled() and not foo
  error('Cannot enable feat when foo is not also enabled')
endif
dep = dependency('foo', required : opt)

This could be simplified to

opt = get_option('feature').disable_if(not foo, error_message : 'Cannot enable feature when foo is not also enabled')
dep = dependency('foo', required : opt)

For a real life example, here is some code in mesa:

_llvm = get_option('llvm')
dep_llvm = null_dep
with_llvm = false
if _llvm.allowed()
  dep_llvm = dependency(
    'llvm',
    version : _llvm_version,
    modules : llvm_modules,
    optional_modules : llvm_optional_modules,
    required : (
      with_amd_vk or with_gallium_radeonsi or with_gallium_opencl or with_clc
      or _llvm.enabled()
    ),
    static : not _shared_llvm,
    fallback : ['llvm', 'dep_llvm'],
    include_type : 'system',
  )
  with_llvm = dep_llvm.found()
endif
if with_llvm
  ...
elif with_amd_vk and with_aco_tests
  error('ACO tests require LLVM, but LLVM is disabled.')
elif with_gallium_radeonsi or with_swrast_vk
  error('The following drivers require LLVM: RadeonSI, SWR, Lavapipe. One of these is enabled, but LLVM is disabled.')
elif with_gallium_opencl
  error('The OpenCL "Clover" state tracker requires LLVM, but LLVM is disabled.')
elif with_clc
  error('The CLC compiler requires LLVM, but LLVM is disabled.')
else
  draw_with_llvm = false
endif

simplified to:

_llvm = get_option('llvm') \
  .enable_if(with_amd_vk and with_aco_tests, error_message : 'ACO tests requires LLVM') \
  .enable_if(with_gallium_radeonsi, error_message : 'RadeonSI requires LLVM') \
  .enable_if(with_swrast_vk, error_message : 'Vulkan SWRAST requires LLVM') \
  .enable_if(with_gallium_opencl, error_message : 'The OpenCL Clover state trackers requires LLVM') \
  .enable_if(with_clc, error_message : 'CLC library requires LLVM')

dep_llvm = dependency(
  'llvm',
  version : _llvm_version,
  modules : llvm_modules,
  optional_modules : llvm_optional_modules,
  required : _llvm,
  static : not _shared_llvm,
  fallback : ['llvm', 'dep_llvm'],
  include_type : 'system',
)
with_llvm = dep_llvm.found()

Generated objects can be passed in the objects: keyword argument

In previous versions of Meson, generated objects could only be passed as sources of a build target. This was confusing, therefore generated objects can now be passed in the objects: keyword argument as well.

The project function now supports setting the project license files

This goes together with the license name. The license files can be automatically installed via meson.install_dependency_manifest(), or queried via meson.project_license_files().

A new core directory option "licensedir" is available

This will install a dependency manifest to the specified directory, if none is is explicitly set.

sudo meson install now drops privileges when rebuilding targets

It is common to install projects using sudo, which should not affect build outputs but simply install the results. Unfortunately, since the ninja backend updates a state file when run, it's not safe to run ninja as root at all.

It has always been possible to carefully build with:

ninja && sudo meson install --no-rebuild

Meson now tries to be extra safe as a general solution. sudo meson install will attempt to rebuild, but has learned to run ninja as the original (pre-sudo or pre-doas) user, ensuring that build outputs are generated/compiled as non-root.

meson install now supports user-preferred root elevation tools

Previously, when installing a project, if any files could not be installed due to insufficient permissions the install process was automatically re-run using polkit. Now it prompts to ask whether that is desirable, and checks for CLI-based tools such as sudo or opendoas or $MESON_ROOT_CMD, first.

Meson will no longer attempt privilege elevation at all, when not running interactively.

Support for reading options from meson.options

Support has been added for reading options from meson.options instead of meson_options.txt. These are equivalent, but not using the .txt extension for a build file has a few advantages, chief among them many tools and text editors expect a file with the .txt extension to be plain text files, not build scripts.

Redirect introspection outputs to stderr

meson introspect used to disable logging to stdout to not interfere with generated json. It now redirect outputs to stderr to allow printing warnings to the console while keeping stdout clean for json outputs.

New "none" backend

The --backend=none option has been added, to configure a project that has no build rules, only install rules. This avoids depending on ninja.

compiler.preprocess()

Dependencies keyword argument can now be passed to compiler.preprocess() to add include directories or compiler arguments.

Generated sources such as custom targets are now allowed too.

New pybind11 custom dependency

dependency('pybind11') works with pkg-config and cmake without any special support, but did not handle the pybind11-config script.

This is useful because the config-tool will work out of the box when pybind11 is installed, but the pkg-config and cmake files are shoved into python's site-packages, which makes it impossible to use in an out of the box manner.

Allow --reconfigure and --wipe of empty builddir

meson setup --reconfigure builddir and meson setup --wipe builddir are now accepting builddir/ to be empty or containing a previously failed setup attempt. Note that in that case previously passed command line options must be repeated as only a successful build saves configured options.

This is useful for example with scripts that always repeat all options, meson setup builddir --wipe -Dfoo=bar will always work regardless whether it is a first invocation or not.

Allow custom install scripts to run with --dry-run option

An new dry_run keyword is added to meson.add_install_script() to allow a custom install script to run when meson is invoked with meson install --dry-run.

In dry run mode, the MESON_INSTALL_DRY_RUN environment variable is set.