New features (in development)

add_project_dependencies() function

Dependencies can now be added to all build products using add_project_dependencies(). This can be useful in several cases:

  • with special dependencies such as dependency('threads')
  • with system libraries such as find_library('m')
  • with the include_directories keyword argument of declare_dependency(), to add both source and build directories to the include search path

Coverage targets now respect tool config files

gcovr >= 4.2 supports gcovr.cfg in the project source root to configure how coverage is generated. If Meson detects that gcovr will load this file, it no longer excludes the subprojects/ directory from coverage. It's a good default for Meson to guess that projects want to ignore it, but not all projects prefer that and it is assumed that if a gcovr.cfg exists then it will manually include/exclude desired paths.

lcov supports .lcovrc, but only as a systemwide or user setting. This is non-ideal for projects, so Meson will now detect one in the project source root and, if present, manually tell lcov to use it.

D compiler checks

Some compiler checks are implemented for D:

  • run
  • sizeof
  • has_header (to check if a module is present)
  • alignment

Example:

ptr_size = meson.get_compiler('d').sizeof('void*')

Deprecate an option and replace it with a new one

The deprecated keyword argument can now take the name of a new option that replace this option. In that case, setting a value on the deprecated option will set the value on both the old and new names, assuming they accept the same values.

# A boolean option has been replaced by a feature with another name, old true/false values
# are accepted by the new option for backward compatibility.
option('o1', type: 'boolean', value: 'true', deprecated: 'o2')
option('o2', type: 'feature', value: 'enabled', deprecated: {'true': 'enabled', 'false': 'disabled'})

# A project option is replaced by a module option
option('o3', type: 'string', value: '', deprecated: 'python.platlibdir')

Running Windows executables with Wine in meson devenv

When cross compiling for Windows, meson devenv now sets WINEPATH pointing to all directories containing needed DLLs and executables.

Diff files for wraps

Wrap files can now define diff_files, a list of local patch files in diff format. Meson will apply the diff files after extracting or cloning the project, and after applying the overlay archive (patch_*). For this feature, the patch or git command-line tool must be available.

Added preserve_path arg to install_headers

The install_headers() function now has an optional argument preserve_path that allows installing multi-directory headerfile structures that live alongside sourcecode with a single command.

For example, the headerfile structure

headers = [
  'one.h',
  'two.h',
  'alpha/one.h',
  'alpha/two.h',
  'alpha/three.h'
  'beta/one.h'
]

can now be passed to install_headers(headers, subdir: 'mylib', preserve_path: true) and the resulting directory tree will look like

{prefix}
└── include
    └── mylib
        ├── alpha
        │   ├── one.h
        │   ├── two.h
        │   └── three.h
        ├── beta
        │   └── one.h
        ├── one.h
        └── two.h

JAR Resources

The ability to add resources to a JAR has been added. Use the java_resources keyword argument. It takes a sturctured_src object.

jar(
  meson.project_name(),
  sources,
  main_class: 'com.mesonbuild.Resources',
  java_resources: structured_sources(
    files('resources/resource1.txt'),
    {
      'subdir': files('resources/subdir/resource2.txt'),
    }
  )
)

To access these resources in your Java application:

try (InputStreamReader reader = new InputStreamReader(
        Resources.class.getResourceAsStream("/resource1.txt"),
        StandardCharsets.UTF_8)) {
    // ...
}

try (InputStreamReader reader = new InputStreamReader(
        Resources.class.getResourceAsStream("/subdir/resource2.txt"),
        StandardCharsets.UTF_8)) {
    // ...
}

Support for mold linker added

The high performance linker mold can be selected via CC_LD or CXX_LD for Clang and GCC >= 12.0.1.

MSVC now sets the __cplusplus #define accurately

MSVC will always return 199711L for __cplusplus, even when a newer c++ standard is explicitly requested, unless you pass a specific option to the compiler for MSVC 2017 15.7 and newer. Older versions are unaffected by this.

Microsoft's stated rationale is that "a lot of existing code appears to depend on the value of this macro matching 199711L", therefore for compatibility with such (MSVC-only) code they will require opting in to the standards-conformant value.

Meson now always sets the option if it is available, as it is unlikely that users want the default behavior, and impossible to use the default behavior in cross-platform code (which frequently breaks as soon as the first person tries to compile using MSVC).

Added debug function

In addition to the message(), warning() and error() functions there is now the debug() function to log messages that only end up in the meson-log.txt logfile and are not printed to stdout at configure time.

Compiler options can be set per subproject

All compiler options can now be set per subproject. See here for details on how the default value is inherited from 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 subproject's default_options is now respected.

Per-subproject languages

Subprojects does not inherit languages added by main project or other subprojects any more. This could break subprojects that wants to compile e.g. .c files but did not add c language, either in project() or add_languages(), and were relying on the main project to do it for them.

Installed pkgconfig files can now be relocatable

The pkgconfig module now has a module option pkgconfig.relocatable. When set to true, the pkgconfig files generated will have their prefix variable set to be relative to their install_dir.

For example to enable it from the command line run:

meson setup builddir -Dpkgconfig.relocatable=true …

It will only work if the install_dir for the generated pkgconfig files are located inside the install prefix of the package. Not doing so will cause an error.

This should be useful on Windows or any other platform where relocatable packages are desired.

New prefer_static built-in option

Users can now set a boolean, prefer_static, that controls whether or not static linking should be tried before shared linking. This option acts as strictly a preference. If the preferred linking method is not successful, then Meson will fallback and try the other linking method. Specifically setting the static kwarg in the meson.build will take precedence over the value of prefer_static for that specific dependency or find_library call.

Python extension modules now depend on the python library by default

Python extension modules are usually expected to link to the python library and/or its headers in order to build correctly (via the default embed: false, which may not actually link to the library itself). This means that every single use of .extension_module() needed to include the dependencies: py_installation.dependency() kwarg explicitly.

In the interest of doing the right thing out of the box, this is now the default for extension modules that don't already include a dependency on python. This is not expected to break anything, because it should always be needed. Nevertheless, py_installation.dependency().partial_dependency() will be detected as already included while providing no compile/link args.

Python extension modules now build with hidden visibility

Python extension modules are usually expected to only export a single symbol, decorated with the PyMODINIT_FUNC macro and providing the module entry point. On versions of python >= 3.9, the python headers contain GNU symbol visibility attributes to mark the init function with default visibility; it is then safe to set the shared_module() inherited kwarg gnu_symbol_visibility: 'hidden'.

In the interest of doing the right thing out of the box, this is now the default for extension modules for found installations that are new enough to have this set, which is not expected to break anything, but remains possible to set explicitly (in which case that will take precedence).

Added support for multiline fstrings

Added support for multiline f-strings which use the same syntax as f-strings for string substition.

x = 'hello'
y = 'world'

msg = f'''Sending a message...
"@x@ @y@"
'''

which produces:

Sending a message....

"hello world"

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