docs/markdown/Release-notes-for-0.56.0.md

---
title: Release 0.56.0
short-description: Release notes for 0.56.0
...

# New features

## Python 3.5 support will be dropped in the next release

The final [Python 3.5 release was 3.5.10 in September](https://www.python.org/dev/peps/pep-0478/#id4).
This release series is now End-of-Life (EOL). The only LTS distribution that
still only ships Python 3.5 is Ubuntu 16.04, which will be
[EOL in April 2021](https://ubuntu.com/about/release-cycle).

Python 3.6 has numerous features that we find useful such as improved support
for the `typing` module, f-string support, and better integration with the
`pathlib` module.

As a result, we will begin requiring Python 3.6 or newer in Meson 0.57, which
is the next release. Starting with Meson 0.56, we now print a `NOTICE:` when
a `meson` command is run on Python 3.5 to inform users about this. This notice
has also been backported into the 0.55.2 stable release.

## `meson test` can now filter tests by subproject

You could always specify a list of tests to run by passing the names as
arguments to `meson test`. If there were multiple tests with that name (in the
same project or different subprojects), all of them would be run. Now you can:

1. Run all tests with the specified name from a specific subproject: `meson test subprojname:testname`
1. Run all tests defined in a specific subproject: `meson test subprojectname:`

As before, these can all be specified multiple times and mixed:

```sh
# Run:
# * All tests called 'name1' or 'name2' and
# * All tests called 'name3' in subproject 'bar' and
# * All tests in subproject 'foo'
$ meson test name1 name2 bar:name3 foo:
```

## Native (build machine) compilers not always required by `project()`

When cross-compiling, native (build machine) compilers for the languages
specified in `project()` are not required, if no targets use them.

## New `extra_files` key in target introspection

The target introspection (`meson introspect --targets`, `intro-targets.json`)
now has the new `extra_files` key which lists all files specified via the
`extra_files` kwarg of a build target (see `executable()`, etc.)


## Preliminary AIX support

AIX is now supported when compiling with gcc. A number of features are not
supported yet. For example, only gcc is supported (not xlC). Archives with both
32-bit and 64-bit dynamic libraries are not generated automatically. The rpath
includes both the build and install rpath, no attempt is made to change the
rpath at install time. Most advanced features (eg. link\_whole) are not
supported yet.

## Wraps from subprojects are automatically promoted

It is not required to promote wrap files for subprojects into the main project
any more. When configuring a subproject, meson will look for any wrap file or
directory in the subproject's `subprojects/` directory and add them into the
global list of available subprojects, to be used by any future `subproject()`
call or `dependency()` fallback. If a subproject with the same name already exists,
the new wrap file or directory is ignored. That means that the main project can
always override any subproject's wrap files by providing their own, it also means
the ordering in which subprojects are configured matters, if 2 subprojects provide
foo.wrap only the one from the first subproject to be configured will be used.

This new behavior can be disabled by passing `--wrap-mode=nopromote`.

## `meson.build_root()` and `meson.source_root()` are deprecated

Those function are common source of issue when used in a subproject because they
point to the parent project root which is rarely what is expected and is a
violation of subproject isolation.

`meson.current_source_dir()` and `meson.current_build_dir()` should be used instead
and have been available in all Meson versions. New functions `meson.project_source_root()`
and `meson.project_build_root()` have been added in Meson 0.56.0 to get the root
of the current (sub)project.

## `dep.as_link_whole()`

Dependencies created with `declare_dependency()` now has new method `as_link_whole()`.
It returns a copy of the dependency object with all link_with arguments changed
to link_whole. This is useful for example for fallback dependency from a
subproject built with `default_library=static`.

```meson
somelib = static_library('somelib', ...)
dep = declare_dependency(..., link_with: somelib)
library('someotherlib', ..., dependencies: dep.as_link_whole())
```

## Add support for all Windows subsystem types

It is now possible to build things like Windows kernel drivers with
the new `win_subsystem` keyword argument. This replaces the old
`gui_app` keyword argument, which is now deprecated. You should update
your project to use the new style like this:

```meson
# Old way
executable(..., gui_app: 'true')
# New way
executable(..., win_subsystem: 'windows')
```

The argument supports versioning [as described on MSDN
documentation](https://docs.microsoft.com/en-us/cpp/build/reference/subsystem-specify-subsystem).
Thus to build a Windows kernel driver with a specific version you'd
write something like this:

```meson
executable(..., win_subsystem: 'native,6.02')
```

## Added NVidia HPC SDK compilers

Added support for `nvidia_hpc` NVidia HPC SDK compilers, which are currently in public beta testing.

## Project and built-in options can be set in native or cross files

A new set of sections has been added to the cross and native files, `[project
options]` and `[<subproject_name>:project options]`, where `subproject_name`
is the name of a subproject. Any options that are allowed in the project can
be set from this section. They have the lowest precedent, and will be
overwritten by command line arguments.


```meson
option('foo', type : 'string', value : 'foo')
```

```ini
[project options]
foo = 'other val'
```

```console
meson build --native-file my.ini
```

Will result in the option foo having the value `other val`,

```console
meson build --native-file my.ini -Dfoo='different val'
```

Will result in the option foo having the value `different val`,


Subproject options are assigned like this:

```ini
[zlib:project options]
foo = 'some val'
```

Additionally meson level options can be set in the same way, using the
`[built-in options]` section.

```ini
[built-in options]
c_std = 'c99'
```

These options can also be set on a per-subproject basis, although only
`default_library` and `werror` can currently be set:
```ini
[zlib:built-in options]
default_library = 'static'
```

## `unstable-keyval` is now stable `keyval`

The `unstable-keyval` has been renamed to `keyval` and now promises stability
guarantees.

Meson will print a warning when you load an `unstable-` module that has been
stabilised (so `unstable-keyval` is still accepted for example).

## CMake subproject cross compilation support

Meson now supports cross compilation for CMake subprojects. Meson will try to
automatically guess most of the required CMake toolchain variables from existing
entries in the cross and native files. These variables will be stored in an
automatically generate CMake toolchain file in the build directory. The
remaining variables that can't be guessed can be added by the user in the
new `[cmake]` cross/native file section.

## Machine file keys are stored case sensitive

Previous the keys were always lowered, which worked fine for the values that
were allowed in the machine files. With the addition of per-project options
we need to make these sensitive to case, as the options in meson_options.txt
are sensitive to case already.

## Consistency between `declare_dependency()` and `pkgconfig.generate()` variables

The `variables` keyword argument in `declare_dependency()` used to only support
dictionary and `pkgconfig.generate()` only list of strings. They now both support
dictionary and list of strings in the format `'name=value'`. This makes easier
to share a common set of variables for both:

```meson
vars = {'foo': 'bar'}
dep = declare_dependency(..., variables: vars)
pkg.generate(..., variables: vars)
```

## Qt5 compile_translations now supports qresource preprocessing

When using qtmod.preprocess() in combination with qtmod.compile_translations()
to embed translations using rcc, it is no longer required to do this:

```meson
ts_files = ['list', 'of', 'files']
qtmod.compile_translations(ts_files)
# lang.qrc also contains the duplicated list of files
lang_cpp = qtmod.preprocess(qresources: 'lang.qrc')
```

Instead, use:
```meson
lang_cpp = qtmod.compile_translations(qresource: 'lang.qrc')
```

which will automatically detect and generate the needed compile_translations
targets.

## Controlling subproject dependencies with  `dependency(allow_fallback: ...)`

As an alternative to the `fallback` keyword argument to `dependency`,
you may use `allow_fallback`, which accepts a boolean value. If `true`
and the dependency is not found on the system, Meson will fallback
to a subproject that provides this dependency, even if the dependency
is optional. If `false`, Meson will not fallback even if a subproject
provides this dependency.

## Custom standard library

- It is not limited to cross builds any more, `<lang>_stdlib` property can be
  set in native files.
- The variable name parameter is no longer required as long as the subproject
  calls `meson.override_dependency('c_stdlib', mylibc_dep)`.

## Improvements for the builtin curses dependency

This method has been extended to use config-tools, and a fallback to
find_library for lookup as well as pkg-config.

## HDF5 dependency improvements

HDF5 has been improved so that the internal representations have been split.
This allows selecting pkg-config and config-tool dependencies separately.
Both work as proper dependencies of their type, so `get_variable` and similar
now work correctly.

It has also been fixed to use the selected compiler for the build instead of
the default compiler.

## External projects

A new experimental module `unstable_external_project` has been added to build
code using other build systems than Meson. Currently only supporting projects
with a configure script that generates Makefiles.

```meson
project('My Autotools Project', 'c',
  meson_version : '>=0.56.0',
)

mod = import('unstable_external_project')

p = mod.add_project('configure',
  configure_options : ['--prefix=@PREFIX@',
                       '--libdir=@LIBDIR@',
                       '--incdir=@INCLUDEDIR@',
                       '--enable-foo',
                      ],
)

mylib_dep = p.dependency('mylib')
```


## Per subproject `warning_level` option

`warning_level` can now be defined per subproject, in the same way as
`default_library` and `werror`.

## `meson subprojects` command

A new `--types` argument has been added to all subcommands to run the command only
on wraps with the specified types. For example this command will only print `Hello`
for each git subproject: `meson subprojects foreach --types git echo "Hello"`.
Multiple types can be set as comma separated list e.g. `--types git,file`.

Subprojects with no wrap file are now taken into account as well. This happens
for example for subprojects configured as git submodule, or downloaded manually
by the user and placed into the `subprojects/` directory.

The `checkout` subcommand now always stash any pending changes before switching
branch. Note that `update` subcommand was already stashing changes before updating
the branch.

If the command fails on any subproject the execution continues with other
subprojects, but at the end an error code is now returned.

The `update` subcommand has been reworked:
- In the case the URL of `origin` is different as the `url` set in wrap file,
  the subproject will not be updated unless `--reset` is specified (see below).
- In the case a subproject directory exists and is not a git repository but has
  a `[wrap-git]`, meson used to run git commands that would wrongly apply to the
  main project. It now skip the subproject unless `--reset` is specified (see below).
- The `--rebase` behaviour is now the default for consistency: it was
  already rebasing when current branch and revision are the same, it is
  less confusing to rebase when they are different too.
- Add `--reset` mode that checkout the new branch and hard reset that
  branch to remote commit. This new mode guarantees that every
  subproject are exactly at the wrap's revision. In addition the URL of `origin`
  is updated in case it changed in the wrap file. If the subproject directory is
  not a git repository but has a `[wrap-git]` the directory is deleted and the
  new repository is cloned.
- Local changes are always stashed first to avoid any data loss. In the
  worst case scenario the user can always check reflog and stash list to
  rollback.

## Added CompCert C compiler

Added experimental support for the [CompCert formally-verified C compiler](https://github.com/AbsInt/CompCert). The current state of the implementation is good enough to build the [picolibc project](https://github.com/picolibc/picolibc) with CompCert, but might still need additional adjustments for other projects.

## Dependencies listed in test and benchmark introspection

The introspection data for tests and benchmarks now includes the target
ids for executables and built files that are needed by the test.  IDEs can
use this feature to update the build more quickly before running a test.

## `include_type` support for the CMake subproject object dependency method

The `dependency()` method of the CMake subproject object now also supports the
`include_type` kwarg which is similar to the sane kwarg in the `dependency()`
function.

## Deprecate Dependency.get_pkgconfig_variable and Dependency.get_configtool_variable

These have been replaced with the more versatile `get_variable()` method
already, and shouldn't be used anymore.