docs/markdown/Vala.md - meson - Git at Google

 ---
 title: Vala
 short-description: Compiling Vala and Genie programs
 ...

 # Compiling Vala applications and libraries
 Meson supports compiling applications and libraries written in
 [Vala](https://vala-project.org/) and
 [Genie](https://wiki.gnome.org/Projects/Genie) . A skeleton `meson.build` file:

 ```meson
 project('vala app', 'vala', 'c')

 dependencies = [
     dependency('glib-2.0'),
     dependency('gobject-2.0'),
 ]

 sources = files('app.vala')

 executable('app_name', sources, dependencies: dependencies)
 ```

 You must always specify the `glib-2.0` and `gobject-2.0` libraries as
 dependencies, because all current Vala applications use them.
 [GLib](https://developer.gnome.org/glib/stable/) is used for basic data types
 and [GObject](https://developer.gnome.org/gobject/stable/) is used for the
 runtime type system.


 ## Using libraries
 Meson uses the [`dependency()`](Reference-manual.md#dependency) function to find
 the relevant VAPI, C headers and linker flags when it encounters a Vala source
 file in a build target. Vala needs a VAPI file and a C header or headers to use
 a library. The VAPI file helps map Vala code to the library's C programming
 interface. It is the
 [`pkg-config`](https://www.freedesktop.org/wiki/Software/pkg-config/) tool that
 makes finding these installed files all work seamlessly behind the scenes. When
 a `pkg-config` file doesn't exist for the library then the
 [`find_library()`](Reference-manual.md#find_library) method of the [compiler
 object](Reference-manual.md#compiler-object) needs to be used. Examples are
 given later.

 Note Vala uses libraries that follow the C Application Binary Interface (C ABI).
 The library, however, could be written in C, Vala, Rust, Go, C++ or any other
 language that can generate a binary compatible with the C ABI and so provides C
 headers.


 ### The simplest case
 This first example is a simple addition to the `meson.build` file because:

  * the library has a `pkg-config` file, `gtk+-3.0.pc`
  * the VAPI is distributed with Vala and so installed with the Vala compiler
  * the VAPI is installed in Vala's standard search path
  * the VAPI, `gtk+-3.0.vapi`, has the same name as the `pkg-config` file

 Everything works seamlessly in the background and only a single extra line is
 needed:

 ```meson
 project('vala app', 'vala', 'c')

 dependencies = [
     dependency('glib-2.0'),
     dependency('gobject-2.0'),
     dependency('gtk+-3.0'),
 ]

 sources = files('app.vala')

 executable('app_name', sources, dependencies: dependencies)
 ```

 GTK+ is the graphical toolkit used by GNOME, elementary OS and other desktop
 environments. The binding to the library, the VAPI file, is distributed with
 Vala.

 Other libraries may have a VAPI that is distributed with the library itself.
 Such libraries will have their VAPI file installed along with their other
 development files. The VAPI is installed in Vala's standard search path and so
 works just as seamlessly using the `dependency()` function.


 ### Targetting a version of GLib
 Meson's [`dependency()`](Reference-manual.md#dependency) function allows a
 version check of a library. This is often used to check a minimum version is
 installed. When setting a minimum version of GLib, Meson will also pass this to
 the Vala compiler using the `--target-glib` option.

 This is needed when using GTK+'s user interface definition files with Vala's
 `[GtkTemplate]`, `[GtkChild]` and `[GtkCallback]` attributes. This requires
 `--target-glib 2.38`, or a newer version, to be passed to Vala. With Meson this
 is simply done with:

 ```meson
 project('vala app', 'vala', 'c')

 dependencies = [
     dependency('glib-2.0', version: '>=2.38'),
     dependency('gobject-2.0'),
     dependency('gtk+-3.0'),
 ]

 sources = files('app.vala')

 executable('app_name', sources, dependencies: dependencies)
 ```

 Using `[GtkTemplate]` also requires the GTK+ user interface definition files to
 be built in to the binary as GResources. For completeness, the next example
 shows this:

 ```meson
 project('vala app', 'vala', 'c')

 dependencies = [
     dependency('glib-2.0', version: '>=2.38'),
     dependency('gobject-2.0'),
     dependency('gtk+-3.0'),
 ]

 sources = files('app.vala')

 sources += import( 'gnome' ).compile_resources(
     'project-resources',
     'src/resources/resources.gresource.xml',
     source_dir: 'src/resources',
 )

 executable('app_name', sources, dependencies: dependencies)
 ```


 ### Adding to Vala's search path
 So far we have covered the cases where the VAPI file is either distributed with
 Vala or the library. A VAPI can also be included in the source files of your
 project. The convention is to put it in the `vapi` directory of your project.

 This is needed when a library does not have a VAPI or your project needs to link
 to another component in the project that uses the C ABI. For example if part of
 the project is written in C.

 The Vala compiler's `--vapidir` option is used to add the project directory to
 the VAPI search path. In Meson this is done with the `add_project_arguments()`
 function:

 ```meson
 project('vala app', 'vala', 'c')

 vapi_dir = meson.current_source_dir() / 'vapi'

 add_project_arguments(['--vapidir', vapi_dir], language: 'vala')

 dependencies = [
     dependency('glib-2.0'),
     dependency('gobject-2.0'),
     dependency('foo'), # 'foo.vapi' will be resolved as './vapi/foo.vapi'
 ]

 sources = files('app.vala')

 executable('app_name', sources, dependencies: dependencies)
 ```

 If the VAPI is for an external library then make sure that the VAPI name
 corresponds to the pkg-config file name.

 The [`vala-extra-vapis` repository](https://gitlab.gnome.org/GNOME/vala-extra-vapis)
 is a community maintained repository of VAPIs that are not distributed.
 Developers use the repository to share early work on new bindings and
 improvements to existing bindings. So the VAPIs can frequently change. It is
 recommended VAPIs from this repository are copied in to your project's source
 files.

 This also works well for starting to write new bindings before they are shared
 with the `vala-extra-vapis` repository.


 ### Libraries without pkg-config files
 A library that does not have a corresponding pkg-config file may mean
 `dependency()` is unsuitable for finding the C and Vala interface files. In this
 case it is necessary to use the `find_library()` method of the compiler object.

 The first example uses Vala's POSIX binding. There is no pkg-config file because
 POSIX includes the standard C library on Unix systems. All that is needed is the
 VAPI file, `posix.vapi`. This is included with Vala and installed in Vala's
 standard search path. Meson just needs to be told to only find the library for
 the Vala compiler:

 ```meson
 project('vala app', 'vala', 'c')

 dependencies = [
     dependency('glib-2.0'),
     dependency('gobject-2.0'),
     meson.get_compiler('vala').find_library('posix'),
 ]

 sources = files('app.vala')

 executable('app_name', sources, dependencies: dependencies)
 ```

 The next example shows how to link with a C library where no additional VAPI is
 needed. The standard maths functions are already bound in `glib-2.0.vapi`, but
 the GNU C library requires linking to the maths library separately. In this
 example Meson is told to find the library only for the C compiler:

 ```meson
 project('vala app', 'vala', 'c')

 dependencies = [
     dependency('glib-2.0'),
     dependency('gobject-2.0'),
     meson.get_compiler('c').find_library('m', required: false),
 ]

 sources = files('app.vala')

 executable('app_name', sources, dependencies: dependencies)
 ```
 The `required: false` means the build will continue when using another C library
 that does not separate the maths library. See [Add math library (-lm)
 portably](howtox.md#add-math-library-lm-portably).

 The final example shows how to use a library that does not have a pkg-config
 file and the VAPI is in the `vapi` directory of your project source files:
 ```meson
 project('vala app', 'vala', 'c')

 vapi_dir = meson.current_source_dir() / 'vapi'

 add_project_arguments(['--vapidir', vapi_dir], language: 'vala')

 dependencies = [
     dependency('glib-2.0'),
     dependency('gobject-2.0'),
     meson.get_compiler('c').find_library('foo'),
     meson.get_compiler('vala').find_library('foo', dir: vapi_dir),
 ]

 sources = files('app.vala')

 executable('app_name', sources, dependencies: dependencies)
 ```
 The `find_library()` method of the C compiler object will try to find the C
 header files and the library to link with.

 The `find_library()` method of the Vala compiler object needs to have the `dir`
 keyword added to include the project VAPI directory. This is not added
 automatically by `add_project_arguments()`.


 ## Building libraries


 ### Changing C header and VAPI names
 Meson's [`library`](Reference-manual.md#library) target automatically outputs
 the C header and the VAPI. They can be renamed by setting the `vala_header` and
 `vala_vapi` arguments respectively:

 ```meson
 foo_lib = shared_library('foo', 'foo.vala',
                   vala_header: 'foo.h',
                   vala_vapi: 'foo-1.0.vapi',
                   dependencies: [glib_dep, gobject_dep],
                   install: true,
                   install_dir: [true, true, true])
 ```
 In this example, the second and third elements of the `install_dir` array
 indicate the destination with `true` to use default directories (i.e. `include`
 and `share/vala/vapi`).


 ### GObject Introspection and language bindings
 A 'binding' allows another programming language to use a library written in
 Vala. Because Vala uses the GObject type system as its runtime type system it is
 very easy to use introspection to generate a binding. A Meson build of a Vala
 library can generate the GObject introspection metadata. The metadata is then
 used in separate projects with [language specific
 tools](https://wiki.gnome.org/Projects/Vala/LibraryWritingBindings) to generate
 a binding.

 The main form of metadata is a GObject Introspection Repository (GIR) XML file.
 GIRs are mostly used by languages that generate bindings at compile time.
 Languages that generate bindings at runtime mostly use a typelib file, which is
 generated from the GIR.

 Meson can generate a GIR as part of the build.  For a Vala library the
 `vala_gir` option has to be set for the `library`:

 ```meson
 foo_lib = shared_library('foo', 'foo.vala',
                   vala_gir: 'Foo-1.0.gir',
                   dependencies: [glib_dep, gobject_dep],
                   install: true,
                   install_dir: [true, true, true, true])
 ```

 The `true` value in `install_dir` tells Meson to use the default directory (i.e.
 `share/gir-1.0` for GIRs). The fourth element in the `install_dir` array
 indicates where the GIR file will be installed.

 To then generate a typelib file use a custom target with the `g-ir-compiler`
 program and a dependency on the library:

 ```meson
 g_ir_compiler = find_program('g-ir-compiler')
 custom_target('foo typelib', command: [g_ir_compiler, '--output', '@OUTPUT@', '@INPUT@'],
               input: meson.current_build_dir() / 'Foo-1.0.gir',
               output: 'Foo-1.0.typelib',
               depends: foo_lib,
               install: true,
               install_dir: get_option('libdir') / 'girepository-1.0')
 ```
	---
	title: Vala
	short-description: Compiling Vala and Genie programs
	...

	# Compiling Vala applications and libraries
	Meson supports compiling applications and libraries written in
	[Vala](https://vala-project.org/) and
	[Genie](https://wiki.gnome.org/Projects/Genie) . A skeleton `meson.build` file:

	```meson
	project('vala app', 'vala', 'c')

	dependencies = [
	dependency('glib-2.0'),
	dependency('gobject-2.0'),
	]

	sources = files('app.vala')

	executable('app_name', sources, dependencies: dependencies)
	```

	You must always specify the `glib-2.0` and `gobject-2.0` libraries as
	dependencies, because all current Vala applications use them.
	[GLib](https://developer.gnome.org/glib/stable/) is used for basic data types
	and [GObject](https://developer.gnome.org/gobject/stable/) is used for the
	runtime type system.


	## Using libraries
	Meson uses the [`dependency()`](Reference-manual.md#dependency) function to find
	the relevant VAPI, C headers and linker flags when it encounters a Vala source
	file in a build target. Vala needs a VAPI file and a C header or headers to use
	a library. The VAPI file helps map Vala code to the library's C programming
	interface. It is the
	[`pkg-config`](https://www.freedesktop.org/wiki/Software/pkg-config/) tool that
	makes finding these installed files all work seamlessly behind the scenes. When
	a `pkg-config` file doesn't exist for the library then the
	[`find_library()`](Reference-manual.md#find_library) method of the [compiler
	object](Reference-manual.md#compiler-object) needs to be used. Examples are
	given later.

	Note Vala uses libraries that follow the C Application Binary Interface (C ABI).
	The library, however, could be written in C, Vala, Rust, Go, C++ or any other
	language that can generate a binary compatible with the C ABI and so provides C
	headers.


	### The simplest case
	This first example is a simple addition to the `meson.build` file because:

	* the library has a `pkg-config` file, `gtk+-3.0.pc`
	* the VAPI is distributed with Vala and so installed with the Vala compiler
	* the VAPI is installed in Vala's standard search path
	* the VAPI, `gtk+-3.0.vapi`, has the same name as the `pkg-config` file

	Everything works seamlessly in the background and only a single extra line is
	needed:

	```meson
	project('vala app', 'vala', 'c')

	dependencies = [
	dependency('glib-2.0'),
	dependency('gobject-2.0'),
	dependency('gtk+-3.0'),
	]

	sources = files('app.vala')

	executable('app_name', sources, dependencies: dependencies)
	```

	GTK+ is the graphical toolkit used by GNOME, elementary OS and other desktop
	environments. The binding to the library, the VAPI file, is distributed with
	Vala.

	Other libraries may have a VAPI that is distributed with the library itself.
	Such libraries will have their VAPI file installed along with their other
	development files. The VAPI is installed in Vala's standard search path and so
	works just as seamlessly using the `dependency()` function.


	### Targetting a version of GLib
	Meson's [`dependency()`](Reference-manual.md#dependency) function allows a
	version check of a library. This is often used to check a minimum version is
	installed. When setting a minimum version of GLib, Meson will also pass this to
	the Vala compiler using the `--target-glib` option.

	This is needed when using GTK+'s user interface definition files with Vala's
	`[GtkTemplate]`, `[GtkChild]` and `[GtkCallback]` attributes. This requires
	`--target-glib 2.38`, or a newer version, to be passed to Vala. With Meson this
	is simply done with:

	```meson
	project('vala app', 'vala', 'c')

	dependencies = [
	dependency('glib-2.0', version: '>=2.38'),
	dependency('gobject-2.0'),
	dependency('gtk+-3.0'),
	]

	sources = files('app.vala')

	executable('app_name', sources, dependencies: dependencies)
	```

	Using `[GtkTemplate]` also requires the GTK+ user interface definition files to
	be built in to the binary as GResources. For completeness, the next example
	shows this:

	```meson
	project('vala app', 'vala', 'c')

	dependencies = [
	dependency('glib-2.0', version: '>=2.38'),
	dependency('gobject-2.0'),
	dependency('gtk+-3.0'),
	]

	sources = files('app.vala')

	sources += import( 'gnome' ).compile_resources(
	'project-resources',
	'src/resources/resources.gresource.xml',
	source_dir: 'src/resources',
	)

	executable('app_name', sources, dependencies: dependencies)
	```


	### Adding to Vala's search path
	So far we have covered the cases where the VAPI file is either distributed with
	Vala or the library. A VAPI can also be included in the source files of your
	project. The convention is to put it in the `vapi` directory of your project.

	This is needed when a library does not have a VAPI or your project needs to link
	to another component in the project that uses the C ABI. For example if part of
	the project is written in C.

	The Vala compiler's `--vapidir` option is used to add the project directory to
	the VAPI search path. In Meson this is done with the `add_project_arguments()`
	function:

	```meson
	project('vala app', 'vala', 'c')

	vapi_dir = meson.current_source_dir() / 'vapi'

	add_project_arguments(['--vapidir', vapi_dir], language: 'vala')

	dependencies = [
	dependency('glib-2.0'),
	dependency('gobject-2.0'),
	dependency('foo'), # 'foo.vapi' will be resolved as './vapi/foo.vapi'
	]

	sources = files('app.vala')

	executable('app_name', sources, dependencies: dependencies)
	```

	If the VAPI is for an external library then make sure that the VAPI name
	corresponds to the pkg-config file name.

	The [`vala-extra-vapis` repository](https://gitlab.gnome.org/GNOME/vala-extra-vapis)
	is a community maintained repository of VAPIs that are not distributed.
	Developers use the repository to share early work on new bindings and
	improvements to existing bindings. So the VAPIs can frequently change. It is
	recommended VAPIs from this repository are copied in to your project's source
	files.

	This also works well for starting to write new bindings before they are shared
	with the `vala-extra-vapis` repository.


	### Libraries without pkg-config files
	A library that does not have a corresponding pkg-config file may mean
	`dependency()` is unsuitable for finding the C and Vala interface files. In this
	case it is necessary to use the `find_library()` method of the compiler object.

	The first example uses Vala's POSIX binding. There is no pkg-config file because
	POSIX includes the standard C library on Unix systems. All that is needed is the
	VAPI file, `posix.vapi`. This is included with Vala and installed in Vala's
	standard search path. Meson just needs to be told to only find the library for
	the Vala compiler:

	```meson
	project('vala app', 'vala', 'c')

	dependencies = [
	dependency('glib-2.0'),
	dependency('gobject-2.0'),
	meson.get_compiler('vala').find_library('posix'),
	]

	sources = files('app.vala')

	executable('app_name', sources, dependencies: dependencies)
	```

	The next example shows how to link with a C library where no additional VAPI is
	needed. The standard maths functions are already bound in `glib-2.0.vapi`, but
	the GNU C library requires linking to the maths library separately. In this
	example Meson is told to find the library only for the C compiler:

	```meson
	project('vala app', 'vala', 'c')

	dependencies = [
	dependency('glib-2.0'),
	dependency('gobject-2.0'),
	meson.get_compiler('c').find_library('m', required: false),
	]

	sources = files('app.vala')

	executable('app_name', sources, dependencies: dependencies)
	```
	The `required: false` means the build will continue when using another C library
	that does not separate the maths library. See [Add math library (-lm)
	portably](howtox.md#add-math-library-lm-portably).

	The final example shows how to use a library that does not have a pkg-config
	file and the VAPI is in the `vapi` directory of your project source files:
	```meson
	project('vala app', 'vala', 'c')

	vapi_dir = meson.current_source_dir() / 'vapi'

	add_project_arguments(['--vapidir', vapi_dir], language: 'vala')

	dependencies = [
	dependency('glib-2.0'),
	dependency('gobject-2.0'),
	meson.get_compiler('c').find_library('foo'),
	meson.get_compiler('vala').find_library('foo', dir: vapi_dir),
	]

	sources = files('app.vala')

	executable('app_name', sources, dependencies: dependencies)
	```
	The `find_library()` method of the C compiler object will try to find the C
	header files and the library to link with.

	The `find_library()` method of the Vala compiler object needs to have the `dir`
	keyword added to include the project VAPI directory. This is not added
	automatically by `add_project_arguments()`.



	## Building libraries


	### Changing C header and VAPI names
	Meson's [`library`](Reference-manual.md#library) target automatically outputs
	the C header and the VAPI. They can be renamed by setting the `vala_header` and
	`vala_vapi` arguments respectively:

	```meson
	foo_lib = shared_library('foo', 'foo.vala',
	vala_header: 'foo.h',
	vala_vapi: 'foo-1.0.vapi',
	dependencies: [glib_dep, gobject_dep],
	install: true,
	install_dir: [true, true, true])
	```
	In this example, the second and third elements of the `install_dir` array
	indicate the destination with `true` to use default directories (i.e. `include`
	and `share/vala/vapi`).


	### GObject Introspection and language bindings
	A 'binding' allows another programming language to use a library written in
	Vala. Because Vala uses the GObject type system as its runtime type system it is
	very easy to use introspection to generate a binding. A Meson build of a Vala
	library can generate the GObject introspection metadata. The metadata is then
	used in separate projects with [language specific
	tools](https://wiki.gnome.org/Projects/Vala/LibraryWritingBindings) to generate
	a binding.

	The main form of metadata is a GObject Introspection Repository (GIR) XML file.
	GIRs are mostly used by languages that generate bindings at compile time.
	Languages that generate bindings at runtime mostly use a typelib file, which is
	generated from the GIR.

	Meson can generate a GIR as part of the build. For a Vala library the
	`vala_gir` option has to be set for the `library`:

	```meson
	foo_lib = shared_library('foo', 'foo.vala',
	vala_gir: 'Foo-1.0.gir',
	dependencies: [glib_dep, gobject_dep],
	install: true,
	install_dir: [true, true, true, true])
	```

	The `true` value in `install_dir` tells Meson to use the default directory (i.e.
	`share/gir-1.0` for GIRs). The fourth element in the `install_dir` array
	indicates where the GIR file will be installed.

	To then generate a typelib file use a custom target with the `g-ir-compiler`
	program and a dependency on the library:

	```meson
	g_ir_compiler = find_program('g-ir-compiler')
	custom_target('foo typelib', command: [g_ir_compiler, '--output', '@OUTPUT@', '@INPUT@'],
	input: meson.current_build_dir() / 'Foo-1.0.gir',
	output: 'Foo-1.0.typelib',
	depends: foo_lib,
	install: true,
	install_dir: get_option('libdir') / 'girepository-1.0')
	```