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322 lines
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322 lines
11 KiB
--- |
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title: Vala |
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short-description: Compiling Vala and Genie programs |
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... |
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# Compiling Vala applications and libraries |
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Meson supports compiling applications and libraries written in |
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[Vala](https://vala-project.org/) and |
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[Genie](https://wiki.gnome.org/Projects/Genie) . A skeleton `meson.build` file: |
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```meson |
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project('vala app', 'vala', 'c') |
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dependencies = [ |
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dependency('glib-2.0'), |
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dependency('gobject-2.0'), |
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] |
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sources = files('app.vala') |
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executable('app_name', sources, dependencies: dependencies) |
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``` |
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You must always specify the `glib-2.0` and `gobject-2.0` libraries as |
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dependencies, because all current Vala applications use them. |
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[GLib](https://developer.gnome.org/glib/stable/) is used for basic data types |
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and [GObject](https://developer.gnome.org/gobject/stable/) is used for the |
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runtime type system. |
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## Using libraries |
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Meson uses the [`dependency()`](Reference-manual.md#dependency) function to find |
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the relevant VAPI, C headers and linker flags when it encounters a Vala source |
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file in a build target. Vala needs a VAPI file and a C header or headers to use |
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a library. The VAPI file helps map Vala code to the library's C programming |
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interface. It is the |
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[`pkg-config`](https://www.freedesktop.org/wiki/Software/pkg-config/) tool that |
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makes finding these installed files all work seamlessly behind the scenes. When |
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a `pkg-config` file doesn't exist for the library then the |
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[`find_library()`](Reference-manual.md#find_library) method of the [compiler |
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object](Reference-manual.md#compiler-object) needs to be used. Examples are |
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given later. |
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Note Vala uses libraries that follow the C Application Binary Interface (C ABI). |
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The library, however, could be written in C, Vala, Rust, Go, C++ or any other |
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language that can generate a binary compatible with the C ABI and so provides C |
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headers. |
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### The simplest case |
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This first example is a simple addition to the `meson.build` file because: |
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* the library has a `pkg-config` file, `gtk+-3.0.pc` |
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* the VAPI is distributed with Vala and so installed with the Vala compiler |
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* the VAPI is installed in Vala's standard search path |
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* the VAPI, `gtk+-3.0.vapi`, has the same name as the `pkg-config` file |
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Everything works seamlessly in the background and only a single extra line is |
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needed: |
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```meson |
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project('vala app', 'vala', 'c') |
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dependencies = [ |
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dependency('glib-2.0'), |
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dependency('gobject-2.0'), |
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dependency('gtk+-3.0'), |
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] |
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sources = files('app.vala') |
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executable('app_name', sources, dependencies: dependencies) |
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``` |
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GTK+ is the graphical toolkit used by GNOME, elementary OS and other desktop |
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environments. The binding to the library, the VAPI file, is distributed with |
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Vala. |
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Other libraries may have a VAPI that is distributed with the library itself. |
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Such libraries will have their VAPI file installed along with their other |
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development files. The VAPI is installed in Vala's standard search path and so |
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works just as seamlessly using the `dependency()` function. |
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### Targeting a version of GLib |
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Meson's [`dependency()`](Reference-manual.md#dependency) function allows a |
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version check of a library. This is often used to check a minimum version is |
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installed. When setting a minimum version of GLib, Meson will also pass this to |
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the Vala compiler using the `--target-glib` option. |
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This is needed when using GTK+'s user interface definition files with Vala's |
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`[GtkTemplate]`, `[GtkChild]` and `[GtkCallback]` attributes. This requires |
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`--target-glib 2.38`, or a newer version, to be passed to Vala. With Meson this |
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is simply done with: |
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```meson |
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project('vala app', 'vala', 'c') |
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dependencies = [ |
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dependency('glib-2.0', version: '>=2.38'), |
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dependency('gobject-2.0'), |
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dependency('gtk+-3.0'), |
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] |
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sources = files('app.vala') |
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executable('app_name', sources, dependencies: dependencies) |
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``` |
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Using `[GtkTemplate]` also requires the GTK+ user interface definition files to |
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be built in to the binary as GResources. For completeness, the next example |
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shows this: |
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```meson |
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project('vala app', 'vala', 'c') |
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dependencies = [ |
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dependency('glib-2.0', version: '>=2.38'), |
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dependency('gobject-2.0'), |
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dependency('gtk+-3.0'), |
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] |
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sources = files('app.vala') |
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sources += import( 'gnome' ).compile_resources( |
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'project-resources', |
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'src/resources/resources.gresource.xml', |
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source_dir: 'src/resources', |
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) |
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executable('app_name', sources, dependencies: dependencies) |
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``` |
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### Adding to Vala's search path |
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So far we have covered the cases where the VAPI file is either distributed with |
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Vala or the library. A VAPI can also be included in the source files of your |
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project. The convention is to put it in the `vapi` directory of your project. |
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This is needed when a library does not have a VAPI or your project needs to link |
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to another component in the project that uses the C ABI. For example if part of |
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the project is written in C. |
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The Vala compiler's `--vapidir` option is used to add the project directory to |
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the VAPI search path. In Meson this is done with the `add_project_arguments()` |
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function: |
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```meson |
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project('vala app', 'vala', 'c') |
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vapi_dir = meson.current_source_dir() / 'vapi' |
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add_project_arguments(['--vapidir', vapi_dir], language: 'vala') |
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dependencies = [ |
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dependency('glib-2.0'), |
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dependency('gobject-2.0'), |
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dependency('foo'), # 'foo.vapi' will be resolved as './vapi/foo.vapi' |
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] |
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sources = files('app.vala') |
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executable('app_name', sources, dependencies: dependencies) |
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``` |
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If the VAPI is for an external library then make sure that the VAPI name |
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corresponds to the pkg-config file name. |
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The [`vala-extra-vapis` repository](https://gitlab.gnome.org/GNOME/vala-extra-vapis) |
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is a community maintained repository of VAPIs that are not distributed. |
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Developers use the repository to share early work on new bindings and |
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improvements to existing bindings. So the VAPIs can frequently change. It is |
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recommended VAPIs from this repository are copied in to your project's source |
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files. |
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This also works well for starting to write new bindings before they are shared |
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with the `vala-extra-vapis` repository. |
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### Libraries without pkg-config files |
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A library that does not have a corresponding pkg-config file may mean |
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`dependency()` is unsuitable for finding the C and Vala interface files. In this |
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case it is necessary to use the `find_library()` method of the compiler object. |
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The first example uses Vala's POSIX binding. There is no pkg-config file because |
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POSIX includes the standard C library on Unix systems. All that is needed is the |
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VAPI file, `posix.vapi`. This is included with Vala and installed in Vala's |
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standard search path. Meson just needs to be told to only find the library for |
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the Vala compiler: |
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```meson |
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project('vala app', 'vala', 'c') |
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dependencies = [ |
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dependency('glib-2.0'), |
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dependency('gobject-2.0'), |
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meson.get_compiler('vala').find_library('posix'), |
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] |
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sources = files('app.vala') |
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executable('app_name', sources, dependencies: dependencies) |
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``` |
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The next example shows how to link with a C library where no additional VAPI is |
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needed. The standard maths functions are already bound in `glib-2.0.vapi`, but |
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the GNU C library requires linking to the maths library separately. In this |
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example Meson is told to find the library only for the C compiler: |
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```meson |
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project('vala app', 'vala', 'c') |
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dependencies = [ |
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dependency('glib-2.0'), |
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dependency('gobject-2.0'), |
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meson.get_compiler('c').find_library('m', required: false), |
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] |
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sources = files('app.vala') |
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executable('app_name', sources, dependencies: dependencies) |
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``` |
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The `required: false` means the build will continue when using another C library |
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that does not separate the maths library. See [Add math library (-lm) |
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portably](howtox.md#add-math-library-lm-portably). |
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The final example shows how to use a library that does not have a pkg-config |
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file and the VAPI is in the `vapi` directory of your project source files: |
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```meson |
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project('vala app', 'vala', 'c') |
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vapi_dir = meson.current_source_dir() / 'vapi' |
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add_project_arguments(['--vapidir', vapi_dir], language: 'vala') |
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dependencies = [ |
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dependency('glib-2.0'), |
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dependency('gobject-2.0'), |
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meson.get_compiler('c').find_library('foo'), |
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meson.get_compiler('vala').find_library('foo', dirs: vapi_dir), |
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] |
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sources = files('app.vala') |
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executable('app_name', sources, dependencies: dependencies) |
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``` |
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The `find_library()` method of the C compiler object will try to find the C |
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header files and the library to link with. |
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The `find_library()` method of the Vala compiler object needs to have the `dir` |
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keyword added to include the project VAPI directory. This is not added |
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automatically by `add_project_arguments()`. |
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### Working with the Vala Preprocessor |
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Passing arguments to [Vala's preprocessor](https://wiki.gnome.org/Projects/Vala/Manual/Preprocessor) requires specifying the language as `c`. For example, the following statement sets the preprocessor symbol `FUSE_USE_VERSION` to the value `26`: |
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```meson |
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add_project_arguments('-DFUSE_USE_VERSION=26', language: 'c') |
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``` |
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## Building libraries |
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### Changing C header and VAPI names |
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Meson's [`library`](Reference-manual.md#library) target automatically outputs |
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the C header and the VAPI. They can be renamed by setting the `vala_header` and |
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`vala_vapi` arguments respectively: |
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```meson |
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foo_lib = shared_library('foo', 'foo.vala', |
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vala_header: 'foo.h', |
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vala_vapi: 'foo-1.0.vapi', |
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dependencies: [glib_dep, gobject_dep], |
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install: true, |
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install_dir: [true, true, true]) |
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``` |
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In this example, the second and third elements of the `install_dir` array |
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indicate the destination with `true` to use default directories (i.e. `include` |
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and `share/vala/vapi`). |
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### GObject Introspection and language bindings |
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A 'binding' allows another programming language to use a library written in |
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Vala. Because Vala uses the GObject type system as its runtime type system it is |
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very easy to use introspection to generate a binding. A Meson build of a Vala |
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library can generate the GObject introspection metadata. The metadata is then |
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used in separate projects with [language specific |
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tools](https://wiki.gnome.org/Projects/Vala/LibraryWritingBindings) to generate |
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a binding. |
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The main form of metadata is a GObject Introspection Repository (GIR) XML file. |
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GIRs are mostly used by languages that generate bindings at compile time. |
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Languages that generate bindings at runtime mostly use a typelib file, which is |
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generated from the GIR. |
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Meson can generate a GIR as part of the build. For a Vala library the |
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`vala_gir` option has to be set for the `library`: |
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```meson |
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foo_lib = shared_library('foo', 'foo.vala', |
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vala_gir: 'Foo-1.0.gir', |
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dependencies: [glib_dep, gobject_dep], |
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install: true, |
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install_dir: [true, true, true, true]) |
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``` |
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The `true` value in `install_dir` tells Meson to use the default directory (i.e. |
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`share/gir-1.0` for GIRs). The fourth element in the `install_dir` array |
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indicates where the GIR file will be installed. |
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To then generate a typelib file use a custom target with the `g-ir-compiler` |
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program and a dependency on the library: |
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```meson |
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g_ir_compiler = find_program('g-ir-compiler') |
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custom_target('foo typelib', command: [g_ir_compiler, '--output', '@OUTPUT@', '@INPUT@'], |
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input: meson.current_build_dir() / 'Foo-1.0.gir', |
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output: 'Foo-1.0.typelib', |
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depends: foo_lib, |
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install: true, |
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install_dir: get_option('libdir') / 'girepository-1.0') |
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```
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