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350 lines
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350 lines
12 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) |
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function to find the relevant VAPI, C headers and linker flags when it |
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encounters a Vala source file in a build target. Vala needs a VAPI |
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file and a C header or headers to use a library. The VAPI file helps |
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map Vala code to the library's C programming interface. It is the |
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[`pkg-config`](https://www.freedesktop.org/wiki/Software/pkg-config/) |
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tool that makes finding these installed files all work seamlessly |
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behind the scenes. When a `pkg-config` file doesn't exist for the |
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library then the [`find_library()`](Reference-manual.md#find_library) |
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method of the [compiler object](Reference-manual.md#compiler-object) |
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needs to be used. Examples are 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 |
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desktop environments. The binding to the library, the VAPI file, is |
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distributed with Vala. |
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Other libraries may have a VAPI that is distributed with the library |
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itself. Such libraries will have their VAPI file installed along with |
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their other development files. The VAPI is installed in Vala's |
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standard search path and so works just as seamlessly using the |
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`dependency()` function. |
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### Targeting a version of GLib |
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Meson's [`dependency()`](Reference-manual.md#dependency) function |
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allows a version check of a library. This is often used to check a |
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minimum version is installed. When setting a minimum version of GLib, |
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Meson will also pass this to the Vala compiler using the |
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`--target-glib` option. |
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This is needed when using GTK+'s user interface definition files with |
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Vala's `[GtkTemplate]`, `[GtkChild]` and `[GtkCallback]` attributes. |
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This requires `--target-glib 2.38`, or a newer version, to be passed |
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to Vala. With Meson this 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 |
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files to be built in to the binary as GResources. For completeness, |
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the next example 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 |
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distributed with Vala or the library. A VAPI can also be included in |
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the source files of your project. The convention is to put it in the |
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`vapi` directory of your project. |
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This is needed when a library does not have a VAPI or your project |
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needs to link to another component in the project that uses the C ABI. |
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For example if part of the project is written in C. |
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The Vala compiler's `--vapidir` option is used to add the project |
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directory to the VAPI search path. In Meson this is done with the |
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`add_project_arguments()` 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 |
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name corresponds to the pkg-config file name. |
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The [`vala-extra-vapis` |
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repository](https://gitlab.gnome.org/GNOME/vala-extra-vapis) is a |
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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. |
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It is recommended VAPIs from this repository are copied in to your |
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project's source files. |
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This also works well for starting to write new bindings before they |
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are shared 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 |
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files. In this case it is necessary to use the `find_library()` method |
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of the compiler object. |
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The first example uses Vala's POSIX binding. There is no pkg-config |
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file because POSIX includes the standard C library on Unix systems. |
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All that is needed is the VAPI file, `posix.vapi`. This is included |
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with Vala and installed in Vala's standard search path. Meson just |
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needs to be told to only find the library for 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 |
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additional VAPI is needed. The standard maths functions are already |
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bound in `glib-2.0.vapi`, but the GNU C library requires linking to |
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the maths library separately. In this example Meson is told to find |
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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 |
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C library that does not separate the maths library. See [Add math |
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library (-lm) 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 |
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pkg-config file and the VAPI is in the `vapi` directory of your |
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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 |
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preprocessor](https://wiki.gnome.org/Projects/Vala/Manual/Preprocessor) |
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requires specifying the language as `vala`. For example, the following |
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statement sets the preprocessor symbol `USE_FUSE`: |
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```meson |
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add_project_arguments('-D', 'USE_FUSE', language: 'vala') |
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``` |
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If you need to pass an argument to the C pre-processor then specify |
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the language as c. For example to set FUSE_USE_VERSION to 26 use: |
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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 |
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outputs the C header and the VAPI. They can be renamed by setting the |
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`vala_header` and `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` |
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array indicate the destination with `true` to use default directories |
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(i.e. `include` 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 |
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written in Vala. Because Vala uses the GObject type system as its |
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runtime type system it is very easy to use introspection to generate a |
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binding. A Meson build of a Vala library can generate the GObject |
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introspection metadata. The metadata is then used in separate projects |
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with [language specific |
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tools](https://wiki.gnome.org/Projects/Vala/LibraryWritingBindings) to |
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generate a binding. |
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The main form of metadata is a GObject Introspection Repository (GIR) |
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XML file. GIRs are mostly used by languages that generate bindings at |
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compile time. Languages that generate bindings at runtime mostly use a |
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typelib file, which is 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 |
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directory (i.e. `share/gir-1.0` for GIRs). The fourth element in the |
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`install_dir` array indicates where the GIR file will be installed. |
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To then generate a typelib file use a custom target with the |
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`g-ir-compiler` 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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