The gnome-3-38 extension | Snapcraft documentation

The gnome-3-38 extension helps with the creation of snaps that use GTK 3, GNOME 3.38, and/or GLib. It’s an updated version of the gnome-3-34 extension that works specifically with the core20 base snap built from Ubuntu 20.04 LTS. Previous Gnome extensions were built to use core18, based on Ubuntu 18.04 LTS .

Experimental support:

The gnome-3-38 extension is considered experimental and requires the --enable-experimental-extensions argument added to the snapcraft command for versions of Snapcraft lesser than 4.6.

This extension provides many of the components needed for general desktop applications making it useful for a broader set of applications outside of those tailored for the GNOME desktop.

How to use it: adding the necessary keywords to your snapcraft.yaml
Interface connections: which interfaces are accessible from the extension
Included packages: a list of the packages the extension is build from and provides
Environment variables: variables used during build and snap runntime
Layout set: layouts used by this extension to access files on the host

Snapcraft extensions enable snap developers to easily incorporate a set of common requirements into a snap. See Snapcraft extensions for further details.

How to use it

This extension currently only works with the core20 base snap (see Base snaps for details). To use it, add extensions: [gnome-3-38] to the application definition in your snapcraft.yaml file. For instance:

apps:
    tali:
        extensions: [gnome-3-38]
        command: usr/bin/tali
[...]

See GTK3 applications for a comprehensive overview of using extensions with GNOME applications.

Interface connections

The following plugs are provided by the extension and implicitly included in your snapcraft.yaml:

plugs:
  gnome-3-38-2004:
    default-provider: gnome-3-38-2004
    interface: content
    target: $SNAP/gnome-platform
  gtk-3-themes:
    default-provider: gtk-common-themes
    interface: content
    target: $SNAP/data-dir/themes
  icon-themes:
    default-provider: gtk-common-themes
    interface: content
    target: $SNAP/data-dir/icons
  sound-themes:
    default-provider: gtk-common-themes
    interface: content
    target: $SNAP/data-dir/sounds

Your app may still need additional plugs, but you can expect the following plugs to be automatically available to your apps as well:

plugs: [ desktop, desktop-legacy, gsettings, opengl,wayland, x11 ]

See Adding interfaces for more details.

Included packages

The GNOME extension is derived from two separate snaps; a build snap and a platform snap.

The build snap builds compiles libraries from source that are commonly used across GNOME applications. Examples include glib, gtk, and gnome-desktop. These are built to provide newer versions of these packages that exist in the core20 base snap (a subset of the Ubuntu 20.04 archive).

It is common for GNOME applications to release a gnome-3-38 branch of their project when the 3.38 version of GNOME is released (or shortly thereafter). Keeping this in mind, the build snap looks for this first to provide access to various GNOME libraries on their gnome-3-38 branch, to distribute the latest stable version that corresponds to the GNOME 3.38 release.

The platform snap takes the build snap and makes all of those libraries available to your snap at build time without needing to include the pieces of the build snap that are unnecessary at runtime (like compilers) in your final snap.

Environment variables

In addition to using the build and platform snaps, the gnome-3-38 extension also sets a collection of environment variables, links, default plugs for the app to use, and a default build-environment for each part in your snap to use.

Build variables

The following “build-environment” section is made available to each part built in your snap.

If you define other build-environment variables, then those will get added to these and the set is used. If you define another value for one of these variables, then the value you’ve defined will be used instead of the value defined within the extension.

build-environment:
    - PATH: /snap/gnome-3-38-2004-sdk/current/usr/bin:$PATH
    - XDG_DATA_DIRS: $SNAPCRAFT_STAGE/usr/share:/snap/gnome-3-38-2004-sdk/current/usr/share:/usr/share:$XDG_DATA_DIRS
    - LD_LIBRARY_PATH: /snap/gnome-3-38-2004-sdk/current/lib/$SNAPCRAFT_ARCH_TRIPLET:/snap/gnome-3-38-2004-sdk/current/usr/lib/$SNAPCRAFT_ARCH_TRIPLET:/snap/gnome-3-38-2004-sdk/current/usr/lib:/snap/gnome-3-38-2004-sdk/current/usr/lib/vala-current:/snap/gnome-3-38-2004-sdk/current/usr/lib/$SNAPCRAFT_ARCH_TRIPLET/pulseaudio${LD_LIBRARY_PATH:+:$LD_LIBRARY_PATH}
    - PKG_CONFIG_PATH: /snap/gnome-3-38-2004-sdk/current/usr/lib/$SNAPCRAFT_ARCH_TRIPLET/pkgconfig:/snap/gnome-3-38-2004-sdk/current/usr/lib/pkgconfig:/snap/gnome-3-38-2004-sdk/current/usr/share/pkgconfig:$PKG_CONFIG_PATH
    - GETTEXTDATADIRS: /snap/gnome-3-38-2004-sdk/current/usr/share/gettext-current:$GETTEXTDATADIRS
    - GDK_PIXBUF_MODULE_FILE: /snap/gnome-3-38-2004-sdk/current/usr/lib/$SNAPCRAFT_ARCH_TRIPLET/gdk-pixbuf-current/loaders.cache
    - ACLOCAL_PATH: /snap/gnome-3-38-2004-sdk/current/usr/share/aclocal${ACLOCAL_PATH:+:$ACLOCAL_PATH}
    - PYTHONPATH: /snap/gnome-3-38-2004-sdk/current/usr/lib/python3.8:/snap/gnome-3-38-2004-sdk/current/usr/lib/python3/dist-packages${PYTHONPATH:+:$PYTHONPATH}

Runtime variables

The following environment is set when your application is run:

environment:
  GTK_USE_PORTAL: '1'
  SNAP_DESKTOP_RUNTIME: $SNAP/gnome-platform

Layouts set

The host’s gjs, webkit2gtk-4.0, and iso-codes are used so they don’t need to be packaged as part of the snap (would greatly inflate the size).

layout:
  /usr/lib/$SNAPCRAFT_ARCH_TRIPLET/webkit2gtk-4.0:
    bind: $SNAP/gnome-platform/usr/lib/$SNAPCRAFT_ARCH_TRIPLET/webkit2gtk-4.0
  /usr/share/xml/iso-codes:
    bind: $SNAP/gnome-platform/usr/share/xml/iso-codes

See Snap layouts for further details.

Last updated 2 years ago.

Help improve this document in the forum.