The kde-neon extension

The kde-neon extension helps developers to create snaps that use Qt 5, with or without the add-on KDE Frameworks 5 libraries.

Snapcraft extensions simplify and streamline the process of adding commonly used elements to a snap, such as libraries, themes and environment variables. See Snapcraft extensions for further details.

The extension is maintained and supported for use with the core22 base snap. Whilst older versions of the extension are still available for core20 and core18, these bases are no longer actively supported.

The kde-neon extension is designed for C++ based Qt/KDE Frameworks applications. It does not provide the bindings needed for Qt for Python (PySide2) nor PyQt applications. In addition, the extension does not provide all of the optional Qt 5 libraries; for example, it does not include Qt3D, QtCharts, QtDataVisualization or QtGamepad.

How to use it

To use the extension, add the extensions keyword with the value kde-neon to each app defined in your snapcraft.yaml file. For example:

apps:
  kcalc-example:
    command: usr/bin/kcalc
    extensions:
      - kde-neon
    ...

See Qt 5 and KDE Frameworks applications for an example of how to use this extension to build a Qt 5 and KDE Frameworks 5 based application.

Interface connections

The extension connects your snap to the following run-time content snaps:

• kf5-5-113-qt-5-15-11-core22 for the Qt 5 and KDE Frameworks run-time libraries
• gtk-common-themes for common icon, cursor and sound themes

The extension achieves this by adding the following plugs to your snapcraft.yaml at build time:

plugs:
    desktop:
        mount-host-font-cache: false
    icon-themes:
        interface: content
        target: $SNAP/data-dir/icons
        default-provider: gtk-common-themes
    sound-themes:
        interface: content
        target: $SNAP/data-dir/sounds
        default-provider: gtk-common-themes
    kf5-5-113-qt-5-15-11-core22:
        content: kf5-5-113-qt-5-15-11-core22-all
        interface: content
        default-provider: kf5-5-113-qt-5-15-11-core22
        target: $SNAP/kf5

In addition, the following plugs are added to each app that includes the kde-neon extension entry:

apps:
  <app name>:
    ...
    plugs:
      - desktop
      - desktop-legacy
      - opengl
      - wayland
      - x11
    ...

See Adding interfaces for more details.

Included packages

The kde-neon extension depends on two separate snaps: a build snap and a platform/content snap.

The build snap ensures that the relevant Qt 5 and KDE Frameworks development libraries and supporting files are available during the build process. These libraries are sourced from the Ubuntu-based KDE neon Linux distribution, which provides more recent versions of Qt 5 and the KDE Frameworks than are available in the core22 software archive.

The platform snap makes the corresponding run-time libraries available to your snap when it is launched by your users. If the platform snap isn’t already present on a user’s machine, then it will be installed automatically and simultaneously with the kde-neon extension based snap.

By relying on a standalone platform snap, developers can avoid bundling the Qt/KDE Frameworks libraries in their snap, keeping the file size of the snap to a minimum. The same installation of the platform snap can be used by multiple snaps that rely on the kde-neon extension.

The build environment

The kde-neon extension defines the PATH, XDG_DATA_DIRS and SNAPCRAFT_CMAKE_ARGS build-time environment variables by adding a build-environment section to each of your snap’s build parts:

build-environment:
-   PATH: /snap/kf5-5-113-qt-5-15-11-core22-sdk/current/usr/bin${PATH:+:$PATH}
-   XDG_DATA_DIRS: $CRAFT_STAGE/usr/share:/snap/kf5-5-113-qt-5-15-11-core22-sdk/current/usr/share:/usr/share${XDG_DATA_DIRS:+:$XDG_DATA_DIRS}
-   SNAPCRAFT_CMAKE_ARGS: -DCMAKE_FIND_ROOT_PATH=/snap/kf5-5-113-qt-5-15-11-core22-sdk/current${SNAPCRAFT_CMAKE_ARGS:+:$SNAPCRAFT_CMAKE_ARGS}

You can override these defaults and/or define other build-time environment variables on a part-by-part basis by adding your own build-environment sections to snapcraft.yaml.

The run time environment

The extension also sets various run-time environment variables.

Most of these variables are set at launch by a command-chain shell script named desktop-launch:

apps:
  <app name>:
    ...
    command-chain:
    - snap/command-chain/desktop-launch
    ...

This shell script is added to the snap by a build part named kde-neon/sdk:

parts:
  kde-neon/sdk:
      source: /snap/snapcraft/current/share/snapcraft/extensions/desktop/kde-neon
      plugin: make
      make-parameters:
      - PLATFORM_PLUG=kf5-5-113-qt-5-15-11-core22
      build-snaps:
      - kf5-5-113-qt-5-15-11-core22-sdk

This part assembles the desktop-launch script from the following component scripts:

• init
• desktop-exports
• launcher-specific
• mark-and-exec

In addition to running the desktop-launch script at run time, the extension sets SNAP_DESKTOP_RUNTIME using an environment parameter:

environment:
  SNAP_DESKTOP_RUNTIME: $SNAP/kf5

Layout

The extension sets the following layout:

layout:
  /usr/share/X11:
    symlink: $SNAP/kf5/usr/share/X11

Hooks

The extension defines a configure hook that runs a script named hooks-configure-desktop upon installation of the snap, every time the snap is refreshed, and whenever the user changes a configuration option using snap set or snap unset:

hooks:
  configure:
    plugs:
    - desktop
    command-chain:
    - snap/command-chain/hooks-configure-desktop

The hooks-configure-desktop script is a copy of this fonts script.

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Last updated 5 months ago.