KDE neon extensions¶

The KDE neon extensions help authors create snaps that use Qt, with or without the KDE Frameworks libraries. This page covers the architecture of the extension and its effect on project files during build.

This a family of extensions for two versions of KDE neon paired with Qt:

KDE neon 6, internally named kde-neon-6
KDE neon 5, internally named kde-neon

Compatibility¶

The KDE neon 6 extension is supported with the core24 and core22 bases.

The KDE neon 5 extension is supported with the core22 base. An older version of the extension is also available for core20.

Important

As of February 2024, KDE no longer supports KDE neon 5.

Base	Versions	Platform snap	Build snap
core24	Qt 6 and KDE Frameworks 6	kf6-core24	kf6-core24-sdk
core22	Qt 6 and KDE Frameworks 6	kf6-core22	kf6-core22-sdk
core22	Qt 5.15.11 and KDE Frameworks 5.113	kf5-5-113-qt-5-15-11-core22	kf5-5-113-qt-5-15-11-core22-sdk

The extensions are designed for C++ based Qt/KDE Frameworks apps. They don’t provide the bindings needed for PySide2 (Qt for Python) or PyQt apps. The extensions also don’t provide all of the optional Qt libraries. For example, they don’t include Qt3D, QtCharts, QtDataVisualization or QtGamepad.

Included interfaces¶

The KDE neon 6 extension connects the snap to the following runtime content snaps:

The snaps for Qt and KDE Frameworks run-time libraries.
The gtk-common-themes snap for common icon, cursor and sound themes.

The extension automatically includes the required plugs for these runtime libraries.

In addition, the extension adds the following plugs to each app that uses it:

Included packages¶

The KDE neon 6 extension depends on two separate snaps – a build snap and a combination platform-content snap.

The build snap ensures that the relevant Qt and KDE Frameworks development libraries and supporting files are available during the build process. These libraries are sourced from the KDE neon project, which provides more recent versions of Qt and the KDE Frameworks.

The platform snap makes the corresponding run-time libraries available to the snap when it’s launched by the user. 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, authors can avoid bundling the Qt and 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 extensions.

Included build environment variables¶

The KDE neon 6 extension sets environment variables so the project’s parts can build correctly. The project’s main part receives the following variables.

Included runtime environment variables¶

The KDE neon 6 extension also set various runtime environment variables for apps.

The main runtime variables apply to the whole snap.

The rest of the runtime variables are set at launch by a command-chain shell script included by a configure hook:

The KDE neon 6 extension adds this shell script to the snap through a special part.

The part assembles the shell script from shared scripts in Snapcraft’s source:

Included layouts¶

The KDE neon 6 extension adds the following layouts.

Included hooks¶

The KDE neon 6 extension adds a hook that sets runtime environment variables.

Example expanded project files¶

Here are examples of the result of a project file that uses the KDE neon extensions. They demonstrate the added plugs, packages, variables, and layouts that the extensions add to project files immediately prior to build.

These examples contain the difference between the original files and the output of the snapcraft expand-extensions command. Some of the text has been altered for ease of reading.

KDE neon 6

The original is a project file for a snapped version of Keysmith.

Expanded project file for Keysmith

 name: keysmith
 base: core24
 adopt-info: keysmith
 confinement: strict
 grade: stable

-build-packages:
-  - libsodium-dev
-  - libssl-dev
-  - libproxy1v5

 parts:
   keysmith:
-    parse-info:
-      - usr/share/metainfo/org.kde.keysmith.appdata.xml
     plugin: cmake
     source: .
     source-type: local
     cmake-parameters:
       - -DCMAKE_INSTALL_PREFIX=/usr
       - -DCMAKE_BUILD_TYPE=Release
       - -DQT_MAJOR_VERSION=6
       - -DBUILD_WITH_QT6=ON
       - -DBUILD_TESTING=OFF
       - -DCMAKE_INSTALL_SYSCONFDIR=/etc
       - -DCMAKE_INSTALL_LOCALSTATEDIR=/var
       - -DCMAKE_EXPORT_NO_PACKAGE_REGISTRY=ON
       - -DCMAKE_FIND_USE_PACKAGE_REGISTRY=OFF
       - -DCMAKE_FIND_PACKAGE_NO_PACKAGE_REGISTRY=ON
       - -DCMAKE_INSTALL_RUNSTATEDIR=/run
       - -DCMAKE_SKIP_INSTALL_ALL_DEPENDENCY=ON
       - -DCMAKE_VERBOSE_MAKEFILE=ON
       - -DCMAKE_INSTALL_LIBDIR=lib/$CRAFT_ARCH_TRIPLET_BUILD_FOR
       - --log-level=STATUS
       - -DCMAKE_LIBRARY_PATH=lib/$CRAFT_ARCH_TRIPLET_BUILD_FOR
     prime:
       - -usr/lib/*/cmake/*
       - -usr/include/*
       - -usr/share/ECM/*
       - -usr/share/man/*
       - -usr/bin/X11
       - -usr/lib/gcc/$CRAFT_ARCH_TRIPLET_BUILD_FOR/6.0.0
       - -usr/lib/aspell/*
       - -usr/share/lintian
+    build-environment:
+      - PATH: /snap/kde-qt6-core24-sdk/current/usr/bin:/snap/kf6-core24-sdk/current/usr/bin${PATH:+:$PATH}
+      - XDG_DATA_DIRS: $CRAFT_STAGE/usr/share:/snap/kde-qt6-core24-sdk/current/usr/share:/snap/kf6-core24-sdk/current/usr/share:/usr/share${XDG_DATA_DIRS:+:$XDG_DATA_DIRS}
+      - XDG_CONFIG_HOME: $CRAFT_STAGE/etc/xdg:/snap/kde-qt6-core24-sdk/current/etc/xdg:/snap/kf6-core24-sdk/current/etc/xdg:/etc/xdg${XDG_CONFIG_HOME:+:$XDG_CONFIG_HOME}
+      - LD_LIBRARY_PATH: /snap/kde-qt6-core24-sdk/current/usr/lib/${CRAFT_ARCH_TRIPLET_BUILD_FOR}:/snap/kde-qt6-core24-sdk/current/usr/lib:/snap/kf6-core24-sdk/current/usr/lib/${CRAFT_ARCH_TRIPLET_BUILD_FOR}:/snap/kf6-core24-sdk/current/usr/lib/${CRAFT_ARCH_TRIPLET_BUILD_FOR}/blas:/snap/kf6-core24-sdk/current/usr/lib/${CRAFT_ARCH_TRIPLET_BUILD_FOR}/lapack:/snap/kf6-core24-sdk/current/usr/lib/${CRAFT_ARCH_TRIPLET_BUILD_FOR}/libproxy:/snap/kf6-core24-sdk/current/usr/lib:$CRAFT_STAGE/usr/lib/${CRAFT_ARCH_TRIPLET_BUILD_FOR}:$CRAFT_STAGE/usr/lib:$CRAFT_STAGE/lib/${LD_LIBRARY_PATH:+:$LD_LIBRARY_PATH}
+      - CMAKE_PREFIX_PATH: $CRAFT_STAGE;/snap/kde-qt6-core24-sdk/current;/snap/kf6-core24-sdk/current;/usr${CMAKE_PREFIX_PATH:+;$CMAKE_PREFIX_PATH}
+      - CMAKE_FIND_ROOT_PATH: $CRAFT_STAGE;/snap/kde-qt6-core24-sdk/current;/snap/kf6-core24-sdk/current;/usr${CMAKE_FIND_ROOT_PATH:+;$CMAKE_FIND_ROOT_PATH}
   cleanup:
     after:
       - keysmith
     plugin: nil
     build-snaps:
       - core24
       - kf6-core24
       - qt-common-themes
     override-prime: |
       # Remove duplicate files in the dependent snaps from the final snap.
       for snap in "core24" "kf6-core24" "qt-common-themes"; do
           cd "/snap/$snap/current" && find . -type f,l -print | sed 's|^./|/root/prime/|' | xargs rm -f
       done
+    build-environment:
+      - PATH: /snap/kde-qt6-core24-sdk/current/usr/bin:/snap/kf6-core24-sdk/current/usr/bin${PATH:+:$PATH}
+      - XDG_DATA_DIRS: $CRAFT_STAGE/usr/share:/snap/kde-qt6-core24-sdk/current/usr/share:/snap/kf6-core24-sdk/current/usr/share:/usr/share${XDG_DATA_DIRS:+:$XDG_DATA_DIRS}
+      - XDG_CONFIG_HOME: $CRAFT_STAGE/etc/xdg:/snap/kde-qt6-core24-sdk/current/etc/xdg:/snap/kf6-core24-sdk/current/etc/xdg:/etc/xdg${XDG_CONFIG_HOME:+:$XDG_CONFIG_HOME}
+      - LD_LIBRARY_PATH: /snap/kde-qt6-core24-sdk/current/usr/lib/${CRAFT_ARCH_TRIPLET_BUILD_FOR}:/snap/kde-qt6-core24-sdk/current/usr/lib:/snap/kf6-core24-sdk/current/usr/lib/${CRAFT_ARCH_TRIPLET_BUILD_FOR}:/snap/kf6-core24-sdk/current/usr/lib/${CRAFT_ARCH_TRIPLET_BUILD_FOR}/blas:/snap/kf6-core24-sdk/current/usr/lib/${CRAFT_ARCH_TRIPLET_BUILD_FOR}/lapack:/snap/kf6-core24-sdk/current/usr/lib/${CRAFT_ARCH_TRIPLET_BUILD_FOR}/libproxy:/snap/kf6-core24-sdk/current/usr/lib:$CRAFT_STAGE/usr/lib/${CRAFT_ARCH_TRIPLET_BUILD_FOR}:$CRAFT_STAGE/usr/lib:$CRAFT_STAGE/lib/${LD_LIBRARY_PATH:+:$LD_LIBRARY_PATH}
+      - CMAKE_PREFIX_PATH: $CRAFT_STAGE;/snap/kde-qt6-core24-sdk/current;/snap/kf6-core24-sdk/current;/usr${CMAKE_PREFIX_PATH:+;$CMAKE_PREFIX_PATH}
+      - CMAKE_FIND_ROOT_PATH: $CRAFT_STAGE;/snap/kde-qt6-core24-sdk/current;/snap/kf6-core24-sdk/current;/usr${CMAKE_FIND_ROOT_PATH:+;$CMAKE_FIND_ROOT_PATH}
+  snapcraft/core:
+    build-packages:
+      - libsodium-dev
+      - libssl-dev
+      - libproxy1v5
+    plugin: nil
+    build-environment:
+      - PATH: /snap/kde-qt6-core24-sdk/current/usr/bin:/snap/kf6-core24-sdk/current/usr/bin${PATH:+:$PATH}
+      - XDG_DATA_DIRS: $CRAFT_STAGE/usr/share:/snap/kde-qt6-core24-sdk/current/usr/share:/snap/kf6-core24-sdk/current/usr/share:/usr/share${XDG_DATA_DIRS:+:$XDG_DATA_DIRS}
+      - XDG_CONFIG_HOME: $CRAFT_STAGE/etc/xdg:/snap/kde-qt6-core24-sdk/current/etc/xdg:/snap/kf6-core24-sdk/current/etc/xdg:/etc/xdg${XDG_CONFIG_HOME:+:$XDG_CONFIG_HOME}
+      - LD_LIBRARY_PATH: /snap/kde-qt6-core24-sdk/current/usr/lib/${CRAFT_ARCH_TRIPLET_BUILD_FOR}:/snap/kde-qt6-core24-sdk/current/usr/lib:/snap/kf6-core24-sdk/current/usr/lib/${CRAFT_ARCH_TRIPLET_BUILD_FOR}:/snap/kf6-core24-sdk/current/usr/lib/${CRAFT_ARCH_TRIPLET_BUILD_FOR}/blas:/snap/kf6-core24-sdk/current/usr/lib/${CRAFT_ARCH_TRIPLET_BUILD_FOR}/lapack:/snap/kf6-core24-sdk/current/usr/lib/${CRAFT_ARCH_TRIPLET_BUILD_FOR}/libproxy:/snap/kf6-core24-sdk/current/usr/lib:$CRAFT_STAGE/usr/lib/${CRAFT_ARCH_TRIPLET_BUILD_FOR}:$CRAFT_STAGE/usr/lib:$CRAFT_STAGE/lib/${LD_LIBRARY_PATH:+:$LD_LIBRARY_PATH}
+      - CMAKE_PREFIX_PATH: $CRAFT_STAGE;/snap/kde-qt6-core24-sdk/current;/snap/kf6-core24-sdk/current;/usr${CMAKE_PREFIX_PATH:+;$CMAKE_PREFIX_PATH}
+      - CMAKE_FIND_ROOT_PATH: $CRAFT_STAGE;/snap/kde-qt6-core24-sdk/current;/snap/kf6-core24-sdk/current;/usr${CMAKE_FIND_ROOT_PATH:+;$CMAKE_FIND_ROOT_PATH}
+  kde-neon-6/sdk:
+    source: /snap/snapcraft/current/share/snapcraft/extensions/desktop/command-chain-kde
+    plugin: make
+    build-snaps:
+      - kde-qt6-core24-sdk
+      - kf6-core24-sdk
+    build-packages:
+      - gettext
+      - doxygen
+      - graphviz
+      - libxml2-utils
+      - docbook-xml
+      - docbook-xsl
+      - libglx-dev
+      - libgl-dev
+      - libglvnd-dev
+    make-parameters:
+      - GPU_WRAPPER=gpu-2404-wrapper
+compression: lzo

+layout:
+  /usr/share/X11:
+    symlink: $SNAP/kf6/usr/share/X11
+  /usr/share/qt6:
+    symlink: $SNAP/kf6/usr/share/qt6
+  /usr/share/libdrm:
+    bind: $SNAP/gpu-2404/libdrm
+  /usr/share/drirc.d:
+    symlink: $SNAP/gpu-2404/drirc.d

+assumes:
+  - snapd2.58.3
+hooks:
+  configure:
+    command-chain:
+      - snap/command-chain/hooks-configure-desktop
+    plugs:
+      - desktop

 apps:
   keysmith:
     command: usr/bin/keysmith
     common-id: org.kde.keysmith.desktop
     desktop: usr/share/applications/org.kde.keysmith.desktop
     plugs:
+      - desktop
+      - desktop-legacy
+      - opengl
+      - wayland
+      - x11
+      - audio-playback
+      - unity7
+      - network
+      - network-bind
       - home
+    command-chain:
+      - snap/command-chain/gpu-2404-wrapper
+      - snap/command-chain/desktop-launch

+plugs:
+  desktop:
+    mount-host-font-cache: false
+  gtk-2-themes:
+    interface: content
+    target: $SNAP/data-dir/themes
+    default-provider: gtk-common-themes
+  gtk-3-themes:
+    interface: content
+    target: $SNAP/data-dir/themes
+    default-provider: gtk-common-themes
+  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
+  kf6-core24:
+    content: kf6-core24-all
+    interface: content
+    target: $SNAP/kf6
+    default-provider: kf6-core24
+  gpu-2404:
+    interface: content
+    target: $SNAP/gpu-2404
+    default-provider: mesa-2404

 slots:
   session-dbus-interface:
     interface: dbus
     name: org.kde.keysmith
     bus: session

+environment:
+  SNAP_DESKTOP_RUNTIME: $SNAP/kf6
+  GTK_USE_PORTAL: "1"
+  QT_VERSION: "6"

KDE neon 5

The original project file comes from the KCalc snap.

We provide a review of the unmodified file in Craft a Qt5 KDE app.

Expanded project file for KCalc

 name: kcalc
 version: "19.08.0"
 grade: stable
 adopt-info: kcalc

 confinement: strict
 base: core18

 apps:
   kcalc:
     command: kcalc
-    extensions: [kde-neon]
     common-id: org.kde.kcalc.desktop
     plugs:
+      - desktop
+      - desktop-legacy
+      - opengl
+      - wayland
+      - x11
       - kde-frameworks-5-plug
       - home
-      - opengl
       - network
       - network-bind
       - pulseaudio

+    command-chain:
+      - snap/command-chain/desktop-launch
 slots:
   session-dbus-interface:
     interface: dbus
     name: org.kde.kcalc.desktop
     bus: session

 parts:
   kcalc:
     plugin: cmake
     source: https://download.kde.org/stable/applications/19.08.0/src/kcalc-19.08.0.tar.xz
     parse-info:
       - usr/share/metainfo/org.kde.kcalc.appdata.xml
     build-snaps:
       - kde-frameworks-5-core18-sdk
       - kde-frameworks-5-core18
     build-packages:
       - libmpfr-dev
       - libgmp-dev
       - kdoctools-dev
     stage-packages:
       - libmpfr6
       - libgmp10
     configflags:
-      - "-DKDE_INSTALL_USE_QT_SYS_PATHS=ON"
-      - "-DCMAKE_INSTALL_PREFIX=/usr"
-      - "-DCMAKE_BUILD_TYPE=Release"
-      - "-DENABLE_TESTING=OFF"
-      - "-DBUILD_TESTING=OFF"
-      - "-DKDE_SKIP_TEST_SETTINGS=ON"
+      - -DKDE_INSTALL_USE_QT_SYS_PATHS=ON
+      - -DCMAKE_INSTALL_PREFIX=/usr
+      - -DCMAKE_BUILD_TYPE=Release
+      - -DENABLE_TESTING=OFF
+      - -DBUILD_TESTING=OFF
+      - -DKDE_SKIP_TEST_SETTINGS=ON
+  kde-neon-extension:
+    build-packages:
+      - g++
+    build-snaps:
+      - kde-frameworks-5-core18-sdk/latest/stable
+    make-parameters:
+      - PLATFORM_PLUG=kde-frameworks-5-core18
+    plugin: make
+    source: $SNAPCRAFT_EXTENSIONS_DIR/desktop
+    source-subdir: kde-neon
+assumes:
+  - snapd2.43
+compression: lzo
+plugs:
+  desktop:
+    mount-host-font-cache: false
+  icon-themes:
+    default-provider: gtk-common-themes
+    interface: content
+    target: $SNAP/data-dir/icons
+  kde-frameworks-5-core18:
+    content: kde-frameworks-5-core18-all
+    default-provider: kde-frameworks-5-core18
+    interface: content
+    target: $SNAP/kf5
+  sound-themes:
+    default-provider: gtk-common-themes
+    interface: content
+    target: $SNAP/data-dir/sounds
+environment:
+  SNAP_DESKTOP_RUNTIME: $SNAP/kf5
+hooks:
+  configure:
+    command-chain:
+      - snap/command-chain/hooks-configure-desktop
+    plugs:
+      - desktop
+layout:
+  /usr/share/X11:
+    symlink: $SNAP/kf5/usr/share/X11