Example Qt5 KDE app

This how-to guide covers the steps, decisions, and implementation details that are unique when crafting a snap for an app that uses Qt5 KDE. We’ll work through the aspects unique to Qt5 KDE apps by examining an existing recipe.

Example recipe for KCalc

The following code comprises the recipe of a Qt5 KDE project, KCalc. This project is the calculator of KDE Gear.

KCalc recipe
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:
      - kde-frameworks-5-plug
      - home
      - opengl
      - network
      - network-bind
      - pulseaudio

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"

Add an app that uses KDE

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

Apps that use KDE runtime libraries require the kde-neon. The extension configures the runtime environment of the app so that all desktop functionality is correctly initialised. As desktop environment apps, they also need special configuration for AppStream and .desktop file compatibility.

To add a GTK4 app:

  1. Declare the general app keys, such as command, plugs, after, and so on.

  2. For extensions, add kde-neon.

  3. Set common-id to the app’s unique AppStream ID. Doing so links the app to the .desktop launcher specified in the AppStream file.

Add a part written for Qt5 KDE

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"

Qt5 KDE parts don’t require a special plugin. Instead, they need extra snap dependencies.

To add a Qt5 KDE part:

  1. Declare the general part keys, such as plugin, source, build-packages, and so on.

  2. So that the app has access to its AppStream metadata, for parse-info add a path to the AppStream .xml file on the host system. Since we set adopt-info: kcalc at the start of the recipe, the AppStream file of the kcalc part will be used to fill in the summary, description and icon of this snap and copy the AppStream file. See Using AppStream metadata for technical details about how this works.

  3. For build-snaps, list the following dependencies:

    - kde-frameworks-5-core18-sdk
- kde-frameworks-5-core18