Get Involved/development

From KDE Community Wiki

By joining the ranks of KDE developers, you will get to implement new features and defeat bugs both daunting and simple, all while collaborating to make coherent and stable releases. Developers collaborate in teams based on what area they are working in. These can be small teams working on a single application, up to large teams working on a group of related pieces of software. Many developers are in more than one team.

KDE runs or participates in several mentoring programs to help new developers, including an informal list of people who are willing to help newcomers get started. See the Mentoring page for more details.

Information

While any operating system can be used to patch or develop KDE software, it's easiest if you use a Linux distribution that provides relatively recent versions of Qt and KDE Frameworks, such as Arch/Manjaro, Fedora, KDE Neon, openSUSE Tumbleweed, or non-LTS versions of Kubuntu.

Support for Windows, macOS, and Linux distros that ship older software (such as Debian, Ubuntu/Kubuntu 18.04, and openSUSE Leap 15) is still experimental, and you may have a better experience doing your development in a virtual machine when using one of the distributions mentioned above.


New to C++/Qt software development?

Most KDE software is written in C++ using the Qt toolkit and KDE Frameworks. Though prior experience with these technologies or other programming languages is helpful, you don't need to be a C++ programmer to get started! For example, no programming knowledge whatsoever is required to do things like improve text labels.

If you'd like to dive deeper, the Qt wiki contains a list of online books for learning Qt programming. Qt also provides lots of examples you can look at. For visual learners, this YouTube playlist of QML tutorials by KDE patron KDAB may be useful. Finally, information about KDE Frameworks can be found on the KDE Developer Platform and KDE API website.

One-time setup: your development environment

To build software, you need a development environment: a set of tools that allows you to access and edit the source code, compile it into a form that the computer can run, and deploy it to a safe location. We will now go through the process of setting one up. To accomplish these tasks, you will need to enter commands using a terminal program, such as KDE's Konsole (but any terminal program will suffice).

If you're not familiar with the command line interface, you can find a reasonable tutorial here. However advanced command-line skills are not required, and you will learn what you need along the way!

Note

Everything in this section only needs to be done once. Once you've done it, your development environment is set up and you can use it to submit patches and develop KDE Software!


Note

As an alternative to the set-up process described here, you can install Docker and the KDE PIM Docker image. It provides a development environment that is isolated from your day-to-day system. However, it is based on KDE Neon Unstable, which might not be to your taste.


If you are a visual learner, you might consider watching the video version at https://www.youtube.com/embed/B4xoc0K5iA4

Install basic tools

First you will need to use your operating system's package manager to install some basic tools:

  • Arch/Manjaro: sudo pacman -S git cmake dialog extra-cmake-modules
  • Fedora: sudo dnf install git cmake dialog perl perl-IPC-Cmd perl-MD5 perl-FindBin
  • KDE Neon/Kubuntu/Ubuntu/Debian: sudo apt install git cmake dialog
  • openSUSE Leap & Tumbleweed: sudo zypper install git breezy cmake dialog


Configure Git

We need to set your authorship information properly so that any changes you make can be properly attributed to you: 

git config --global user.name "Your Name"
git config --global user.email "[email protected]"

Note

The name you provide should be your actual name, not your KDE Identity username.

The email address you specify above must be the same as the email address used for your https://bugs.kde.org account. If they don't match, then the BUG: and FEATURE: keywords won't work (see this page for more information).


In order to authenticate yourself when pushing code changes, you need to add an ssh key to your GitLab profile as described here.

Set up kdesrc-build

Next, we need a method of managing dependencies. Every software has dependencies: other pieces of software that provide the functionality they rely on. In order to compile any piece of software, its dependencies must be available.

Most Linux-based operating systems do not provide development packages that are up-to-date enough for working on KDE software, so we will compile all the KDE dependencies ourselves. To do this, we use a command-line tool called kdesrc-build to download, manage, and build KDE source code repositories. Let's set it up now! First, we create a new directory for all the KDE source code we will be using; you will need many GB of free disk space. We then clone the source code repository that holds kdesrc-build in that directory, so we have a local copy of it on our computer. 

mkdir -p ~/kde/src
cd ~/kde/src/
git clone https://invent.kde.org/sdk/kdesrc-build.git && cd kdesrc-build

Next, it's time to set up kdesrc-build and pick up the changes it made to your ~/.bashrc (or ~/.zshrc for zsh users) for the current terminal session: 

./kdesrc-build --initial-setup
source ~/.bashrc

Check that source has worked by checking the new path for "~/kde/src/kdesrc-build"
echo $PATH

Warning

Do not quote or escape any file paths entered in the wizard! And do not run the command kdesrc-build by itself without any arguments because this will build everything, which is probably overkill right now.


Note

If you use zsh and selected yes for auto-completions during the initial setup for kdesrc-build, add the following to ~/.zshrc if it is not already there. 
autoload -U +X compinit && compinit
autoload -U +X bashcompinit && bashcompinit


The initial setup tries to install the basic packages for compiling Qt and KDE software on your distro. It also creates a ~/.config/kdesrc-buildrc configuration file. If you want a more guided setup process for kdesrc-build, run the command kdesrc-build-setup instead. However, unlike --initial-setup, it won't install packages from your distro for compiling programs so you will have to do that yourself.

Consult the kdesrc-build manual for more information and options.

Set up Qt

By default, kdesrc-build will not build from source all the dependencies that a program or framework needs, including the Qt toolkit itself, because the include-dependencies option is set as default in the ~/.config/kdesrc-buildrc file.

If your Linux distribution provides a recent version of Qt (5.15 or newer), you can save some time and disk space and use that version instead of building your own. To configure kdesrc-build to skip building Qt, open the configuration file ~/.config/kdesrc-buildrc and confirm that qtdir and any lines that begin with include and are related to qt5 are commented out, and confirm the line that includes kf5-qt5-build-include has not been commented out.

For example, comment/disable (put a # at the start of the line) or delete these lines if you want to use your distro's Qt packages (actual paths may vary): 

qtdir  ~/kde/qt5 # Where to find Qt5
include /path/to/kdesrc-build/qt5-build-include
include /path/to/kdesrc-build/custom-qt5-libs-build-include

Disable indexing for your development environment

You'll want to disable indexing for your development-related git repos and the files they will build and install. Add ~/kde to the exclusions list in System Settings > File Search, like so:

Download non-KDE dependencies

Even though kdesrc-build will take care of the KDE dependencies for you, it does not yet have the ability to install non-KDE dependencies (see https://invent.kde.org/sdk/kdesrc-build/-/issues/9), which are typically acquired using your package manager. To install the required non-KDE dependencies, read this page and follow the instructions laid out there.

Reboot your computer and log back in so the package changes, and the changed ~/.bashrc take effect on your user account.

Once that's done, your development environment is set up and ready to build software! Let's take it for a spin.

Building software with kdesrc-build

It can take an hour or more to compile a KDE Application, Framework, or Plasma itself for the first time. The reason for this is that kdesrc-build is compiling all of the KDE dependencies (See https://invent.kde.org/sdk/kdesrc-build/-/issues/17). The next time you want to compile that or any other piece of KDE software, it will be much faster since most of the dependencies will have already been compiled. If you don't want to build all dependencies (e.g., because you are using a rolling release distro that provides recent versions of software), edit the same configuration file and simply set include-dependencies to false or add the --no-include-dependencies option when running kdesrc-build.

Warning

A 2021 issue with kdesrc-build means building may spawn dozens of processes, exhausting your computer's memory and crashing programs. You can either run kdesrc-build --initial-setup to recreate your ~/.config/kdesrc-buildrc file, or remove the line make-options -j ${num-cores}.


Applications

KDE Applications like Dolphin, Okular, Konsole and Gwenview are standalone apps that can be run on multiple platforms, such as Plasma, GNOME, even macOS and Windows! New versions of KDE Applications are released three times a year. Note that the Discover app store (git repo name: plasma-discover) and System Settings app (git repo name: systemsettings) are distributed alongside Plasma, but they build like apps using the below instructions. A list of all KDE applications can be found here: https://userbase.kde.org/Applications.

The general steps required to build and run an application are described in the following using Dolphin as an example: 

kdesrc-build dolphin

As a part of this process, Dolphin was installed to ~/kde/usr/bin/dolphin. There is no need to manually install anything; kdesrc-build installed it for you! Source the project's auto-generated prefix.sh file every time you want to run your custom-compiled version of Dolphin: 

source ~/kde/build/dolphin/prefix.sh
~/kde/usr/bin/dolphin

Or using kdesrc-run wrapper: 

kdesrc-run dolphin

Did it run? If so, then congratulations, you just compiled your own version of Dolphin from source code!

Frameworks

KDE Frameworks are libraries of tools and features that can be used by any application or Plasma itself. New versions of KDE Frameworks are released once a month. A list of all frameworks can be found here: https://api.kde.org/frameworks.

For example, here is how to build the KIO framework: 

kdesrc-build kio

Now you can run an existing app using your custom-made version of the framework! For example, the following will run Dolphin, but it will be using the KIO library that you just built: 

source ~/kde/build/kio/prefix.sh
~/kde/usr/bin/dolphin

Plasma

KDE Plasma is the environment in which you can run apps. Plasma is responsible for providing a desktop with wallpaper, app launchers, and widgets; displaying notifications; managing wired and wireless networks; and similar operating-system level tasks. New versions of Plasma are released three times a year. Plasma has multiple shells: Plasma Desktop for desktop, laptop, and 2-in-1 computers, Plasma Mobile for mobile phones, Plasma Bigscreen for televisions, and so on. They all share certain common components, such as a window manager, networking stack, basic graphical components, and so on. Here is how to build them: 

kdesrc-build plasma-workspace plasma-framework plasma-nm plasma-pa plasma-thunderbolt plasma-vault plasma-firewall plasma-workspace-wallpapers kdeplasma-addons krunner milou kwin kscreen sddm-kcm plymouth-kcm breeze discover print-manager plasma-sdk kaccounts-integration kaccounts-providers kdeconnect-kde plasma-browser-integration xdg-desktop-portal-kde kde-gtk-config khotkeys kgamma5 breeze-gtk --include-dependencies

Plasma Desktop

To build the plasma Desktop environment and its related apps, also build the following: 

kdesrc-build plasma-desktop systemsettings ksysguard plasma-disks plasma-systemmonitor ksystemstats kinfocenter kmenuedit --include-dependencies

To get translations in your self-built Plasma, you must build plasma-workspacewith -DKDE_L10N_SYNC_TRANSLATIONS=true. The easiest way to do this is go into the build directory (~/kde/build/plasma-workspace by default), run ccmake ., turn on that setting, and then rebuild the project.

Now it's time to make your built-from-source Plasma session accessible from the SDDM login screen, and also copy the built-from-source DBus files into a location where they are visible to them system bus. To do this, run the following command: 

~/kde/build/plasma-workspace/login-sessions/install-sessions.sh

Note

SELinux can interfere with the new DBus services working correctly, and the path of least resistance may be to simply turn it off if you are using a distro that ships with it on by default (for example, Fedora). See https://www.tecmint.com/disable-selinux-in-centos-rhel-fedora/ for more information.

After this, you can log out and select your new plasma session in SDDM's session chooser menu (which is located in the bottom-left corner of the screen if you're using the Breeze SDDM theme).

Alternatively, you can run the new version of plasma on top of your existing system for quick testing like so: 

source ~/kde/build/plasma-desktop/prefix.sh
~/kde/usr/bin/plasmashell --replace

Plasma Mobile

To build the Plasma Mobile environment, also build the following: 

kdesrc-build plasma-nano plasma-mobile plasma-settings --include-dependencies

You can run your custom-built Plasma Mobile in a phone-sized window within your existing session like so: 

export XDG_RUNTIME_DIR=/tmp/
export QT_QPA_PLATFORM=wayland
export QT_QPA_PLATFORMTHEME=KDE
export QT_WAYLAND_DISABLE_WINDOWDECORATION=1
export XDG_CURRENT_DESKTOP=KDE
export KSCREEN_BACKEND=QScreen
export KDE_FULL_SESSION=1
export KDE_SESSION_VERSION=5
export QT_QUICK_CONTROLS_MOBILE=1
export PLASMA_PLATFORM=phone:handheld
export $(dbus-launch)
dbus-run-session kwin_wayland --width 360 --height 720 --xwayland "plasmashell -p org.kde.plasma.phoneshell"

Plasma Mobile can also be run on a mobile device itself. For information on how to do that, see https://community.kde.org/Plasma/Mobile/DevGuide#Mobile_device_running_plasma_mobile.

For more information, see https://community.kde.org/Plasma/Mobile/DevGuide.

Iterating on a single project

When you're working on a project and you want to rebuild it to test your changes, you can save a lot of time by only rebuilding that project, rather than the entire stack. For example if you are working on plasma-desktop, you can rebuild only that project rather than everything by running kdesrc-build --no-src --no-include-dependencies plasma-desktop.

How to solve build problems

Did one or more modules fail to build (displayed in red font) using kdesrc-build? Here's what to do:

  1. Try building the failing module again from scratch using kdesrc-build [failing module] --refresh-build
  2. Make sure that you have all the dependencies for the failing module. Go back to the #Download non-KDE dependencies section and re-install the non-KDE dependencies. If that doesn't fix the problem, open the log file for the failing module, which kdesrc-build will print the path at the end of its output. Scroll to the bottom of the log file and read the output to see what missing dependency it is complaining about, then find and install the corresponding package using your distro's package manager your distro. If several look relevant, install them all just to be safe. When you have the necessary dependencies, you can save time and resume from the failing module by adding --resume-from [the name of the module that failed] to your kdesrc-build command.
  3. Check the list of currently broken modules on the KDE build server. If it's broken there, then it's not your fault. :)
  4. Ask for help in the the #kde-devel channel on Matrix or Libera Chat IRC. See Get Involved/development#Communicate with the team

Choose what to do

Now that you can compile and deploy custom versions of KDE software, you can open your editor and start hacking on the source code! The code for the version of Dolphin that you built earlier is located at ~/kde/src/dolphin/; other projects you build with kdesrc-build will live in similar locations.

You may wish to look over the instructions for setting up an IDE for development with KDE projects.

A good place to start is with a small bug or feature in an existing piece of software that affects you personally ("scratch your own itch"). Get in touch with the existing developers (see Communicate with the team, below) and they can help you out, by pointing you to the right place in the code and giving advice about how to tackle the problem.

Try not to start by proposing or working on major features or significant design changes. These can be controversial, and the smoothest way to get going is by working on relatively non-controversial bugfixes. Start slowly and build trust!

Here are some other ideas for starting points:

  • Improve awkwardly-worded messages and labels that are written in English. This is a great way for non-programmers to contribute! If you can compile software and have a good grasp of English, you can make a big difference here.
  • Work on Junior Jobs, which are small tasks that are suitable for beginners (both bugs and features).
  • Work on Bugs related to KDE's Usability & Productivity initiative, many of which are small and easy.

Test your changes

Once you've made some changes, make sure the project still compiles and installs, and make sure the changes have the desired effect when you run the software. Then it's time to run the project's unit tests: 

cd ~/kde/build/dolphin/
source ./prefix.sh
ctest --output-on-failure

If any test fails, that needs to be investigated and fixed before you can proceed. Once the tests pass, then run the software again to make sure it still behaves properly. If it doesn't, then go back and work on your patch some more, then re-compile and re-deploy, and test again, until the program does what you'd like it to do and all tests pass.

Submit a Merge Request

Once you're happy with your patch and have verified that it does what you want, it's time to submit your changes for the review!

KDE uses GitLab for merge request submission and review. Learn how to submit a Merge Request with GitLab.

Communicate with the team

There are several ways to get in touch with KDE developers, either generally or for a specific project. The most important communications channels are:

These are general KDE development communication channels, and you may get directed to a more appropriate place for the project you are interested in. There is a list of mailing lists if you want to find a mailing list for a specific team directly. Many teams have their own real-time chat channels, too.

You can also try looking for the team's section on the Main Page of this wiki. Many teams have information there for new contributors.

Source code cross referencing

To search for a class, method, signal name... etc in all KDE repos, KDE uses a code referencing tool to index code in the various KDE repositories, you can search using the web interface available at https://lxr.kde.org/ . This is a very useful tool if you e.g. want to search for code usage examples in existing code... etc.

Usage:

  • From the Branch group menu, you can select either kf5-qt5, to search the code in the Git master branches or stable-kf5-qt5 to search only the stable (released) branches
  • There are two search modes:
    • On the Identifier search page, you can search for (note that this is case sensitive):
      • class names, e.g. RenameDialog, StatJob, and of course any Qt class (used in KDE code, which is pretty much all of them), QLatin1String, QListWidget
      • method names, e.g. addConfigSources() (from the KConfig framework) and signal names e.g. mimeTypeFound()
    • on the General search page, you can search for strings, e.g. in Dolphin's context menu (accessed by right- clicking any empty space) there is Paste Clipboard Contents, if you want to find in which source file this string is defined, search for Paste Clipboard Contents; this search includes classes/methods/signals names.

Next steps

Sharpen your skills by going through the KDE development tutorials.

Set up graphical development tools or an Integrated Development Environment (IDE). You may want to try out KDevelop, the KDE IDE.

After you have had several drama-free patches accepted, a KDE developer is likely to suggest you get a Developer account, which will allow you to commit directly to KDE projects. With very few limits on where you can commit, you will be expected to act responsibly. At this point, congratulations! You are officially a KDE developer!

You may also want to set up a more customized development environment. See Guidelines and HOWTOs/Build from source.

Best practices & other useful information

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