Get Involved/development: Difference between revisions

From KDE Community Wiki

Revision as of 16:03, 11 February 2023

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.

Requirements

Prerequisite skills

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.

More learning resources.

Operating system

We recommend that you set up the development environment (kdesrc-build) on a Linux operating system installed on your laptop or computer or on a Linux operating system installed in a virtual machine.

Support for Windows and macOS is still experimental and you may have a better experience doing your development in a virtual machine using a Linux distribution.

Linux

The Linux distribution should provide relatively recent versions of Qt and KDE Frameworks.

Linux distributions that are better suited for kdesrc-build are rolling-release Linux distributions (Arch, openSUSE Tumbleweed, KDE neon) or the latest version of Fedora KDE Spin or Kubuntu.

Note

While you can still build KDE software using kdesrc-build on other Linux distributions or FreeBSD, you may have a better experience doing your development in a virtual machine using one of the Linux distributions mentioned above.

Microsoft Windows, Apple macOS, FreeBSD

Setting up a development environment on Microsoft Windows, Apple macOS or FreeBSD is an advanced topic.

Integrated Development Environment (IDE)

While it is not required to edit code, it is recommended to set up graphical development tools or an Integrated Development Environment (IDE). You may want to try out KDevelop, the KDE IDE.

Setting up the development environment

Information

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

This procedure will set up kdesrc-build for Qt5 and KDE Frameworks 5.
Setting up kdesrc-build for Qt6 and KDE Frameworks 6 and setting up kdesrc-build inside a Docker container are advanced topics.

Source code for KDE software lives on KDE Invent. But before you can work on it, you'll need to set up 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!

Video version

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

Install basic tools

Set up kdesrc-build - Step 1/6.

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

Set up kdesrc-build - Step 2/6.

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.

E.g. the KDE application kcalc depends on more than 20 other KDE git repositories: KDE Frameworks and other KDE libraries.

Most Linux operating systems do not provide development packages of the KDE Frameworks 5 and of other KDE libraries that are up-to-date enough. We will not be able to build from the "master" branch of the KDE git repositories.

Therefore we will compile all of the KDE git repositories ourselves, including KDE Frameworks 5 and other KDE libraries. We should not use KDE files (binaries, libraries and other files) from the OS (i.e. the /usr directory). To do this, we use a command-line tool called kdesrc-build to download, manage, build, and install KDE git 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. Budget 50 GB for KDE Frameworks + KDE Plasma, and 10-30 more for some apps as well. We then clone the kdesrc-build git repository in that directory.

# If you have an old installation of kdesrc-build and you want a clean kdesrc-build installation, run a command line like: # mv ~/.config/kdesrc-buildrc ~/.config/kdesrc-buildrc~bak ; mv ~/kde ~/kde~bak
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:

# For supported operating systems (OSes), it installs all of the OS packages needed in order to build all of the KDE Frameworks 5.
./kdesrc-build --initial-setup
source ~/.bashrc

# Check that the command line above has worked by seeing if the PATH environment variable contains "~/kde/src/kdesrc-build".
echo $PATH

Warning

Do not run the command kdesrc-build 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 creates the kdesrc-build configuration file ~/.config/kdesrc-buildrc.

Warning

Make sure that the file ~/.config/kdesrc-buildrc, after the line global, contains the line branch-group kf5-qt5.

Run kdesrc-build --help for the kdesrc-build command line help.

Set up Qt

Qt is the fundamental framework that is needed for pretty much all KDE development. We need a recent enough version of Qt to proceed. If you are just getting started, we recommend that you use a Linux distribution that is better suited for kdesrc-build either as the primary operating system or in a virtual machine.

You can look up the version of the Qt framework installed on your operating system by opening the application "Info Center" (KInfoCenter) > Basic Information > About this System > "Qt Version:". Or starting any installed KDE application (e.g. the KDE calculator app (kcalc)) and from the application's main menu > Help > About application > Components tab > "Qt".

If you have Qt 5.15 or any later version installed, you are already done with the "Set up Qt" step and can proceed to the next section. 🎉

...otherwise we now need to install a more recent version from somewhere. Your distribution might have one available. Alternatively, we need to configure kdesrc-build to build and install a recent Qt version for you. Building Qt using kdesrc-build is a more advanced topic.

Disable indexing for your development environment (optional)

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

Set up kdesrc-build - Step 3/6.

If your distribution is supported, kdesrc-build --initial-setup will install the distribution packages which are needed in order to build KDE software. kdesrc-build is used in order to build any of the KDE git repositories. The packages for Qt and the rest of the dependencies are acquired using your Linux distribution's package manager.

Please install at least all of the dependencies needed in order to build all of the KDE Frameworks. Steps 4 and 5 of setting up kdesrc-build are here.

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.

Note

If you happen to find an external dependency needed to build KDE software that was not installed with kdesrc-build --initial-setup, once you finish this tutorial, you may send a merge request to https://invent.kde.org/sdk/kdesrc-build/-/blob/master/modules/ksb/FirstRun.pm in order to include the respective distro package to the list.

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 Frameworks 5 modules plus any other KDE module that is a dependency of the module that you tell kdesrc-build to build.

kdesrc-build by default has the option "--include-dependencies" enabled so it will ignore all KDE packages that were installed using the distribution's package manager and will instead build all needed KDE modules from source.

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.

KDE Frameworks

Set up kdesrc-build - Step 6/6.

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 of the frameworks can be found here: https://api.kde.org/frameworks.

After you install all of the dependencies needed in order to build all of the KDE Frameworks, the first thing that you should do using kdesrc-build is to build all of the KDE Frameworks:

kdesrc-build frameworks

Applications

KDE Applications like Calculator (KCalc), 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://apps.kde.org/.

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

kdesrc-build kcalc

As a part of this process, kcalc was installed to ~/kde/usr/bin/kcalc. 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 kcalc:

source ~/kde/build/kcalc/prefix.sh
kcalc
# You can check that "/home/username/kde/usr/bin" is the first directory in $PATH.
# echo $PATH

Or using the kdesrc-run command:

kdesrc-run kcalc

Did it run? If so, then congratulations, you just compiled your own version of the KDE calculator (kcalc) from source code!

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-integration bluedevil powerdevil 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 drkonqi phonon flatpak-kcm --include-dependencies

Plasma Desktop

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

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

To get translations in your self-built Plasma, you must build plasma-workspace with -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 off enforcement if you are using a distro that ships with it on by default (for example, Fedora). To do this, set the value of SELINUX to permissive in the file /etc/selinux.

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 an emulated phone session using a phone-sized window within your existing desktop. Note that you probably want that this emulated phone session does not use the settings of your current user. E.g. you want in the emulated phone session to use Angelfish, not Mozilla Firefox as your web browser. Instructions:

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"

Alternative instructions for starting an emulated phone session.

export QT_WAYLAND_DISABLE_WINDOWDECORATION=1
export QT_QUICK_CONTROLS_MOBILE=1
export PLASMA_PLATFORM=phone:handheld

QT_QPA_PLATFORM=wayland dbus-run-session kwin_wayland --xwayland "plasmashell -p org.kde.plasma.phoneshell" --width 360 --height 720

Plasma Mobile can also be run on a mobile device itself. For more information, see the 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:

Try building the failing module again from scratch using kdesrc-build [failing module] --refresh-build
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 the package manager of your distribution. 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.
Check the list of currently broken modules on the KDE build server. If it's broken there, then it's not your fault. :)
Ask for help in the the #kde-devel channel on Matrix or Libera Chat IRC. See Get Involved/development#Communicate with the team
Looking into the error log is also helpful. For example, the build stopped at kwallet. You will need to go into kde/src/log/latest/kwallet/error.log and find what packages are missing.
If you know what files are missing, but you don't know what packages provide them, you can ask your package manager. See https://wiki.archlinux.org/index.php/Pacman/Rosetta (see "Query the package which provides FILE").
The problem might be in ~/kde/usr. E.g. a file in ~/kde/usr/include which was renamed or moved. You can help yourself by seeing if you can reproduce this issue in a clean new Virtual Machine (VM). If you cannot reproduce the issue in your VM, then a possible solution is to start with a new and clean kdesrc-build installation. I.e. run something like mv ~/.config/kdesrc-buildrc ~/.config/kdesrc-buildrc~bak ; mv ~/kde ~/kde~bak. Then install kdesrc-build from scratch using this wiki page.

Submitting changes

Now that you can compile and deploy custom versions of KDE software, you can open your editor and start hacking on the source code!

Choose what to do

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.
More easy tasks.

Make your changes and test them

The code for the version of the KDE Calculator (kcalc) that you built earlier is located at ~/kde/src/kcalc; other projects you build with kdesrc-build will live in similar locations.

You may wish to look over the instructions for setting up an Integrated Development Environment (IDE) for development with KDE projects. You can use the debugger inside an IDE to go over the lines of source code that you change.

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 test suite:

cd ~/kde/build/kcalc
source prefix.sh
ctest --output-on-failure # or make test

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 their own GitLab instance called Invent for submitting merge requests and code review. See the GitLab page to learn how to submit a merge request.

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:

The #kde-devel channel on Matrix or the Libera Chat IRC, which is where KDE developers chat in real-time about their work.
The kde-devel mailing list is the primary development mailing list. Learn more about mailing lists.

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.

Other ways to search across all of the KDE git repositories:

If you have a github.com account. Log into github.com. Go to https://github.com/KDE , in the top left search bar, search for your search term e.g. KMessageBox, select "In this organization".
kdesrc-build --src-only will download the source code of more than 300 KDE git repositories in ~/kde/src. Search inside this directory. E.g. using Microsoft Visual Studio Code code ~/kde/src, from the vscode main menu > Edit > Find in Files Ctrl+Shift+F.

Next steps

Sharpen your skills by going through the KDE development tutorials.

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!

Best practices & other useful information

This page continues with more advanced topics.

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