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This page is the continuation with more advanced topics of the page [[Get_Involved/development]].
This page is the continuation with more advanced topics of the page [[Get_Involved/development]].
== kde-builder is an alternative to kdesrc-build ==
kdesrc-build and kde-builder are two KDE build frameworks. They are used at the command line and have identical command line syntax, just replace the string "kdesrc-build" with "kde-builder". They use the same configuration file, named <code>kdesrc-buildrc</code>.
kde-builder is newer and regularly gets new features and is written in Python.
kdesrc-build is in maintenance mode and feature frozen and written in Perl.
The "how to install kde-builder" procedure is here https://invent.kde.org/sdk/kde-builder/-/blob/master/README.md .


== Develop in a Linux container ==
== Develop in a Linux container ==


When you start programming for KDE, it is recommended that you [[Get_Involved/development|use kdesrc-build in your main operating system or in a virtual machine]] running on a rolling-release Linux distribution (Arch, openSUSE Tumbleweed, KDE neon) or running on e.g. the latest version of Fedora KDE Spin or Kubuntu.
When you start programming for KDE, it is recommended that you [[Get_Involved/development|use kdesrc-build in your main operating system or in a virtual machine]] running on a [[Get_Involved/development#Operating_system|Linux operating system that is better supported by kdesrc-build]].


As an alternative, you can run kdesrc-build in a Linux container (docker, podman, toolbx, distrobox).
As an alternative, you can run kdesrc-build in a Linux container (docker, podman, toolbx, distrobox).
Line 15: Line 25:
It is possible to start developing KDE software using container images that are able to see inside your home folder. This can be done using distrobox and podman.
It is possible to start developing KDE software using container images that are able to see inside your home folder. This can be done using distrobox and podman.


First, install distrobox and podman from your distribution repositories:
This solution is particularly useful for users on immutable distributions like Fedora Kinoite, openSUSE Kalpa or the Steam Deck's SteamOS.


* Debian/Ubuntu: sudo apt install distrobox podman
To learn how to build KDE software with distrobox, see: https://develop.kde.org/docs/getting-started/building/containers-distrobox/
* openSUSE: sudo zypper install distrobox podman
* Fedora: sudo dnf install distrobox podman
* Arch: sudo pacman --sync distrobox podman


==== Building without kdesrc-build ====
== Other operating systems ==


You can build a single repository using the [https://community.kde.org/Neon/Containers KDE Neon Unstable docker image]. We will be using the <code>plasma:unstable</code> image, which comes with the latest KDE software and libraries, and we will be using the minimal version, which requires you to install development libraries before compiling your projects.
=== Kubuntu >= 23.10 ===


After installing distrobox and podman, run the following to create a new distrobox container:
The default configuration of kdesrc-build requires Qt version 6.6. Kubuntu 23.10 and 24.04 have Qt version 6.4.2. It is recommended that you use a [[Get_Involved/development#Operating_system|Linux OS that is better supported by kdesrc-build]].


{{Input|
If you are a more seasoned developer you might be able to use Kubuntu for kdesrc-build by [[Get_Involved/development/More#Qt_6_installed_using_the_Qt_online_installer|installing Qt6 using the Qt online installer]] or by [[Get_Involved/development/More#Build_Qt_using_kdesrc-build|building Qt6 using kdesrc-build]].
podman pull invent-registry.kde.org/neon/docker-images/plasma:unstable
distrobox create --image invent-registry.kde.org/neon/docker-images/plasma:unstable
}}


This will create a distrobox container named '''plasma-unstable'''.
=== Alpine Linux ===


{{Note|The plasma:unstable image size is 5.6 GB.}}
<pre>
apk add git perl doas-sudo-shim
</pre>


Lastly, enter the generated container:
=== FreeBSD ===


{{Input|
Install the latest release of FreeBSD with KDE Plasma Desktop on your hardware computer or in a virtual machine.
distrobox enter plasma-unstable
}}


You can then just clone the desired repository in your home folder and build it while being inside the container. If any development libraries are missing, you can just install them the same way you would install on Debian/Ubuntu/KDE Neon:
Your user should be member of the "wheel" user group (e.g. this can be configured in the FreeBSD installer, when creating your user you can select additional user groups for your user). Your user should be able to use sudo:


{{Input|
<pre>
sudo apt install packagename-dev
pkg install sudo
}}
visudo
# Uncomment the line: %wheel ALL=(ALL:ALL) ALL
</pre>


You can also use <code>build-dep</code> to let apt install the required libraries for the program you will be compiling. For example, to install the development libraries for Kate, you can run:
Then set up kdesrc-build using the same procedure as when installing kdesrc-build on a Linux operating system. FreeBSD is currently supported by kdesrc-build. See https://www.youtube.com/watch?v=8MqBnb3Y9JU


{{Input|
=== OpenBSD >= 7.5 ===
sudo apt-get build-dep kate
}}


==== Building with kdesrc-build ====
Install OpenBSD version greater than or equal to 7.5. In the installer keep the defaults, the user created by the installer is named "administrator" in this example.
<pre>
# Enable doas
su -
cp /etc/examples/doas.conf /etc/doas.conf
exit
# kdesrc-build needs sudo.
mkdir -p ~/.local/bin ; ln -s /usr/bin/doas ~/.local/bin/sudo
echo "export PATH=~/.local/bin:\$PATH" >> ~/.bashrc


First, install distrobox and podman from your distribution repositories. Then run:
# Test doas.
doas su
# kde-builder needs bash.
pkg_add bash
chsh -s /usr/local/bin/bash
exit


{{Input|
# As user administrator
distrobox enter
chsh -s /usr/local/bin/bash
}}


This should create a container based on your current Linux OS and enter it. It is preferable to use one of the Linux distributions that is better suited for kdesrc-build, as mentioned [[Get_Involved/development#Operating_system|in this wiki page]], so if your distribution does not provide very up-to-date packages, you can download and use a different container image for your distrobox from [https://hub.docker.com/search?type=image Dockerhub]. For example, with openSUSE Tumbleweed:
# As per https://rsadowski.de/posts/2024-01-09-openbsd-kde/ , https://openports.pl/path/meta/kde,-plasma
doas su
pkg_add kde-plasma kate


{{Input|
# I recommend that you use tigervnc. https://nmariusp.github.io/install-os.html#openbsd--75
podman pull opensuse/tumbleweed
</pre>
distrobox create --image opensuse/tumbleweed --name tumbleweed
distrobox enter tumbleweed
}}


Then it's a matter of downloading and running kdesrc-build as detailed in [[Get_Involved/development/Set_up_a_development_environment]]:
After you install kdesrc-build:
 
<pre>
<syntaxhighlight lang="bash">
# Edit the kdesrc-buildrc file e.g.:
mkdir -p ~/kde/src
cmake-options -DCMAKE_BUILD_TYPE=RelWithDebInfo -DKF_IGNORE_PLATFORM_CHECK=ON
cd ~/kde/src
git clone https://invent.kde.org/sdk/kdesrc-build.git
cd kdesrc-build
./kdesrc-build --initial-setup
source ~/.bashrc
</syntaxhighlight>
 
From this point on, one important thing to bear in mind is that a distrobox container is transparent in its user space and containerized in its root space: when you are inside a distrobox container, you can see the content of system's home folder, but not your system's root folders, only the container's root folders. This means that you can install packages inside the container using root privileges and access those packages to compile your programs stored in your home, without ever installing those packages in your actual system!
 
You can take advantage of this by installing, for instance, Qt development packages used for kdesrc-build from inside the container. This way, it is not necessary to compile Qt with kdesrc-build. This is particularly convenient if you want to compile KDE software with Qt6 quickly.
 
Likewise, you should [https://community.kde.org/Get_Involved/development/Install_the_dependencies install the required dependencies] from inside the distrobox rather than from your system's repositories. Then you can start compiling as usual.
 
After compiling your program with kdesrc-build from inside the distrobox, you can run it with <code>kdesrc-build run</code>, and despite it originating from inside a container and using the libraries from the container, it will run just fine as a GUI application on your system!
 
The only few gotchas to using this method are:
 
* You cannot use a [[Get_Involved/development/Build_software_with_kdesrc-build#Plasma|full Plasma Desktop session]] made from git.
* You will need qqc2-desktop-style and Breeze to show the correct theme for your applications.
* You will need the QtWayland library and its respective development package to run your applications natively on a Wayland session.
 
== Other operating systems ==
 
=== Kubuntu 23.10 ===
 
The default configuration of kdesrc-build requires Qt version 6.6. Kubuntu 23.10 has Qt version 6.4.2. It is recommended that you [[Get_Involved/development/More#Build_Qt6_using_kdesrc-build|build Qt in Kubuntu]] or use a [[Get_Involved/development#Operating_system|Linux OS that is better supported by kdesrc-build]].
 
=== FreeBSD ===


Install the latest release of FreeBSD with KDE Plasma Desktop on your hardware computer or in a virtual machine.
# Also set environment variable:
 
export CMAKE_PREFIX_PATH=/usr/local/lib/qt6/cmake
Your user should be member of the "wheel" user group (e.g. this can be configured in the FreeBSD installer, when creating your user you can select additional user groups for your user). Your user should be able to use sudo:
# Or
 
export CMAKE_PREFIX_PATH=/usr/local/lib/qt5/cmake
<pre>
pkg install sudo
visudo
# Uncomment the line: %wheel ALL=(ALL:ALL) ALL
</pre>
</pre>
Then set up kdesrc-build using the same procedure as when installing kdesrc-build on a Linux operating system. FreeBSD is currently supported by kdesrc-build. See https://www.youtube.com/watch?v=8MqBnb3Y9JU


=== Microsoft Windows ===
=== Microsoft Windows ===
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See https://community.kde.org/Get_Involved/development/Install_the_dependencies .
See https://community.kde.org/Get_Involved/development/Install_the_dependencies .


== Advanced kdesrc-build ==
== Project Documentation ==
 
After you have edited a git repository and you want to build it, <code>--no-src</code> will make sure that <code>kdesrc-build</code> does not overwrite your local source code changes with the latest source code from the official git repository (remote "origin" / https://invent/kde.org).
 
<code>--no-include-dependencies</code> only builds the git repository that you give as parameter to <code>kdesrc-build</code>.
 
<code>--debug</code> shows verbose output.
 
<code>--refresh-build</code> forces a rebuild (not an incremental build) and a full reinstall.
 
E.g. you have edited kcalc. You run:
<pre>
kdesrc-build kcalc --no-src --no-include-dependencies --refresh-build --debug |& tee ~/a.txt
</pre>
 
For details, see:
<pre>
kdesrc-build --help
</pre>


Note: the resources below might not be up to date.
* [https://docs.kde.org/trunk5/en/kdesrc-build/kdesrc-build/ Handbook]
* [https://invent.kde.org/sdk/kdesrc-build/-/blob/master/README.md Readme #1]
* [https://invent.kde.org/sdk/kdesrc-build/-/blob/master/doc/README.md Readme #2]


See the [https://docs.kde.org/trunk5/en/kdesrc-build/kdesrc-build/ kdesrc-build manual], [https://invent.kde.org/sdk/kdesrc-build/-/blob/master/README.md Readme #1], [https://invent.kde.org/sdk/kdesrc-build/-/blob/master/doc/README.md Readme #2], [https://invent.kde.org/sdk/kdesrc-build/-/blob/master/doc/source-reference/index.adoc Document #3] for more kdesrc-build information and options.
Developer's documentation can be found in the {{ic|doc/source-reference}} in the project repo.


== kf6-qt6 vs. kf5-qt5 ==
== kf6-qt6 vs. kf5-qt5 ==
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== Build Qt using kdesrc-build ==
== Build Qt using kdesrc-build ==


If you cannot build the KDE frameworks using {{ic|kdesrc-build}} and the Qt provided by your Linux distribution is outdated, you might want to build it using {{ic|kdesrc-build}}.
=== Qt6 ===
If you cannot build the KDE frameworks using {{ic|kdesrc-build}} and the Qt provided by your Linux distribution is outdated, you might want to build the Qt framework using {{ic|kdesrc-build}}.


In your configuration file use the {{ic|qt-install-dir}} option (in the ''global'' section) with non-empty value, for example:
In your configuration file use the {{ic|qt-install-dir}} option (in the ''global'' section) with non-empty value, for example:
Line 173: Line 139:
{{bc|
{{bc|
global
global
   qt-install-dir ~/kde6/usr_qt
   qt-install-dir ~/kde/usr
   branch-group kf6-qt6
   branch-group kf6-qt6
end global
end global
}}
}}


Then build it: {{bc|kdesrc-build qt6-set}}
It is recommended that if you build Qt6 using kdesrc-build, you also build qtwebengine. Edit the file {{ic|~/.local/state/sysadmin-repo-metadata/module-definitions/qt6.ksb}}. Follow the instructions found in the file: if you want qtwebengine, add it to use-modules after "qtwebchannel" and comment out the line "ignore-modules qtwebengine".
 
<pre>
kdesrc-build qtbase --refresh-build --debug
</pre>
Press Ctrl+C after the CMake configure summary for qtbase. Make sure that you have the needed dependencies. Should find libb2-dev, libproxy-dev, libmd4c-dev, libmd4c-html0-dev, libxcb-xinput-dev, libatspi2.0-dev, libsqlite3-dev, unixodbc-dev, libmysqlclient-dev, postgresql-client, libecpg-dev, libpq-dev. Optional dependencies libsctp-dev, libts-dev.
 
<pre>
kdesrc-build qtwebengine
</pre>
This will build the Qt6 modules from qtbase up to qtwebengine. qtwebengine will probably be built incorrectly because some needed dependencies are missing.
 
<pre>
kdesrc-build qtwebengine --refresh-build --debug
</pre>
Press Ctrl+C after the CMake configure summary for qtwebengine. Make sure that you have the needed dependencies. Should find node.js >= 14, libdbus-1-dev, libxcomposite-dev, libxshmfence-dev, libxdamage-dev, libharfbuzz-dev, libvpx-dev, libpci-dev, libevent-dev, libre2-dev, libsnappy-dev, libcups2-dev, libxkbfile-dev.


If you want the same for Qt5, change {{ic|branch-group}} option and use {{ic|qt5-set}} instead of {{ic|qt6-set}}.
Then build Qt6: {{bc|kdesrc-build qt6-set}}


To compile Qt6 with Qt X11 Extras (which is a necessary library to compile [https://api.kde.org/frameworks/kwindowsystem/html/ KWindowSystem]), you should enable XCB feature during compilation  
To compile Qt6 with Qt X11 Extras (which is a necessary library to compile [https://api.kde.org/frameworks/kwindowsystem/html/ KWindowSystem]), you should enable XCB feature during compilation  
Line 186: Line 167:
{{bc|1=kdesrc-build qt6-set --cmake-options="-DQT_FEATURE_xcb=ON"}}
{{bc|1=kdesrc-build qt6-set --cmake-options="-DQT_FEATURE_xcb=ON"}}


After that, you can build other modules.
=== Qt5 ===
If you want the same for Qt5, change {{ic|branch-group}} option and use {{ic|qt5-set}} instead of {{ic|qt6-set}}.
 
== Qt 6 installed using the Qt online installer ==
 
A screen recording version is available https://www.youtube.com/watch?v=3BIbYN2vIZw
 
The homepage of the Qt Framework is https://www.qt.io . Go to this web page, create an online account. https://www.qt.io/download-open-source > "Download the Qt Online Installer" > Linux > "Qt Online Installer for Linux (64-bit)" > download a file named e.g. qt-unified-linux-x64-4.6.1-online.run into the directory e.g. "~/Downloads".
 
<pre>
ls -la ~/Downloads # The downloaded file needs to have the "executable" chmod bit set.
chmod u+x ~/Downloads/qt-unified-linux-x64-4.6.1-online.run
~/Downloads/qt-unified-linux-x64-4.6.1-online.run
</pre>
 
A graphical user interface (GUI) installer wizard starts. Login using your Qt online account. Next > check the checkbox "I have read and agree to the terms and conditions of using OpenSource Qt", check the checkbox "I'm an individual and do not use Qt for any company" > Next > Next > enable "Help us improve" > Next > Custom installation, notice that the install directory is "~/Qt" > Next. Install the latest version of Qt6 and the latest version of the Qt Creator integrated development environment (IDE). There are some Qt6 components that are not used by KDE and can be left out when installing Qt6 e.g. Qt Design Studio, WebAssembly, Android, Sources, Qt Quick 3D, Qt 3D, Qt Quick 3D Physics, "Qt Debug Information Files". Next > enable "I have read and agree" > Next > Install.
 
In the KDE Plasma app launcher (start menu) you now have the application "Qt Maintenance Tool".
 
Set up kdesrc-build from scratch as usual.
 
Edit the file kdesrc-buildrc to look like:
 
<pre>
global
...
    qt-install-dir  ~/Qt/6.7.0/gcc_64 # Where to install Qt6 if kdesrc-build supplies it
    libname lib
...
end global
</pre>


== Two independent kdesrc-build configurations: kf6-qt6 and kf5-qt5 ==
== Two independent kdesrc-build configurations: kf6-qt6 and kf5-qt5 ==
Line 214: Line 225:


See https://community.kde.org/Get_Involved/development/Install_the_dependencies
See https://community.kde.org/Get_Involved/development/Install_the_dependencies
=== wayland-protocols is too old, e.g. "kdesrc-build kidletime" fails ===
<pre>
mkdir -p ~/kde/misc && cd ~/kde/misc
wget https://gitlab.freedesktop.org/wayland/wayland-protocols/-/releases/1.31/downloads/wayland-protocols-1.31.tar.xz
tar -xJvf wayland-protocols-*.tar.xz && mv wayland-protocols-*/ wayland-protocols
cd wayland-protocols
meson setup builddir --prefix $HOME/kde/usr
meson compile -C builddir
meson install -C builddir
</pre>


=== "kdesrc-build kpat" fails because of black-hole-solitaire ===
=== "kdesrc-build kpat" fails because of black-hole-solitaire ===

Revision as of 05:04, 16 August 2024

This page is the continuation with more advanced topics of the page Get_Involved/development.

kde-builder is an alternative to kdesrc-build

kdesrc-build and kde-builder are two KDE build frameworks. They are used at the command line and have identical command line syntax, just replace the string "kdesrc-build" with "kde-builder". They use the same configuration file, named kdesrc-buildrc.

kde-builder is newer and regularly gets new features and is written in Python.

kdesrc-build is in maintenance mode and feature frozen and written in Perl.

The "how to install kde-builder" procedure is here https://invent.kde.org/sdk/kde-builder/-/blob/master/README.md .

Develop in a Linux container

When you start programming for KDE, it is recommended that you use kdesrc-build in your main operating system or in a virtual machine running on a Linux operating system that is better supported by kdesrc-build.

As an alternative, you can run kdesrc-build in a Linux container (docker, podman, toolbx, distrobox).

Option 1. The KDE PIM Docker image

You can install Docker and the KDE PIM Docker image. It provides a development environment that is isolated from your day-to-day system. It is based on KDE Neon Unstable.

Option 2. distrobox

It is possible to start developing KDE software using container images that are able to see inside your home folder. This can be done using distrobox and podman.

This solution is particularly useful for users on immutable distributions like Fedora Kinoite, openSUSE Kalpa or the Steam Deck's SteamOS.

To learn how to build KDE software with distrobox, see: https://develop.kde.org/docs/getting-started/building/containers-distrobox/

Other operating systems

Kubuntu >= 23.10

The default configuration of kdesrc-build requires Qt version 6.6. Kubuntu 23.10 and 24.04 have Qt version 6.4.2. It is recommended that you use a Linux OS that is better supported by kdesrc-build.

If you are a more seasoned developer you might be able to use Kubuntu for kdesrc-build by installing Qt6 using the Qt online installer or by building Qt6 using kdesrc-build.

Alpine Linux

apk add git perl doas-sudo-shim

FreeBSD

Install the latest release of FreeBSD with KDE Plasma Desktop on your hardware computer or in a virtual machine.

Your user should be member of the "wheel" user group (e.g. this can be configured in the FreeBSD installer, when creating your user you can select additional user groups for your user). Your user should be able to use sudo: 

pkg install sudo
visudo
# Uncomment the line: %wheel ALL=(ALL:ALL) ALL

Then set up kdesrc-build using the same procedure as when installing kdesrc-build on a Linux operating system. FreeBSD is currently supported by kdesrc-build. See https://www.youtube.com/watch?v=8MqBnb3Y9JU

OpenBSD >= 7.5

Install OpenBSD version greater than or equal to 7.5. In the installer keep the defaults, the user created by the installer is named "administrator" in this example. 

# Enable doas
su -
cp /etc/examples/doas.conf /etc/doas.conf
exit
# kdesrc-build needs sudo.
mkdir -p ~/.local/bin ; ln -s /usr/bin/doas ~/.local/bin/sudo
echo "export PATH=~/.local/bin:\$PATH" >> ~/.bashrc

# Test doas.
doas su
# kde-builder needs bash.
pkg_add bash
chsh -s /usr/local/bin/bash
exit

# As user administrator
chsh -s /usr/local/bin/bash

# As per https://rsadowski.de/posts/2024-01-09-openbsd-kde/ , https://openports.pl/path/meta/kde,-plasma
doas su
pkg_add kde-plasma kate

# I recommend that you use tigervnc. https://nmariusp.github.io/install-os.html#openbsd--75

After you install kdesrc-build: 

# Edit the kdesrc-buildrc file e.g.:
cmake-options -DCMAKE_BUILD_TYPE=RelWithDebInfo -DKF_IGNORE_PLATFORM_CHECK=ON

# Also set environment variable:
export CMAKE_PREFIX_PATH=/usr/local/lib/qt6/cmake
# Or
export CMAKE_PREFIX_PATH=/usr/local/lib/qt5/cmake

Microsoft Windows

You can build and develop KDE projects using the Microsoft Windows operating system.

Apple macOS

You can build and develop KDE projects using the Apple macOS operating system.

What to do if CMake configure fails because a build dependency is missing

See https://community.kde.org/Get_Involved/development/Install_the_dependencies .

Project Documentation

Developer's documentation can be found in the doc/source-reference in the project repo.

kf6-qt6 vs. kf5-qt5

Many KDE git repositories can build correctly and run correctly using "kdesrc-build kf6-qt6".

The KDE git repositories that can build correctly and run correctly using "kdesrc-build kf6-qt6" have two long lived git branches:

  • A long lived git branch that does not contain the deprecated symbols from kf5-qt5, named e.g. "master".
  • And another long lived git branch for qt5-kf5, where the deprecated symbols still exist.

What is "kf6-qt6"? You just set up kdesrc-build following the procedure. The resulting kdesrc-build installation will be of type kf6-qt6. In kdesrc-buildrc in the "global" section you will have "branch-group kf6-qt6". The git repositories that have only one long lived git branch e.g. named "master" will use that. The git repositories that have a second long lived git branch, will use the git branch where the deprecated symbols do not exist e.g. named "master".

What is "kf5-qt5"? Follow the chapter "kdesrc-build Qt5". The resulting kdesrc-build installation will be of type kf5-qt5. In kdesrc-buildrc in the "global" section you will have "branch-group kf5-qt5". The git repositories that have only one long lived git branch e.g. named "master" will use that. The git repositories that have a second long lived git branch where the deprecated symbols still exist e.g. named "kf5" will use that.

Build Qt using kdesrc-build

Qt6

If you cannot build the KDE frameworks using kdesrc-build and the Qt provided by your Linux distribution is outdated, you might want to build the Qt framework using kdesrc-build.

In your configuration file use the qt-install-dir option (in the global section) with non-empty value, for example: 

global
  qt-install-dir ~/kde/usr
  branch-group kf6-qt6
end global

It is recommended that if you build Qt6 using kdesrc-build, you also build qtwebengine. Edit the file ~/.local/state/sysadmin-repo-metadata/module-definitions/qt6.ksb. Follow the instructions found in the file: if you want qtwebengine, add it to use-modules after "qtwebchannel" and comment out the line "ignore-modules qtwebengine". 

kdesrc-build qtbase --refresh-build --debug

Press Ctrl+C after the CMake configure summary for qtbase. Make sure that you have the needed dependencies. Should find libb2-dev, libproxy-dev, libmd4c-dev, libmd4c-html0-dev, libxcb-xinput-dev, libatspi2.0-dev, libsqlite3-dev, unixodbc-dev, libmysqlclient-dev, postgresql-client, libecpg-dev, libpq-dev. Optional dependencies libsctp-dev, libts-dev. 

kdesrc-build qtwebengine

This will build the Qt6 modules from qtbase up to qtwebengine. qtwebengine will probably be built incorrectly because some needed dependencies are missing. 

kdesrc-build qtwebengine --refresh-build --debug

Press Ctrl+C after the CMake configure summary for qtwebengine. Make sure that you have the needed dependencies. Should find node.js >= 14, libdbus-1-dev, libxcomposite-dev, libxshmfence-dev, libxdamage-dev, libharfbuzz-dev, libvpx-dev, libpci-dev, libevent-dev, libre2-dev, libsnappy-dev, libcups2-dev, libxkbfile-dev.

Then build Qt6: 

kdesrc-build qt6-set

To compile Qt6 with Qt X11 Extras (which is a necessary library to compile KWindowSystem), you should enable XCB feature during compilation 

kdesrc-build qt6-set --cmake-options="-DQT_FEATURE_xcb=ON"

Qt5

If you want the same for Qt5, change branch-group option and use qt5-set instead of qt6-set.

Qt 6 installed using the Qt online installer

A screen recording version is available https://www.youtube.com/watch?v=3BIbYN2vIZw

The homepage of the Qt Framework is https://www.qt.io . Go to this web page, create an online account. https://www.qt.io/download-open-source > "Download the Qt Online Installer" > Linux > "Qt Online Installer for Linux (64-bit)" > download a file named e.g. qt-unified-linux-x64-4.6.1-online.run into the directory e.g. "~/Downloads". 

ls -la ~/Downloads # The downloaded file needs to have the "executable" chmod bit set.
chmod u+x ~/Downloads/qt-unified-linux-x64-4.6.1-online.run
~/Downloads/qt-unified-linux-x64-4.6.1-online.run

A graphical user interface (GUI) installer wizard starts. Login using your Qt online account. Next > check the checkbox "I have read and agree to the terms and conditions of using OpenSource Qt", check the checkbox "I'm an individual and do not use Qt for any company" > Next > Next > enable "Help us improve" > Next > Custom installation, notice that the install directory is "~/Qt" > Next. Install the latest version of Qt6 and the latest version of the Qt Creator integrated development environment (IDE). There are some Qt6 components that are not used by KDE and can be left out when installing Qt6 e.g. Qt Design Studio, WebAssembly, Android, Sources, Qt Quick 3D, Qt 3D, Qt Quick 3D Physics, "Qt Debug Information Files". Next > enable "I have read and agree" > Next > Install.

In the KDE Plasma app launcher (start menu) you now have the application "Qt Maintenance Tool".

Set up kdesrc-build from scratch as usual.

Edit the file kdesrc-buildrc to look like: 

global
...
    qt-install-dir  ~/Qt/6.7.0/gcc_64 # Where to install Qt6 if kdesrc-build supplies it
    libname lib
...
end global

Two independent kdesrc-build configurations: kf6-qt6 and kf5-qt5

You can switch between configurations with --rc-file command line option. Generate another config, make the changes for the source-dir, build-dir, install-dir, and other changes you want. Make sure you use different value for persistent-data-file option, to not mix things up.

As an alternative, you can utilize custom variable to make switch from a single config: 

global
    _ver 5  # <-- Change this to switch
    source-dir ~/kde${_ver}/src
    build-dir ~/kde${_ver}/build
    install-dir ~/kde${_ver}/usr
    persistent-data-file ~/kde${_ver}/persistent-options.json
end global

include ~/.local/share/kdesrc-build/data/build-include/kf${_ver}-qt${_ver}.ksb

Other CPU architectures than x86_64/amd64 and x86

You can build and develop KDE projects using a Linux OS installed on an ARM architecture CPU.

kdesrc-build issues

See https://community.kde.org/Get_Involved/development/Install_the_dependencies

"kdesrc-build kpat" fails because of black-hole-solitaire

This happens on Debian/Ubuntu/Kubuntu. Because there is no Linux distribution binary package for https://github.com/shlomif/black-hole-solitaire.

Solution: append at the end of kdesrc-buildrc file: 

options kpat
    cmake-options -DWITH_BH_SOLVER=OFF
end options

libdisplay-info is not available

If your Linux OS does not have a package for libdisplay-info. Append at the end of the file kdesrc-buildrc: 

module libdisplay-info
  repository https://gitlab.freedesktop.org/emersion/libdisplay-info.git
end module
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