make failed after successful CMake run - c++

Question

So, I am trying to follow this tutorial, I copied the code and CMakeLists.txt, which I later edited. Now when I run cmake everything is fine, but then when I run make it just fail with this error:
main.cpp:1:10: fatal error: QApplication: No such file or directory
1 | #include <QApplication>
| ^~~~~~~~~~~~~~
Here is my CMakeLists.txt
cmake_minimum_required(VERSION 3.0)
project(kparttut1)
set(QT_MIN_VERSION "5.11.0")
set(KF_MIN_VERSION "5.55.0")
find_package(ECM ${KF_MIN_VERSION} REQUIRED NO_MODULE)
set(CMAKE_MODULE_PATH ${ECM_MODULE_PATH})
include(KDEInstallDirs)
include(KDECMakeSettings)
include(KDECompilerSettings NO_POLICY_SCOPE)
include(ECMInstallIcons)
include(FeatureSummary)
find_package(Qt5 ${QT_MIN_VERSION} CONFIG REQUIRED COMPONENTS Core Gui Widgets)
find_package(KF5 ${KF_MIN_VERSION} REQUIRED COMPONENTS
CoreAddons
Crash
DBusAddons
DocTools
I18n
XmlGui
TextEditor
Parts
)
set(kparttut1_SRCS
main.cpp
mainwindow.cpp
)
add_executable(kparttut1 main.cpp)
########### install files ###############
#install(TARGETS kparttut1 ${KDE_INSTALL_TARGETS_DEFAULT_ARGS})
#install(FILES kparttut1ui.rc
# DESTINATION ${DATA_INSTALL_KXMLGUI5DIR}/kparttut)
#feature_summary(WHAT ALL INCLUDE_QUIET_PACKAGES FATAL_ON_MISSING_REQUIRED_PACKAGES)
I am using latest Arch Linux with Qt version 5.15.2

Answer 1

The tutorial you followed has some problem, you should check the KF5 tutorial which has a correct CMake setup.
You did the find_package thing, but you forgot to link the library to your executable!
In CMake, linking to a library adds compile definitions, include directory and of course linking to the library.
Here's what to add to make it work:
target_link_libraries(kparttut1 PUBLIC
Qt5::Widgets
KF5::CoreAddons
KF5::I18n
KF5::WidgetsAddons
)
This adds all the necessary stuff to the compiler arguments so all linked libraries are found.