I have created a new CMake project with main window using QT Creator. I then added a new MyWidget (.ui + .h + .cpp) using Add to project: PromoteWidget.
I then added a widget to mainwindow.ui and promoted this widget to MyWidget.

I left it as default as possible, however I get an error: D:DocumentsProgrammingTestQTPromoteWidgetbuildDesktop_Qt_6_6_0_MinGW_64_bit-DebugPromoteWidget_autogenincludeui_mainwindow.h:20: error: mywidget.h: No such file or directory In file included from D:/Documents/Programming/Test/QT/PromoteWidget/mainwindow.cpp:2: D:/Documents/Programming/Test/QT/PromoteWidget/build/Desktop_Qt_6_6_0_MinGW_64_bit-Debug/PromoteWidget_autogen/include/ui_mainwindow.h:20:10: fatal error: mywidget.h: No such file or directory 20 | #include "mywidget.h" | ^~~~~~~~~~~~

Do I need to change CMakeLists.txt to make mywidget.h visible in generated ui_mainwindow.h file?

My CMakeLists.txt is here

cmake_minimum_required(VERSION 3.5)

project(PromoteWidget VERSION 0.1 LANGUAGES CXX)

set(CMAKE_AUTOUIC ON)
set(CMAKE_AUTOMOC ON)
set(CMAKE_AUTORCC ON)


set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

find_package(QT NAMES Qt6 Qt5 REQUIRED COMPONENTS Widgets)
find_package(Qt${QT_VERSION_MAJOR} REQUIRED COMPONENTS Widgets)

set(PROJECT_SOURCES
        main.cpp
        mainwindow.cpp
        mainwindow.h
        mainwindow.ui
)

if(${QT_VERSION_MAJOR} GREATER_EQUAL 6)
    qt_add_executable(PromoteWidget
        MANUAL_FINALIZATION
        ${PROJECT_SOURCES}
        mywidget.h mywidget.cpp mywidget.ui


    )
# Define target properties for Android with Qt 6 as:
#    set_property(TARGET PromoteWidget APPEND PROPERTY QT_ANDROID_PACKAGE_SOURCE_DIR
#                 ${CMAKE_CURRENT_SOURCE_DIR}/android)
# For more information, see https://doc.qt.io/qt-6/qt-add-executable.html#target-creation
else()
    if(ANDROID)
        add_library(PromoteWidget SHARED
            ${PROJECT_SOURCES}
        )
# Define properties for Android with Qt 5 after find_package() calls as:
#    set(ANDROID_PACKAGE_SOURCE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/android")
    else()
        add_executable(PromoteWidget
            ${PROJECT_SOURCES}
        )
    endif()
endif()

target_link_libraries(PromoteWidget PRIVATE Qt${QT_VERSION_MAJOR}::Widgets)

# Qt for iOS sets MACOSX_BUNDLE_GUI_IDENTIFIER automatically since Qt 6.1.
# If you are developing for iOS or macOS you should consider setting an
# explicit, fixed bundle identifier manually though.
if(${QT_VERSION} VERSION_LESS 6.1.0)
  set(BUNDLE_ID_OPTION MACOSX_BUNDLE_GUI_IDENTIFIER com.example.PromoteWidget)
endif()
set_target_properties(PromoteWidget PROPERTIES
    ${BUNDLE_ID_OPTION}
    MACOSX_BUNDLE_BUNDLE_VERSION ${PROJECT_VERSION}
    MACOSX_BUNDLE_SHORT_VERSION_STRING ${PROJECT_VERSION_MAJOR}.${PROJECT_VERSION_MINOR}
    MACOSX_BUNDLE TRUE
    WIN32_EXECUTABLE TRUE
)

include(GNUInstallDirs)
install(TARGETS PromoteWidget
    BUNDLE DESTINATION .
    LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
    RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
)

if(QT_VERSION_MAJOR EQUAL 6)
    qt_finalize_executable(PromoteWidget)
endif()

and project structure is as follows:
QT Creator File System

I wanted to split .ui files and include them separately, but this fails with No such file or directory even with the most default config.