C++ Utilities: Build system

C++ Utilities 5.32.1 Useful C++ classes and routines such as argument parser, IO and conversion utilities

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Build system

Documents variables to control the build system and provided CMake modules.

# Variables passable as CMake arguments

## Useful variables provided by CMake itself

- CMAKE_INSTALL_PREFIX=path: specifies the final install prefix (temporary install prefix is set via make argument DESTDIR=path)
- CMAKE_BUILD_TYPE=Release/Debug: specifies whether to do a debug or a release build
- BUILD_SHARED_LIBS=ON/OFF: whether to build shared libraries (ON) or static libraries (OFF); it is not possible to build both at the same time within the same build process
- CMAKE_SKIP_BUILD_RPATH=OFF: ensures the rpath is set in the build tree
- CMAKE_INSTALL_RPATH=rpath: sets the rpath used when installing
- CMAKE_CXX_FLAGS: sets flags to be passed to the C++ compiler
- CMAKE_FIND_LIBRARY_SUFFIXES: sets the library suffixes the build script will consider, e.g., set to .a;.lib to prefer static Windows libraries or to .dll;.dll.a to prefer shared Windows libraries
- CMAKE_FIND_DEBUG_MODE=ON/OFF or --debug-find flag: whether verbose debug output for finding libraries should be enabled
- variables provided by GNUInstallDirs

## Custom variables

The following variables are read by the CMake modules provided by c++utilities and qtutilities.

None of these are enabled or set by default, unless stated otherwise.

- LIB_SUFFIX=suffix: suffix for the library install directory
- LIB_SUFFIX_32=suffix: suffix for the library install directory
  - used when building for 32-bit platforms
  - overrides general LIB_SUFFIX when building for 32-bit platforms
- LIB_SUFFIX_64=suffix: suffix for the library install directory
  - used when building for 64-bit platforms
  - overrides general LIB_SUFFIX when building for 64-bit platforms
- SHELL_COMPLETION_ENABLED=ON/OFF: enables shell completion in general (enabled by default)
- BASH_COMPLETION_ENABLED=ON/OFF: enables Bash completion (enabled by default)
- LOGGING_ENABLED=ON/OFF: enables further logging in some applications
- FORCE_OLD_ABI=ON/OFF: forces the use of the old C++ ABI
  - sets _GLIBCXX_USE_CXX11_ABI=0
  - only relevant when using libstdc++
- EXCLUDE_TESTS_FROM_ALL=ON/OFF: excludes tests from the all target (enabled by default)
- APPEND_GIT_REVISION=ON/OFF: whether the build script should attempt to append the Git revision and the latest commit ID to the version
  - displayed via --help
  - enabled by default but has no effect when the source directory is not a Git checkout or Git is not installed
- CLANG_FORMAT_ENABLED=ON/OFF: enables the tidy target for code formatting via clang-format
  - can be made unavailable by setting META_NO_TIDY in the project file
  - only available if format rules are available
  - also enables the tidy check executed via the check target
- CMAKE_FORMAT_ENABLED=ON/OFF: enables the tidy target for code formatting via cmake-format
  - can be made unavailable by setting META_NO_TIDY in the project file
  - options can be adjusted by setting META_CMAKE_FORMAT_OPTIONS in the project file
- CLANG_TIDY_ENABLED=ON/OFF: enables the target static-check for static code analysis with clang-tidy
  - can be made unavailable by setting META_NO_STATIC_ANALYSIS in the project file
  - the variable CMAKE_<LANG>_CLANG_TIDY provided by CMake itself provides a similar functionality
- CLANG_SOURCE_BASED_COVERAGE_ENABLED=ON/OFF: enables the coverage target to determine source-based test coverage using Clang/llvm
  - only available when building with Clang under UNIX
  - the coverage report is stored in the build directory
- ENABLE_INSTALL_TARGETS=ON/OFF: enables the creation of install targets (enabled by default)
- ENABLE_ESCAPE_CODES_BY_DEAULT=ON/OFF: enables the use of escape codes for formatted output by default
  - enabled by default
  - see ApplicationUtilities::NoColorArgument and EscapeCodes::enabled
  - has to be set when building c++utilities; projects using that build of c++utilities will then use this default
- USE_NATIVE_FILE_BUFFER=ON/OFF: use native functions to open file streams
  - Allows opening files that have non-ASCII characters in the path under Windows.
  - Allows the use of native file descriptors, which is required to open files from URLs provided by Android's Storage Access Framework.
  - Changing this option alters the ABI of c++utilities and other libraries exposing that ABI (e.g., tagparser and passwordfile).
  - This feature is implemented in c++utilities, so the option must be specified when building c++utilities. Specifying it only when building, e.g., tagparser has no effect.
- USE_STANDARD_FILESYSTEM=ON/OFF: enables the use of std::filesystem (default)
  - Disabling this is required when building for macOS and Android at the time of writing this documentation.
  - Bash completion will not be able to suggest files and directories when disabled.
- USER_DEFINED_ADDITIONAL_LIBRARIES: specifies additional libraries to link against (added after any other libraries to the linker line)
  - Use case: Some platforms/standard libraries/compilers require linking against additional libraries for certain features. Adding additional libraries for std::filesystem is covered by use_standard_filesystem(). However, it makes no sense to add such a function for every specific platform/feature. For instance, it seems to be required to add "-latomic" to the linker line for armv7-none-linux-androideabi/libc++/clang (not for aarch64-none-linux-androidabi), but it is better to cover such details on the packaging level and only allow passing such flags here.
  - Using CMAKE_EXE_LINKER_FLAGS or CMAKE_SHARED_LINKER_FLAGS is often not helpful because the additional flags need to be added at the end of the linker line most of the time.
- CONFIGURATION_NAME: specifies a name to be incorporated into install paths as a suffix
  - Builds with different configuration names can be installed alongside within the same install prefix.
  - Use cases:
    - Installing static and shared libraries within the same prefix.
    - Installing different versions of the library within the same prefix.
    - Installing the version linked against Qt 5 and the version linked against Qt 6 within the same prefix (when Qt 6 is released).
  - Does not affect library names, because their filenames might differ anyway between different configurations (e.g., static vs. shared libraries).
  - Set CONFIGURATION_TARGET_SUFFIX in accordance so library names are affected as well.
  - Set CONFIGURATION_PACKAGE_SUFFIX when building consuming libraries to use libraries (and their headers and other files) built with CONFIGURATION_NAME.
- NAMESPACE: specifies a name to be incorporated into install paths as a prefix
  - Builds with different namespaces can be installed alongside within the same install prefix.
  - This may be used by packagers who want to give the package a more unique name, e.g., Debian is using NAMESPACE=martchus for c++utilities and qtutilities. Supposedly, this should be avoided for developer-facing packaging like vcpkg, as it is likely not expected by those users.
  - Set PACKAGE_NAMESPACE_PREFIX when building consuming libraries to use libraries (and their headers and other files) built with NAMESPACE.
- ENABLE_WARNINGS: enables GCC/Clang warnings I consider useful
- TREAT_WARNINGS_AS_ERRORS: treat CCC/Clang warnings as errors
- ENABLE_DEVEL_DEFAULTS: enables defaults I find useful for development (warnings, treat warnings as errors, build tests as part of all/default target, enable tidy targets, build by default shared libs when targeting GNU/Linux, …)

### Variables for specifying the location of 3rd party dependencies

The build script tries to find the required dependencies at standard locations using the CMake functions find_library and find_package. The behavior of those functions can be controlled by setting some variables, e.g., using a toolchain file. Check out the CMake documentation for this.

If the detection does not work as expected or a library from a non-standard location should be used, one can also just pass the library path directly by specifying the relevant CMake cache variable on the CMake invocation.

### Windows specific

- FORCE_UTF8_CODEPAGE=ON/OFF: forces the use of the UTF-8 codepage in the terminal
- WINDOWS_RESOURCES_ENABLED=ON/OFF: enables creating resources for application metadata and icon (enabled by default)

### macOS specific

- BUNDLE_INSTALL_DESTINATION=/some/path: specifies the install destination for application bundles; if not specified, the default bin directory is used

### Qt specific

- WIDGETS_GUI=ON/OFF: enables Qt Widgets GUI for projects where it is available and optional
- QUICK_GUI=ON/OFF: enables Qt Quick GUI for projects where it is available and optional
- QT_PACKAGE_PREFIX=Qt5: sets the prefix for Qt packages, by default Qt5
  - use QT_PACKAGE_PREFIX=Qt6 to build against Qt 6
- KF_PACKAGE_PREFIX=KF5: sets the prefix for KDE Frameworks packages, by default KF5
- ENABLE_QT_TRANSLATIONS=ON/OFF: enables translations for Qt applications, enabled by default
- BUILTIN_TRANSLATIONS=ON/OFF: enables built-in translations instead of installing translations as separate files
- BUILTIN_TRANSLATIONS_OF_QT=ON/OFF: enables built-in translations also for Qt's own translation files when building an application
  - enabled by default when BUILTIN_TRANSLATIONS is enabled
  - useful when deploying Qt itself anyway, e.g., Windows builds
  - better turned off when using system Qt and the system provides a translations package for Qt, e.g., GNU/Linux builds
  - when building a library, Qt's translations are never built-in
  - has no effect when BUILTIN_TRANSLATIONS is disabled
- BUILTIN_ICON_THEMES=breeze;breeze-dark;...: specifies icon themes to be built-in
- BUILTIN_ICON_THEMES_IN_LIBRARIES=breeze;breeze-dark;...: same as above but also affects libraries
- SVG_SUPPORT=ON/OFF: enables linking against the static SVG image format plugin
  - enabled by default
  - requires the Qt Svg module
  - only relevant when using static Qt
- SVG_ICON_SUPPORT=ON/OFF: enables linking against the static SVG icon engine plugin provided by the Qt Svg module
  - enabled by default
  - requires the Qt Svg module
  - only relevant when using static Qt
  - required to use the Breeze icon theme (or any other SVG icon theme)
- IMAGE_FORMAT_SUPPORT: enables linking against the specified static image format plugins
  - comma-separated list
  - by default set to "Gif;ICO;Jpeg", so support for Gif, ICO, and Jpeg is enabled by default
  - note that PNG support is not provided via a plugin, so it should be always available and not be affected by this option
  - further image formats require building the plugins contained by the additional qtimageformats repository
  - only relevant when using static Qt
- QT_PLUGIN_DIR: specifies the directory to install Qt plugins to
  - When installing plugins to a non-standard directory (e.g., during development), set the QT_PLUGIN_PATH environment variable accordingly so the plugin can be found.
  - The install directory defaults to qmake -query QT_INSTALL_PLUGINS unless that directory would be outside the specified CMAKE_INSTALL_PREFIX.
- WEBVIEW_PROVIDER=auto/webkit/webengine/none: specifies the Qt module to use for the web view
- JS_PROVIDER=qml/script/none: specifies the Qt module to use for the JavaScript engine
- WEBVIEW_PROVIDER=webengine/webkit/none: specifies the Qt module to use for the built-in web view

# Variables to be set in the project file

The following variables are read by the CMake modules provided by c++utilities and qtutilities.

## Metadata and overall project configuration

- META_PROJECT_NAME=name: specifies the project name, which is used as the application/library name; must not contain spaces
- META_APP_NAME=The Name: specifies a more readable version of the project name used, for instance, in the about dialog and desktop file
- META_APP_AUTHOR: specifies the author shown, for instance, in the about dialog
- META_APP_DESCRIPTION: specifies a description shown, for instance, in the about dialog and desktop file
- META_GENERIC_NAME: specifies a generic name for the desktop file
- META_VERSION_MAJOR/MINOR/PATCH=number: specifies the application/library version; the default is 0
- META_PROJECT_TYPE=application/library/plugin/qtplugin: specifies whether to build an application, a library, or a plugin
- META_CXX_STANDARD=11/14/..: specifies the C++ version; the default is 14
- META_NO_TIDY: disables the availability of enabling formatting via CLANG_FORMAT_ENABLED for this project
- META_NO_INSTALL_TARGETS: the project is not meant to be installed, e.g., a private test helper; prevents the creation of install targets
- META_ADD_DEFAULT_CPP_UNIT_TEST_APPLICATION: implicitly add a source file with a main()-entry point to the test target for running CppUnit test cases
- TLS_SUPPORT: enables TLS support
  - enabled by default for projects using Qt Network; should be disabled when using Qt Network but no TLS is required
  - currently only relevant when using static Qt (6.2.0 or newer) to link against an appropriate TLS plugin for TLS support in Qt Network
- META_TLS_PLUGINS: specifies an additional list of Qt TLS plugins to check before the known TLS plugins
  - can be used to give other TLS plugins precedence over the plugins that are checked by default

## Files

- HEADER_FILES/SRC_FILES: specifies C++ header/source files
- TEST_HEADER_FILES/TEST_SRC_FILES: specifies C++ header/source files of the tests
- TS_FILES: specifies Qt translations
- RES_FILES: specifies Qt resource files
- DBUS_FILES: specifies files for Qt DBus
- WIDGETS_HEADER_FILES/WIDGETS_SRC_FILES: specifies C++ header/source files only required for the Qt Widgets GUI
- QML_HEADER_FILES/QML_SRC_FILES/QML_RES_FILES: specifies C++ header/source files and Qt resource files only required for the Qt Quick GUI
- EXCLUDED_FILES: specifies C++ files that are part of the project (and therefore should be formatted by the tidy target, added to the documentation, and considered for translations) but are excluded from the actual build; when adding files conditionally to the other _FILES variables, be sure to add them at least to EXCLUDED_FILES
- DOC_FILES: additional markdown files to be included in the documentation created via Doxygen; the first file is used as the main page
- REQUIRED_ICONS: names of the icons required by the application and the used libraries (can be generated with findicons)
- CMAKE_MODULE_FILES/CMAKE_TEMPLATE_FILES: specifies CMake modules/templates provided by the project; those files are installed so they can be used by other projects

## Additional build variables

- META_PRIVATE_COMPILE_DEFINITIONS/META_PUBLIC_COMPILE_DEFINITIONS: specifies private/public compile definitions
- META_PRIVATE_COMPILE_OPTIONS/META_PUBLIC_COMPILE_OPTIONS: specifies private/public compile options
- META_SOVERSION: specifies the soversion for libraries (defaults to META_VERSION_MAJOR)
- PUBLIC_LIBRARIES/PRIVATE_LIBRARIES: specifies the public/private libraries to link against
- PUBLIC_INCLUDE_DIRS/PRIVATE_INCLUDE_DIRS: specifies the public/private include directories
- ADDITIONAL_QT_MODULES: specifies additional Qt modules to link against
- ADDITIONAL_KF_MODULES: specifies additional KDE frameworks modules to link against
- META_QT_VERSION: specifies the minimum Qt version to require

# Provided modules

c++utilities and qtutilities provide CMake modules to reduce boilerplate code in the CMake files of my projects. Those modules implement the functionality controlled by the variables documented above. The most important modules are:

- BaseConfig: does basic configuration, reads most of the META-variables
- QtConfig: does basic Qt-related configuration, reads most of the Qt-specific variables documented above
- QtGuiConfig: does Qt-related configuration for building a Qt Widgets or Qt Quick based GUI application/library
  - must be included before QtConfig
- WebViewProviderConfig: configures the webview provider
  - used by Tag Editor and Syncthing Tray to select between Qt WebEngine, Qt WebKit, or disabling the built-in webview
- LibraryTarget: does further configuration for building dynamic and static libraries and plugins; META_PROJECT_TYPE can be left empty or set explicitly to library
- AppTarget: does further configuration for building an application; META_PROJECT_TYPE must be set to application
- ShellCompletion: enables shell completion
  - only works when using the argument parser provided by the ApplicationUtilities::ArgumentParser class, of course
- TestTarget: adds the test target check
  - the check target is not required by the target all
  - the test target is comprised of files specified in the TEST_HEADER_FILES/TEST_SRC_FILES variables
  - the test target will automatically link against cppunit, which is the test framework used by most of my projects; set META_NO_CPP_UNIT=OFF in the project file to prevent this
- TestUtilities: provides the configure_test_target macro for creating test targets manually
  - see the CMakeLists.txt of qtutilities for an example
- AndroidApk: adds a target to create an APK package for Android using androiddeployqt; ignored on other platforms
- Doxygen: adds a target to generate documentation using Doxygen
- WindowsResources: handles the creation of Windows resources to set application metadata and icon; ignored on other platforms
- ConfigHeader: generates resources/config.h; must be included as the last module (when all configuration is done)

Since those modules make use of the variables explained above, the modules must be included after setting those variables. The inclusion order of the modules matters as well.

For an example, check out the project file of c++utilities itself. The project files of Syncthing Tray should cover everything (library, plugin, application, tests, desktop file, Qt resources and translations, ...).