// Copyright (C) 2020 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only

/*!
    \page configure-options.html
    \title Qt Configure Options
    \brief Configuring Qt's compile options.

    \b configure is a command-line tool that supports you in building a custom
    version of Qt from source. It's part of the main Qt source directory.

    Since Qt 6, configure is a wrapper around \b{cmake}. CMake can also
    be invoked directly. configure provides additional error checking and
    compatibility with Qt 5.

    This page discusses some of the configure options. For the full list of
    options, enter the command \b{configure -h}.

    \note Unless stated otherwise, the commands on this page are for the Linux
    platforms. On \macos and Windows, the PATH and directory structure
    are different, therefore the commands will vary. Also, on Windows systems,
    the configure script is called configure.bat.

    \section1 Configure Workflow

    configure must be called in a working build environment where
    CMake, compilers, and required build tools are readily available.
    \l{Building Qt Sources} lists such dependencies per platform.

    After setting up such an environment, the typical workflow is to create
    a separate build directory, and then first run configure,
    then build Qt, and then install Qt:

    \badcode
    ~/qt-source/configure
    cmake --build . --parallel
    cmake --install .
    \endcode

    You might want to experiment with different configure flags, and therefore
    run configure multiple times. Note that CMake caches configure options
    and information about the environment in a file called CMakeCache.txt.
    Delete this file when you want to start over without cached information.

    \section1 Source, Build, and Install Directories

    The \e source directory contains the source code that is obtained from
    the source package or git repository. The \e build directory is where the
    build-related files, such as build system files, object files, and other
    intermediate files are stored. The \e install directory is where the
    binaries and libraries are installed, for use either by the system or by
    the application.

    It's recommended to keep these directories separate by shadow-building and
    using the \b -prefix option. This enables you to keep the Qt \e source tree
    clean from the build artifacts and binaries, which are stored in a separate
    directory. This method is very convenient if you want to have multiple
    builds from the same source tree, but for different configurations. To
    shadow-build, run configure from a separate directory:

    \badcode
    mkdir ~/qt-build
    cd ~/qt-build
    ~/qt-source/configure -prefix /opt/Qt6
    \endcode

    Configuring with the -prefix option means that the Qt binaries and
    libraries are installed into another directory, which is /opt/Qt6 in
    this case.

    \section1 Examples, Tests, and Tools

    By default, configure only configures Qt's libraries and tools.
    You can use \b{-make examples} or \b{-make tests} to also build
    the examples or tests that come with Qt:

    \badcode
    ~/qt-source/configure -make examples -make tests
    \endcode

    You can also configure Qt such that examples, tests, and tools are
    configured, but not built by default. If you set the CMake variables
    \b{QT_BUILD_EXAMPLES_BY_DEFAULT}, \b{QT_BUILD_TESTS_BY_DEFAULT}, and
    \b{QT_BUILD_TOOLS_BY_DEFAULT} to OFF, the respective parts will not be
    built by \c{cmake --build .}. Instead, CMake will generate individual targets
    that you can then build individually.

    Here we build Qt libraries and tools, but also the
    \l{Getting Started Programming with Qt Widgets}{NotePad Example}:

    \badcode
    ~/qt-source/configure -make examples -- -D QT_BUILD_EXAMPLES_BY_DEFAULT=OFF
    cmake --build . --parallel
    cmake --build . --parallel --target notepad
    \endcode

    \note The -developer-build option builds tests by default.
    See also \l{Developer Builds} below.

    \section1 Build Configurations

    You can build Qt libraries and tools in various variants, each of them
    optimized for a different use case.

    \section2 Debug and Release Builds

    \b{-release} tells the compiler to optimize the code, and not provide
    additional debug symbols alongside Qt and its tools.

    \b{-debug} skips some optimizations to make it easier to debug Qt
    and its tools. This option also enables the generation of debug symbols that
    let you inspect the code and state of the built libraries in a debugger.

    Finally, \b{-debug-and-release} lets you build both a debug and release
    variant of Qt libraries in one go. This is only supported if you configure
    a build for Windows.

    There are further options to tweak the configurations:

    \list
    \li \b{-force-debug-info}: Creates a release build with debug information.
    \li \b{-separate-debug-info}: Extracts the debug information into a separate
        file.
    \li \b{-optimize-size}: Optimizes release builds for size instead of speed.
    \endlist

    \section2 Static and Shared Builds

    Qt Modules can be built as separate libraries that an executable
    links to and loads at start time (for Qt libraries), or runtime
    (for Qt plugins). This is called a \e shared build and is the default
    configuration on most platforms. The matching configure option is
    \b{-shared}.

    You can also build Qt such that an executable binary will include all Qt
    modules it links to and all Qt plugins it needs. This is called a
    \e static build and can be selected when configuring with the \b{-static}
    option.

    \section1 CMake Generators

    When configuring, you can select a CMake generator. Note that CMake supports
    generators that cannot be used with Qt. Therefore, configure
    automatically selects a generator for you.

    configure always uses the \b Ninja generator and build tool if a ninja
    executable is available. Ninja is both cross-platform, feature-rich,
    and performant, and recommended on all platforms. Use of other generators
    might work, but is not officially supported.

    \section1 Modules and Features

    The Qt source code is organized in several top-level directories
    called submodules, for example, \c{qtbase}, \c{qtdeclarative} or
    \c{qtmultimedia}. Inside these submodules, you find the source code
    for the different \l{All Modules}{Qt Modules}. \l{Qt Core}, \l{Qt
    Quick}, and \l{Qt Multimedia} are examples of such Qt modules.

    \note Many submodules (top-level source directories) have the same
    name as the \l{All Modules}{Qt Modules} they implement, but this is
    not always the case. For instance, \c{qtdeclarative} contains \l{Qt
    Quick} and \l{Qt Qml}, and various related modules. Consult the
    README.md file in the respective directories to get an overview.

    Submodules can be explicitly included or excluded to limit build
    times. Furthermore, each Qt module might have features that can also
    be explicitly enabled or disabled.

    \section2 Including and Excluding Qt Submodules

    \c configure's \b -skip option is used to exclude submodules
    (top-level source directories) from the Qt build. Excluding a
    submodule excludes all \l{All Modules}{Qt Modules} inside that
    submodule. The \c{qtwayland} submodule contains both the \l{Qt
    Wayland Compositor} and the Qt Wayland QPA plugin. Specifying
    \c{-skip qtwayland} as a configure option will therefore exclude
    both \l{All Modules}{Qt Modules}.

    \badcode
    ~/qt-source/configure -skip qtwayland
    \endcode

    \c configure's \b -submodules option can be used to configure a
    build that only builds the listed submodules and their dependencies.
    For example, by specifying the \c{qtmultimedia} submodule,
    \l{Qt Multimedia} and all its dependencies will be included in the
    build. Multiple submodules can be separated by commas.

    \badcode
    ~/qt-source/configure -submodules qtmultimedia,qtactiveqt
    \endcode

    \section2 Including or Excluding Features

    The \b{-feature-}\e{<feature>} and \b{-no-feature-}\e{<feature>} options
    include and exclude specific features, respectively.

    For example, you can use the \b -no-feature-accessibility configure option
    to disable \l Accessibility support in Qt:

    \badcode
    ~/qt-source/configure -no-feature-accessibility
    \endcode

    Use \b{configure -list-features} to show a list of all available features
    on the command line. Note that features can depend on other features, so
    disabling a feature might have side-effects on other features.

    \section1 Third-Party Libraries

    The Qt source packages include third-party libraries. To set whether Qt
    should use the system's versions of the libraries or to use the bundled
    version, pass either \b -system or \b -qt before the name of the library to
    configure.

    The table below summarizes some third-party options:
    \table
    \header
        \li Library Name
        \li Bundled in Qt
        \li Installed in System
    \row
        \li zlib
        \li \b -qt-zlib
        \li \b -system-zlib
    \row
        \li libjpeg
        \li \b -qt-libjpeg
        \li \b -system-libjpeg
    \row
        \li libpng
        \li \b -qt-libpng
        \li \b -system-libpng
    \row
        \li freetype
        \li \b -qt-freetype
        \li \b -system-freetype
    \row
        \li PCRE
        \li \b -qt-pcre
        \li \b -system-pcre
    \row
        \li HarfBuzz-NG
        \li \b -qt-harfbuzz
        \li \b -system-harfbuzz
    \endtable

    It's also possible to disable support for most of these libraries by using
    \b -no instead of \b{-qt}.

    configure in Qt 6 relies on CMake to locate third-party libraries.
    It does so by checking various system paths. If you installed libraries
    somewhere else, you can let CMake know this by setting or extending the
    \b CMAKE_PREFIX_PATH variable.

    For a full list of options, consult the help with \b{configure -help}.

    \section2 SSL

    Qt Network can be configured to support communication for Secure Sockets
    Layer (SSL) but does not implement the actual algorithms itself. It needs
    to leverage other libraries instead.

    On Windows, Qt can use the system's Secure Channel library for this
    purpose (configure option \b{-schannel}). On \macos and iOS, Qt can be
    configured to use the SecureTransport API (configure option
    \b{-securetransport}).

    The most feature-complete support that also works on almost all target
    platforms is provided by the \l {OpenSSL Toolkit} (option \b{-openssl}).
    Qt does require OpenSSL 1.1.1 or later.

    Qt can be configured to use OpenSSL in three ways:
    \list
        \li Qt Network loads OpenSSL libraries (DLLs) when first needed, at
            runtime. If not found, the application continues to run but fails
            to handle SSL communication. This is enabled by using the
            configure option \b{-openssl-runtime}.

        \li Qt Network links against the OpenSSL libraries. If they cannot be
            found at load time, the application fails to start. This is enabled
            by using the configure option \b{-openssl-linked}.

        \li Qt Network compiles against a static version of the OpenSSL
            libraries, and OpenSSL becomes part of the Qt Network library.
            This is enabled by using the configure option \b{openssl-linked}
            and setting the \b{OPENSSL_USE_STATIC_LIBS} variable to \b{ON}.
    \endlist

    Set the CMake variable \b{OPENSSL_ROOT_DIR} if OpenSSL is not installed in
    a standard location, and therefore not found by configure.

    See \l {Secure Sockets Layer (SSL) Classes} for further instructions on
    Qt with SSL support.

    \section1 Cross-Compilation Options

    To configure Qt for cross-platform development and deployment, you need
    to have a matching Qt version for the host machine first. Also, the
    development toolchain for the target platform needs to be set up. This
    set up varies among the \l{Supported Platforms}.

    Common options are:
    \list
    \li \b -external-hostbindir - Path to Qt tools built for this machine.
    \li \b -device - Select devices/mkspec for the qmake companion files.
    \li \b -device-option - sets additional qmake variables.
    \endlist

    \note Toolchains for non-desktop targets often come with a so-called \e
    sysroot that Qt needs to be configured against.

    \section1 Developer Builds

    The \b -developer-build configure option is a convenience option that
    optimizes the build for developing Qt itself. It shouldn't be used for
    building Qt variants that ship to customers.

    Libraries in a developer build contain more exported symbols than a
    standard build, and all Qt code compiles with a higher warning
    level. It also changes the default prefix to the build directory, avoiding
    the need to install Qt before testing things, and finally enables the
    compilation of Qt's auto-tests by default.

    \section1 Reconfiguring Existing Builds

    The Qt build system has basic support for reconfiguring existing Qt builds
    with a different set of configure options, but it is not very robust due
    to the way CMake works internally.

    The safest way to reconfigure an existing build is to pass the \b -redo
    option to configure. That will remove the build's \b CMakeCache.txt file,
    ensuring a relatively safe state for reconfiguration. The initial
    configure flags will still apply to the reconfigured build.

    \section1 Specific Options for Platforms

    The following pages provide guidelines on how to configure Qt for specific
    platform development:
    \list
    \li \l{Building Qt for QNX}
    \li \l{Building Qt for VxWorks}
    \li \l{Configure an Embedded Linux Device}
    \li \l{Qt for Android - Building from Source}
    \li \l{Qt for Linux/X11 - Building from Source}
    \li \l{Qt for Windows - Building from Source}
    \li \l{Qt for \macos - Building from Source}
    \li \l{Qt for INTEGRITY - Monolith Project Tutorial}
    \li \l{Qt for iOS - Building from Source}
    \li \l{wasm-building-qt-from-source}{Qt for WebAssembly - Building from Source}
    \endlist
*/
