// -*- mode:doc; -*-
  // vim: set syntax=asciidoc:
  
  === Infrastructure for CMake-based packages
  
  [[cmake-package-tutorial]]
  
  ==== +cmake-package+ tutorial
  
  First, let's see how to write a +.mk+ file for a CMake-based package,
  with an example :
  
  ------------------------
  01: ################################################################################
  02: #
  03: # libfoo
  04: #
  05: ################################################################################
  06:
  07: LIBFOO_VERSION = 1.0
  08: LIBFOO_SOURCE = libfoo-$(LIBFOO_VERSION).tar.gz
  09: LIBFOO_SITE = http://www.foosoftware.org/download
  10: LIBFOO_INSTALL_STAGING = YES
  11: LIBFOO_INSTALL_TARGET = NO
  12: LIBFOO_CONF_OPTS = -DBUILD_DEMOS=ON
  13: LIBFOO_DEPENDENCIES = libglib2 host-pkgconf
  14:
  15: $(eval $(cmake-package))
  ------------------------
  
  On line 7, we declare the version of the package.
  
  On line 8 and 9, we declare the name of the tarball (xz-ed tarball recommended)
  and the location of the tarball on the Web. Buildroot will automatically
  download the tarball from this location.
  
  On line 10, we tell Buildroot to install the package to the staging
  directory. The staging directory, located in +output/staging/+
  is the directory where all the packages are installed, including their
  development files, etc. By default, packages are not installed to the
  staging directory, since usually, only libraries need to be installed in
  the staging directory: their development files are needed to compile
  other libraries or applications depending on them. Also by default, when
  staging installation is enabled, packages are installed in this location
  using the +make install+ command.
  
  On line 11, we tell Buildroot to not install the package to the
  target directory. This directory contains what will become the root
  filesystem running on the target. For purely static libraries, it is
  not necessary to install them in the target directory because they will
  not be used at runtime. By default, target installation is enabled; setting
  this variable to NO is almost never needed. Also by default, packages are
  installed in this location using the +make install+ command.
  
  On line 12, we tell Buildroot to pass custom options to CMake when it is
  configuring the package.
  
  On line 13, we declare our dependencies, so that they are built
  before the build process of our package starts.
  
  Finally, on line line 15, we invoke the +cmake-package+
  macro that generates all the Makefile rules that actually allows the
  package to be built.
  
  [[cmake-package-reference]]
  
  ==== +cmake-package+ reference
  
  The main macro of the CMake package infrastructure is
  +cmake-package+. It is similar to the +generic-package+ macro. The ability to
  have target and host packages is also available, with the
  +host-cmake-package+ macro.
  
  Just like the generic infrastructure, the CMake infrastructure works
  by defining a number of variables before calling the +cmake-package+
  macro.
  
  First, all the package metadata information variables that exist in
  the generic infrastructure also exist in the CMake infrastructure:
  +LIBFOO_VERSION+, +LIBFOO_SOURCE+, +LIBFOO_PATCH+, +LIBFOO_SITE+,
  +LIBFOO_SUBDIR+, +LIBFOO_DEPENDENCIES+, +LIBFOO_INSTALL_STAGING+,
  +LIBFOO_INSTALL_TARGET+.
  
  A few additional variables, specific to the CMake infrastructure, can
  also be defined. Many of them are only useful in very specific cases,
  typical packages will therefore only use a few of them.
  
  * +LIBFOO_SUBDIR+ may contain the name of a subdirectory inside the
    package that contains the main CMakeLists.txt file. This is useful,
    if for example, the main CMakeLists.txt file is not at the root of
    the tree extracted by the tarball. If +HOST_LIBFOO_SUBDIR+ is not
    specified, it defaults to +LIBFOO_SUBDIR+.
  
  * +LIBFOO_CONF_ENV+, to specify additional environment variables to
    pass to CMake. By default, empty.
  
  * +LIBFOO_CONF_OPTS+, to specify additional configure options to pass
    to CMake. By default, empty. A number of common CMake options are
    set by the +cmake-package+ infrastructure; so it is normally not
    necessary to set them in the package's +*.mk+ file unless you want
    to override them:
  
  ** +CMAKE_BUILD_TYPE+ is driven by +BR2_ENABLE_DEBUG+;
  ** +CMAKE_INSTALL_PREFIX+;
  ** +BUILD_SHARED_LIBS+ is driven by +BR2_STATIC_LIBS+;
  ** +BUILD_DOC+, +BUILD_DOCS+ are disabled;
  ** +BUILD_EXAMPLE+, +BUILD_EXAMPLES+ are disabled;
  ** +BUILD_TEST+, +BUILD_TESTS+, +BUILD_TESTING+ are disabled.
  
  * +LIBFOO_SUPPORTS_IN_SOURCE_BUILD = NO+ should be set when the package
    cannot be built inside the source tree but needs a separate build
    directory.
  
  * +LIBFOO_MAKE+, to specify an alternate +make+ command. This is
    typically useful when parallel make is enabled in the configuration
    (using +BR2_JLEVEL+) but that this feature should be disabled for
    the given package, for one reason or another. By default, set to
    +$(MAKE)+. If parallel building is not supported by the package,
    then it should be set to +LIBFOO_MAKE=$(MAKE1)+.
  
  * +LIBFOO_MAKE_ENV+, to specify additional environment variables to
    pass to make in the build step. These are passed before the +make+
    command. By default, empty.
  
  * +LIBFOO_MAKE_OPTS+, to specify additional variables to pass to make
    in the build step. These are passed after the +make+ command. By
    default, empty.
  
  * +LIBFOO_INSTALL_STAGING_OPTS+ contains the make options used to
    install the package to the staging directory. By default, the value
    is +DESTDIR=$(STAGING_DIR) install+, which is correct for most
    CMake packages. It is still possible to override it.
  
  * +LIBFOO_INSTALL_TARGET_OPTS+ contains the make options used to
    install the package to the target directory. By default, the value
    is +DESTDIR=$(TARGET_DIR) install+. The default value is correct
    for most CMake packages, but it is still possible to override it if
    needed.
  
  With the CMake infrastructure, all the steps required to build and
  install the packages are already defined, and they generally work well
  for most CMake-based packages. However, when required, it is still
  possible to customize what is done in any particular step:
  
  * By adding a post-operation hook (after extract, patch, configure,
    build or install). See xref:hooks[] for details.
  
  * By overriding one of the steps. For example, even if the CMake
    infrastructure is used, if the package +.mk+ file defines its own
    +LIBFOO_CONFIGURE_CMDS+ variable, it will be used instead of the
    default CMake one. However, using this method should be restricted
    to very specific cases. Do not use it in the general case.