Provided by: extra-cmake-modules_5.62.0-0ubuntu1_amd64 bug

NAME

       ecm-developer - ECM Developer Reference

WRITING MODULES

       The  CMake  3  documentation  (and  cmake-developer(7)  in particular) has a lot of useful
       information about writing CMake  modules,  including  a  large  section  devoted  to  find
       modules.  This  guide  will  only  highlight things that are particular to the Extra CMake
       Modules project.

       Most of these are stylistic points. For example, the license header for a  module  in  ECM
       should look like:

          #=============================================================================
          # Copyright 20XX Your Name <your.email@example.com>
          #
          # Redistribution and use in source and binary forms, with or without
          # modification, are permitted provided that the following conditions
          # are met:
          #
          # 1. Redistributions of source code must retain the copyright
          #    notice, this list of conditions and the following disclaimer.
          # 2. Redistributions in binary form must reproduce the copyright
          #    notice, this list of conditions and the following disclaimer in the
          #    documentation and/or other materials provided with the distribution.
          # 3. The name of the author may not be used to endorse or promote products
          #    derived from this software without specific prior written permission.
          #
          # THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
          # IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
          # OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
          # IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
          # INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
          # NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
          # DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
          # THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
          # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
          # THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

       Functions  should be used instead of macros unless there is a good reason not to (and that
       reason should be noted in a comment), and lowercase should be used for  macros,  functions
       and commands.

       4  spaces is the generally-recommended indent, although there are several files that use 2
       spaces; consistency within a file is more important than consistency across files.

       If in doubt, look at how other modules in Extra CMake Modules are written, and follow  the
       same pattern.

   Find Modules
       A good template for find module documentation is:

          #.rst:
          # FindFoo
          # -------
          #
          # Finds the Foo library.
          #
          # This will define the following variables:
          #
          # ``Foo_FOUND``
          #     True if (the requested version of) Foo is available
          # ``Foo_VERSION``
          #     The version of Foo, if it is found
          # ``Foo_LIBRARIES``
          #     This can be passed to target_link_libraries() instead of the ``Foo::Foo``
          #     target
          # ``Foo_INCLUDE_DIRS``
          #     This should be passed to target_include_directories() if the target is not
          #     used for linking
          # ``Foo_DEFINITIONS``
          #     This should be passed to target_compile_options() if the target is not
          #     used for linking
          #
          # If ``Foo_FOUND`` is TRUE, it will also define the following imported target:
          #
          # ``Foo::Foo``
          #     The Foo library
          #
          # In general we recommend using the imported target, as it is easier to use.
          # Bear in mind, however, that if the target is in the link interface of an
          # exported library, it must be made available by the package config file.

       Note the use of definition lists for the variables.

       Because  of  the  ECMUseFindModules  module, projects may easily make local copies of find
       modules, and may install those copies with their own CMake project config files. For  this
       reason, find modules should include the full BSD 3-clause license:

          #=============================================================================
          # Copyright 20XX Your Name <your.email@example.com>
          #
          # Redistribution and use in source and binary forms, with or without
          # modification, are permitted provided that the following conditions
          # are met:
          #
          # 1. Redistributions of source code must retain the copyright
          #    notice, this list of conditions and the following disclaimer.
          # 2. Redistributions in binary form must reproduce the copyright
          #    notice, this list of conditions and the following disclaimer in the
          #    documentation and/or other materials provided with the distribution.
          # 3. The name of the author may not be used to endorse or promote products
          #    derived from this software without specific prior written permission.
          #
          # THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
          # IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
          # OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
          # IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
          # INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
          # NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
          # DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
          # THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
          # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
          # THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
          #=============================================================================

       Find  modules  should  always  provide  imported  targets  in  addition to the traditional
       variables (like Foo_LIBRARIES, etc).

       Unlike find modules shipped with CMake, if the module requires a specific CMake version it
       is  not  enough  to  warn when the minimum required version is not high enough: you should
       also produce an error when the actual CMake version being used is not  high  enough.  This
       can be done with:

          if(CMAKE_VERSION VERSION_LESS 2.8.12)
              message(FATAL_ERROR "CMake 2.8.12 is required by FindFoo.cmake")
          endif()
          if(CMAKE_MINIMUM_REQUIRED_VERSION VERSION_LESS 2.8.12)
              message(AUTHOR_WARNING "Your project should require at least CMake 2.8.12 to use FindFoo.cmake")
          endif()

       The  ECMFindModuleHelpers  module has several useful functions and macros. For example, it
       allows you to replace the above version check with:

          ecm_find_package_version_check(Foo)

   Components
       Using  ECMFindModuleHelpers,  creating  a  find  module  for  a   library   with   several
       inter-dependent  components  is  reasonably  straightforward. After the documentation, you
       need to include the module and do the usual version check:

          include(ECMFindModuleHelpers)
          ecm_find_package_version_check(Foo)

       The      important      macros       are       ecm_find_package_parse_components       and
       ecm_find_package_handle_library_components.   These  take  a list of components, and query
       other variables you provide to find out the information they require.   The  documentation
       for ECMFindModuleHelpers provides more information, but a simple setup might look like:

          set(Foo_known_components Bar Baz)
          set(Foo_Bar_pkg_config "foo-bar")
          set(Foo_Bar_lib "bar")
          set(Foo_Bar_header "foo/bar.h")
          set(Foo_Bar_pkg_config "foo-baz")
          set(Foo_Baz_lib "baz")
          set(Foo_Baz_header "foo/baz.h")

       If Baz depends on Bar, for example, you can specify this with

          set(Foo_Baz_component_deps "Bar")

       Then call the macros:

          ecm_find_package_parse_components(Foo
              RESULT_VAR Foo_components
              KNOWN_COMPONENTS ${Foo_known_components}
          )
          ecm_find_package_handle_library_components(Foo
              COMPONENTS ${Foo_components}
          )

       Of   course,   if  your  components  need  unusual  handling,  you  may  want  to  replace
       ecm_find_package_handle_library_components with, for example,  a  foreach  loop  over  the
       components  (the  body  of  which should implement most of what a normal find module does,
       including setting Foo_<component>_FOUND).

       At this point, you should set Foo_VERSION using whatever information  you  have  available
       (such as from parsing header files).  Note that ecm_find_package_handle_library_components
       will set it to the version reported by pkg-config of the first component found,  but  this
       depends on the presence of pkg-config files, and the version of a component may not be the
       same as the version of the whole package.  After that, finish off with

          include(FindPackageHandleStandardArgs)
          find_package_handle_standard_args(Foo
              FOUND_VAR
                  Foo_FOUND
              REQUIRED_VARS
                  Foo_LIBRARIES
              VERSION_VAR
                  Foo_VERSION
              HANDLE_COMPONENTS
          )

          include(FeatureSummary)
          set_package_properties(Foo PROPERTIES
              URL "https://www.foo.example.com/"
              DESCRIPTION "A library for doing useful things")

SUBMITTING MODULES

       Proposed new modules should be submitted using the  KDE  Review  Board  instance,  and  be
       assigned  to the buildsystem and extracmakemodules groups.  You should be able to point to
       two separate projects that will make use of the module.

       The mailing list can be found at https://mail.kde.org/mailman/listinfo/kde-buildsystem.

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