Help: Rewrite the cmake-developer.7 find module documentation
As well as the traditional variables, providing imported targets is suggested, and the relative advantages and disadvantages briefly discussed. A mini-tutorial walking through creating a simple find module is provided. This changes the recommended version variable from Foo_VERSION_STRING to Foo_VERSION, because there is really no need to have different variable names for package version files vs. find modules. It notes the old variable name, though, and suggests setting it for compatibility.
This commit is contained in:
Alex Merry
Brad King
parent
5ada4be81b
commit
fcdf86d004
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@ -664,213 +664,408 @@ For example, a ``Modules/Findxxx.cmake`` module may contain:
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<code>
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endmacro()
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After the top documentation block, leave a *BLANK* line, and then add a
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copyright and licence notice block like this one (change only the year
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range and name)
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.. code-block:: cmake
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#=============================================================================
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# Copyright 2009-2011 Your Name
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#
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# Distributed under the OSI-approved BSD License (the "License");
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# see accompanying file Copyright.txt for details.
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#
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# This software is distributed WITHOUT ANY WARRANTY; without even the
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# implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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# See the License for more information.
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#=============================================================================
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# (To distribute this file outside of CMake, substitute the full
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# License text for the above reference.)
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Test the documentation formatting by running
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``cmake --help-module <module-name>``, and also by enabling the
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``SPHINX_HTML`` and ``SPHINX_MAN`` options to build the documentation.
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Edit the comments until generated documentation looks satisfactory. To
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have a .cmake file in this directory NOT show up in the modules
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documentation, simply leave out the ``Help/module/<module-name>.rst``
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file and the ``Help/manual/cmake-modules.7.rst`` toctree entry.
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Find Modules
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------------
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A "find module" is a ``Modules/Find<package>.cmake`` file to be loaded
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by the :command:`find_package` command when invoked for ``<package>``.
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We would like all ``FindXxx.cmake`` files to produce consistent variable
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names. Please use the following consistent variable names for general use.
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The primary task of a find module is to determine whether a package
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exists on the system, set the ``<package>_FOUND`` variable to reflect
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this and provide any variables, macros and imported targets required to
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use the package.
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Xxx_INCLUDE_DIRS
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The final set of include directories listed in one variable for use by client
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code. This should not be a cache entry.
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The traditional approach is to use variables for everything, including
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libraries and executables: see the `Standard Variable Names`_ section
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below. This is what most of the existing find modules provided by CMake
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do.
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Xxx_LIBRARIES
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The libraries to link against to use Xxx. These should include full paths.
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This should not be a cache entry.
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The more modern approach is to behave as much like
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``<package>Config.cmake`` files as possible, by providing imported
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targets. As well as matching how ``*Config.cmake`` files work, the
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libraries, include directories and compile definitions are all set just
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by using the target in a :command:`target_link_libraries` call. The
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disadvantage is that ``*Config.cmake`` files of projects that use
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imported targets from find modules may require more work to make sure
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those imported targets that are in the link interface are available.
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Xxx_DEFINITIONS
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Definitions to use when compiling code that uses Xxx. This really shouldn't
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include options such as (-DHAS_JPEG)that a client source-code file uses to
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decide whether to #include <jpeg.h>
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In either case (or even when providing both variables and imported
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targets), find modules should provide backwards compatibility with old
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versions that had the same name.
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Xxx_EXECUTABLE
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Where to find the Xxx tool.
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A FindFoo.cmake module will typically be loaded by the command::
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Xxx_Yyy_EXECUTABLE
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Where to find the Yyy tool that comes with Xxx.
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find_package(Foo [major[.minor[.patch[.tweak]]]]
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[EXACT] [QUIET] [REQUIRED]
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[[COMPONENTS] [components...]]
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[OPTIONAL_COMPONENTS components...]
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[NO_POLICY_SCOPE])
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Xxx_LIBRARY_DIRS
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Optionally, the final set of library directories listed in one variable for
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use by client code. This should not be a cache entry.
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See the :command:`find_package` documentation for details on what
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variables are set for the find module. Most of these are dealt with by
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using :module:`FindPackageHandleStandardArgs`.
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Xxx_ROOT_DIR
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Where to find the base directory of Xxx.
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Briefly, the module should only locate versions of the package
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compatible with the requested version, as described by the
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``Foo_FIND_VERSION`` family of variables. If ``Foo_FIND_QUIETLY`` is
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set to true, it should avoid printing messages, including anything
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complaining about the package not being found. If ``Foo_FIND_REQUIRED``
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is set to true, the module should issue a ``FATAL_ERROR`` if the package
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cannot be found. If neither are set to true, it should print a
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non-fatal message if it cannot find the package.
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Xxx_VERSION_Yy
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Expect Version Yy if true. Make sure at most one of these is ever true.
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Packages that find multiple semi-independent parts (like bundles of
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libraries) should search for the components listed in
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``Foo_FIND_COMPONENTS`` if it is set , and only set ``Foo_FOUND`` to
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true if for each searched-for component ``<c>`` that was not found,
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``Foo_FIND_REQUIRED_<c>`` is not set to true. The ``HANDLE_COMPONENTS``
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argument of ``find_package_handle_standard_args()`` can be used to
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implement this.
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Xxx_WRAP_Yy
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If False, do not try to use the relevant CMake wrapping command.
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If ``Foo_FIND_COMPONENTS`` is not set, which modules are searched for
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and required is up to the find module, but should be documented.
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Xxx_Yy_FOUND
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If False, optional Yy part of Xxx sytem is not available.
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For internal implementation, it is a generally accepted convention that
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variables starting with underscore are for temporary use only.
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Xxx_FOUND
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Set to false, or undefined, if we haven't found, or don't want to use Xxx.
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Like all modules, find modules should be properly documented. To add a
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module to the CMake documentation, follow the steps in the `Module
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Documentation`_ section above.
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Xxx_NOT_FOUND_MESSAGE
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Should be set by config-files in the case that it has set Xxx_FOUND to FALSE.
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The contained message will be printed by the find_package() command and by
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find_package_handle_standard_args() to inform the user about the problem.
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Xxx_RUNTIME_LIBRARY_DIRS
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Optionally, the runtime library search path for use when running an
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executable linked to shared libraries. The list should be used by user code
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to create the PATH on windows or LD_LIBRARY_PATH on unix. This should not be
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a cache entry.
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Xxx_VERSION_STRING
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A human-readable string containing the version of the package found, if any.
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Standard Variable Names
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~~~~~~~~~~~~~~~~~~~~~~~
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Xxx_VERSION_MAJOR
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The major version of the package found, if any.
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For a ``FindXxx.cmake`` module that takes the approach of setting
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variables (either instead of or in addition to creating imported
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targets), the following variable names should be used to keep things
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consistent between find modules. Note that all variables start with
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``Xxx_`` to make sure they do not interfere with other find modules; the
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same consideration applies to macros, functions and imported targets.
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Xxx_VERSION_MINOR
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The minor version of the package found, if any.
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``Xxx_INCLUDE_DIRS``
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The final set of include directories listed in one variable for use by
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client code. This should not be a cache entry.
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Xxx_VERSION_PATCH
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The patch version of the package found, if any.
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``Xxx_LIBRARIES``
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The libraries to link against to use Xxx. These should include full
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paths. This should not be a cache entry.
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You do not have to provide all of the above variables. You should provide
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Xxx_FOUND under most circumstances. If Xxx is a library, then Xxx_LIBRARIES,
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should also be defined, and Xxx_INCLUDE_DIRS should usually be defined (I
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guess libm.a might be an exception)
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``Xxx_DEFINITIONS``
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Definitions to use when compiling code that uses Xxx. This really
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shouldn't include options such as ``-DHAS_JPEG`` that a client
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source-code file uses to decide whether to ``#include <jpeg.h>``
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``Xxx_EXECUTABLE``
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Where to find the Xxx tool.
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``Xxx_Yyy_EXECUTABLE``
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Where to find the Yyy tool that comes with Xxx.
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``Xxx_LIBRARY_DIRS``
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Optionally, the final set of library directories listed in one
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variable for use by client code. This should not be a cache entry.
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``Xxx_ROOT_DIR``
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Where to find the base directory of Xxx.
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``Xxx_VERSION_Yy``
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Expect Version Yy if true. Make sure at most one of these is ever true.
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``Xxx_WRAP_Yy``
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If False, do not try to use the relevant CMake wrapping command.
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``Xxx_Yy_FOUND``
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If False, optional Yy part of Xxx sytem is not available.
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``Xxx_FOUND``
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Set to false, or undefined, if we haven't found, or don't want to use
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Xxx.
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``Xxx_NOT_FOUND_MESSAGE``
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Should be set by config-files in the case that it has set
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``Xxx_FOUND`` to FALSE. The contained message will be printed by the
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:command:`find_package` command and by
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``find_package_handle_standard_args()`` to inform the user about the
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problem.
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``Xxx_RUNTIME_LIBRARY_DIRS``
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Optionally, the runtime library search path for use when running an
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executable linked to shared libraries. The list should be used by
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user code to create the ``PATH`` on windows or ``LD_LIBRARY_PATH`` on
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UNIX. This should not be a cache entry.
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``Xxx_VERSION``
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The full version string of the package found, if any. Note that many
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existing modules provide ``Xxx_VERSION_STRING`` instead.
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``Xxx_VERSION_MAJOR``
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The major version of the package found, if any.
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``Xxx_VERSION_MINOR``
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The minor version of the package found, if any.
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``Xxx_VERSION_PATCH``
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The patch version of the package found, if any.
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The following names should not usually be used in CMakeLists.txt files, but
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they may be usefully modified in users' CMake Caches to control stuff.
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are typically cache variables for users to edit and control the
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behaviour of find modules (like entering the path to a library manually)
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Xxx_LIBRARY
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Name of Xxx Library. A User may set this and Xxx_INCLUDE_DIR to ignore to
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force non-use of Xxx.
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``Xxx_LIBRARY``
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The path of the Xxx library (as used with :command:`find_library`, for
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example).
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Xxx_Yy_LIBRARY
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Name of Yy library that is part of the Xxx system. It may or may not be
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required to use Xxx.
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``Xxx_Yy_LIBRARY``
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The path of the Yy library that is part of the Xxx system. It may or
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may not be required to use Xxx.
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Xxx_INCLUDE_DIR
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Where to find xxx.h, etc. (Xxx_INCLUDE_PATH was considered bad because a path
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includes an actual filename.)
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``Xxx_INCLUDE_DIR``
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Where to find headers for using the Xxx library.
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Xxx_Yy_INCLUDE_DIR
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Where to find xxx_yy.h, etc.
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``Xxx_Yy_INCLUDE_DIR``
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Where to find headers for using the Yy library of the Xxx system.
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For tidiness's sake, try to keep as many options as possible out of the cache,
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leaving at least one option which can be used to disable use of the module, or
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locate a not-found library (e.g. Xxx_ROOT_DIR). For the same reason, mark
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To prevent users being overwhelmed with settings to configure, try to
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keep as many options as possible out of the cache, leaving at least one
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option which can be used to disable use of the module, or locate a
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not-found library (e.g. ``Xxx_ROOT_DIR``). For the same reason, mark
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most cache options as advanced.
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If you need other commands to do special things then it should still begin
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with ``Xxx_``. This gives a sort of namespace effect and keeps things tidy for the
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user. You should put comments describing all the exported settings, plus
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descriptions of any the users can use to control stuff.
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While these are the standard variable names, you should provide
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backwards compatibility for any old names that were actually in use.
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Make sure you comment them as deprecated, so that no-one starts using
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them.
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You really should also provide backwards compatibility any old settings that
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were actually in use. Make sure you comment them as deprecated, so that
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no-one starts using them.
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To add a module to the CMake documentation, follow the steps in the
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`Module Documentation`_ section above. Test the documentation formatting
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by running ``cmake --help-module FindXxx``, and also by enabling the
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``SPHINX_HTML`` and ``SPHINX_MAN`` options to build the documentation.
|
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Edit the comments until generated documentation looks satisfactory.
|
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To have a .cmake file in this directory NOT show up in the modules
|
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documentation, simply leave out the ``Help/module/<module-name>.rst`` file
|
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and the ``Help/manual/cmake-modules.7.rst`` toctree entry.
|
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After the documentation, leave a *BLANK* line, and then add a
|
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copyright and licence notice block like this one::
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A Sample Find Module
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~~~~~~~~~~~~~~~~~~~~
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#=============================================================================
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# Copyright 2009-2011 Your Name
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#
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# Distributed under the OSI-approved BSD License (the "License");
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# see accompanying file Copyright.txt for details.
|
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#
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# This software is distributed WITHOUT ANY WARRANTY; without even the
|
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# implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
|
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# See the License for more information.
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#=============================================================================
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# (To distribute this file outside of CMake, substitute the full
|
||||
# License text for the above reference.)
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We will describe how to create a simple find module for a library
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``Foo``.
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The layout of the notice block is strictly enforced by the ``ModuleNotices``
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test. Only the year range and name may be changed freely.
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The first thing that is needed is documentation. CMake's documentation
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system requires you to start the file with a documentation marker and
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the name of the module. You should follow this with a simple statement
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of what the module does.
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A FindXxx.cmake module will typically be loaded by the command::
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.. code-block:: cmake
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FIND_PACKAGE(Xxx [major[.minor[.patch[.tweak]]]] [EXACT]
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[QUIET] [[REQUIRED|COMPONENTS] [components...]])
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#.rst:
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# FindFoo
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# -------
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#
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# Finds the Foo library
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#
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If any version numbers are given to the command it will set the following
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variables before loading the module:
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More description may be required for some packages. If there are
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caveats or other details users of the module should be aware of, you can
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add further paragraphs below this. Then you need to document what
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variables and imported targets are set by the module, such as
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Xxx_FIND_VERSION
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full requested version string
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.. code-block:: cmake
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Xxx_FIND_VERSION_MAJOR
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major version if requested, else 0
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# This will define the following variables::
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#
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# Foo_FOUND - True if the system has the Foo library
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# Foo_VERSION - The version of the Foo library which was found
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#
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# and the following imported targets::
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#
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# Foo::Foo - The Foo library
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Xxx_FIND_VERSION_MINOR
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minor version if requested, else 0
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If the package provides any macros, they should be listed here, but can
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be documented where they are defined. See the `Module
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Documentation`_ section above for more details.
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Xxx_FIND_VERSION_PATCH
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patch version if requested, else 0
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After the documentation, leave a blank line, and then add a copyright and
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licence notice block
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Xxx_FIND_VERSION_TWEAK
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tweak version if requested, else 0
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.. code-block:: cmake
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Xxx_FIND_VERSION_COUNT
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number of version components, 0 to 4
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#=============================================================================
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# Copyright 2009-2011 Your Name
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#
|
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# Distributed under the OSI-approved BSD License (the "License");
|
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# see accompanying file Copyright.txt for details.
|
||||
#
|
||||
# This software is distributed WITHOUT ANY WARRANTY; without even the
|
||||
# implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
|
||||
# See the License for more information.
|
||||
#=============================================================================
|
||||
# (To distribute this file outside of CMake, substitute the full
|
||||
# License text for the above reference.)
|
||||
|
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Xxx_FIND_VERSION_EXACT
|
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true if EXACT option was given
|
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If the module is new to CMake, you may want to provide a warning for
|
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projects that do not require a high enough CMake version.
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If the find module supports versioning it should locate a version of
|
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the package that is compatible with the version requested. If a
|
||||
compatible version of the package cannot be found the module should
|
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not report success. The version of the package found should be stored
|
||||
in "Xxx_VERSION..." version variables documented by the module.
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.. code-block:: cmake
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|
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If the QUIET option is given to the command it will set the variable
|
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Xxx_FIND_QUIETLY to true before loading the FindXxx.cmake module. If
|
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this variable is set the module should not complain about not being
|
||||
able to find the package. If the
|
||||
REQUIRED option is given to the command it will set the variable
|
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Xxx_FIND_REQUIRED to true before loading the FindXxx.cmake module. If
|
||||
this variable is set the module should issue a FATAL_ERROR if the
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package cannot be found.
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If neither the QUIET nor REQUIRED options are given then the
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FindXxx.cmake module should look for the package and complain without
|
||||
error if the module is not found.
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if(CMAKE_MINIMUM_REQUIRED_VERSION VERSION_LESS 3.0.0)
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message(AUTHOR_WARNING "Your project should require at least CMake 3.0.0 to use FindFoo.cmake")
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endif()
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FIND_PACKAGE() will set the variable CMAKE_FIND_PACKAGE_NAME to
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contain the actual name of the package.
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Now the actual libraries and so on have to be found. The code here will
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||||
obviously vary from module to module (dealing with that, after all, is the
|
||||
point of find modules), but there tends to be a common pattern for libraries.
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||||
|
||||
A package can provide sub-components.
|
||||
Those components can be listed after the COMPONENTS (or REQUIRED) or
|
||||
OPTIONAL_COMPONENTS keywords. The set of all listed components will be
|
||||
specified in a Xxx_FIND_COMPONENTS variable.
|
||||
For each package-specific component, say Yyy, a variable Xxx_FIND_REQUIRED_Yyy
|
||||
will be set to true if it listed after COMPONENTS and it will be set to false
|
||||
if it was listed after OPTIONAL_COMPONENTS.
|
||||
Using those variables a FindXxx.cmake module and also a XxxConfig.cmake
|
||||
package configuration file can determine whether and which components have
|
||||
been requested, and whether they were requested as required or as optional.
|
||||
For each of the requested components a Xxx_Yyy_FOUND variable should be set
|
||||
accordingly.
|
||||
The per-package Xxx_FOUND variable should be only set to true if all requested
|
||||
required components have been found. A missing optional component should not
|
||||
keep the Xxx_FOUND variable from being set to true.
|
||||
If the package provides Xxx_INCLUDE_DIRS and Xxx_LIBRARIES variables, the
|
||||
include dirs and libraries for all components which were requested and which
|
||||
have been found should be added to those two variables.
|
||||
First, we try to use ``pkg-config`` to find the library. Note that we
|
||||
cannot rely on this, as it may not be available, but it provides a good
|
||||
starting point.
|
||||
|
||||
To get this behavior you can use the FIND_PACKAGE_HANDLE_STANDARD_ARGS()
|
||||
macro, as an example see FindJPEG.cmake.
|
||||
.. code-block:: cmake
|
||||
|
||||
For internal implementation, it's a generally accepted convention that
|
||||
variables starting with underscore are for temporary use only. (variable
|
||||
starting with an underscore are not intended as a reserved prefix).
|
||||
find_package(PkgConfig)
|
||||
pkg_check_modules(PC_Foo QUIET Foo)
|
||||
|
||||
This should define some variables starting ``PC_Foo_`` that contain the
|
||||
information from the ``Foo.pc`` file.
|
||||
|
||||
Now we need to find the libraries and include files; we use the
|
||||
information from ``pkg-config`` to provide hints to CMake about where to
|
||||
look.
|
||||
|
||||
.. code-block:: cmake
|
||||
|
||||
find_path(Foo_INCLUDE_DIR
|
||||
NAMES foo.h
|
||||
PATHS ${PC_Foo_INCLUDE_DIRS}
|
||||
# if you need to put #include <Foo/foo.h> in your code, add:
|
||||
PATH_SUFFIXES Foo
|
||||
)
|
||||
find_library(Foo_LIBRARY
|
||||
NAMES foo
|
||||
PATHS ${PC_Foo_LIBRARY_DIRS}
|
||||
)
|
||||
|
||||
If you have a good way of getting the version (from a header file, for
|
||||
example), you can use that information to set ``Foo_VERSION`` (although
|
||||
note that find modules have traditionally used ``Foo_VERSION_STRING``,
|
||||
so you may want to set both). Otherwise, attempt to use the information
|
||||
from ``pkg-config``
|
||||
|
||||
.. code-block:: cmake
|
||||
|
||||
set(Foo_VERSION ${PC_Foo_VERSION})
|
||||
|
||||
Now we can use :module:`FindPackageHandleStandardArgs` to do most of the
|
||||
rest of the work for us
|
||||
|
||||
.. code-block:: cmake
|
||||
|
||||
include(FindPackageHandleStandardArgs)
|
||||
find_package_handle_standard_args(Foo
|
||||
FOUND_VAR Foo_FOUND
|
||||
REQUIRED_VARS
|
||||
Foo_LIBRARY
|
||||
Foo_INCLUDE_DIR
|
||||
VERSION_VAR Foo_VERSION
|
||||
)
|
||||
|
||||
This will check that the ``REQUIRED_VARS`` contain values (that do not
|
||||
end in ``-NOTFOUND``) and set ``Foo_FOUND`` appropriately. It will also
|
||||
cache those values. If ``Foo_VERSION`` is set, and a required version
|
||||
was passed to :command:`find_package`, it will check the requested version
|
||||
against the one in ``Foo_VERSION``. It will also print messages as
|
||||
appropriate; note that if the package was found, it will print the
|
||||
contents of the first required variable to indicate where it was found.
|
||||
|
||||
At this point, we have to provide a way for users of the find module to
|
||||
link to the library or libraries that were found. There are two
|
||||
approaches, as discussed in the `Find Modules`_ section above. The
|
||||
traditional variable approach looks like
|
||||
|
||||
.. code-block:: cmake
|
||||
|
||||
if(Foo_FOUND)
|
||||
set(Foo_LIBRARIES ${Foo_LIBRARY})
|
||||
set(Foo_INCLUDE_DIRS ${Foo_INCLUDE_DIR})
|
||||
set(Foo_DEFINITIONS ${PC_Foo_CFLAGS_OTHER})
|
||||
endif()
|
||||
|
||||
If more than one library was found, all of them should be included in
|
||||
these variables (see the `Standard Variable Names`_ section for more
|
||||
information).
|
||||
|
||||
When providing imported targets, these should be namespaced (hence the
|
||||
``Foo::`` prefix); CMake will recognize that values passed to
|
||||
:command:`target_link_libraries` that contain ``::`` in their name are
|
||||
supposed to be imported targets (rather than just library names), and
|
||||
will produce appropriate diagnostic messages if that target does not
|
||||
exist (see policy :policy:`CMP0028`).
|
||||
|
||||
.. code-block:: cmake
|
||||
|
||||
if(Foo_FOUND AND NOT TARGET Foo::Foo)
|
||||
add_library(Foo::Foo UNKNOWN IMPORTED)
|
||||
set_target_properties(Foo::Foo PROPERTIES
|
||||
IMPORTED_LOCATION "${Foo_LIBRARY}"
|
||||
INTERFACE_COMPILE_OPTIONS "${PC_Foo_CFLAGS_OTHER}"
|
||||
INTERFACE_INCLUDE_DIRECTORIES "${Foo_INCLUDE_DIR}"
|
||||
)
|
||||
endif()
|
||||
|
||||
One thing to note about this is that the ``INTERFACE_INCLUDE_DIRECTORIES`` and
|
||||
similar properties should only contain information about the target itself, and
|
||||
not any of its dependencies. Instead, those dependencies should also be
|
||||
targets, and CMake should be told that they are dependencies of this target.
|
||||
CMake will then combine all the necessary information automatically.
|
||||
|
||||
We should also provide some information about the package, such as where to
|
||||
download it.
|
||||
|
||||
.. code-block:: cmake
|
||||
|
||||
include(FeatureSummary)
|
||||
set_package_properties(Foo PROPERTIES
|
||||
URL "http://www.foo.example.com/"
|
||||
DESCRIPTION "A library for doing useful things"
|
||||
)
|
||||
|
||||
Most of the cache variables should be hidden in the ``ccmake`` interface unless
|
||||
the user explicitly asks to edit them.
|
||||
|
||||
.. code-block:: cmake
|
||||
|
||||
mark_as_advanced(
|
||||
Foo_INCLUDE_DIR
|
||||
Foo_LIBRARY
|
||||
)
|
||||
|
||||
If this module replaces an older version, you should set compatibility variables
|
||||
to cause the least disruption possible.
|
||||
|
||||
.. code-block:: cmake
|
||||
|
||||
# compatibility variables
|
||||
set(Foo_VERSION_STRING ${Foo_VERSION})
|
||||
|
|
|
|||
Loading…
Reference in New Issue