1ECM-DEVELOPER(7) Extra CMake Modules ECM-DEVELOPER(7)
2
6 ecm-developer - ECM Developer Reference
7
9 The CMake 3 documentation (and cmake-developer(7) in particular) has a
10 lot of useful information about writing CMake modules, including a
11 large section devoted to find modules. This guide will only highlight
12 things that are particular to the Extra CMake Modules project.
13 Most of these are stylistic points. For example, the license header for
15 a module in ECM should look like:
16 #=============================================================================
18 # Copyright 20XX Your Name <your.email@example.com>
19 #
20 # Redistribution and use in source and binary forms, with or without
21 # modification, are permitted provided that the following conditions
22 # are met:
23 #
24 # 1. Redistributions of source code must retain the copyright
25 # notice, this list of conditions and the following disclaimer.
26 # 2. Redistributions in binary form must reproduce the copyright
27 # notice, this list of conditions and the following disclaimer in the
28 # documentation and/or other materials provided with the distribution.
29 # 3. The name of the author may not be used to endorse or promote products
30 # derived from this software without specific prior written permission.
31 #
32 # THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
33 # IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
34 # OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
35 # IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
36 # INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
37 # NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
38 # DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
39 # THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
40 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
41 # THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
42 Functions should be used instead of macros unless there is a good rea‐
44 son not to (and that reason should be noted in a comment), and lower‐
45 case should be used for macros, functions and commands.
46 4 spaces is the generally-recommended indent, although there are sev‐
48 eral files that use 2 spaces; consistency within a file is more impor‐
49 tant than consistency across files.
50 If in doubt, look at how other modules in Extra CMake Modules are writ‐
52 ten, and follow the same pattern.
53 Find Modules
55 A good template for find module documentation is:
56 #.rst:
58 # FindFoo
59 # -------
60 #
61 # Finds the Foo library.
62 #
63 # This will define the following variables:
64 #
65 # ``Foo_FOUND``
66 # True if (the requested version of) Foo is available
67 # ``Foo_VERSION``
68 # The version of Foo, if it is found
69 # ``Foo_LIBRARIES``
70 # This can be passed to target_link_libraries() instead of the ``Foo::Foo``
71 # target
72 # ``Foo_INCLUDE_DIRS``
73 # This should be passed to target_include_directories() if the target is not
74 # used for linking
75 # ``Foo_DEFINITIONS``
76 # This should be passed to target_compile_options() if the target is not
77 # used for linking
78 #
79 # If ``Foo_FOUND`` is TRUE, it will also define the following imported target:
80 #
81 # ``Foo::Foo``
82 # The Foo library
83 #
84 # In general we recommend using the imported target, as it is easier to use.
85 # Bear in mind, however, that if the target is in the link interface of an
86 # exported library, it must be made available by the package config file.
87 Note the use of definition lists for the variables.
89 Because of the ECMUseFindModules module, projects may easily make local
91 copies of find modules, and may install those copies with their own
92 CMake project config files. For this reason, find modules should
93 include the full BSD 3-clause license:
94 #=============================================================================
96 # Copyright 20XX Your Name <your.email@example.com>
97 #
98 # Redistribution and use in source and binary forms, with or without
99 # modification, are permitted provided that the following conditions
100 # are met:
101 #
102 # 1. Redistributions of source code must retain the copyright
103 # notice, this list of conditions and the following disclaimer.
104 # 2. Redistributions in binary form must reproduce the copyright
105 # notice, this list of conditions and the following disclaimer in the
106 # documentation and/or other materials provided with the distribution.
107 # 3. The name of the author may not be used to endorse or promote products
108 # derived from this software without specific prior written permission.
109 #
110 # THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
111 # IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
112 # OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
113 # IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
114 # INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
115 # NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
116 # DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
117 # THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
118 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
119 # THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
120 #=============================================================================
121 Find modules should always provide imported targets in addition to the
123 traditional variables (like Foo_LIBRARIES, etc).
124 Unlike find modules shipped with CMake, if the module requires a spe‐
126 cific CMake version it is not enough to warn when the minimum required
127 version is not high enough: you should also produce an error when the
128 actual CMake version being used is not high enough. This can be done
129 with:
130 if(CMAKE_VERSION VERSION_LESS 2.8.12)
132 message(FATAL_ERROR "CMake 2.8.12 is required by FindFoo.cmake")
133 endif()
134 if(CMAKE_MINIMUM_REQUIRED_VERSION VERSION_LESS 2.8.12)
135 message(AUTHOR_WARNING "Your project should require at least CMake 2.8.12 to use FindFoo.cmake")
136 endif()
137 The ECMFindModuleHelpers module has several useful functions and
139 macros. For example, it allows you to replace the above version check
140 with:
141 ecm_find_package_version_check(Foo)
143 Components
145 Using ECMFindModuleHelpers, creating a find module for a library with
146 several inter-dependent components is reasonably straightforward. After
147 the documentation, you need to include the module and do the usual ver‐
148 sion check:
149 include(ECMFindModuleHelpers)
151 ecm_find_package_version_check(Foo)
152 The important macros are ecm_find_package_parse_components and
154 ecm_find_package_handle_library_components. These take a list of com‐
155 ponents, and query other variables you provide to find out the informa‐
156 tion they require. The documentation for ECMFindModuleHelpers provides
157 more information, but a simple setup might look like:
158 set(Foo_known_components Bar Baz)
160 set(Foo_Bar_pkg_config "foo-bar")
161 set(Foo_Bar_lib "bar")
162 set(Foo_Bar_header "foo/bar.h")
163 set(Foo_Bar_pkg_config "foo-baz")
164 set(Foo_Baz_lib "baz")
165 set(Foo_Baz_header "foo/baz.h")
166 If Baz depends on Bar, for example, you can specify this with
168 set(Foo_Baz_component_deps "Bar")
170 Then call the macros:
172 ecm_find_package_parse_components(Foo
174 RESULT_VAR Foo_components
175 KNOWN_COMPONENTS ${Foo_known_components}
176 )
177 ecm_find_package_handle_library_components(Foo
178 COMPONENTS ${Foo_components}
179 )
180 Of course, if your components need unusual handling, you may want to
182 replace ecm_find_package_handle_library_components with, for example, a
183 foreach loop over the components (the body of which should implement
184 most of what a normal find module does, including setting Foo_<compo‐
185 nent>_FOUND).
186 At this point, you should set Foo_VERSION using whatever information
188 you have available (such as from parsing header files). Note that
189 ecm_find_package_handle_library_components will set it to the version
190 reported by pkg-config of the first component found, but this depends
191 on the presence of pkg-config files, and the version of a component may
192 not be the same as the version of the whole package. After that, fin‐
193 ish off with
194 include(FindPackageHandleStandardArgs)
196 find_package_handle_standard_args(Foo
197 FOUND_VAR
198 Foo_FOUND
199 REQUIRED_VARS
200 Foo_LIBRARIES
201 VERSION_VAR
202 Foo_VERSION
203 HANDLE_COMPONENTS
204 )
205 include(FeatureSummary)
207 set_package_properties(Foo PROPERTIES
208 URL "https://www.foo.example.com/"
209 DESCRIPTION "A library for doing useful things")
210
212 Proposed new modules should be submitted using the KDE Review Board
213 instance, and be assigned to the buildsystem and extracmakemodules
214 groups. You should be able to point to two separate projects that will
215 make use of the module.
216 The mailing list can be found at
218 https://mail.kde.org/mailman/listinfo/kde-buildsystem.
219
221 KDE Developers
2225.79 Feb 06, 2021 ECM-DEVELOPER(7)