Difference between revisions of "Policies/CMake Coding Style"

Revision as of 16:42, 17 September 2011

This document describes the recommended coding style for CMake files in KDE, i.e. CMakeLists.txt files and *.cmake files.

Indentation

Indent all code correctly, i.e. the body of

• if/else/endif
• foreach/endforeach
• while/endwhile
• macro/endmacro
• function/endfunction (CMake 2.6)

Use spaces for indenting, 2, 3 or 4 spaces preferably. Use the same amount of spaces for indenting as is used in the rest of the file. Do not use tabs.

Upper/lower casing

CMake commands are case-insensitive (only the commands, not the arguments or variable names). So all the following versions work:

add_executable(foo foo.c)
ADD_EXECUTABLE(bar bar.c)
Add_Executable(hello hello.c)
aDd_ExEcUtAbLe(blub blub.c)

But this would be ugly.

In KDE the all-lowercase style is preferred. The all-uppercase style is also ok. Mixing upper- and lowercase should not be done in KDE CMake files. Although all-lowercase is preferred, if a file is apparently in all-uppercase style, then stay consistent and also use all-uppercase in this file.

(Not) Using pkg-config

You are free to use pkg-config in FindXXX.cmake modules, as long as the following conditions are met:

• the FindXXX.cmake must also work without pkg-config, as long as the package is either installed to one of the default locations (as /usr or /usr/local) or if CMAKE_PREFIX_PATH is set accordingly
• use only FIND_PACKAGE(PkgConfig), don't use INCLUDE(UsePkgConfig), this one is deprecated
• make sure the variables created by PKG_CHECK_MODULES() are all prefixed with "PC_", so they don't mix up with other variables, e.g. set via FIND_PATH() etc.
• FindLibXml2.cmake as shipped with CMake 2.8.5 is a good example how pkg-config should be handled
• putting something like if(NOT WIN32) around the pkg-config stuff is not necessary (and should be removed if it is somewhere). If pkg-config is not found, e.g. on Windows, the macros simply do nothing.

Writing CMake Find-modules

• Follow the style guide from CMake when writing some FindFoo.cmake module:

readme.txt

• For checking the results inside the Find-module, the macro find_package_handle_standard_args() (coming with CMake) should be used, using the new extended syntax, which supports also version checking.

• Micro-optimizations like

if(FOO_LIBRARY AND FOO_INCLUDE_DIR)
  set(FOO_FOUND TRUE)
else()
  ... execute the whole find-logic
endif()

should be removed, the find-logic should be executed always. These shortcuts can cause problems e.g. when the same file is used from multiple directories but e.g. with different required versions or components etc.