CMake使用之一

　概述

　　CMake是一个比make更高级的编译配置工具，它可以根据不同平台、不同的编译器，生成相应的Makefile或者vcproj项目。　　
　　通过编写CMakeLists.txt，可以控制生成的Makefile，从而控制编译过程。CMake自动生成的Makefile不仅可以通过make命令构建项目生成目标文件，还支持安装（make install）、测试安装的程序是否能正确执行（make test，或者ctest）、生成当前平台的安装包（make package）、生成源码包（make package_source）、产生Dashboard显示数据并上传等高级功能，只要在CMakeLists.txt中简单配置，就可以完成很多复杂的功能，包括写测试用例。

　　如果有嵌套目录，子目录下可以有自己的CMakeLists.txt。

　　总之，CMake是一个非常强大的编译自动配置工具，支持各种平台，KDE也是用它编译的，

 # CMake要求的最低版本号
 cmake_minimum_required( VERSION 2.8 )

 # 项目名称
 project( ycm_support_libs )
 # 设置客户端lib和服务端lib的变量名称
 set( CLIENT_LIB "ycm_client_support" )
 set( SERVER_LIB "ycm_core" )

 # 设置Python的版本号变量
 set( Python_ADDITIONAL_VERSIONS 2.7 2.6 )
 # 进行Python包的查找，这里是REQUIRED表示必须
 find_package( PythonLibs 2.6 REQUIRED )

 # 如果Python版本号低于3..0就进行FATAL_ERROR的出错信息
 if ( NOT PYTHONLIBS_VERSION_STRING VERSION_LESS "3.0.0" )
   message( FATAL_ERROR
     "CMake found python3 libs instead of python2 libs. YCM works only with "
     "python2.\n" )
 endif()

 # 各种option
 option( USE_DEV_FLAGS "Use compilation flags meant for YCM developers" OFF )
 # 这个变量就是我上文讲到的很关键的一个变量，来判断当前用户需要不需要libclang
 option( USE_CLANG_COMPLETER "Use Clang semantic completer for C/C++/ObjC" OFF )
 # install.sh中的--system-libclang就与这个变量进行交互
 option( USE_SYSTEM_LIBCLANG "Set to ON to use the system libclang library" OFF )
 # YCM作者推荐的用法，在这里直接写入Clang的相关路径 注意这里的CACHE PATH,表示当用户如果命令行
 # 进行指定，那优先会去读用户的命令行，而不是用这里的set,并且把相关的值写入Cache中
 set( PATH_TO_LLVM_ROOT "" CACHE PATH "Path to the root of a LLVM+Clang binary distribution" )
 # YCM作者推荐的另外一种安装方法，直接将libclang.so全路径写死
 set( EXTERNAL_LIBCLANG_PATH "" CACHE PATH "Path to the libclang library to use" )

 # 如果你使用libclang但是没有指定用不用系统的libclang,没有指定llvm_root,没有指定额外的libclang.so，那么就会带你去下载
 if ( USE_CLANG_COMPLETER AND
      NOT USE_SYSTEM_LIBCLANG AND
      NOT PATH_TO_LLVM_ROOT AND
      NOT EXTERNAL_LIBCLANG_PATH )
   message( "Downloading Clang 3.4" )

   # 这就是llvm官网的3.4下载路径
   set( CLANG_URL "http://llvm.org/releases/3.4" )

   # 如果当前客户端是苹果 Mac OS X
   if ( APPLE )
       # 设置Clang的文件夹名称
     set( CLANG_DIRNAME "clang+llvm-3.4-x86_64-apple-darwin10.9" )
       # 设置Clang的MD5校验码
     set( CLANG_MD5 "4f43ea0e87090ae5e7bec12373ca4927" )
       # 设置Clang文件名称为之后加上tar.gz
     set( CLANG_FILENAME "${CLANG_DIRNAME}.tar.gz" )
   else()
       # 如果是64位平台
     if ( 64_BIT_PLATFORM )
       # 设置Clang的文件夹名称
       set( CLANG_DIRNAME "clang+llvm-3.4-x86_64-unknown-ubuntu12.04" )
       # 设置Clang的MD5校验码
       set( CLANG_MD5 "6077459d20a7ff412eefc6ce3b9f5c85" )
       # 设置Clang文件名称为之后加上tar.gz
       set( CLANG_FILENAME "${CLANG_DIRNAME}.tar.xz" )
     else()
       # 表示此时为32位的Linux，下载3.3版本
       message( "No pre-built Clang 3.4 binaries for 32 bit linux, "
                "downloading Clang 3.3" )
       set( CLANG_URL "http://llvm.org/releases/3.3" )
       # 设置Clang的文件夹名称
       set( CLANG_DIRNAME "clang+llvm-3.3-i386-debian6" )
       # 设置Clang的MD5校验码
       set( CLANG_MD5 "415d033b60659433d4631df894673802" )
       # 设置Clang文件名称为之后加上tar.gz
       set( CLANG_FILENAME "${CLANG_DIRNAME}.tar.bz2" )
     endif()
   endif()

       # 下载命令
   file(
     DOWNLOAD "${CLANG_URL}/${CLANG_FILENAME}" "./${CLANG_FILENAME}"
     SHOW_PROGRESS EXPECTED_MD5 "${CLANG_MD5}"
   )

   # 文件名正则表达式匹配,进行相应的解压
   if ( CLANG_FILENAME MATCHES ".+bz2" )
       # 执行相关的外部命令 tar
     execute_process( COMMAND tar -xjf ${CLANG_FILENAME} )
   elseif( CLANG_FILENAME MATCHES ".+xz" )
     execute_process( COMMAND tar -xJf ${CLANG_FILENAME} )
   else()
     execute_process( COMMAND tar -xzf ${CLANG_FILENAME} )
   endif()

   # 设置PATH_TO_LLVM_ROOT的路径为当前CMake二进制路径下的Clang目录
   set( PATH_TO_LLVM_ROOT "${CMAKE_CURRENT_BINARY_DIR}/../${CLANG_DIRNAME}" )
 endif()

 # 如果设置了PATH_TO_LLVM_ROOT或者用户使用系统libclang或者有额外的libclang，就开启USE_CLANG_COMPLETER
 # 这个变量我上文提过，很关键
 if ( PATH_TO_LLVM_ROOT OR USE_SYSTEM_LIBCLANG OR EXTERNAL_LIBCLANG_PATH )
   set( USE_CLANG_COMPLETER TRUE )
 endif()

 # 开始使用这个变量，如果用户确定使用libclang,但是没有root没有系统clang没有额外clang,那么
 # 进行错误性提示
 if ( USE_CLANG_COMPLETER AND
      NOT PATH_TO_LLVM_ROOT AND
      NOT USE_SYSTEM_LIBCLANG AND
      NOT EXTERNAL_LIBCLANG_PATH )
   message( FATAL_ERROR
     "You have not specified which libclang to use. You have several options:\n"
     " 1. Set PATH_TO_LLVM_ROOT to a path to the root of a LLVM+Clang binary "
     "distribution. You can download such a binary distro from llvm.org. This "
     "is the recommended approach.\n"
     " 2. Set USE_SYSTEM_LIBCLANG to ON; this makes YCM search for the system "
     "version of libclang.\n"
     " 3. Set EXTERNAL_LIBCLANG_PATH to a path to whatever "
     "libclang.[so|dylib|dll] you wish to use.\n"
     "You HAVE to pick one option. See the docs for more information.")
 endif()

 # 进行用户提醒，提醒用户当前是否使用libclang
 if ( USE_CLANG_COMPLETER )
   message( "Using libclang to provide semantic completion for C/C++/ObjC" )
 else()
   message( "NOT using libclang, no semantic completion for C/C++/ObjC will be "
            "available" )
 endif()

 # 如果设置了root就设置CLANG_INCLUDES_DIR为root下的include
 # 否则CLANG_INCLUDES_DIR为CMake下llvm/include
 if ( PATH_TO_LLVM_ROOT )
   set( CLANG_INCLUDES_DIR "${PATH_TO_LLVM_ROOT}/include" )
 else()
   set( CLANG_INCLUDES_DIR "${CMAKE_SOURCE_DIR}/llvm/include" )
 endif()

 # 如果当前的include路径不是绝对路径
 if ( NOT IS_ABSOLUTE "${CLANG_INCLUDES_DIR}" )
     # 设置它为绝对路径
   get_filename_component(CLANG_INCLUDES_DIR
     "${CMAKE_BINARY_DIR}/${CLANG_INCLUDES_DIR}" ABSOLUTE)
 endif()

 # 如果没有额外的libclang,但是有root
 if ( NOT EXTERNAL_LIBCLANG_PATH AND PATH_TO_LLVM_ROOT )
     if ( MINGW ) # 如果是MINGW
         # 设置libclang的寻找路径(后面的find_library会去寻找)
     set( LIBCLANG_SEARCH_PATH "${PATH_TO_LLVM_ROOT}/bin" )
   else()
     set( LIBCLANG_SEARCH_PATH "${PATH_TO_LLVM_ROOT}/lib" )
   endif()

   # 这里TEMP会被find_library去寻找clang,和libclang两个so,并且复制路径给TEMP
   find_library( TEMP NAMES clang libclang
                 PATHS ${LIBCLANG_SEARCH_PATH}
                 NO_DEFAULT_PATH )

             message("temp is ${TEMP}")
             # 设置额外的libclang为这个路径
   set( EXTERNAL_LIBCLANG_PATH ${TEMP} )
 endif()

  # 如果当前为苹果，设置额外的flag
 if ( APPLE )
   set( CMAKE_INCLUDE_SYSTEM_FLAG_CXX "-isystem " )
 endif()

 # 如果用户使用系统自带的boost
 if ( USE_SYSTEM_BOOST )
     # 进行find boost命令，会用到python,filesystem,system,regex,thread等components
   find_package( Boost REQUIRED COMPONENTS python filesystem system regex thread )
 else()
     # 使用自己的Boost
   set( Boost_INCLUDE_DIR ${BoostParts_SOURCE_DIR} )
   set( Boost_LIBRARIES BoostParts )
 endif()

  # 相关头文件的加入，Boost,Python和Clang
 include_directories(
   SYSTEM
   ${Boost_INCLUDE_DIR}
   ${PYTHON_INCLUDE_DIRS}
   ${CLANG_INCLUDES_DIR}
   )

 # 全局递归查找h,cpp文件给SERVER_SOURCES
 file( GLOB_RECURSE SERVER_SOURCES *.h *.cpp )

 # 全局递归查找测试相关文件
 file( GLOB_RECURSE to_remove tests/*.h tests/*.cpp CMakeFiles/*.cpp *client* )

 if( to_remove )
     # 学习list相关的REMOVE_ITEM命令
   list( REMOVE_ITEM SERVER_SOURCES ${to_remove} )
 endif()

 # 这里就是这个变量最关键的地方，它会去include并且开启宏
 if ( USE_CLANG_COMPLETER )
   include_directories(
     ${CMAKE_CURRENT_SOURCE_DIR}
     "${CMAKE_CURRENT_SOURCE_DIR}/ClangCompleter" )
   add_definitions( -DUSE_CLANG_COMPLETER )
 else()
     # 否则的话寻找所有ClangCompleter下的头和源文件进行删除
   file( GLOB_RECURSE to_remove_clang ClangCompleter/*.h ClangCompleter/*.cpp )

   if( to_remove_clang )
     list( REMOVE_ITEM SERVER_SOURCES ${to_remove_clang} )
   endif()
 endif()

 # 如果用户使用额外的libclang或者使用系统自带的libclang
 if ( EXTERNAL_LIBCLANG_PATH OR USE_SYSTEM_LIBCLANG )
   if ( USE_SYSTEM_LIBCLANG ) # 如果是系统自带
     if ( APPLE )
         set( ENV_LIB_PATHS ENV DYLD_LIBRARY_PATH ) # 将环境变量下的DYLD_LIBRARY_PATH给ENV_LIB_PATHS
     elseif ( UNIX )
       set( ENV_LIB_PATHS ENV LD_LIBRARY_PATH ) # 这也是我之前讲的一定要把你编译的libclang加入到这个环境变量中，因为它会根据这个去寻找
   elseif ( WIN32 )
       set( ENV_LIB_PATHS ENV PATH )
     else ()
       set( ENV_LIB_PATHS "" )
     endif()
     file( GLOB SYS_LLVM_PATHS "/usr/lib/llvm*/lib" )

     # 进行相关的libclang查找，在你之前给它指定的环境变量中
     find_library( TEMP clang
                   PATHS
                   ${ENV_LIB_PATHS}
                   /usr/lib
                   /usr/lib/llvm
                   ${SYS_LLVM_PATHS}
                   /Library/Developer/CommandLineTools/usr/lib,
                   /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib )
               # 将寻找到的变量给EXTERNAL_LIBCLANG_PATH
     set( EXTERNAL_LIBCLANG_PATH ${TEMP} )
   else()
     if ( NOT APPLE )
       # 设置相关rpath
       set( CMAKE_BUILD_WITH_INSTALL_RPATH TRUE )
       # 设置make install之后的rpath
       set( CMAKE_INSTALL_RPATH "\$ORIGIN" )
     endif()
   endif()

   set( LIBCLANG_TARGET "" )
   message(
     "Using external libclang: ${EXTERNAL_LIBCLANG_PATH}" )
 message("libclang_target is ${LIBCLANG_TARGET}")
 else()
   set( LIBCLANG_TARGET )
 endif()

 # 如果有额外的rpath,在这里进行设置
 if ( EXTRA_RPATH )
   set( CMAKE_INSTALL_RPATH "${EXTRA_RPATH}:${CMAKE_INSTALL_RPATH}" )
 endif()

 # 如果在Linux下需要额外的rt库
 if ( UNIX AND NOT APPLE )
   set( EXTRA_LIBS rt )
 endif()

 # 将目录下所有的h和cpp给CLIENT_SOURCES
 file( GLOB CLIENT_SOURCES *.h *.cpp )
 # 相应SERVER_SPECIFIC赋值
 file( GLOB SERVER_SPECIFIC *ycm_core* )

 if( SERVER_SPECIFIC )
     # 移除相关CLIEN_SOURCES下的SERVER_SPECIFIC
   list( REMOVE_ITEM CLIENT_SOURCES ${SERVER_SPECIFIC} )
 endif()

 # 创建client的library，并且是动态库
 add_library( ${CLIENT_LIB} SHARED
              ${CLIENT_SOURCES}
            )

        # 将这个库与之前的rt,Boost,Python进行链接
 target_link_libraries( ${CLIENT_LIB}
                        ${Boost_LIBRARIES}
                        ${PYTHON_LIBRARIES}
                        ${EXTRA_LIBS}
                      )

 # 创建server的library，并且是动态库
 add_library( ${SERVER_LIB} SHARED
              ${SERVER_SOURCES}
            )

        # 将这个库与之前的rt,Boost,Python,libclang,而外的server lib进行链接
 target_link_libraries( ${SERVER_LIB}
                        ${Boost_LIBRARIES}
                        ${PYTHON_LIBRARIES}
                        ${LIBCLANG_TARGET}
                        ${EXTRA_LIBS}
                      )

 # 如果定义了LIBCLANG_TARGET
 if( LIBCLANG_TARGET )
   if( NOT WIN32 )
       # 在非WIN32情况下增加自定义命令,将libclang.so/dll拷贝到自己目录下
     add_custom_command(
       TARGET ${SERVER_LIB}
       POST_BUILD
       COMMAND ${CMAKE_COMMAND} -E copy "${LIBCLANG_TARGET}" "$<TARGET_FILE_DIR:${SERVER_LIB}>"
     )
   else()
     add_custom_command(
       TARGET ${SERVER_LIB}
       POST_BUILD
       COMMAND ${CMAKE_COMMAND} -E copy "${PATH_TO_LLVM_ROOT}/bin/libclang.dll" "$<TARGET_FILE_DIR:${SERVER_LIB}>")
   endif()
 endif()

 # 建立依赖关系，表示这个项目需要这两个库共同完成
 add_custom_target( ${PROJECT_NAME}
                    DEPENDS ${CLIENT_LIB} ${SERVER_LIB} )

 # Mac下的相关设置，如果是利用rpath的话Mac下还是会去寻找系统库，即使用户显示指定
 # 这里需要改用@loader_path
 if ( EXTERNAL_LIBCLANG_PATH AND APPLE )
   add_custom_command( TARGET ${SERVER_LIB}
                       POST_BUILD
                       COMMAND install_name_tool
                       "-change"
                       "@rpath/libclang.dylib"
                       "@loader_path/libclang.dylib"
                       "$<TARGET_FILE:${SERVER_LIB}>"
                     )
 endif()

 # 将这些库的前缀lib去掉，因为会扰乱Python模块的查找
 set_target_properties( ${CLIENT_LIB} PROPERTIES PREFIX "")
 set_target_properties( ${SERVER_LIB} PROPERTIES PREFIX "")

 if ( WIN32 OR CYGWIN )
     # 进行Windows下相关库的转移存放
   set_target_properties( ${CLIENT_LIB} PROPERTIES
     RUNTIME_OUTPUT_DIRECTORY ${PROJECT_SOURCE_DIR}/../.. )
   set_target_properties( ${SERVER_LIB} PROPERTIES
     RUNTIME_OUTPUT_DIRECTORY ${PROJECT_SOURCE_DIR}/../.. )
   foreach( OUTPUTCONFIG ${CMAKE_CONFIGURATION_TYPES} )
     string( TOUPPER ${OUTPUTCONFIG} OUTPUTCONFIG )
     set_target_properties( ${CLIENT_LIB} PROPERTIES
       RUNTIME_OUTPUT_DIRECTORY_${OUTPUTCONFIG} ${PROJECT_SOURCE_DIR}/../.. )
     set_target_properties( ${SERVER_LIB} PROPERTIES
       RUNTIME_OUTPUT_DIRECTORY_${OUTPUTCONFIG} ${PROJECT_SOURCE_DIR}/../.. )
   endforeach()

   if ( WIN32 )
     # 建立后缀名.pyd
     set_target_properties( ${CLIENT_LIB} PROPERTIES SUFFIX ".pyd")
     set_target_properties( ${SERVER_LIB} PROPERTIES SUFFIX ".pyd")
   elseif ( CYGWIN )
     # CYGIN下后缀为dll
     set_target_properties( ${CLIENT_LIB} PROPERTIES SUFFIX ".dll")
     set_target_properties( ${SERVER_LIB} PROPERTIES SUFFIX ".dll")
   endif()
 else()
   # Mac和Linux下都为.so,虽然Mac下应该默认为.dylib,但Python识别不了dylib,因此这里还是设置成.so
   set_target_properties( ${CLIENT_LIB} PROPERTIES SUFFIX ".so")
   set_target_properties( ${SERVER_LIB} PROPERTIES SUFFIX ".so")
 endif()

  # 设置相关lib的输出目录
 set_target_properties( ${CLIENT_LIB} PROPERTIES
   LIBRARY_OUTPUT_DIRECTORY ${PROJECT_SOURCE_DIR}/../.. )
 set_target_properties( ${SERVER_LIB} PROPERTIES
   LIBRARY_OUTPUT_DIRECTORY ${PROJECT_SOURCE_DIR}/../.. )

 if ( USE_DEV_FLAGS AND ( CMAKE_COMPILER_IS_GNUCXX OR COMPILER_IS_CLANG ) AND
      NOT CMAKE_GENERATOR_IS_XCODE )
   # 增加相应flag
   set( CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra -Werror" )
 endif()

 # 提出警告在使用C++11特性下
 if ( USE_DEV_FLAGS AND COMPILER_IS_CLANG AND NOT CMAKE_GENERATOR_IS_XCODE AND
      NOT SYSTEM_IS_FREEBSD )
   set( CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wc++98-compat" )
 endif()

 if( SYSTEM_IS_SUNOS )
     # SunOS需要-pthreads这个flag才能正常使用
   set( CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -pthreads" )
 endif()

 # 增加测试子目录tests
 add_subdirectory( tests )