CMakeLists实战解读--YouCompleteMe

# 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3.0.0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 )