cmake不会在更改时重建externalProject

Question

我有以下CMakeLists.txt:

cmake_minimum_required( VERSION 3.0)
project(addProject)
include (ExternalProject)

set(ExternalProjectCMakeArgs
  -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}
  -DCMAKE_INSTALL_PREFIX=${PROJECT_BINARY_DIR}/external/genLib
)

ExternalProject_Add(genLib
SOURCE_DIR ${PROJECT_SOURCE_DIR}/external/genLib
BINARY_DIR ${PROJECT_BINARY_DIR}/external/genLib
INSTALL_COMMAND ""
INSTALL_DIR ${PROJECT_BINARY_DIR}/external
CMAKE_ARGS ${ExternalProjectCMakeArgs}
)
add_custom_command( OUTPUT "generated.cpp"
COMMAND ${PROJECT_BINARY_DIR}/external/genLib/genLib "generated.cpp"
WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})

add_executable(add main.cpp ${CMAKE_CURRENT_BINARY_DIR}/generated.cpp)
add_dependencies (add genLib)

第一次构建总是正确的:

mkdir build; cd build; cmake -GNinja ../; ninja

给出以下输出:

-- The C compiler identification is GNU 4.4.7
-- The CXX compiler identification is GNU 4.4.7
-- Check for working C compiler using: Ninja
-- Check for working C compiler using: Ninja -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler using: Ninja
-- Check for working CXX compiler using: Ninja -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: /Devel/scratc/testingExternalProject2/build
41% 5/12@2.7 0: Performing configure step for 'genLib'
-- The C compiler identification is GNU 4.4.7
-- The CXX compiler identification is GNU 4.4.7
-- Check for working C compiler using: Ninja
-- Check for working C compiler using: Ninja -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler using: Ninja
-- Check for working CXX compiler using: Ninja -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: /Devel/scratc/testingExternalProject2/build/external/genLib
50% 6/12@3.0 0: Performing build step for 'genLib'
50% 1/2@? 1: Building CXX object CMakeFiles/genLib.dir/genLib.cpp.o
100% 2/2@40.2 1: Linking CXX executable genLib
100% 12/12@5.6 0: Linking CXX executable add

现在,如果我在外部项目中修改源文件:touch ../external/genLib/genLib.cpp

并重新编译忍者没有任何变化:忍者:没有工作要做.

我用make而不是Ninja测试了它的行为完全相同.我还测试过在我的custom_command中添加DEPENDS子句,该子句适用于单个文件但不适用于整个项目(并且将外部项目的所有源文件添加为DEPENDS子句似乎非常hacky ...)

有没有人有更多使用外部项目的经验,可以解释cmake决定重建或不依赖的行为？

Answer 1

如果您至少可以使用cmake 3.1版,请尝试添加BUILD_ALWAYS 1到您的ExternalProject_Add命令:

ExternalProject_Add(genLib
    SOURCE_DIR ${PROJECT_SOURCE_DIR}/external/genLib
    BINARY_DIR ${PROJECT_BINARY_DIR}/external/genLib
    BUILD_ALWAYS 1
    INSTALL_COMMAND ""
    INSTALL_DIR ${PROJECT_BINARY_DIR}/external
    CMAKE_ARGS ${ExternalProjectCMakeArgs}
)

根据ExternalProject_Add命令的文档

启用此选项会强制始终运行构建步骤.这可以是最有效地确保外部项目自己的构建依赖项得到评估而不是依赖于默认的基于成功时间戳的方法的方法.通常不需要此选项,除非开发人员需要修改外部项目构建所依赖的内容,而这种方式是通过步骤目标依赖项无法检测到的(例如,在没有下载方法的情况下使用SOURCE_DIR,开发人员可能会修改SOURCE_DIR中的源代码).