c++ - CMake:默认情况下如何使 add_custom_command 输出保持最新？

Question

我有一个基于 CMake 3.11.4 和 Python 3.7 的软件环境。

我的库/程序有一个 config.txt以我指定的格式描述它们的依赖关系的文件。然后，我有一个 Python 脚本( scripts/configure.py )生成 CMakeLists.txt即时调用 CMake 以生成可由 Visual Studio 2015 构建的解决方案。

我希望 Python 在 config.txt 时自动再次运行由用户编辑。

所以我让我的 Python 脚本在生成的 CMakeLists.txt 中添加了一个自定义命令语句.以下是名为“myproject”的项目的外观，其中包括两个库“lib1”和“lib2”。
${SDE_ROOT_DIR}/build/myproject/CMakeLists.txt包含:

# Automatically re-run configure project when an input file changes:
set( PROJECT_DEPENDENCIES )
list( APPEND PROJECT_DEPENDENCIES "${SDE_ROOT_DIR}/lib/lib1/config.txt" )
list( APPEND PROJECT_DEPENDENCIES "${SDE_ROOT_DIR}/lib/lib2/config.txt" )
ADD_CUSTOM_COMMAND( OUTPUT ${SDE_ROOT_DIR}/build/myproject/CMakeLists.txt COMMAND tools/python/Python370/python.exe scripts/configure.py myproject WORKING_DIRECTORY ${SDE_ROOT_DIR} DEPENDS ${PROJECT_DEPENDENCIES} )

这是我所做的:

我运行我的脚本( scripts/configure.py myproject )以获得 CMakeLists.txt以及生成的 Visual Studio 解决方案。

然后我打开解决方案

我第一次构建时，它报告Generating CMakeLists.txt我看到我的脚本 scripts/configure.py被调用。 这不是预期的!

我第二次构建时，什么也没有发生。还行吧。

如果我编辑 config.txt , 下次构建时看到 Generating CMakeLists.txt我看到我的脚本 scripts/configure.py被调用。那挺好的。

除了第一次编译项目时我的脚本运行之外，这几乎是我的预期。如 CMakeLists.txt刚刚生成，绝对比 config.txt 新，我不明白为什么它需要生成 CMakeLists.txt再次。

知道我可能做错了什么吗？是否有任何额外的命令我应该添加到 CMakeLists.txt使这个自定义命令的输出默认为“最新”？

这是一个 MCVE( config.txt 被替换为 prgname.txt ):
prg/main.cpp :

#include <iostream>

int main( int argc, char* argv[] )
{
    std::cout << "Hello World!" << std::endl;
    return 0;
}

prg/prgname.txt :

myprogram

scripts/configure.py :

import sys
import subprocess
import argparse
import os
from contextlib import contextmanager

@contextmanager
def pushd(newDir):
    previousDir = os.getcwd()
    os.chdir(newDir)
    yield
    os.chdir(previousDir)

def configure_project():

    # check configuration args
    parser = argparse.ArgumentParser(description="CMakeLists generator.")
    parser.add_argument('project',  metavar='project', type=str, help='project name')
    args = parser.parse_args()

    working_directory = os.getcwd()

    project = args.project

    buildfolder = os.path.normpath(os.path.join( os.path.dirname(os.path.abspath(__file__)), os.pardir, "build", project ))

    if not os.path.isdir(buildfolder):
        os.makedirs(buildfolder)

    prgsourcefolder = os.path.normpath(os.path.join( os.path.dirname(os.path.abspath(__file__)), os.pardir, "prg" ))
    prgbuildfolder = os.path.join( buildfolder, "prg" )
    if not os.path.isdir(prgbuildfolder):
        os.makedirs(prgbuildfolder)

    prgnamepath = os.path.join( prgsourcefolder, "prgname.txt" )
    with open( prgnamepath, "r" ) as prgnamefile:
        prgname = prgnamefile.read()

    with open( os.path.join( prgbuildfolder, "CMakeLists.txt" ), "w" ) as cmakelists:
        cmakelists.write( "add_executable(" + prgname + " " + os.path.join(prgsourcefolder,"main.cpp").replace("\\","/") + ")\n" )

    cmakelistspath = os.path.join( buildfolder, "CMakeLists.txt" )
    with open( cmakelistspath, "w" ) as maincmakelists:
        maincmakelists.write( "cmake_minimum_required(VERSION 3.11)\n" )
        maincmakelists.write( "project(" + project + ")\n" )
        maincmakelists.write( "add_subdirectory(prg)\n" )

        maincmakelists.write( "add_custom_command( OUTPUT " + cmakelistspath.replace("\\","/") + " COMMAND python " + " ".join( [ x.replace("\\","/") for x in sys.argv] ) + " WORKING_DIRECTORY " + working_directory.replace("\\","/") + " DEPENDS " + prgnamepath.replace("\\","/") + ")\n" )

    # Run CMake:
    with pushd( buildfolder ):
        cmd = ['cmake.exe', '-G', 'Visual Studio 14 2015 Win64', buildfolder]
        proc = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
        while True:
            out = proc.stdout.read(1)
            if proc.poll() != None:
                break   
            sys.stdout.write(out.decode())
            sys.stdout.flush()
        proc.wait()

if __name__ == "__main__":
    import sys
    sys.exit( configure_project() )

将 CMake 和 Python 添加到您的 PATH

从脚本文件夹运行 python configure.py myproject

开通 build/myproject/myproject.sln

点击“全部编译”，你会看到意想不到的消息 Generating CMakeLists.txt在日志中

Answer 1

这是一个“解决方法”，而不是“解决方案”。

我只是添加一个状态文件来告诉何时应该跳过从 VS 调用的 generate ，因为我知道解决方案是最新的:

向解析器添加新参数:

parser.add_argument('--from_vs', action='store_true', help='identify that configure is ran from VS to prevent useless regeneration, don't set this manually please')

从脚本本身正确维护此文件:

vs_force_up_to_date_file = os.path.join( buildfolder, "vs_force_up_to_date" )
if args.from_vs:
    is_up_to_date = False

    if os.path.isfile( vs_force_up_to_date_file ):
        with open( vs_force_up_to_date_file, "r" ) as file:
            content = file.readlines()[0]
            is_up_to_date = ( content == "True" )

    if is_up_to_date:
        # It's the first time VS runs this script, we know it is up-to-date, so let's not regenerate
        # See https://stackoverflow.com/questions/59861101/cmake-how-can-i-make-add-custom-command-output-up-to-date-by-default
        print( "First time calling generate from VS, project is likely up-to-date, let's not reconfigure!" )
        # Make next generate from VS be skipped
        with open( vs_force_up_to_date_file, "w" ) as file:
            file.write( str(False) )
        exit(0)
    else:
        # need to generate, let's continue!
        pass
else:
    # Generating from console, let's make VS believe it is up to date for first time it will generate
    if os.path.isfile( vs_force_up_to_date_file ):
        # Let the file as it is, "True" if VS generate never ran, else False
        pass
    else:
        # Create the file to prevent first VS generate to rerun this script while it does not need to be ran
        with open( vs_force_up_to_date_file, "w" ) as file:
            file.write( str(True) )

从 VS 运行时设置这个新参数:

run_args = " ".join( [ x.replace("\\","/") for x in sys.argv] )
if not args.from_vs:
    run_args += " --from_vs"
maincmakelists.write( "add_custom_command( OUTPUT " + cmakelistspath.replace("\\","/") + " COMMAND python " + run_args + " WORKING_DIRECTORY " + working_directory.replace("\\","/") + " DEPENDS " + prgnamepath.replace("\\","/") + ")\n" )

这使得 VS 无用的调用配置第一次生成请求被跳过和信，所需的调用将按预期工作。

编辑

实际上，这并不像预期的那样有效。因为 VS 每次第一次都会为每个配置运行脚本。因此，在 Release 模式下构建一次后，切换到 Debug 最终将再次生成 CMakeLists.txt 而它不应该因为第一代在 vs_force_up_to_date 文件中写了 False。这是一个太幼稚的解决方案。

相反，我最终采用的解决方案是将所有输入文件 (prgname.txt) 和输出文件 (CMakeLists.txt) 的路径传递给脚本，并让它检查所有输出是否比所有输入更新，跳过生成。然后，无论对脚本 VS 的意外调用可能会做什么，它们都会由脚本本身正确处理。