从CMake创建Python虚拟环境后find_program查找Conan失败问题排查

我们在CMake中调用Conan等Python包，Python 3.12强制要求使用虚拟环境。参考相关内容实现了虚拟环境内的依赖安装，但find_program无法找到Conan，执行后报错：Could not find CONAN_CMD using the following names: conan。以下是对应的CMake代码：

macro(create_venv)
  find_package(Python3 3.9 REQUIRED COMPONENTS Interpreter Development)
  set(SYSTEM_PYTHON_EXE_PATH ${Python3_EXECUTABLE})
  message(STATUS "+++++++++++++++++  Found system python located at ${SYSTEM_PYTHON_EXE_PATH}++++++++++++++++")
  execute_process(COMMAND "${Python3_EXECUTABLE}" -m venv "${PROJECT_BINARY_DIR}/venv" --upgrade-deps COMMAND_ERROR_IS_FATAL ANY)

  # 模拟activate脚本设置VIRTUAL_ENV变量
  set(VENV_PATH "${PROJECT_BINARY_DIR}/venv")
  set(ENV{VIRTUAL_ENV} "${VENV_PATH}")

  #[[
  启用此行会强制Conan使用虚拟环境缓存的包（新创建时为空），
  意味着每次清理CMake缓存都要重新编译/下载第三方依赖，会增加配置时间
  调试Conan配置时可以打开此行，避免影响本地构建
  ]]
  # set (ENV{CONAN_USER_HOME} "${PROJECT_BINARY_DIR}/conan")
  set(Python3_FIND_VIRTUALENV FIRST)
  unset(Python3_EXECUTABLE)
  # 重新查找虚拟环境中的Python
  find_package(Python3 3.9 REQUIRED COMPONENTS Interpreter Development)
  message(STATUS "+++++++++++++++++  Found venv python located at ${Python3_EXECUTABLE}++++++++++++++++")
  if(SYSTEM_PYTHON_EXE_PATH STREQUAL Python3_EXECUTABLE)
    message(FATAL_ERROR "Python3 executable is the same as the system one, this is not expected")
  endif()

  message(STATUS "Trying to install deps")
  execute_process(
    COMMAND "${Python3_EXECUTABLE}" -m pip install -r "${TOOLBOX_SOURCE_DIR}/python3/requirements_win32.txt" COMMAND_ERROR_IS_FATAL ANY
  )

  find_program(CONAN_CMD conan REQUIRED)
  if(NOT CONAN_CMD)
    message(FATAL_ERROR "Conan executable not found! Please install conan.")
  endif()

endmacro()

核心问题是CMake的PATH环境变量未包含虚拟环境的可执行文件目录，find_program依赖PATH查找工具，刚安装在虚拟环境里的conan不在搜索路径中，所以找不到。

具体修改步骤：

1. 根据操作系统确定虚拟环境的可执行文件目录：
   • Linux/macOS：虚拟环境下的bin目录
   • Windows：虚拟环境下的Scripts目录
2. 将该目录添加到PATH最前端，确保CMake优先查找虚拟环境内的工具。

修改后的关键代码如下，插入到pip install之后、find_program之前：

# 确定虚拟环境的可执行文件目录
if(WIN32)
  set(VENV_BIN_DIR "${VENV_PATH}/Scripts")
else()
  set(VENV_BIN_DIR "${VENV_PATH}/bin")
endif()

# 更新PATH环境变量，优先使用虚拟环境内的工具
if(WIN32)
  set(ENV{PATH} "${VENV_BIN_DIR};$ENV{PATH}")
else()
  set(ENV{PATH} "${VENV_BIN_DIR}:$ENV{PATH}")
endif()

# 现在查找Conan就能定位到虚拟环境里的版本了
find_program(CONAN_CMD conan REQUIRED)

额外提一句：你代码里定义了REQUIREMENTS_ARG变量但没实际使用，不过这和当前问题无关。

内容的提问来源于stack exchange，提问作者JuliusCaesar