How to propagate -Wno-dev to cmake using FetchContent_Declare?

Question

I am using the FetchContent feature from CMake (3.12) and declaring it like this:

FetchContent_Declare(libsndfile
      GIT_REPOSITORY    ${LIBSNDFILE_GIT_REPO}
      GIT_TAG           ${LIBSNDFILE_GIT_TAG}
      GIT_CONFIG        advice.detachedHead=false
      SOURCE_DIR        "${CMAKE_BINARY_DIR}/libsndfile"
      BINARY_DIR        "${CMAKE_BINARY_DIR}/libsndfile-build"
      CMAKE_ARGS        "-Wno-dev"
      CONFIGURE_COMMAND ""
      BUILD_COMMAND     ""
      INSTALL_COMMAND   ""
      TEST_COMMAND      ""
      )

According to the CMake documentation:

FetchContent_Declare: The <contentOptions> can be any of the download or update/patch options that the ExternalProject_Add() command understands

And according to the ExternalProject_Add documentation, "The specified arguments are passed to the cmake command line" when using CMAKE_ARGS.

The -Wno-dev option does not seem to be passed along as I continue to see this warning messages in the output:

CMake Warning (dev) at /Volumes/Vault/misc/src/libsndfile/CMakeLists.txt:446 (add_executable):
  Policy CMP0063 is not set: Honor visibility properties for all target
  types.  Run "cmake --help-policy CMP0063" for policy details.  Use the
  cmake_policy command to set the policy and suppress this warning.

  Target "sndfile-interleave" of type "EXECUTABLE" has the following
  visibility properties set for C:

    C_VISIBILITY_PRESET

  For compatibility CMake is not honoring them for this target.
This warning is for project developers.  Use -Wno-dev to suppress it.

I believe I am following the documentation but it seems I must be doing something wrong. Any idea what could be wrong?

Edit: As requested in comment, here is a complete example:

File CMakeLists.txt

cmake_minimum_required(VERSION 3.12)
project(self_contained_libsndfile_example)

set(CMAKE_CXX_STANDARD 14)

# This is in order to trigger the warnings in FetchContent
set(CMAKE_C_VISIBILITY_PRESET hidden)

include(FetchContent)

set(LIBSNDFILE_GIT_REPO "https://github.com/erikd/libsndfile" CACHE STRING "libsndfile git repository url" FORCE)
set(LIBSNDFILE_GIT_TAG b4bd397ca74f4c72b9cabaae66fef0c3d5a8c527 CACHE STRING "libsndfile git tag" FORCE)

FetchContent_Declare(libsndfile
      GIT_REPOSITORY    ${LIBSNDFILE_GIT_REPO}
      GIT_TAG           ${LIBSNDFILE_GIT_TAG}
      GIT_CONFIG        advice.detachedHead=false
      SOURCE_DIR        "${CMAKE_BINARY_DIR}/libsndfile"
      BINARY_DIR        "${CMAKE_BINARY_DIR}/libsndfile-build"
      CMAKE_ARGS        "-Wno-dev"
      CONFIGURE_COMMAND ""
      BUILD_COMMAND     ""
      INSTALL_COMMAND   ""
      TEST_COMMAND      ""
      )

FetchContent_GetProperties(libsndfile)

if(NOT libsndfile_POPULATED)
  FetchContent_Populate(libsndfile)
endif()

set(LIBSNDFILE_ROOT_DIR ${libsndfile_SOURCE_DIR})
set(LIBSNDFILE_INCLUDE_DIR "${libsndfile_BINARY_DIR}/src")
add_subdirectory(${libsndfile_SOURCE_DIR} ${libsndfile_BINARY_DIR} EXCLUDE_FROM_ALL)
file(COPY "${libsndfile_SOURCE_DIR}/src/sndfile.hh" DESTINATION ${LIBSNDFILE_INCLUDE_DIR})

include_directories(${LIBSNDFILE_INCLUDE_DIR})

set(target self_contained_libsndfile_example)

add_executable(${target} main.cpp)
target_link_libraries(${target} PRIVATE sndfile)

Answer 1

With the fix of this CMake-issue, which will go into CMake 3.17, you could point variable CMAKE_PROJECT_sndfile_INCLUDE_BEFORE to a file which sets the CMake-policy CMP0063 appropriately and which will automatically be included before the call to project(sndfile). As a result you won't get this warning for your fetched project.