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

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.

Answer 2

This is a misunderstanding of the CMake documentation. The CMAKE_ARGS is part of the Configure Step options not download or update/patch options of the ExternalProject_Add() and is ignored.
Looking at the documentation for CMake (3.12) [https://cmake.org/cmake/help/v3.12/module/FetchContent.html]
The contentOptions can be any of the download or update/patch
options that the ExternalProject_Add() command understands. The
configure, build, install and test steps are explicitly disabled and
therefore options related to them will be ignored.
To avoid the messages you see you need to invoke cmake as cmake -Wno-dev on the command line when building your project.