I have the following sample project illustrating the issue:
cmake_minimum_required(VERSION 3.16)
project(proj LANGUAGES CXX)
# Allow using response files.
if(APPLE)
set(CMAKE_CXX_ARCHIVE_CREATE "libtool -o <TARGET> <LINK_FLAGS> <OBJECTS>")
endif()
set(cpp_file "${CMAKE_CURRENT_BINARY_DIR}/core.cpp")
file(WRITE "${cpp_file}" "int core() { return 1;}")
set(response_file "${CMAKE_CURRENT_BINARY_DIR}/response_file.rsp")
file(WRITE "${response_file}" "-v")
add_library(foo STATIC "${cpp_file}")
target_sources(foo PRIVATE "${response_file}")
set_target_properties(foo PROPERTIES STATIC_LIBRARY_OPTIONS "@${response_file}")
# Make foo archiving rerun if the response file changes.
# Doesn't work for static libraries, only works for shared library targets.
set_target_properties(foo PROPERTIES LINK_DEPENDS "${response_file}")
I have a static library foo built by cmake, which is supposed to additionally apply the options from an external response file. The response file is generated outside of CMake.
I add the response file to STATIC_LIBRARY_OPTIONS of the target.
With the current project, if i touch the response file, foo is not rebuilt.
If foo were a shared library, I could use the LINK_DEPENDS property to achieve my goal.
Is there a way to model this in CMake with static libraries?
Note I would like a solution that works for any arbitrary file as a dependency (e.g. a timestamp file), not necessarily something that appears on the command line of the archiver invocation or in `STATIC_LIBRARY_OPTIONS`.
Thanks!
The best I could come up with so far is to create an object library with an empty source file, add the response file to its OBJECT_DEPENDS property, and then link the object library into the static library.
set(object_file "${CMAKE_CURRENT_BINARY_DIR}/object.cpp")
file(WRITE "${object_file}" "")
add_library(obj OBJECT "${object_file}")
set_property(SOURCE "${object_file}" PROPERTY OBJECT_DEPENDS "${response_file}")
target_link_libraries(foo PRIVATE $<LINK_ONLY:obj>)
This achieves the rebuilding part, but is suboptimal due to extra needless compilation.