Missing zconf.h when using zlib as a git submodule (with CMake)

[JPGygax68]

I used add_subdirectory() to integrate zlib into my CMake-controlled project. This works well, but there is the problem that git detects a "false update" and constantly asks me to commit a change that I didn't make.

Apparently, something in the build process renames zconf.h to zconf.h.included, so git detects the former as deleted and the latter as new.

Is there a way to work around that, or better yet, fix it ?

[mtl1979]

I think there was a commit in somewhere here that removed the rename from CMakeLists.txt, it did involve adding some includes in the source files... This however doesn't fix the issue that zconf.h gets modified during build process.

[minexew]

I'm running into the same problem, except in my case, the missing zconf.h outright causes a fatal error whenever I try to #include "zlib.h" in my project.

How did you manage to solve this?

[mtl1979]

@minexew add_subdirectory() should automatically add directory containing zlib.h to include path... If it doesn't, you need to make sure cmake is upgraded to latest available and that zlib.h actually exists in directory specified in second parameter of add_subdirectory().

[minexew]

Oh no, zlib.h is just fine. However, one of the first things it does inside is #include "zconf.h". This causes an error, because zconf.h had been renamed to zconf.h.included by CMake.

[mtl1979]

@minexew All cmake-generated files should be inside the binary directory, so it should find them if the second parameter is correctly defined.

[minexew]

I'm starting to understand. Do you have an example of the intended usage when zlib is a submodule?

I'm currently (trying to) do this:

add_subdirectory(dependencies/zlib)
add_dependencies(${PROJECT_NAME} zlibstatic)
target_link_libraries(${PROJECT_NAME} zlibstatic)

[mtl1979]

@minexew Second parameter of add_subdirectory should be something like:

"${CMAKE_CURRENT_BINARY_DIR}/zlib_build"

[minexew]

Ok.

Just wondering, why is it neccessary to add the include paths manually?
E.g. why does zlib's CMake declare
include_directories(${CMAKE_CURRENT_BINARY_DIR} ${CMAKE_SOURCE_DIR})
instead of
target_include_directories(zlib PUBLIC ${CMAKE_CURRENT_BINARY_DIR} ${CMAKE_SOURCE_DIR})?

The latter would automatically propagate include paths whenever somebody does target_link_libraries(... zlib)
Not only would that be more convenient, it would also better encapsulate the library and reduce the amount of "interfaces" (in this case directory paths) that the library user needs to worry about.

[mtl1979]

@minexew target_include_directories() didn't exist in older cmake versions.

[robiwano]

Maybe zconf.h should be added to the .gitignore file so that changes are hidden ?

[robiwano]

Regarding target_include_directories(), since it was available from CMake 3.0 (over 2 years ago) I would think it is safe to require at least CMake 3.0 for zlib now.

[mtl1979]

@robiwano I think it was added in 2.8.11 (see https://cmake.org/cmake/help/v2.8.11/cmake.html#section_Commands), but as zlib is all for backwards support for even oldest operating systems, I doubt @madler will want to require minimum CMake of 2.8.11 or 3.0. Removing zconf.h from git repository and adapting Makefiles for Windows and other non-bash operating systems to copy it from zconf.h.in would solve false update notifications. That's what I did for zlib-ng.

[minexew]

Yeah, in Debian world for example, "2 years ago" is basically "yesterday".
Thanks for mentioning zlib-ng, I didn't know about it and it seems really nice.

[mtl1979]

@minexew Development on zlib-ng has been quite slow for last 13 months because @Dead2 has been busy with other projects, but it does support more (read: better) "recent" architectures than stock zlib. I've been mostly working on the MinGW/MSYS2 support and optimized ARM and Visual C++ code based on what was posted here.

[kymikoloco]

If zlib is not going to use even 2.8.12, then note that you should probably be setting the INTERFACE_INCLUDE_DIRECTORIES property of the zlib target(s). It has no effect unless someone is using CMake 2.8.11 or above, but will allow users of add_subdirectory() and the target name in target_link_libraries to get the interface that zlib requires without having to make manual include directory changes to their own projects.

set_target_properties(zlib PROPERTIES 
    DEFINE_SYMBOL ZLIB_DLL
    SOVERSION 1
+    INTERFACE_INCLUDE_DIRECTORIES "${CMAKE_CURRENT_SOURCE_DIR};${CMAKE_CURRENT_BINARY_DIR}"
)