How to statically link a fetched zlib?

[stumpylog]

In particular to support Windows users of my Python wheel, I want to statically link zlib, which is fetched. (expat is also fetched/linked). But I'm running into some issues with this, which go out of my knowledge of CMake.

A mocked up, minimal example:

cmake_minimum_required(VERSION 3.24)
project(myproject VERSION 0.0.1)

set(BUILD_SHARED_LIBS OFF CACHE BOOL "Build a static library for all libraries" FORCE)

# Some other library configuration here, like disabling Brotli, etc

FetchContent_Declare(
  Zlib
  GIT_REPOSITORY https://github.com/madler/zlib.git
  GIT_TAG v1.3.1
  GIT_SHALLOW TRUE
  OVERRIDE_FIND_PACKAGE)
FetchContent_MakeAvailable(Zlib)
add_library(ZLIB::ZLIB ALIAS zlibstatic)

FetchContent_Declare(
  EXPAT
  GIT_REPOSITORY https://github.com/libexpat/libexpat.git
  GIT_TAG R_2_7_1
  GIT_SHALLOW TRUE
  SOURCE_SUBDIR expat OVERRIDE_FIND_PACKAGE)

FetchContent_MakeAvailable(expat)
add_library(EXPAT::EXPAT ALIAS expat)

FetchContent_Declare(
  exiv2
  GIT_REPOSITORY https://github.com/Exiv2/exiv2.git
  GIT_TAG v0.28.5
  GIT_SHALLOW TRUE)
FetchContent_MakeAvailable(exiv2)

target_link_libraries(mytarget PRIVATE Exiv2::exiv2lib)

If I do not include the add_library with ALIAS:

  Target "exiv2lib" links to:

    EXPAT::EXPAT
  Target "exiv2lib" links to:

    ZLIB::ZLIB

But with those, I get:

CMake Error: install(EXPORT "exiv2Targets" ...) includes target "exiv2lib" which requires target "zlibstatic" that is not in any export set.

I'm not really sure what that is saying or how to resolve it. I would appriciate any help or ideas from those more knowledgeable in CMake.

[clanmills]

@stumpylog I don't know the answer to your question, however I have a question for you!

Does the code in mylibrary reference zlib or expat?

If mylibrary doesn't explicitly use zlib or expat I believe you should only link/add_library Exiv2::exiv2lib.

[stumpylog]

The only target_link_libraries is to Exiv2. The rest was just hacks to get it happy enough to configure and build.

The full, not so trivial file: https://github.com/stumpylog/exifmwg/blob/develop/CMakeLists.txt

[clanmills]

Well done, @stumpylog for digging into this. Your code is very neat and clear. Good Job.

I'm not a CMake expert, however I'm surprised you need so much code in CMakeLists.txt. I wrote instructions about linking code for exiv2 v0.27. I only needed 8 lines in CMakeLists.txt

2.6 Consuming Exiv2 with CMake

When exiv2 is installed, the files required to consume Exiv2 are installed in ${CMAKE_INSTALL_PREFIX}/lib/cmake/exiv2

You can build samples/exifprint.cpp as follows:

$ cd <exiv2dir>
$ mkdir exifprint
$ cd    exifprint
$ cat - > CMakeLists.txt <<EOF
cmake_minimum_required(VERSION 3.8)
project(exifprint VERSION 0.0.1 LANGUAGES CXX)

set(CMAKE_CXX_STANDARD 98)
set(CMAKE_CXX_EXTENSIONS OFF)

find_package(exiv2 REQUIRED CONFIG NAMES exiv2)    # search ${CMAKE_INSTALL_PREFIX}/lib/cmake/exiv2/
add_executable(exifprint ../samples/exifprint.cpp) # compile this
target_link_libraries(exifprint exiv2lib)          # link exiv2lib
EOF
$ cmake .                                          # generate the makefile
$ make                                             # build the code
$ ./exifprint                                      # test your executable
Usage: bin/exifprint [ path | --version | --version-test ]
$

Anyway, you've written some nice code which will be of use to another user. Thanks for your contribution.