fix detecting & using utf8c++ 4.0.0 or newer

[mbunkus]

find_package with version constraint 3.2.0 does not consider 4.x.y to be compatible. Therefore also look for 4.x.y in a secondary find_package call.

The fallback for cloning from git if neither version is found via cmake remains in place.

Furthermore, linking against a distro-provided 4.x.y doesn't seem to work with the existing target_link_libraries(ebml PRIVATE $<BUILD_INTERFACE:utf8cpp>) & requires PRIVATE utf8cpp::utf8cpp. However, that doesn't work with a git-cloned copy; that still requires PRIVATE $<BUILD_INTERFACE:utf8cpp>; so make that argument depend on the package detection, too.

fixes #344 ; see #345

[mbunkus]

Soooooo… it seems my solution doesn't actually work with a distro-packaged 3.x. Interesting. Will have to switch that case back to PRIVATE $<BUILD_INTERFACE:utf8cpp>, too? Maaaaan I just have no clue about cmake… 😂

[mbunkus]

Alright, 67a2dbb works fine on:

• Ubuntu 24.04 with distro-packaged 3.2.x
• Ubuntu 26.04 with distro-packaged 4.0.x
• Ubuntu 26.04 without distro-packaged, cloning from git

…and the checks agree.

@marillat & @ReillyBrogan I'd appreciate some testing on your end, too. Thanks a lot!

[mbunkus]

While we're at it we could also bump the version we get from git in case of "no distro-packaged found" to 4.0.x & use PRIVATE utf8cpp::utf8cpp there, too. Thoughts?

[marillat]

Build fine for me, but with a cmake warning:

CMake Warning at CMakeLists.txt:52 (find_package):
  Could not find a configuration file for package "utf8cpp" that is
  compatible with requested version "3.2.0".

  The following configuration files were considered but not accepted:

    /usr/share/cmake/utf8cpp/utf8cppConfig.cmake, version: 4.1.0
      The version found is not compatible with the version requested.

[robUx4]

Build fine for me, but with a cmake warning:

There is a QUIET parameter that could be used, in both calls. In the end we show in the summary what we are using (system or internal).

[robUx4]

OK for me. We need the same in the master branch.

[robUx4]

After rebasing on v1.x we should see in the CI that the 4.x.x version is properly picked.

[ReillyBrogan]

Build fine for me, but with a cmake warning:

There is a QUIET parameter that could be used, in both calls. In the end we show in the summary what we are using (system or internal).

Speaking as a packager I usually check the cmake output to see what new dependencies I may need to add to the build recipe. So at least one of them should continue to be not-QUIET so it's noticeable in the output.

But honestly looking at repology utf8cpp >= 4.0 is already very widespread in the various distribution repos. It's in the latest stable Debian, the latest LTS Ubuntu, all supported Fedora releases, etc. Given that libebml appears to compile and work with it just fine why not just require 4.0 unconditionally? If a user is on a distribution that doesn't have it they can just enable networking so that fetch_content can pull down a 4.0 release.

Another approach that could be used here is to use alias targets instead.

Something like this:

if(NOT utf8cpp_FOUND)
  include(FetchContent REQUIRED)
  FetchContent_Declare(
        utf8cpp
        GIT_REPOSITORY https://github.com/nemtrif/utfcpp.git
        GIT_TAG v3.2.5
        GIT_PROGRESS TRUE
        DOWNLOAD_EXTRACT_TIMESTAMP ON
        OVERRIDE_FIND_PACKAGE
    )
    FetchContent_MakeAvailable(utf8cpp)
    add_library(utf8cpp::utf8cpp ALIAS utf8cpp)
endif()

...

target_link_libraries(ebml PRIVATE utf8cpp::utf8cpp)

(note that I'm not sure what target the fetch_content for utf8cpp actually exports so that might need to be adjusted).

Then if utf8cpp is ever referenced anywhere else in cmake you can just use utf8cpp::utf8cpp and it will use the system or vendored version correctly.

[mbunkus]

Thank y'all very much for your feedback. I've taken it into account & produced a new version that

a) gets rid of the version requirement altogether and
b) makes then link thingy to use depend on the availability of the utf8cpp::utf8cpp target instead of the version number/git clone status.

As for the version requirement: I had investigated using QUIET, but I wasn't a fan. Yes, it gets rid of the warnings, but I concur with @ReillyBrogan that having some kind of warning if neither is found is definitely required. Furthermore, QUIET also gets rid of the message that cmake is using the package if it is found, which I also disliked.

Therefore I opt not to restrict the version number at all. At the moment all known-deployed versions work just fine, and I say that we just deal with the bug reports of something breaking with utf8cpp 5.whatever when those come in.

Furthermore, there are two cases wrt. the target to use:

• version ≥ 4 which requires utf8cpp::utf8cpp and
• version < 4 (either distro-packaged or from git as we check out a specific version < 4) which requires the existing one

Given that version ≥ 4 is the future, we can simply check if the target utf8cpp::utf8cpp is known to cmake with if(TARGET utf8cpp::utf8cpp) & use that if so, otherwise the old one.

…and while I write this I realize I could've simply moved that check to the location of target_link_libraries(), duplicated that call in the two branches & not used a variable. Might have been nicer.

As before I've verified this to be working on:

• Ubuntu 26.04 with distro-packaged 4.0.x
• Ubuntu 24.04 with distro-packaged 3.2.y
• Ubuntu 26.04 without distro-packaged, meaning git-cloned

In the meantime @robUx4 has also added some more checks which now test for some of the same combinations, too.

Again I'd appreciate some feedback before I merge this (and do the same for the master branch — I will do that once we've settled on a specific implementation).

[mbunkus]

Oh, BTW, I wasn't able to make the add_library(utf8cpp::utf8cpp ALIAS utf8cpp) call suggested by @ReillyBrogan work with v3.2.something, unfortunately. Most likely due to my lack of cmake knowledge.

[robUx4]

Not a fan of dropping the version check but I guess if that ever happens some distro will find out and reach out to us (but they usually silently patch).

[marillat]

Build fine for me with commit 7cf88e1