Add the Imported Target ZLIB::ZLIB for CMake.

[hwhsu1231]

It is related to the pull request of the old repository: madler/zlib#337

There are two features I agree to support:

• Add ZLIB::ZLIB target alias (to follow FindZLIB.cmake convention).
• Add Export Targets, Config and ConfigVersion cmake file.

[mtl1979]

I have nothing against adding ZLIB::ZLIB alias when configured for compatibility mode, but when building for normal mode, we should use ZLIBNG::ZLIBNG alias instead...

Only issue I can think of is that when we are building both static and shared version, which one does the alias point to... Do we use STATIC variable like other projects do to decide?

[hwhsu1231]

but when building for normal mode, we should use ZLIBNG::ZLIBNG alias instead

About that, I have some points to ask and discuss.

Usually, the IMPORTED library target name is related to the package name. For example, the IMPORTED target name of fmt library is fmt::fmt. Besides, the REPOSITORY name is often the same as the PROJECT name. However, I noticed that this library uses zlib in its project() command, but the repository name is zlib-ng.

Moreover, there are lots of downstream libraries using zlib as its dependency. For example, openssl, opencv, poco, qt...etc. However, the reason why this library zlib-ng is created is because the original one is no more updated.

Therefore, I have some questions to ask the AUTHOR of this library:

• Will the project name be modified the same as the repository name?

• Is it recommended that those downstream libraries replace zlib with zlib-ng in the future?

• If so, do you think it is better to use different name of IMPORTED library target?

By the way, Conan Package Manager already provides zlib-ng in conan-center-index. And with the generator CMakeDeps, it provides the IMPORTED library target, zlib-ng::zlib-ng, for us to use.

[mtl1979]

By the way, Conan Package Manager already provides zlib-ng in conan-center-index. And with the generator CMakeDeps, it provides the IMPORTED library target, zlib-ng::zlib-ng, for us to use.

We can't rely on some third-party package manager to provide imported targets, as it is not guaranteed that everyone use same package manager. Exact spelling of the imported target is however open for discussion at this stage.

[bebuch]

Are PR #1601 and Issue #1646 related to this Issue?