Do not require dependencies for static linking when exiv2 was built as shared

[pinotree]

exiv2 can be built either as shared library, or static, never both at the same time. Hence, requiring the dependencies needed for static linking to exiv2 when exiv2 was built shared does not make much sense, and it only adds unneeded bits to the exiv2 users.

Hence, fix both the pkg-config file, and the cmake config file, to require the dependencies needed for static linking only in case exiv2 was built as static library. This avoids e.g. having the expat and zlib development bits when using exiv2 in cmake with find_package(exiv2).

See the specific commit messages for longer descriptions.

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Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (b4f145e) 63.89% compared to head (a1ff128) 63.89%.

Additional details and impacted files

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##             main    #2872   +/-   ##
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  Coverage   63.89%   63.89%           
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  Files         103      103           
  Lines       22381    22381           
  Branches    10872    10872           
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  Hits        14301    14301           
  Misses       5857     5857           
  Partials     2223     2223           

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[kmilos]

Some distros ship both static and shared libs, how would you handle that? We still need a single .pc file that handles both. If you don't pass --static to pkg-config there is no harm done, no?

[pinotree]

Some distros ship both static and shared libs,

Do you have examples of this? I checked Arch, Debian (which I maintain) and thus Ubuntu, Fedora, FreeBSD, Gentoo, Mageia, OpenBSD, openSUSE, Void, and other distros are derivatives of the ones mentioned (thus sharing the build configuration). All of the ones I inspected build using the default built type, which is shared, and no static bits are shipped (with the exception of libexiv2-xmp.a, gone in 0.28).

From what I can see (I also mentioned that in my commit messages), you can build only one variant at a time with cmake, and most likely the same with meson. Hence, if the situation you mention must be supported somehow, then I need to see exactly how and what for.

[eli-schwartz]

From what I can see (I also mentioned that in my commit messages), you can build only one variant at a time with cmake, and most likely the same with meson.

No, meson has always supported building both at the same time, and it does this quite well.

This is vital for cross-platform support since unix platforms frequently need this, and it works quite well there. It doesn't work quite so well on Windows (you either need to use .def files or compile every object twice, and then import libraries and static libraries both frequently use .lib) which is usually "this is fine" because on Windows you have to build private copies of your entire dep tree without benefit of a package manager.

And since CMake was primarily designed to work well on Windows, it assumes the Windows model and doesn't bother to support meson -Ddefault_library=both / autotools "--enable-static --enable-shared".

Distros such as Alpine and Debian often package both, when the build system supports both, but won't necessarily go out of their way to run cmake twice in order to build and install both.

[kmilos]

won't necessarily go out of their way to run cmake twice in order to build and install both

OTOH, we frequently do run CMake twice on MSYS2 and install both artifacts.

[eli-schwartz]

Very true, MSYS2 has a somewhat stronger motivation to provide both.