fix pkg-config protobuf library not dependes from utf8_range

[mdionisio]

the .pc file generated insert a dependency to a utf8_range.pc file that is not required

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[acozzette]

@mdionisio If I'm not mistaken, we do need this because we rely on utf8_range, like here for example:

protobuf/src/google/protobuf/generated_message_tctable_lite.cc

Line 1395 in 47f633e

return utf8_range::IsStructurallyValid(field.Get());

[mdionisio]

@acozzette I don't say that utf8_range is not used inside protobuf, I say only that If I use protobuf I don't neet to link my program with utf8_range because all the dependency to utf8_range was statically linked directly inside protobuf library. My change is only on ".pc" that is not used from protobuf but it is used from code that use protobuf.

I test the fix on protobuf 4.25 in yocto environment building and testing code that only used protobuf library and in more complicated example that use grpc.

[acozzette]

Hmm, I don't think I understand. If we remove utf8_range from the dependencies listed in the .pc file then wouldn't that break most users who rely on the .pc file? If utf8_range was statically linked inside libprotobuf then I assume that must have been a local modification you made?

[mdionisio]

@acozzette you are probably right. There is also another issue in cmake that doesn't configure protobuf to explicitly link utf8_range. I don't understand exactly why utf8_range was linked anyway.

I update my pull request to fix also that.

[acozzette]

@mdionisio Maybe I'm missing something but I think this is still not going to work because it will cause utf8_range to be removed from the .pc file even though it's a required dependency. With this change, I find that pkgconfig --libs protobuf no longer includes the linker flag -lutf8_validity, so I would expect this to break builds.

[mdionisio]

@acozzette in my opinion the problem is that utf8_range and utf8_validity are configured in .pc to be a required dependency but is not true. In any of .so library there is any required symbol from utf8_range or utf8_validity. In any case I will double check the yocto recipes that build protobuf for me if there is any strange trick for that.