" if you want to link your software with GPL code, you must also make your software’s source code available. "

Actually, no. The main question is whether it makes your software a _derived_ _work_ or not, in the eyes of a copyright judge.

The notion of derived work is not related to the size of the code being included. A small function could still make your software a derived work, and a big library could still not make your software a derived work of it. And in any case, it's up to the judge to decide.

But otherwise, indeed, linking with GPL code is asking for a judge to possibly force you to deliver your sources.

GPL explicitly cover the library case, a linked library must be relased under GPL too.

Actually, even if it's a license violation only copyright owner (so wordpress contributors) can enforce it.