https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116728
--- Comment #5 from Martin Uecker <muecker at gwdg dot de> --- Sorry, mixed this up with the other bug. Here I would say the behavior is correct as specified in ISO C23. Note that incomplete structs could be completed later also before ISO C23. But incomplete struct types are incompatible to other struct types with the same tag, and the incomplete struct declared in prototype scope is therefor incompatible to the completed one. If you have a forward declaration so that the struct in the function prototype refers to a file scope version that is completed later, it works. https://godbolt.org/z/qPKcvGevM Of course, whether the languages are perfect as specified is a different question. With "typedef" there is the additional issue that "typedef" currently allows redefinition only for identical types, not merely compatible types.
