https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113830
--- Comment #14 from Harald van Dijk <harald at gigawatt dot nl> --- (In reply to Bo Wang from comment #13) > (In reply to Harald van Dijk from comment #12) > > (In reply to Bo Wang from comment #11) > > > I have read the working draft standard of C++20 > > > (https://github.com/cplusplus/draft/tree/c%2B%2B20). > > > > > > Following the subsection "13.9.2 Explicit instantiation" in the section > > > "13.9 Template instantiation and specialization", the statement `template > > > void f<int>();` is an explicit instantiation, which requires instantiating > > > everything in the function. > > > > Where are you getting "everything in the function" from? It seems to say > > rather the opposite in [temp.explicit]p14: > > > > > An explicit instantiation does not constitute a use of a default > > > argument, so default argument instantiation is not done. > > > > Now, the example shows that this was intended to apply to default arguments > > of the function itself, but the actual wording does not limit it to that, so > > I actually think this is a bug in clang, by the current wording this must be > > accepted? > > Please refer to the example in Comment 9 which has no default arguments. Okay, sure, but if we have established that the standard does not say "everything in the function" needs to be instantiated, where does it say that *this* needs to be instantiated? > For the standard, I found this one in "13.9 Template instantiation and > specialization" p6 of C++20, which requires access checking. That explains that the special exception that generally applies to template instantiations does not apply here. This means the usual rules apply, so for instance, you can't refer to a private member of a class unless you're a friend. But for templates, these usual rules apply upon instantiation, so we still need to establish whether or not this is required to be instantiated.
