CWG2945 [basic.link] "Two declarations of an entity" vs corresponding overloads

[Endilll]

Full name of submitter: Vlad Serebrennikov
Reference (section label): [basic.link]

[basic.link]/11 reads:

For any two declarations of an entity E:
— <...>
— If one declares E to be a function template or a (partial specialization of a) variable template, the other shall declare E to be one with an equivalent template-head and type.

Those two bullets don't seem to take into account that in order for [basic.link]/11 to apply, declaration matching ([basic.link]/8) has to establish that two declaration indeed declare the same entity, which involves establishing whether those two declarations correspond ([basic.scope.scope]/4), which relies on the definition of corresponding overloads. The latter puts much more precise and strict requirements on function template declarations ([basic.scope.scope]/4):

Two function or function template declarations declare corresponding overloads if
— both declare functions <...>, or
— both declare function templates with corresponding signatures and equivalent template-heads and trailing requires-clauses (if any).

So I think there's no way to arrive at [basic.link]/11.6 with two declarations of function templates that declare the same entity but don't have equivalent template-heads. I think [basic.link]/11 should either stop caring about that, or sync with corresponding overloads on exact details like trailing requires-clause.

We might want to apply a similar change to [basic.link]/11.1, but in this case [basic.link]/11.1 is stricter than corresponding overloads, because the latter doesn't consider return types (maybe it should?).

Also, while we're looking at [basic.link]/11.6: is it correct to talk about type of a function template and variable template?

Suggested resolution:

For any two declarations of an entity E:
— <...>
— If one declared E to be a function template, the other shall do so.
[Note: Two declarations of the same function template are required to have equivalent template-heads ([basic.scope.scope]). — end note]
— If one declares E to be a function template or a (partial specialization of a) variable template, the other shall declare E to be one with an equivalent template-head and type.

[Endilll]

Also, while we're looking at [basic.link]/11.6: is it correct to talk about type of a function template and variable template?

I forgot to mention that this was discussed a bit on Mattermost: https://chat.isocpp.org/general/pl/zxonhyg8wi86bpys41tpsxpjja

[jensmaurer]

This change drops the "same type" requirement. Two declarations can differ in "noexcept", but otherwise correspond, but that ought to be ill-formed:

template<class T> void f(T);
template<class T> void f(T) noexcept;

[jensmaurer]

CWG2945