https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71463
Jason Merrill <jason at gcc dot gnu.org> changed:
What |Removed |Added
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CC| |jason at gcc dot gnu.org
--- Comment #5 from Jason Merrill <jason at gcc dot gnu.org> ---
(In reply to Martin Sebor from comment #4)
> Second, it's unclear to me what purpose the warning is meant to serve in
> this case. Since a function attribute always applies to the instance of the
> function it decorates and never affects its type the warning doesn't
> indicate anything unusual or unexpected, and only serves to confuse users.
Actually, most of these attributes, including warn_unused_result, apply to the
function type, not to the function declaration. That's why you get the
warning. As an example of this:
__attribute ((warn_unused_result)) int f();
decltype(f)* p;
int main()
{
p(); // warns about unused result, by design.
}
The warning is letting you know that the attribute is being discarded, so you
don't get the warning within a template:
__attribute ((warn_unused_result)) int f();
template <class T>
struct A {
T *p;
void g() { p(); } // no warning
};
int main()
{
A<decltype(f)>().g();
}
Note that the C++17 [[nodiscard]] attribute applies to the function, so it
works differently.
> (In cases where the function is declared in a system header it's also
> unclear how the should be avoided.)
If you don't want this warning, -Wno-ignored-attributes will silence it.
