[GNATS 22694] Spurious diagnostic for expression preceding parentheses

[jhsedg]

Customer bug ID

boost/algorithm_sum_test, storage_adaport_test, storage_adaptor_serialization_test; gnats/22694.C (expanded), 22694a.C (the reduced)

Description

​This reduced Boost test case generates an unexpected diagnostic.
​
​template <class... Ts> auto operator0(Ts... args) -> decltype(0(args...));
​ eccp --c++17 --gnu_version 80100 /tmp/q.C
​"/tmp/q.C", line 1: error: expression preceding parentheses of apparent call
​ must have (pointer-to-) function type
​ template <class... Ts> auto operator0(Ts... args) -> decltype(0(args...));
​ ^
​
​1 error detected in the compilation of "/tmp/q.C".