[Bug c++/96878] New: Failed class template argument deduction in unevaluated, parenthesized context

[sbergman at redhat dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96878

            Bug ID: 96878
           Summary: Failed class template argument deduction in
                    unevaluated, parenthesized context
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sbergman at redhat dot com
  Target Milestone: ---

At least with recent GCC 11 trunk and with gcc-c++-10.2.1-1.fc32.x86_64:

> $ cat test.cc
> template<int N> struct S { S(char const (& s)[N]); };
> auto n = sizeof (S(""));

> $ g++ -std=c++17 -fsyntax-only test.cc
> test.cc:2:18: error: missing template arguments after ‘S<...auto...>’
>     2 | auto n = sizeof (S(""));
>       |                  ^
> test.cc:1:24: note: ‘template<int N> struct S’ declared here
>     1 | template<int N> struct S { S(char const (& s)[N]); };
>       |                        ^

If you change `sizeof (S(""))` to `sizeof S("")`, compilation succeeds.