[Bug c++/63198] decltype in template function declaration yields spurious error

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63198

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |rejects-valid
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-09-08
            Summary|[c++1y] decltype in         |decltype in template
                   |template function           |function declaration yields
                   |declaration yields spurious |spurious error
                   |error                       |
     Ever confirmed|0                           |1

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
struct X { using t1 = int; };
struct Y { X operator=(const Y&); } y;
template <typename T> void f1(decltype(y = y)::t1);

$ g++ -std=c++11 -c d.cc
d.cc:3:50: error: variable or field ‘f1’ declared void
 template <typename T> void f1(decltype(y = y)::t1);
                                                  ^

Using -std=c++1y is not necessary, this doesn't use any C++14 features.

The error only happens if f1 is a template, and only seems to happen if the
decltype expression uses the assignment operator, not any other expression I
tried.