[Bug c++/79021] New: attribute noreturn on function template ignored in generic lambda

[akim.demaille at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79021

            Bug ID: 79021
           Summary: attribute noreturn on function template ignored in
                    generic lambda
           Product: gcc
           Version: 6.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: akim.demaille at gmail dot com
  Target Milestone: ---

When a generic lambda calls a function templates declared noreturn, we still
get warnings about missing return values.

$ cat foo.cc
template <typename T>
[[noreturn]]
int f(T)
{
  throw "error";
}

int g()
{
  f(12);
}

template <typename T>
int h(T)
{
  f(12);
}

int main()
{
  auto g = [](auto a) -> int { f(a); };
}
$ g++-mp-6 --version
g++-mp-6 (MacPorts gcc6 6.2.0_2) 6.2.0
Copyright (C) 2016 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ g++-mp-6 -std=c++14 foo.cc -Wreturn-type
foo.cc: In lambda function:
foo.cc:21:38: warning: no return statement in function returning non-void
[-Wreturn-type]
   auto g = [](auto a) -> int { f(a); };
                                      ^
$ clang++-mp-3.9 -std=c++14 foo.cc -Wreturn-type
$



Please note that:
- if f is not templated, there is no warning
- if the lambda is not generic, there is no warning
- if calling from a function template rather than from a generic template
(i.e., the function h), it does not trigger any warning (even if I do use h).