[Bug c++/86499] New: lambda-expressions with capture-default are allowed at namespace scope

[zhonghao at pku dot org.cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86499

            Bug ID: 86499
           Summary: lambda-expressions with capture-default are allowed at
                    namespace scope
           Product: gcc
           Version: 8.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zhonghao at pku dot org.cn
  Target Milestone: ---

g++ incorrectly accepts this:

  auto l = [=]{};

Per C++1y [expr.lambda]p9 this is ill-formed: only local lambda expressions may
have capture-defaults (even if they don't actually capture anything).