[Bug c++/85109] New: Incorrect warning for constexpr lambda with -Wunused-but-set-variable

[rain.backnet at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85109

            Bug ID: 85109
           Summary: Incorrect warning for constexpr lambda with
                    -Wunused-but-set-variable
           Product: gcc
           Version: 7.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rain.backnet at gmail dot com
  Target Milestone: ---

Created attachment 43792
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43792&action=edit
minimal test case

If a lambda is declared constexpr, and then used within another lambda, with
the flag -Wunused-but-set-variable the compiler produces an incorrect warning
that the constexpr lambda is set but not used, when it is.

See attached minimal test case.