[Bug c++/96182] New: GCC accepts constexpr function with no return-statement

[haoxintu at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96182

            Bug ID: 96182
           Summary: GCC accepts constexpr function with no
                    return-statement
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Keywords: accepts-invalid
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: haoxintu at gmail dot com
  Target Milestone: ---

Hi,all.

This code, test.cc, is an invalid code I guess, but GCC accepts it.

$cat test.cc
constexpr int
foo()
{}

$g++ test.cc
test.cc: In function ‘constexpr int foo()’:
test.cc:3:2: warning: no return statement in function returning non-void
[-Wreturn-type]
    3 | {}
      |  ^

GCC only emits normal -Wreturn-type warning and then accepts it.

Weirdly, this code is rejected under -std=c++11.

$g++ -std=c++11 test.cc
test.cc: In function ‘constexpr int foo()’:
test.cc:3:2: error: body of ‘constexpr’ function ‘constexpr int foo()’ not a
return-statement
    3 | {}
      |  ^
test.cc:3:2: warning: no return statement in function returning non-void
[-type-Wreturn-type]

I think constexpr function is not a deprecated feature in c++14. I also test
this in Clang, it is rejected by both standards.

Every GCC versions from 5.1 to trunk behave the same.

Thanks,
Haoxin