[Bug c/70400] New: GCC compiles a return statement with an expression in a void function (illegal under C90 6.6.6.4) with -std=c90 -pedantic

["ryao at gentoo dot org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70400

            Bug ID: 70400
           Summary: GCC compiles a return statement with an expression in
                    a void function (illegal under C90 6.6.6.4) with
                    -std=c90 -pedantic
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ryao at gentoo dot org
  Target Milestone: ---

Created attachment 38081
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=38081&action=edit
Test case where GCC allows a void function to return an expression

ISO C90 6.6.6.4 says that "A return statement with an expression shall not
appear in a function whose return type is void."

Both Sun Studio and the TenDRA make this a build failure as the specification
requires while Clang does what GCC does. The sudo project had a bug filed
agaisnt it because of Sun Studio:

https://bugzilla.sudo.ws/show_bug.cgi?id=727

GCC will only emit a warning when -pendantic is specified and adding -std=c90
does not change the behavior to a warning. The documentation for -pedantic
clearly states that things disallowed by the specification emit errors:

https://gcc.gnu.org/onlinedocs/gcc-4.9.3/gcc/Warning-Options.html

This probably should be a warning even without `-pendantic`.