https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78737
Bug ID: 78737 Summary: linking error with deferred, undefined user-defined derived-type I/O Product: gcc Version: 7.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: fortran Assignee: unassigned at gcc dot gnu.org Reporter: damian at sourceryinstitute dot org Target Milestone: --- A linking error results when an abstract type defers a user-defined derived type output binding that is not implemented anywhere in the program: $ cat undefined-ud-dtio.f90 module object_interface type, abstract :: object contains procedure(write_formatted_interface), deferred ::write_formatted generic :: write(formatted)=>write_formatted end type abstract interface subroutine write_formatted_interface(this,unit,iotype,vlist,iostat,iomsg) import object class(object), intent(in) :: this integer, intent(in) :: unit character (len=*), intent(in) :: iotype integer, intent(in) :: vlist(:) integer, intent(out) :: iostat character (len=*), intent(inout) :: iomsg end subroutine end interface contains subroutine assert(a) class(object):: a write(*,*) a end subroutine end module end $ gfortran undefined-ud-dtio.f90 Undefined symbols for architecture x86_64: "_write_formatted_interface_", referenced from: ___object_interface_MOD_assert in ccMQHXbf.o ld: symbol(s) not found for architecture x86_64 collect2: error: ld returned 1 exit status rouson@localhost:~/xfr$ gfortran --version GNU Fortran (MacPorts gcc7 7-20161127_0) 7.0.0 20161127 (experimental) Adding a type that defines the binding eliminates the linking error.