MODULE basis_m
implicit none
TYPE basis_t
real :: a
TYPE (basis_t), allocatable :: tab_basis(:)
END TYPE basis_t
END MODULE basis_m

With gfortran, the compilation works fine and I’m using this kind of structure without trouble. However, with nagfor, I obtain:

NAG Fortran Compiler Release 7.1(Hanzomon) Build 7101
Evaluation trial version of NAG Fortran Compiler Release 7.1(Hanzomon) Build 7101
Segmentation violation
Internal error - please report this bug

The workaround is to use pointer instead allocatable and I did use pointer attribute for years for such data structure, but I prefer use allocatable whenever it is possible.

Of course, there is a bug with nagfor and I’ll send a report.

However, I wondering if the piece of code is correct ?

It is compilable by gfortran (as opposed to the similar code where TYPE(basis_t) gets replaced by CLASS(basis_t) ) but are you sure it is working properly? According to the first of cited posts, gfortran-compiled recursive DTs give wrong results in execution.

A test with just a recursive writing subroutine is working well with gfortran.

MODULE basis_m
implicit none
TYPE basis_t
real :: a
TYPE (basis_t), allocatable :: tab_basis(:)
END TYPE basis_t
CONTAINS
RECURSIVE SUBROUTINE Write_Basis(Basis)
TYPE(Basis_t), intent(in) :: Basis
integer :: i
write(6,*) '-------------------------------------------------'
write(6,*) 'Write_Basis'
write(6,*) 'a',Basis%a
IF (allocated(Basis%tab_basis)) THEN
DO i=1,size(Basis%tab_basis)
CALL Write_Basis(Basis%tab_basis(i))
END DO
END IF
write(6,*) '-------------------------------------------------'
END SUBROUTINE Write_Basis
END MODULE basis_m
PROGRAM test
USE basis_m
implicit none
TYPE(basis_t) :: basis
basis%a = 1.
allocate(basis%tab_basis(2))
basis%tab_basis(1)%a = 1.1
basis%tab_basis(2)%a = 1.2
CALL Write_Basis(basis)
END PROGRAM test

The results are as expected:

-------------------------------------------------
Write_Basis
a 1.00000000
-------------------------------------------------
Write_Basis
a 1.10000002
-------------------------------------------------
-------------------------------------------------
Write_Basis
a 1.20000005
-------------------------------------------------
-------------------------------------------------

You have access to NAG technical support for the period of your trial. I can confirm that the latest Build (7106) of the NAG Fortran Compiler Release 7.1 does not have this bug.