[Bug libfortran/88776] New: Namelist read from stdin: loss of data

[anlauf at gmx dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88776

            Bug ID: 88776
           Summary: Namelist read from stdin: loss of data
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libfortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: anlauf at gmx dot de
  Target Milestone: ---

Reading namelist from unit 5 may skip valid data later when an error is
encountered.  This problem does not occur when another unit number is used.

Example:

% cat gfcbug154.f90
program nmlbug
  implicit none
  integer :: i, stat, nnml
  nnml = 5  ! No problem with nnml = 10
! nnml = 10
  open (nnml, file="gfcbug154.dat", action="read")
  do i = 1, 3
     print *, "# Read namelist", i
     call read_nml_type_2
     print *
  end do
contains
  subroutine read_nml_type_2
    !----------------------------------------------------------
    ! variant 2 of namelist input: chan = real char(len=*) real
    !----------------------------------------------------------
    type t_chan
       real              :: ichan = -1.
       character(len=10) :: flag  = ''
       real              :: band  = -1.
    end type t_chan
    type(t_chan)         :: chan(2)
    namelist /CHAN_NML/ chan

    chan(:) = t_chan(-1.,'',-1.)
    stat = 0
    read (nnml, nml=CHAN_NML, iostat=stat, end=99)
    print *, "read_nml_type_2: stat=", stat
    print *, "chan(1)=", chan(1)
    print *, "chan(2)=", chan(2)
    return
99  stop "EOF"
  end subroutine read_nml_type_2
end program nmlbug

% cat gfcbug154.dat
&CHAN_NML
 chan = 3       '#1 '   '0.1'
        6       '#1 '   0.8
/

&CHAN_NML
 chan = 4       '#2 '   0.1
        7       '#2 '   0.2
/

&CHAN_NML
 chan = 5       '#3 '   0.3
        8       '#3 '   0.4
/


The above code outputs:

 # Read namelist           1
 read_nml_type_2: stat=        5010
 chan(1)=   4.00000000     #2          0.100000001    
 chan(2)=   7.00000000     #2          0.200000003    

 # Read namelist           2
 read_nml_type_2: stat=           0
 chan(1)=   5.00000000     #3          0.300000012    
 chan(2)=   8.00000000     #3          0.400000006    

 # Read namelist           3
STOP EOF

whereas with e.g. unit 10 it (correctly) outputs:

 # Read namelist           1
 read_nml_type_2: stat=        5010
 chan(1)=   3.00000000     #1          -1.00000000    
 chan(2)=  -1.00000000                 -1.00000000    

 # Read namelist           2
 read_nml_type_2: stat=           0
 chan(1)=   4.00000000     #2          0.100000001    
 chan(2)=   7.00000000     #2          0.200000003    

 # Read namelist           3
 read_nml_type_2: stat=           0
 chan(1)=   5.00000000     #3          0.300000012    
 chan(2)=   8.00000000     #3          0.400000006    


For some reason, when an error is encountered during the first read,
it correctly sets the error status, but apparently continues to the
second namelist instance.