[Bug libfortran/113223] New: NAMELIST internal write missing leading blank character

["kargl at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113223

            Bug ID: 113223
           Summary: NAMELIST internal write missing leading blank
                    character
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libfortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kargl at gcc dot gnu.org
  Target Milestone: ---

Found at https://github.com/llvm/llvm-project/issues/76798

Program test_namelist_blank
  Integer :: i,j
  Character(300) ::s
  Namelist /nml1/i,j

  i = 99
  j = 42
  Write (s,NML=nml1)
  Write (*,'("Internal ",A)') Merge('ok ','bug',s(1:1)==' ')
  Write (*,NML=nml1)
End Program test_namelist_blank

F2018
13.11.4.3 Namelist output records
...
Except for new records created by explicit formatting within a defined
output procedure or by continuation of delimited character sequences,
each output record begins with a blank character.

Patch

diff --git a/libgfortran/io/write.c b/libgfortran/io/write.c
index f94e180ba33..a7cf5d9b233 100644
--- a/libgfortran/io/write.c
+++ b/libgfortran/io/write.c
@@ -2466,6 +2466,8 @@ namelist_write (st_parameter_dt *dtp)
        dtp->u.p.nml_delim = '\0';
     }

+  if (is_internal_unit (dtp))
+    write_character (dtp, " ", 1, 1, NODELIM);
   write_character (dtp, "&", 1, 1, NODELIM);

   /* Write namelist name in upper case - f95 std.  */