gdb/fortran: add support for accessing fields of extended types

Fortran 2003 supports type extension.  This patch allows access
to inherited members by using their fully qualified name as described
in the Fortran standard.

In doing so the patch also fixes a bug in GDB when trying to access the
members of a base class in a derived class via the derived class' base
class member.

This patch fixes PR22497 and PR26373 on GDB side.

Using the example Fortran program from PR22497

program mvce
  implicit none

  type :: my_type
     integer :: my_int
  end type my_type

  type, extends(my_type) :: extended_type
  end type extended_type

  type(my_type) :: foo
  type(extended_type) :: bar

  foo%my_int = 0
  bar%my_int = 1

  print*, foo, bar

end program mvce

and running this with GDB and setting a BP at 17:

Before:
(gdb) p bar%my_type
A syntax error in expression, near `my_type'.
(gdb) p bar%my_int
There is no member named my_int.
(gdb) p bar%my_type%my_int
A syntax error in expression, near `my_type%my_int'.
(gdb) p bar
$1 = ( my_type = ( my_int = 1 ) )

After:
(gdb) p bar%my_type
$1 = ( my_int = 1 )
(gdb) p bar%my_int
$2 = 1                 # this line requires DW_TAG_inheritance to work
(gdb) p bar%my_type%my_int
$3 = 1
(gdb) p bar
$4 = ( my_type = ( my_int = 1 ) )

In the above example "p bar%my_int" requires the compiler to emit
information about the inheritance relationship between extended_type
and my_type which gfortran and flang currently do not de.  The
respective issue gcc/49475 has been put as kfail.

Co-authored-by: Nils-Christian Kempke <nils-christian.kempke@intel.com>
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=26373
     https://sourceware.org/bugzilla/show_bug.cgi?id=22497

1 files changed, 69 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.fortran/oop_extend_type.f90 b/gdb/testsuite/gdb.fortran/oop_extend_type.f90
new file mode 100755
index 00000000000..dc91c45c60a
--- /dev/null
+++ b/gdb/testsuite/gdb.fortran/oop_extend_type.f90
@@ -0,0 +1,69 @@
+! Copyright 2022 Free Software Foundation, Inc.
+!
+! This program is free software; you can redistribute it and/or modify
+! it under the terms of the GNU General Public License as published by
+! the Free Software Foundation; either version 3 of the License, or
+! (at your option) any later version.
+!
+! This program is distributed in the hope that it will be useful,
+! but WITHOUT ANY WARRANTY; without even the implied warranty of
+! MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+! GNU General Public License for more details.
+!
+! You should have received a copy of the GNU General Public License
+! along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+! Test fortran extends feature (also for chained extends).
+module testmod
+    implicit none
+    type :: point
+	real :: coo(3)
+    end type
+
+    type, extends(point) :: waypoint
+	real :: angle
+    end type
+
+    type, extends(waypoint) :: fancywaypoint
+	logical :: is_fancy
+    end type
+end module
+
+program testprog
+    use testmod
+    implicit none
+
+    logical l
+    type(waypoint) :: wp
+    type(fancywaypoint) :: fwp
+    type(waypoint), allocatable :: wp_vla(:)
+
+    l = .FALSE.
+    allocate(wp_vla(3)) ! Before vla allocation
+
+    l = allocated(wp_vla) ! After vla allocation
+
+    wp%angle = 100.00
+    wp%coo(:) = 1.00
+    wp%coo(2) = 2.00
+
+    fwp%is_fancy = .TRUE.
+    fwp%angle = 10.00
+    fwp%coo(:) = 2.00
+    fwp%coo(1) = 1.00
+
+    wp_vla(1)%angle = 101.00
+    wp_vla(1)%coo(:) = 10.00
+    wp_vla(1)%coo(2) = 12.00
+
+    wp_vla(2)%angle = 102.00
+    wp_vla(2)%coo(:) = 20.00
+    wp_vla(2)%coo(2) = 22.00
+
+    wp_vla(3)%angle = 103.00
+    wp_vla(3)%coo(:) = 30.00
+    wp_vla(3)%coo(2) = 32.00
+
+    print *, wp, wp_vla, fwp ! After value assignment
+
+end program