varobj/Ada: Missing children for interface-wide tagged types

Consider the following code:

   type Element is abstract tagged null record;
   type GADataType is interface;
   type Data_Type is new Element and GADataType with record
      I : Integer := 42;
   end record;
   Result1 : Data_Type;
   GGG1    : GADataType'Class := GADataType'Class (Result1);

When trying to create a varobj for variable ggg1, GDB currently
returns an object which has no child:

    -var-create ggg1 * ggg1
    ^done,name="ggg1",numchild="0",[...]

This is incorrect, it should return an object which has one child
(field "i"). This is because tagged-type objects are dynamic, and
we need to apply a small transformation in order to get their actual
type. This is already done on the GDB/CLI side in ada-valprint,
and it needs to be done on the ada-varobj side as well.

gdb/ChangeLog:

        * ada-varobj.c (ada_varobj_adjust_for_child_access): Convert
        tagged type objects to their actual type.

gdb/testsuite/ChangeLog:

        * gdb.ada/mi_interface: New testcase.

gdb/ada-varobj.c

@@ -219,6 +219,15 @@ ada_varobj_adjust_for_child_access (struct value **value,
       && !ada_is_array_descriptor_type (TYPE_TARGET_TYPE (*type))
       && !ada_is_constrained_packed_array_type (TYPE_TARGET_TYPE (*type)))
     ada_varobj_ind (*value, *type, value, type);
+
+  /* If this is a tagged type, we need to transform it a bit in order
+     to be able to fetch its full view.  As always with tagged types,
+     we can only do that if we have a value.  */
+  if (*value != NULL && ada_is_tagged_type (*type, 1))
+    {
+      *value = ada_tag_value_at_base_address (*value);
+      *type = value_type (*value);
+    }
 }
 
 /* Assuming that the (PARENT_VALUE, PARENT_TYPE) pair is an array

gdb/testsuite/gdb.ada/mi_interface.exp

@@ -0,0 +1,52 @@
+# Copyright 2014 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/>.
+
+load_lib "ada.exp"
+
+standard_ada_testfile foo
+
+if {[gdb_compile_ada "${srcfile}" "${binfile}" executable [list debug additional_flags=-gnat12 ]] != "" } {
+  return -1
+}
+
+load_lib mi-support.exp
+set MIFLAGS "-i=mi"
+
+gdb_exit
+if [mi_gdb_start] {
+    continue
+}
+
+mi_delete_breakpoints
+mi_gdb_reinitialize_dir $srcdir/$subdir
+mi_gdb_load ${binfile}
+
+if ![mi_run_to_main] then {
+   fail "Cannot run to main, testcase aborted"
+   return 0
+}
+
+set bp_location [gdb_get_line_number "BREAK" ${testdir}/foo.adb]
+mi_continue_to_line \
+    "foo.adb:$bp_location" \
+    "stop at start of main Ada procedure"
+
+mi_gdb_test "-var-create ggg1 * ggg1" \
+    "\\^done,name=\"ggg1\",numchild=\"1\",value=\"{...}\",type=\"<ref> pck.gadatatype\",has_more=\"0\"" \
+    "Create ggg1 varobj"
+
+mi_gdb_test "-var-list-children 1 ggg1" \
+    "\\^done,numchild=\"1\",children=\\\[child={name=\"ggg1.i\",exp=\"i\",numchild=\"0\",value=\"42\",type=\"integer\"}\\\],has_more=\"0\"" \
+    "list ggg1's children"

gdb/testsuite/gdb.ada/mi_interface/foo.adb

@@ -0,0 +1,23 @@
+--  Copyright 2014 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/>.
+
+with Pck; use Pck;
+
+procedure Foo is
+   Result1 : Data_Type;
+   GGG1    : GADataType'Class := GADataType'Class (Result1);
+begin
+   Do_Nothing (GGG1'Address);  -- BREAK
+end Foo;

gdb/testsuite/gdb.ada/mi_interface/pck.adb

@@ -0,0 +1,21 @@
+--  Copyright 2014 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/>.
+
+package body Pck is
+   procedure Do_Nothing (A : System.Address) is
+   begin
+      null;
+   end Do_Nothing;
+end Pck;

gdb/testsuite/gdb.ada/mi_interface/pck.ads

@@ -0,0 +1,28 @@
+--  Copyright 2014 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/>.
+
+with System;
+
+package Pck is
+
+   type Element is abstract tagged null record;
+   type GADataType is interface;
+
+   type Data_Type is new Element and GADataType with record
+      I : Integer := 42;
+   end record;
+
+   procedure Do_Nothing (A : System.Address);
+end Pck;