Do not expose stub types to Python

dwarf2read.c will create stub types for Ada "Taft Amendment" types.
These stub types can currently be exposed to Python code, where they
show up as TYPE_CODE_VOID types (but that, mysteriously, can sometimes
be used in other ways).

While it's possible to work with such types by using strip_typedefs,
this seemed unpleasant to me.  This patch takes another approach
instead, which is to try not to expose stub types to Python users.

gdb/ChangeLog
2019-09-26  Tom Tromey  <tromey@adacore.com>

	* python/py-type.c (type_to_type_object): Call check_typedef
	for stub types.

gdb/testsuite/ChangeLog
2019-09-26  Tom Tromey  <tromey@adacore.com>

	* gdb.ada/py_taft.exp: New file.
	* gdb.ada/py_taft/main.adb: New file.
	* gdb.ada/py_taft/pkg.adb: New file.
	* gdb.ada/py_taft/pkg.ads: New file.

gdb/ChangeLog

@@ -1,3 +1,8 @@
+2019-09-26  Tom Tromey  <tromey@adacore.com>
+
+	* python/py-type.c (type_to_type_object): Call check_typedef
+	for stub types.
+
 2019-09-26  Tom Tromey  <tom@tromey.com>
 
 	* utils.h (initialize_utils): Don't declare.

gdb/python/py-type.c

@@ -1334,6 +1334,17 @@ type_to_type_object (struct type *type)
 {
   type_object *type_obj;
 
+  try
+    {
+      /* Try not to let stub types leak out to Python.  */
+      if (TYPE_STUB (type))
+	type = check_typedef (type);
+    }
+  catch (...)
+    {
+      /* Just ignore failures in check_typedef.  */
+    }
+
   type_obj = PyObject_New (type_object, &type_object_type);
   if (type_obj)
     set_type (type_obj, type);

gdb/testsuite/ChangeLog

@@ -1,3 +1,10 @@
+2019-09-26  Tom Tromey  <tromey@adacore.com>
+
+	* gdb.ada/py_taft.exp: New file.
+	* gdb.ada/py_taft/main.adb: New file.
+	* gdb.ada/py_taft/pkg.adb: New file.
+	* gdb.ada/py_taft/pkg.ads: New file.
+
 2019-09-24  Tom de Vries  <tdevries@suse.de>
 
 	PR gdb/24598

gdb/testsuite/gdb.ada/py_taft.exp

@@ -0,0 +1,38 @@
+# Copyright 2019 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"
+load_lib gdb-python.exp
+
+standard_ada_testfile main
+
+if {[gdb_compile_ada "${srcfile}" "${binfile}" executable debug] != ""} {
+    return -1
+}
+
+clean_restart ${testfile}
+
+# Skip this testcase if Python scripting is not enabled.
+if { [skip_python_tests] } { continue }
+
+set bp_location [gdb_get_line_number "STOP" ${testdir}/main.adb]
+runto "main.adb:$bp_location"
+
+gdb_test_no_output "python v = gdb.parse_and_eval('v')"
+
+gdb_test "python print(v.dereference().type.code is gdb.TYPE_CODE_VOID)" \
+    "False"
+gdb_test "python print(v.type.strip_typedefs().target().code is gdb.TYPE_CODE_VOID)" \
+    "False"

gdb/testsuite/gdb.ada/py_taft/main.adb

@@ -0,0 +1,22 @@
+--  Copyright 2019 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 Pkg;
+
+procedure Main is
+   V : Pkg.Value := Pkg.Create (42);
+begin
+   null;				--  STOP
+end Main;

gdb/testsuite/gdb.ada/py_taft/pkg.adb

@@ -0,0 +1,27 @@
+--  Copyright 2019 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 Pkg is
+
+   type Value_Record is record
+      I : Integer;
+   end record;
+
+   function Create (I : Integer) return Value is
+   begin
+      return new Value_Record'(I => I);
+   end Create;
+
+end Pkg;

gdb/testsuite/gdb.ada/py_taft/pkg.ads

@@ -0,0 +1,22 @@
+--  Copyright 2019 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 Pkg is
+   type Value is private;
+   function Create (I : Integer) return Value;
+private
+   type Value_Record;
+   type Value is access all Value_Record;
+end Pkg;