Fix PR python/17386 - add __index__ method to gdb.Value

This patch fixes PR python/17386.

The bug is that gdb.Value does not implement the Python __index__
method.  This method is needed to convert a Python object to an index
and is used by various operations in Python, such as indexing an
array.

The fix is to implement the nb_index method for gdb.Value.

nb_index was added in Python 2.5.  I don't have a good way to test
Python 2.4, but I made an attempt to accomodate it.

I chose to use valpy_long in all cases because this simplifies porting
to Python 3, and because there didn't seem to be any harm.

Built and regtested on x86-64 Fedora 23.

2016-05-24  Tom Tromey  <tom@tromey.com>

	PR python/17386:
	* python/py-value.c (value_object_as_number): Add
	nb_inplace_floor_divide, nb_inplace_true_divide, nb_index.

2016-05-24  Tom Tromey  <tom@tromey.com>

	PR python/17386:
	* gdb.python/py-value.exp (test_value_numeric_ops): Add tests that
	use value as an index.

gdb/ChangeLog

@@ -1,3 +1,9 @@
+2016-05-24  Tom Tromey  <tom@tromey.com>
+
+	PR python/17386:
+	* python/py-value.c (value_object_as_number): Add
+	nb_inplace_floor_divide, nb_inplace_true_divide, nb_index.
+
 2016-05-24  Tom Tromey  <tom@tromey.com>
 
 	* python/py-value.c (value_object_as_number): Add

gdb/python/py-value.c

@@ -1838,7 +1838,13 @@ static PyNumberMethods value_object_as_number = {
   NULL,                       /* nb_inplace_xor */
   NULL,                       /* nb_inplace_or */
   NULL,                       /* nb_floor_divide */
-  valpy_divide                /* nb_true_divide */
+  valpy_divide,               /* nb_true_divide */
+  NULL,			      /* nb_inplace_floor_divide */
+  NULL,			      /* nb_inplace_true_divide */
+#ifndef HAVE_LIBPYTHON_2_4
+  /* This was added in Python 2.5.  */
+  valpy_long,		      /* nb_index */
+#endif /* HAVE_LIBPYTHON_2_4 */
 };
 
 static PyMappingMethods value_object_as_mapping = {

gdb/testsuite/ChangeLog

@@ -1,3 +1,9 @@
+2016-05-24  Tom Tromey  <tom@tromey.com>
+
+	PR python/17386:
+	* gdb.python/py-value.exp (test_value_numeric_ops): Add tests that
+	use value as an index.
+
 2016-05-23  Tom Tromey  <tom@tromey.com>
 
 	PR python/17981:

gdb/testsuite/gdb.python/py-value.exp

@@ -124,6 +124,13 @@ proc test_value_numeric_ops {} {
   gdb_test "python print ('result = ' + str(b-2))" " = 0x3( <.*>)?" "subtract python integer from pointer value"
   gdb_test "python print ('result = ' + str(b-a))" " = 3" "subtract two pointer values"
 
+  gdb_test "python print ('result = ' + 'result'\[gdb.Value(0)\])" \
+    "result = r" "use value as string index"
+  gdb_test "python print ('result = ' + str((1,2,3)\[gdb.Value(0)\]))" \
+    "result = 1" "use value as tuple index"
+  gdb_test "python print ('result = ' + str(\[1,2,3\]\[gdb.Value(0)\]))" \
+    "result = 1" "use value as array index"
+
   # Test some invalid operations.
 
   gdb_test_multiple "python print ('result = ' + str(i+'foo'))" "catch error in python type conversion" {