tuple pretty printer

[Ulrich Drepper <drepper@gmail.com>]

The current tuple pretty printer shows for this variable

std::tuple<int,int,int> a{1,2,3};

the following output:

(gdb) p a
$1 = std::tuple containing = {[1] = 1, [2] = 2, [3] = 3}

I find this quite irritating because the indices don't match the
std::get template parameters.  In a large tuple or arrays of tuples
which are less readable than this simple example this becomes an even
larger problem.  How about the following simple patch which brings the
indices in line?

--- a/libstdc++-v3/python/libstdcxx/v6/printers.py
+++ b/libstdc++-v3/python/libstdcxx/v6/printers.py
@@ -611,9 +611,9 @@ class StdTuplePrinter:
             # the value "as is".
             fields = impl.type.fields ()
             if len (fields) < 1 or fields[0].name != "_M_head_impl":
-                return ('[%d]' % self.count, impl)
+                return ('[%d]' % (self.count - 1), impl)
             else:
-                return ('[%d]' % self.count, impl['_M_head_impl'])
+                return ('[%d]' % (self.count - 1), impl['_M_head_impl'])

     def __init__ (self, typename, val):
         self.typename = strip_versioned_namespace(typename)