RFC: fix std::unique_ptr pretty-printer

[Tom Tromey]

A user reported on irc that the std::unique_ptr pretty-printer yields
bad results.  For example:

(gdb) p uptr
$1 = std::tuple containing = {
  [1] = ,
  [2] = {
    <std::default_delete<datum>> = {<No data fields>}, <No data fields>}
}

This omits the actual pointer and prints some useless stuff instead.

This patch fixes the printer and adds a test.
The new output looks like this:

$11 = std::unique_ptr containing (datum *) 0x6067d0

Let me know what you think.

Tom

b/libstdc++-v3/ChangeLog:
2012-08-10  Tom Tromey  <tro...@redhat.com>

        * testsuite/libstdc++-prettyprinters/cxx11.cc (struct datum):
        New.
        (global): New global.
        (main): Add test for unique_ptr.
        * python/libstdcxx/v6/printers.py
        (UniquePointerPrinter.to_string): Extract the pointer and also
        print its type.

diff --git a/libstdc++-v3/python/libstdcxx/v6/printers.py 
b/libstdc++-v3/python/libstdcxx/v6/printers.py
index 4520f32..dcb98de 100644
--- a/libstdc++-v3/python/libstdcxx/v6/printers.py
+++ b/libstdc++-v3/python/libstdcxx/v6/printers.py
@@ -71,7 +71,8 @@ class UniquePointerPrinter:
         self.val = val
 
     def to_string (self):
-        return self.val['_M_t']
+        v = self.val['_M_t']['_M_head_impl']
+        return 'std::unique_ptr containing (' + str(v.type) + ') ' + str(v)
 
 class StdListPrinter:
     "Print a std::list"
diff --git a/libstdc++-v3/testsuite/libstdc++-prettyprinters/cxx11.cc 
b/libstdc++-v3/testsuite/libstdc++-prettyprinters/cxx11.cc
index 54b3275..7e2e240 100644
--- a/libstdc++-v3/testsuite/libstdc++-prettyprinters/cxx11.cc
+++ b/libstdc++-v3/testsuite/libstdc++-prettyprinters/cxx11.cc
@@ -48,6 +48,14 @@ use(const T &container)
     placeholder(*i);
 }
 
+struct datum
+{
+  std::string s;
+  int i;
+};
+
+std::unique_ptr<datum> global;
+
 int
 main()
 {
@@ -86,6 +94,11 @@ main()
   uoms.insert(5);
 // { dg-final { note-test uoms {std::unordered_multiset with 1 elements = {[0] 
= 5}} } }
 
+  std::unique_ptr<datum> uptr (new datum);
+  uptr->s = "hi bob";
+  uptr->i = 23;
+// { dg-final { regexp-test uptr {std::unique_ptr containing .datum .. 0x.*} } 
}
+
   placeholder(""); // Mark SPOT
   use(efl);
   use(fl);
@@ -93,6 +106,8 @@ main()
   use(eumm);
   use(eus);
   use(eums);
+  use(uoms);
+  use(uptr->s);
 
   return 0;
 }