RFA: fix PR python/11792

[Tom Tromey <tromey@redhat.com>]

This fixes PR python/11792, which is a feature request asking for a new
Value.dynamic_type method.  The PR includes a patch (Andre has an
assignment via his company), but I've tweaked it here and there and also
added docs and a test case.

This needs a doc review.

Built and regtested on x86-64 (compile farm).

Tom

2010-08-23  Andre Poenitz  <andre.poenitz@nokia.com>
	    Tom Tromey  <tromey@redhat.com>

	PR python/11792:
	* python/py-value.c (valpy_get_dynamic_type): New function.
	(value_object_getset): Add "dynamic_type".
	(valpy_get_type): Fail on error.

2010-08-23  Tom Tromey  <tromey@redhat.com>

	PR python/11792:
	* gdb.texinfo (Values From Inferior): Document dynamic_type.

2010-08-23  Tom Tromey  <tromey@redhat.com>

	PR python/11792:
	* gdb.python/py-value.exp (test_subscript_regression): Add
	dynamic_type test.

diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index d7ff5aa..7e9c0c1 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -20737,6 +20737,16 @@ this value, thus it is not available for fetching from the inferior.
 The type of this @code{gdb.Value}.  The value of this attribute is a
 @code{gdb.Type} object.
 @end defivar
+
+@defivar Value dynamic_type
+The dynamic type of this @code{gdb.Value}.  This uses C@t{++} run-time
+type information to determine the dynamic type of the value.  If this
+value is of class type, it will return the class in which the value is
+embedded, if any.  If this value is of pointer or reference to a class
+type, it will compute the dynamic type of the referenced object, and
+return a pointer or reference to that type, respectively.  In all
+other cases, it will return the value's static type.
+@end defivar
 @end table
 
 The following methods are provided:
diff --git a/gdb/python/py-value.c b/gdb/python/py-value.c
index aa18042..0aeea7c 100644
--- a/gdb/python/py-value.c
+++ b/gdb/python/py-value.c
@@ -27,6 +27,7 @@
 #include "valprint.h"
 #include "infcall.h"
 #include "expression.h"
+#include "cp-abi.h"
 
 #ifdef HAVE_PYTHON
 
@@ -62,6 +63,7 @@ typedef struct value_object {
   struct value *value;
   PyObject *address;
   PyObject *type;
+  PyObject *dynamic_type;
 } value_object;
 
 /* List of all values which are currently exposed to Python. It is
@@ -101,6 +103,8 @@ valpy_dealloc (PyObject *obj)
       Py_DECREF (self->type);
     }
 
+  Py_XDECREF (self->dynamic_type);
+
   self->ob_type->tp_free (self);
 }
 
@@ -148,6 +152,7 @@ valpy_new (PyTypeObject *subtype, PyObject *args, PyObject *keywords)
   value_incref (value);
   value_obj->address = NULL;
   value_obj->type = NULL;
+  value_obj->dynamic_type = NULL;
   note_value (value_obj);
 
   return (PyObject *) value_obj;
@@ -218,15 +223,78 @@ valpy_get_type (PyObject *self, void *closure)
     {
       obj->type = type_to_type_object (value_type (obj->value));
       if (!obj->type)
-	{
-	  obj->type = Py_None;
-	  Py_INCREF (obj->type);
-	}
+	return NULL;
     }
   Py_INCREF (obj->type);
   return obj->type;
 }
 
+/* Return dynamic type of the value.  */
+
+static PyObject *
+valpy_get_dynamic_type (PyObject *self, void *closure)
+{
+  value_object *obj = (value_object *) self;
+  volatile struct gdb_exception except;
+  struct type *type = NULL;
+
+  if (obj->dynamic_type != NULL)
+    {
+      Py_INCREF (obj->dynamic_type);
+      return obj->dynamic_type;
+    }
+
+  TRY_CATCH (except, RETURN_MASK_ALL)
+    {
+      struct value *val = obj->value;
+
+      type = value_type (val);
+      CHECK_TYPEDEF (type);
+
+      if (((TYPE_CODE (type) == TYPE_CODE_PTR)
+	   || (TYPE_CODE (type) == TYPE_CODE_REF))
+	  && (TYPE_CODE (TYPE_TARGET_TYPE (type)) == TYPE_CODE_CLASS))
+	{
+	  struct value *target;
+	  int was_pointer = TYPE_CODE (type) == TYPE_CODE_PTR;
+
+	  target = value_ind (val);
+	  type = value_rtti_type (target, NULL, NULL, NULL);
+
+	  if (type)
+	    {
+	      if (was_pointer)
+		type = lookup_pointer_type (type);
+	      else
+		type = lookup_reference_type (type);
+	    }
+	}
+      else if (TYPE_CODE (type) == TYPE_CODE_CLASS)
+	type = value_rtti_type (val, NULL, NULL, NULL);
+      else
+	{
+	  /* Re-use object's static type.  */
+	  type = NULL;
+	}
+    }
+  GDB_PY_HANDLE_EXCEPTION (except);
+
+  if (type == NULL)
+    {
+      /* Ensure that the TYPE field is ready.  */
+      if (!valpy_get_type (self, NULL))
+	return NULL;
+      /* We don't need to incref here, because valpy_get_type already
+	 did it for us.  */
+      obj->dynamic_type = obj->type;
+    }
+  else
+    obj->dynamic_type = type_to_type_object (type);
+
+  Py_INCREF (obj->dynamic_type);
+  return obj->dynamic_type;
+}
+
 /* Implementation of gdb.Value.lazy_string ([encoding] [, length]) ->
    string.  Return a PyObject representing a lazy_string_object type.
    A lazy string is a pointer to a string with an optional encoding and
@@ -994,6 +1062,7 @@ value_to_value_object (struct value *val)
       value_incref (val);
       val_obj->address = NULL;
       val_obj->type = NULL;
+      val_obj->dynamic_type = NULL;
       note_value (val_obj);
     }
 
@@ -1169,6 +1238,8 @@ static PyGetSetDef value_object_getset[] = {
     "Boolean telling whether the value is optimized out (i.e., not available).",
     NULL },
   { "type", valpy_get_type, NULL, "Type of the value.", NULL },
+  { "dynamic_type", valpy_get_dynamic_type, NULL,
+    "Dynamic type of the value.", NULL },
   {NULL}  /* Sentinel */
 };
 
diff --git a/gdb/testsuite/gdb.python/py-value.exp b/gdb/testsuite/gdb.python/py-value.exp
index 13bce9a..0ecb57c 100644
--- a/gdb/testsuite/gdb.python/py-value.exp
+++ b/gdb/testsuite/gdb.python/py-value.exp
@@ -379,6 +379,13 @@ proc test_subscript_regression {lang} {
      # the C++ tests.
      gdb_test "python print bool(gdb.parse_and_eval('base').dynamic_cast(gdb.lookup_type('Derived').pointer()))" \
 	 True
+
+     # Likewise.
+     gdb_test "python print gdb.parse_and_eval('base').dynamic_type" \
+	 "Derived \[*\]"
+     # A static type case.
+     gdb_test "python print gdb.parse_and_eval('5').dynamic_type" \
+	 "int"
  }
 
  gdb_breakpoint [gdb_get_line_number "break to inspect struct and union"]