re PR c++/14263 (Cryptic diagnostic for cast from virtual base class not using dynamic_cast)

/cp
2013-07-05  Paolo Carlini  <paolo.carlini@oracle.com>

	PR c++/14263
	* class.c (build_base_path): Improve diagnostic.

/testsuite
2013-07-05  Paolo Carlini  <paolo.carlini@oracle.com>

	PR c++/14263
	* g++.dg/inherit/virtual10.C: New.

From-SVN: r200718

gcc/cp/ChangeLog

+2013-07-05  Paolo Carlini  <paolo.carlini@oracle.com>
+
+	PR c++/14263
+	* class.c (build_base_path): Improve diagnostic.
+
 2013-07-04  Paolo Carlini  <paolo.carlini@oracle.com>
 
 	PR c++/38634

gcc/cp/class.c

@@ -291,9 +291,31 @@ build_base_path (enum tree_code code,
   if (code == MINUS_EXPR && v_binfo)
     {
       if (complain & tf_error)
-	error ("cannot convert from base %qT to derived type %qT via "
-	       "virtual base %qT", BINFO_TYPE (binfo), BINFO_TYPE (d_binfo),
-	       BINFO_TYPE (v_binfo));
+	{
+	  if (SAME_BINFO_TYPE_P (BINFO_TYPE (binfo), BINFO_TYPE (v_binfo)))
+	    {
+	      if (want_pointer)
+		error ("cannot convert from pointer to base class %qT to "
+		       "pointer to derived class %qT because the base is "
+		       "virtual", BINFO_TYPE (binfo), BINFO_TYPE (d_binfo));
+	      else
+		error ("cannot convert from base class %qT to derived "
+		       "class %qT because the base is virtual",
+		       BINFO_TYPE (binfo), BINFO_TYPE (d_binfo));
+	    }	      
+	  else
+	    {
+	      if (want_pointer)
+		error ("cannot convert from pointer to base class %qT to "
+		       "pointer to derived class %qT via virtual base %qT",
+		       BINFO_TYPE (binfo), BINFO_TYPE (d_binfo),
+		       BINFO_TYPE (v_binfo));
+	      else
+		error ("cannot convert from base class %qT to derived "
+		       "class %qT via virtual base %qT", BINFO_TYPE (binfo),
+		       BINFO_TYPE (d_binfo), BINFO_TYPE (v_binfo));
+	    }
+	}
       return error_mark_node;
     }
 

gcc/testsuite/ChangeLog

+2013-07-05  Paolo Carlini  <paolo.carlini@oracle.com>
+
+	PR c++/14263
+	* g++.dg/inherit/virtual10.C: New.
+
 2013-07-04  Joern Rennecke <joern.rennecke@embecosm.com>
 
 	PR c/57821

gcc/testsuite/g++.dg/inherit/virtual10.C

+// PR c++/14263
+
+struct A { };
+
+struct B : virtual A { };
+
+int main()
+{
+   A* p = new B;
+   B* q = static_cast<B*>(p);  // { dg-error "cannot convert from pointer to base class 'A' to pointer to derived class 'B' because the base is virtual" }
+}