Re: [C++ Patch] PR 50732

[Paolo Carlini]

On 10/14/2011 08:30 PM, Paolo Carlini wrote:

On 10/14/2011 08:23 PM, Paolo Carlini wrote:

Hi,

submitter complains that, at variance with C++11, __is_base_of doesn't handle an incomplete base type (the first parameter). The reason seems simple: in finish_trait_expr we try to complete *both* types instead of doing it where/when necessary.

Hmm, maybe we should be even more careful and call complete (type2) only when

NON_UNION_CLASS_TYPE_P (type1) && NON_UNION_CLASS_TYPE_P (type2) && !same_type_ignoring_top_level_qualifiers_p (type1, type2)

is true?

Like this?

Paolo.

///////////////////


Index: testsuite/g++.dg/ext/is_base_of_incomplete.C
===================================================================
--- testsuite/g++.dg/ext/is_base_of_incomplete.C        (revision 0)
+++ testsuite/g++.dg/ext/is_base_of_incomplete.C        (revision 0)
@@ -0,0 +1,7 @@
+template <typename T>
+struct non_instantiable
+{
+  typedef typename T::THIS_TYPE_CANNOT_BE_INSTANTIATED type;
+};
+
+int check[__is_base_of(non_instantiable<int>, void) ? -1 : 1];
Index: cp/semantics.c
===================================================================
--- cp/semantics.c      (revision 179997)
+++ cp/semantics.c      (working copy)
@@ -5276,10 +5276,6 @@ finish_trait_expr (cp_trait_kind kind, tree type1,
       return trait_expr;
     }
 
-  complete_type (type1);
-  if (type2)
-    complete_type (type2);
-
   switch (kind)
     {
     case CPTK_HAS_NOTHROW_ASSIGN:
@@ -5297,6 +5293,7 @@ finish_trait_expr (cp_trait_kind kind, tree type1,
     case CPTK_IS_POLYMORPHIC:
     case CPTK_IS_STD_LAYOUT:
     case CPTK_IS_TRIVIAL:
+      complete_type (type1);
       if (!check_trait_type (type1))
        {
          error ("incomplete type %qT not allowed", type1);
@@ -5306,11 +5303,14 @@ finish_trait_expr (cp_trait_kind kind, tree type1,
 
     case CPTK_IS_BASE_OF:
       if (NON_UNION_CLASS_TYPE_P (type1) && NON_UNION_CLASS_TYPE_P (type2)
-         && !same_type_ignoring_top_level_qualifiers_p (type1, type2)
-         && !COMPLETE_TYPE_P (type2))
+         && !same_type_ignoring_top_level_qualifiers_p (type1, type2))
        {
-         error ("incomplete type %qT not allowed", type2);
-         return error_mark_node;
+         complete_type (type2);
+         if (!COMPLETE_TYPE_P (type2))
+           {
+             error ("incomplete type %qT not allowed", type2);
+             return error_mark_node;
+           }
        }
       break;