Patchwork [C++] PR 50732

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Submitter Paolo Carlini
Date Oct. 14, 2011, 6:23 p.m.
Message ID <4E987E24.6000707@oracle.com>
Download mbox | patch
Permalink /patch/119892/
State New
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Comments

Paolo Carlini - Oct. 14, 2011, 6:23 p.m.
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.

Tested x86_64-linux. Ok?

Thanks,
Paolo.

///////////////////
/cp
2011-10-14  Paolo Carlini  <paolo.carlini@oracle.com>

	PR c++/50732
	* semantics.c (finish_trait_expr): Do not try to instantiate the
	the base type of an __is_base_of trait.

/testsuite
2011-10-14  Paolo Carlini  <paolo.carlini@oracle.com>

	PR c++/50732
	* g++.dg/ext/is_base_of_incomplete.C: New.
Paolo Carlini - Oct. 14, 2011, 6:30 p.m.
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?

Paolo.

Patch

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);
@@ -5305,6 +5302,7 @@  finish_trait_expr (cp_trait_kind kind, tree type1,
       break;
 
     case CPTK_IS_BASE_OF:
+      complete_type (type2);
       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))