C++ PATCH for c++/38579

[Jason Merrill <jason at redhat dot com>]

This turns out to be a bug I introduced back in 2000, but nobody noticed 
until recently.  I don't know what I was thinking when I wrote that 
"accessible_p will iterate over various values of N"; in fact what 
accessible_p is iterating over is possible values of B in the next 
bullet in class.access.base.

Tested x86_64-pc-linux-gnu, applied to trunk.

2009-01-16  Jason Merrill  <jason@redhat.com>

	PR c++/38579
	* search.c (protected_accessible_p): N doesn't vary.
	* g++.dg/conversion/access1.C: New test.

Index: cp/search.c
===================================================================
*** cp/search.c	(revision 143437)
--- cp/search.c	(working copy)
*************** protected_accessible_p (tree decl, tree 
*** 721,740 ****
  
         m as a member of N is protected, and the reference occurs in a
         member or friend of class N, or in a member or friend of a
!        class P derived from N, where m as a member of P is private or
!        protected.
  
!     Here DERIVED is a possible P and DECL is m.  accessible_p will
!     iterate over various values of N, but the access to m in DERIVED
!     does not change.
! 
!     Note that I believe that the passage above is wrong, and should read
!     "...is private or protected or public"; otherwise you get bizarre results
!     whereby a public using-decl can prevent you from accessing a protected
!     member of a base.  (jason 2000/02/28)  */
  
!   /* If DERIVED isn't derived from m's class, then it can't be a P.  */
!   if (!DERIVED_FROM_P (context_for_name_lookup (decl), derived))
      return 0;
  
    access = access_in_type (derived, decl);
--- 721,733 ----
  
         m as a member of N is protected, and the reference occurs in a
         member or friend of class N, or in a member or friend of a
!        class P derived from N, where m as a member of P is public, private
!        or protected.
  
!     Here DERIVED is a possible P, DECL is m and BINFO_TYPE (binfo) is N.  */
  
!   /* If DERIVED isn't derived from N, then it can't be a P.  */
!   if (!DERIVED_FROM_P (BINFO_TYPE (binfo), derived))
      return 0;
  
    access = access_in_type (derived, decl);
Index: testsuite/g++.dg/conversion/access1.C
===================================================================
*** testsuite/g++.dg/conversion/access1.C	(revision 0)
--- testsuite/g++.dg/conversion/access1.C	(revision 0)
***************
*** 0 ****
--- 1,25 ----
+ // PR c++/38579
+ 
+ struct P 
+ {
+ protected:
+   P() {}
+   P(const P&) {}
+ };
+ 
+ struct B : protected P
+ {
+   B() {}
+ };
+ 
+ struct C : public P
+ {
+   // C can access P's copy ctor, but can't convert b to const P&.
+   C(const B& b) : P(b) {}	// { dg-error "inaccessible base" }
+ };
+ 
+ void foo()
+ {
+   B b;
+   C c(b);
+ }