[PATCH] Fix PR c++/30917: ICE with friend in local class (to a function)

[PATCH] Fix PR c++/30917: ICE with friend in local class (to a function)

[Simon Martin]

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Hi all.

The following testcase currently triggers an ICE in 4.1, 4.2 and 4.3:

=== cut here ===
class QGList; // L1
unsigned count() {
  class QGListIterator {
    friend class QGList; // L2
    QGListIterator( const QGList & );
  };
}
=== cut here ===

If I read the standard properly, the friend declaration in L2 introduces a 
local class QGList, which must not be taken into account during name lookup, 
it is therefore marked as "hidden" (front-end term).

When QGList is looked up in QGListIterator's constructor, the local QGList 
is found, and an assertion fails in 'name_lookup_real', hence the ICE. This 
assertion ensures that only namespace-scope bindings are hidden; this 
constraint is not verified in our case: we have a hidden and non 
namespace-scope binding (the local QGList).

The attached patch fixes this by ensuring that if the binding is hidden, we 
are processing a local class. Moreover, the lookup will fail because there is 
no suitable declaration for QGList: the local one coming from the friend 
declaration is not a candidate, nor is the one at L1 (only a declaration in 
the innermost enclosing nonclass scope - that is 'count' - is to be found). In 
other words, this testcase is invalid, and the compiler will output an error 
(however, please note that icc accepts this snippet, so my interpretation 
might be wrong...).

I have successfully regtested this on i686-pc-linux-gnu. Is it OK for 
mainline? For 4.2?

Best regards,
Simon

:ADDPATCH c++:

[-- Attachment #2: CL_30917 --]
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2007-03-07  Simon Martin  <simartin@users.sourceforge.net>

	PR c++/30917
	* name-lookup.c (lookup_name_real): Non namespace-scope bindings can be
	hidden due to friend declarations in local classes.

[-- Attachment #3: pr30917.patch --]
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Index: gcc/cp/name-lookup.c
===================================================================
--- gcc/cp/name-lookup.c	(revision 122641)
+++ gcc/cp/name-lookup.c	(working copy)
@@ -4010,10 +4010,24 @@ lookup_name_real (tree name, int prefer_
 
 	if (binding)
 	  {
-	    /* Only namespace-scope bindings can be hidden.  */
-	    gcc_assert (!hidden_name_p (binding));
-	    val = binding;
-	    break;
+	    if (hidden_name_p (binding))
+	      {
+		/* A non namespace-scope binding can only be hidden if we
+		   are in a local class, due to friend declarations.  */
+		gcc_assert (current_class_type &&
+			    LOCAL_CLASS_P (current_class_type));
+
+		/* This binding comes from a friend declaration in the local
+		   class. The standard (11.4.8) states that the lookup can
+		   only succeed if there is a non-hidden declaration in the
+		   current scope, which is not the case here.  */
+		POP_TIMEVAR_AND_RETURN (TV_NAME_LOOKUP, NULL_TREE);
+	      }
+	    else
+	      {
+		val = binding;
+		break;
+	      }
 	  }
       }
 

[-- Attachment #4: CL_30917_testsuite --]
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2007-03-07  Simon Martin  <simartin@users.sourceforge.net>

	PR c++/30917
	* g++.dg/lookup/friend11.C: New test.

[-- Attachment #5: friend11.C --]
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/* PR c++/30917 */
/* This used to ICE */
/* { dg-do "compile" } */


// This is invalid: QGList must only be looked up in count.
class QGList;
unsigned count() {
  class QGListIterator {
    friend class QGList;
    QGListIterator( const QGList & ); /* { dg-error "expected|with no type" } */
  };
  return 0;
}

// This is valid.
unsigned count2() {
  class QGList2;
  class QGListIterator2 {
    friend class QGList2;
    QGListIterator2( const QGList2 & );
  };
  return 0;
}

Re: [PATCH] Fix PR c++/30917: ICE with friend in local class (to a function)

[Simon Martin]

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Hi all.

The initial patch:
http://gcc.gnu.org/ml/gcc-patches/2007-03/msg00463.html

has been approved by Mark modulo some minor changes here:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30917#c5

I attach the updated patch (the testsuite bits are unchanged), that I
have successfully tested again on i386-apple-darwin8.10.1, and committed
to the trunk.

I'll test it against 4.2, and commit it there if testing succeeds.

Best regards,
Simon



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2007-07-28  Simon Martin  <simartin@users.sourceforge.net>
	    Mark Mitchell  <mark@codesourcery.com>

	PR c++/30917
	* name-lookup.c (lookup_name_real): Non namespace-scope bindings can be
	hidden due to friend declarations in local classes.


[-- Attachment #3: pr30917_3.patch --]
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Index: gcc/cp/name-lookup.c
===================================================================
--- gcc/cp/name-lookup.c	(revision 126993)
+++ gcc/cp/name-lookup.c	(working copy)
@@ -3990,8 +3990,49 @@ lookup_name_real (tree name, int prefer_
 
 	if (binding)
 	  {
-	    /* Only namespace-scope bindings can be hidden.  */
-	    gcc_assert (!hidden_name_p (binding));
+	    if (hidden_name_p (binding))
+	      {
+		/* A non namespace-scope binding can only be hidden if
+		   we are in a local class, due to friend declarations.
+		   In particular, consider:
+
+		   void f() {
+		     struct A {
+		       friend struct B;
+		       void g() { B* b; } // error: B is hidden
+		     }
+		     struct B {};
+		   }
+
+		   The standard says that "B" is a local class in "f"
+		   (but not nested within "A") -- but that name lookup
+		   for "B" does not find this declaration until it is
+		   declared directly with "f".
+
+		   In particular:
+
+		   [class.friend]
+
+		   If a friend declaration appears in a local class and
+		   the name specified is an unqualified name, a prior
+		   declaration is looked up without considering scopes
+		   that are outside the innermost enclosing non-class
+		   scope. For a friend class declaration, if there is no
+		   prior declaration, the class that is specified 
+		   belongs to the innermost enclosing non-class scope,
+		   but if it is subsequently referenced, its name is not
+		   found by name lookup until a matching declaration is
+		   provided in the innermost enclosing nonclass scope.
+		*/
+		gcc_assert (current_class_type &&
+			    LOCAL_CLASS_P (current_class_type));
+
+		/* This binding comes from a friend declaration in the local
+		   class. The standard (11.4.8) states that the lookup can
+		   only succeed if there is a non-hidden declaration in the
+		   current scope, which is not the case here.  */
+		POP_TIMEVAR_AND_RETURN (TV_NAME_LOOKUP, NULL_TREE);
+	      }
 	    val = binding;
 	    break;
 	  }