PR c++/29028 - Missed unused warning on using declaration

In the example of the patch, g++ fails to warn that the variable N::i
(introduced via a using declaration) is unused.

This is because as we want to emit the warning in poplevel, when we
walk the local bindings returned by getdecls, we forget that a
VAR_DECL introduced by a using declaration is represented by a
TREE_LIST which TREE_VALUE is the VAR_DECL, and we wrongly look for a
bare VAR_DECL.

Fixed thus and tested on x86_64-unknown-linux-gnu against trunk.

gcc/cp/

	* decl.c (poplevel<warn_unused*>): Do not forget that some local
	bindings are represented by a TREE_LIST.

gcc/testsuite/

	* g++.dg/warn/Wunused-var-18.C: New test.

From-SVN: r191829

gcc/cp/ChangeLog

 2012-09-25  Dodji Seketeli  <dodji@redhat.com>
 
+	PR c++/29028 - Missed unused warning on using declaration
+	* decl.c (poplevel<warn_unused*>): Do not forget that some local
+	bindings are represented by a TREE_LIST.
+
+2012-09-25  Dodji Seketeli  <dodji@redhat.com>
+
 	PR c++/53551 - -Wunused-local-typedefs misses uses
 	* decl.c (make_typename_type): Record the use of typedefs.
 

gcc/cp/decl.c

@@ -617,7 +617,12 @@ poplevel (int keep, int reverse, int functionbody)
   /* Before we remove the declarations first check for unused variables.  */
   if ((warn_unused_variable || warn_unused_but_set_variable)
       && !processing_template_decl)
-    for (decl = getdecls (); decl; decl = TREE_CHAIN (decl))
+    for (tree d = getdecls (); d; d = TREE_CHAIN (d))
+      {
+	/* There are cases where D itself is a TREE_LIST.  See in
+	   push_local_binding where the list of decls returned by
+	   getdecls is built.  */
+	decl = TREE_CODE (d) == TREE_LIST ? TREE_VALUE (d) : d;
 	if (TREE_CODE (decl) == VAR_DECL
 	    && (! TREE_USED (decl) || !DECL_READ_P (decl))
 	    && ! DECL_IN_SYSTEM_HEADER (decl)
@@ -637,6 +642,7 @@ poplevel (int keep, int reverse, int functionbody)
 		unused_but_set_errorcount = errorcount;
 	      }
 	  }
+      }
 
   /* Remove declarations for all the DECLs in this level.  */
   for (link = decls; link; link = TREE_CHAIN (link))

gcc/testsuite/ChangeLog

 2012-09-25  Dodji Seketeli  <dodji@redhat.com>
 
+	PR c++/29028 - Missed unused warning on using declaration
+	* g++.dg/warn/Wunused-var-18.C: New test.
+
+2012-09-25  Dodji Seketeli  <dodji@redhat.com>
+
 	PR c++/53551 - -Wunused-local-typedefs misses uses
 	* g++.dg/warn/Wunused-local-typedefs-2.C: New test.
 

gcc/testsuite/g++.dg/warn/Wunused-var-18.C

+// Origin: PR c++/29028
+// { dg-options "-Wunused" }
+// { dg-do compile }
+
+namespace N
+{
+    int i; // { dg-warning "unused variable" }
+}
+
+void
+f ()
+{
+    using N::i;
+}