c++: Find parameter pack in typedef in lambda [92909].

find_parameter_packs_r doesn't look through typedefs, which is normally
correct, but that means we need to handle their declarations specially.

gcc/cp/ChangeLog
2020-03-14  Jason Merrill  <jason@redhat.com>

	PR c++/92909
	* pt.c (find_parameter_packs_r): [DECL_EXPR]: Walk
	DECL_ORIGINAL_TYPE of a typedef.

gcc/cp/ChangeLog

 2020-03-14  Jason Merrill  <jason@redhat.com>
 
+	PR c++/92909
+	* pt.c (find_parameter_packs_r): [DECL_EXPR]: Walk
+	DECL_ORIGINAL_TYPE of a typedef.
+
+2020-03-14  Jason Merrill  <jason@redhat.com>
+
 	PR c++/93248
 	* pt.c (build_deduction_guide): Clear cp_unevaluated_operand for
 	substituting DECL_ARGUMENTS.

gcc/cp/pt.c

@@ -3916,10 +3916,18 @@ find_parameter_packs_r (tree *tp, int *walk_subtrees, void* data)
       return NULL_TREE;
 
     case DECL_EXPR:
-      /* Ignore the declaration of a capture proxy for a parameter pack.  */
-      if (is_capture_proxy (DECL_EXPR_DECL (t)))
-	*walk_subtrees = 0;
-      return NULL_TREE;
+      {
+	tree decl = DECL_EXPR_DECL (t);
+	/* Ignore the declaration of a capture proxy for a parameter pack.  */
+	if (is_capture_proxy (decl))
+	  *walk_subtrees = 0;
+	if (is_typedef_decl (decl))
+	  /* Since we stop at typedefs above, we need to look through them at
+	     the point of the DECL_EXPR.  */
+	  cp_walk_tree (&DECL_ORIGINAL_TYPE (decl),
+			&find_parameter_packs_r, ppd, ppd->visited);
+	return NULL_TREE;
+      }
 
     case TEMPLATE_DECL:
       if (!DECL_TEMPLATE_TEMPLATE_PARM_P (t))

gcc/testsuite/g++.dg/cpp0x/lambda/lambda-variadic10.C

+// PR c++/92909
+// { dg-do compile { target c++11 } }
+
+template <class ... Ts>
+void foo()
+{
+    []
+    {
+        using T = Ts;
+    }();			// { dg-error "not expanded" }
+}
+template void foo<>();