c++: generic lambda fn parm pack [PR104624]

Parameter packs from the enclosing context can be used unexpanded in a
lambda that is itself part of a pack expansion, but not packs that are part
of the lambda itself.  We already check for capture packs; we also need to
check for function parameter packs of the lambda call operator.

	PR c++/104624

gcc/cp/ChangeLog:

	* pt.cc (check_for_bare_parameter_packs): Check for lambda
	function parameter pack.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp1y/lambda-generic-variadic22.C: New test.

gcc/cp/pt.cc

@@ -4341,7 +4341,9 @@ check_for_bare_parameter_packs (tree t, location_t loc /* = UNKNOWN_LOCATION */)
 	 parameter_packs = TREE_CHAIN (parameter_packs))
       {
 	tree pack = TREE_VALUE (parameter_packs);
-	if (is_capture_proxy (pack))
+	if (is_capture_proxy (pack)
+	    || (TREE_CODE (pack) == PARM_DECL
+		&& DECL_CONTEXT (DECL_CONTEXT (pack)) == lam))
 	  break;
       }
 

gcc/testsuite/g++.dg/cpp1y/lambda-generic-variadic22.C

@@ -0,0 +1,15 @@
+// PR c++/104624
+// { dg-do compile { target c++14 } }
+
+template <typename T>
+auto f (T)
+{
+  auto a = [](auto ... i)	// { dg-prune-output "incomplete type" }
+  {
+    int x[][i] = { 0 };		// { dg-error "not expanded" }
+  }();
+}
+void g ()
+{
+  f(0);
+}