Fix support function to work with operators

Previously a support function only optimized function calls
on consts but the operator logic inserts a CoerceToDomain
node before the const as well. This PR allows this case to
also be handled by relaxing the constrainst on args from having
to be constants to having to be merely const-like. That is
the expression cannot reference any vars or use volatile functions.

Author: cevian

extension/src/support.c

@@ -8,6 +8,8 @@
 
 #include <nodes/pathnodes.h>
 #include <nodes/supportnodes.h>
+#include <nodes/bitmapset.h>
+#include <optimizer/optimizer.h>
 
 #ifdef PG_MODULE_MAGIC
 PG_MODULE_MAGIC;
@@ -52,8 +54,13 @@ const_support(PG_FUNCTION_ARGS)
 		}
 		foreach(lc, expr->args)
 		{
+			/* Check that these are expressions that don't reference
+			any vars, i.e. they are constants or expressions of constants */
 			Node *arg = lfirst(lc);
-			if(!IsA(arg, Const))
+			Relids relids = pull_varnos(arg);
+
+			if(bms_membership(relids) != BMS_EMPTY_SET ||
+				contain_volatile_functions(arg))
 			{
 				PG_RETURN_POINTER(NULL);
 			}