Fix for pg_restore_attribute_stats().

Use RelationGetIndexExpressions() rather than rd_indexprs directly.

Author: Corey Huinker <corey.huinker@gmail.com>

src/backend/statistics/attribute_stats.c

@@ -480,12 +480,28 @@ attribute_statistics_update(FunctionCallInfo fcinfo, int elevel)
 static Node *
 get_attr_expr(Relation rel, int attnum)
 {
-	if ((rel->rd_rel->relkind == RELKIND_INDEX
-		 || (rel->rd_rel->relkind == RELKIND_PARTITIONED_INDEX))
-		&& (rel->rd_indexprs != NIL)
-		&& (rel->rd_index->indkey.values[attnum - 1] == 0))
-	{
-		ListCell   *indexpr_item = list_head(rel->rd_indexprs);
+	List	   *index_exprs;
+	ListCell   *indexpr_item;
+
+	/* relation is not an index */
+	if (rel->rd_rel->relkind != RELKIND_INDEX &&
+		rel->rd_rel->relkind != RELKIND_PARTITIONED_INDEX)
+		return NULL;
+
+	index_exprs = RelationGetIndexExpressions(rel);
+
+	/* index has no expressions to give */
+	if (index_exprs == NIL)
+		return NULL;
+
+	/*
+	 * The index attnum points directly to a relation attnum, then it's no an
+	 * expression attribute.
+	 */
+	if (rel->rd_index->indkey.values[attnum - 1] != 0)
+		return NULL;
+
+	indexpr_item = list_head(rel->rd_indexprs);
 
 	for (int i = 0; i < attnum - 1; i++)
 		if (rel->rd_index->indkey.values[i] == 0)
@@ -495,8 +511,6 @@ get_attr_expr(Relation rel, int attnum)
 		elog(ERROR, "too few entries in indexprs list");
 
 	return (Node *) lfirst(indexpr_item);
-	}
-	return NULL;
 }
 
 /*