Re: remaining sql/json patches

one more issue.....

+-- Extension: non-constant JSON path
+SELECT JSON_EXISTS(jsonb '{"a": 123}', '$' || '.' || 'a');
+SELECT JSON_VALUE(jsonb '{"a": 123}', '$' || '.' || 'a');
+SELECT JSON_VALUE(jsonb '{"a": 123}', '$' || '.' || 'b' DEFAULT 'foo'
ON EMPTY);
+SELECT JSON_QUERY(jsonb '{"a": 123}', '$' || '.' || 'a');
+SELECT JSON_QUERY(jsonb '{"a": 123}', '$' || '.' || 'a' WITH WRAPPER);

json path may not be a plain Const.
does the following code in expression_tree_walker_impl need to consider
cases when the `jexpr->path_spec` part is not a Const?

+ case T_JsonExpr:
+ {
+ JsonExpr   *jexpr = (JsonExpr *) node;
+
+ if (WALK(jexpr->formatted_expr))
+ return true;
+ if (WALK(jexpr->result_coercion))
+ return true;
+ if (WALK(jexpr->item_coercions))
+ return true;
+ if (WALK(jexpr->passing_values))
+ return true;
+ /* we assume walker doesn't care about passing_names */
+ if (WALK(jexpr->on_empty))
+ return true;
+ if (WALK(jexpr->on_error))
+ return true;
+ }