问题 如何引用在ON CONFLICT中使用函数的唯一索引？

我正在使用postgres 9.5.3，我有一个这样的表：

CREATE TABLE packages (
  id   SERIAL PRIMARY KEY,
  name VARCHAR NOT NULL
);

我已经定义了一个函数， canonical_name， 喜欢这个：

CREATE FUNCTION canonical_name(text) RETURNS text AS $$
    SELECT replace(lower($1), '-', '_')
$$ LANGUAGE SQL;

我为这个表添加了一个使用该函数的唯一索引：

CREATE UNIQUE INDEX index_package_name
ON packages (canonical_name(name));
CREATE INDEX
# \d+ packages
                                                  Table "public.packages"
 Column |       Type        |                       Modifiers                       | Storage  | Stats target | Description
--------+-------------------+-------------------------------------------------------+----------+--------------+-------------
 id     | integer           | not null default nextval('packages_id_seq'::regclass) | plain    |              |
 name   | character varying | not null                                              | extended |              |
Indexes:
    "packages_pkey" PRIMARY KEY, btree (id)
    "index_package_name" UNIQUE, btree (canonical_name(name::text))

而这个独特的指数正如我所期望的那样工作;它可以防止重复插入：

INSERT INTO packages (name) 
VALUES ('Foo-bar');

INSERT INTO packages (name) 
VALUES ('foo_bar');

ERROR:  duplicate key value violates unique constraint "index_package_name"
DETAIL:  Key (canonical_name(name::text))=(foo_bar) already exists.

我的问题是我想使用这个唯一索引进行upsert，我无法弄清楚我需要如何指定冲突目标。 文档 好像我说我可以指定一个索引表达式：

where conflict_target can be one of:

    ( { index_column_name | ( index_expression ) } [ COLLATE collation ] [ opclass ] [, ...] ) [ WHERE index_predicate ]
    ON CONSTRAINT constraint_name

但是我所尝试的所有这些事情都会产生如图所示的错误，而不是工作上的错误。

我已经尝试匹配索引表达式，因为我指定它：

INSERT INTO packages (name)
VALUES ('foo_bar')
ON CONFLICT (canonical_name(name)) 
DO UPDATE SET name = EXCLUDED.name;

ERROR:  there is no unique or exclusion constraint matching the ON CONFLICT specification

将索引表达式匹配为 \d+ 表明：

INSERT INTO packages (name)
VALUES ('foo_bar')
ON CONFLICT (canonical_name(name::text)) 
DO UPDATE SET name = EXCLUDED.name;


ERROR:  there is no unique or exclusion constraint matching the ON CONFLICT specification

只需命名唯一索引所在的列：

INSERT INTO packages (name)
VALUES ('foo_bar')
ON CONFLICT (name) 
DO UPDATE SET name = EXCLUDED.name;

ERROR:  there is no unique or exclusion constraint matching the ON CONFLICT specification

改为使用索引名称：

INSERT INTO packages (name)
VALUES ('foo_bar')
ON CONFLICT (index_package_name) 
DO UPDATE SET name = EXCLUDED.name;

ERROR:  column "index_package_name" does not exist
LINE 3: ON CONFLICT (index_package_name)

又怎样 做 我指定我想使用这个索引？或者这是一个错误？