[PATCH] Fix quotation logic for unreserved keywords in window specifications

Hi hackers,

I was testing views with pg_dump/pg_restore and found a case where an
unreserved keyword is not quoted correctly.

example:

-- Just a base table
CREATE TABLE t (v int);
INSERT INTO t VALUES (1), (2);

-- Create a view
CREATE VIEW v AS
SELECT count(*) OVER w2 FROM t
WINDOW "rows" AS (PARTITION BY v), w2 AS ("rows" ORDER BY v);

But the problem is, here, that quotation is gone.

-- Problem: Quotation is disappared
SELECT pg_get_viewdef('v');
pg_get_viewdef
-------------------------------------------------------------
SELECT count(*) OVER w2 AS count +
FROM t +
WINDOW rows AS (PARTITION BY v), w2 AS (rows ORDER BY v);
(1 row)

-- If you use this for recovering the view above, You'll face this error.
SELECT count(*) OVER w2 AS count
FROM t
WINDOW rows AS (PARTITION BY v), w2 AS (rows ORDER BY v);
ERROR: syntax error at or near "ORDER"
LINE 3: WINDOW rows AS (PARTITION BY v), w2 AS (rows ORDER BY v);

This breaks pg_dump/restore: the view is lost.
As a result, pg_dump/pg_restore cannot restore the view successfully.

Fortunately, I found this comment in the gram.y:

It says:

* If we see PARTITION, RANGE, ROWS or GROUPS as the first token after the
'('
* of a window_specification, we want the assumption to be that there is
* no existing_window_name; but those keywords are unreserved and so could
* be ColIds.

I think that assumption can be broken when inheritance is used
across multiple window definitions.
I mean this: w2 AS ("rows" ORDER BY v)

Some comments for patch file:

The attached patch quotes the window name when it is a keyword
in get_rule_windowspec().
Output for ordinary window names is unchanged. The window definition itself
is a ColId so no change is needed there; only the refname is quoted.

Maybe this is a known thing on the team's side, but I think, at least,
should not break
compatibility with current tools. That is the motivation of this patch...

I'd appreciate any feedback or suggestions...!!

Best regards...