From: Andrew Gierth <andrew@tao11.riddles.org.uk>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Michael Paquier <michael@paquier.xyz>,  cyg0810@gmail.com,
  pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #17088: FailedAssertion in prepagg.c
In-Reply-To: <1909846.1625692937@sss.pgh.pa.us> (Tom Lane's message of "Wed,
	07 Jul 2021 17:22:17 -0400")
Message-ID: <875yxlrf5x.fsf@news-spur.riddles.org.uk>
References: <17088-e33882b387de7f5c@postgresql.org>
	<YOWJQTovI//DNe8/@paquier.xyz> <1908212.1625690962@sss.pgh.pa.us>
	<87a6mxrggq.fsf@news-spur.riddles.org.uk>
	<1909846.1625692937@sss.pgh.pa.us>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (berkeley-unix)
Date: Wed, 07 Jul 2021 22:32:56 +0100
MIME-Version: 1.0
Content-Type: text/plain
Archived-At: 
 <https://www.postgresql.org/message-id/875yxlrf5x.fsf%40news-spur.riddles.org.uk>
Precedence: bulk

>>>>> "Tom" == Tom Lane <tgl@sss.pgh.pa.us> writes:

 > Andrew Gierth <andrew@tao11.riddles.org.uk> writes:
 >> A number of places in the planner have to explicitly avoid recursing
 >> into GroupingFunc->args when walking trees specifically because they
 >> are not evaluated. It looks to me like some places where that should
 >> have been checked for were missed. Looking into it.

 Tom> Hmm. Maybe it'd be better if the default behavior in
 Tom> expression_tree_walker/mutator did not include recursing into the
 Tom> args, then?

You'd think, but as I recall (I will re-check this to confirm) there
were more places where we _did_ need to recurse (especially during parse
analysis before we've matched up the sortgrouprefs), while most of the
places where recursion needed to be explicitly avoided already needed
special-case handling, so having the default the other way would likely
have required a special-case almost everywhere.

-- 
Andrew.