From: Andrew Gierth <andrew@tao11.riddles.org.uk>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pg@mattyw.net,  pgsql-bugs@lists.postgresql.org,
  Andres Freund <andres@anarazel.de>
Subject: Re: BUG #15471: psql 11 array concatenation in CASE takes on values
 from the CASE expression when using enum_range
In-Reply-To: <8112.1540900775@sss.pgh.pa.us> (Tom Lane's message of "Tue, 30
	Oct 2018 07:59:35 -0400")
Message-ID: <87efc77gh2.fsf@news-spur.riddles.org.uk>
References: <15471-1117f49271989bad@postgresql.org>
	<8112.1540900775@sss.pgh.pa.us>
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Date: Tue, 30 Oct 2018 12:49:25 +0000
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>>>>> "Tom" == Tom Lane <tgl@sss.pgh.pa.us> writes:

 >> Below is an example .sql file that replicates the problem. Put
 >> simply, when we array concat with enum_range in the result of a CASE
 >> statement the concatenation takes the expression from the CASE
 >> statement, not the enum range.

 Tom> Wow, that's ... bizarre. I'm thinking that we probably did
 Tom> something silly in the big expression-execution rewrite, but it's
 Tom> not clear exactly where. Anyway, will look into it if Andres
 Tom> doesn't beat me to it.

I took a look, and what I'm seeing suggests that commit 3decd150a2d
might possibly be relevant here (at least to explain why it breaks in 11
but not 10).

What's going on in eval_const_expressions_mutator is that
context->case_val is set when recursing into the elemexpr in the
ArrayCoerceExpr case, so when that sees a CaseTestExpr inside that, it
replaces it (incorrectly).

-- 
Andrew (irc:RhodiumToad)