Re: BUG #15471: psql 11 array concatenation in CASE takes on values from the CASE expression when using enum_range

Hi,

On 2018-10-30 07:59:35 -0400, Tom Lane wrote:
> =?utf-8?q?PG_Bug_reporting_form?= <noreply@postgresql.org> 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.
> 
> Wow, that's ... bizarre.  I'm thinking that we probably did something
> silly in the big expression-execution rewrite, but it's not clear exactly
> where.

It can't be "the big one", because then it'd be in 10 too, right?

> So somehow the planner is messing up and inserting an outer CaseTestExpr
> value as the source of the elemexpr's coercion expression.  IIRC,
> ruleutils doesn't print the elemexpr at all, which is how come we're not
> seeing the mistake in the EXPLAIN output.
> 
> However, ArrayCoerceExpr has abused CaseTestExpr that way for awhile, so
> it's still not very clear why it broke in v11 and not before ...

Without further analysis, the only commit that looks midly relevant is

commit c12d570fa147d0ec273df53de3a2802925d551ba
Author: Tom Lane <tgl@sss.pgh.pa.us>
Date:   2017-09-30 13:40:56 -0400

    Support arrays over domains.

Greetings,

Andres Freund