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From: Corey Huinker <corey.huinker@gmail.com>
Date: Wed, 14 Jan 2026 17:16:12 -0500
Message-ID: <CADkLM=f0xruKRH+6XvCsM1EVic9y4BL4AFo3VUfvRLdu-Qp5Gg@mail.gmail.com>
Subject: Re: CAST(... ON DEFAULT) - WIP build on top of Error-Safe User Functions
To: jian he <jian.universality@gmail.com>
Cc: Amul Sul <sulamul@gmail.com>, Kirill Reshke <reshkekirill@gmail.com>, 
	Vik Fearing <vik@postgresfriends.org>, Isaac Morland <isaac.morland@gmail.com>, 
	pgsql-hackers@lists.postgresql.org
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>
> > +               /*
> > +                * Here, we cannot deparsing cast_expr directly, since
> > +                * transformTypeSafeCast may have folded it into a simple
> > +                * constant or NULL. Instead, we use source_expr and
> > +                * default_expr to reconstruct the CAST DEFAULT clause.
> > +                */
> >
> > I am wondering how other places handle expression deparsing; do they
> > hold the original expression along with the transformed expression?
>

In my initial implementation of this, I modified CoalesceExpr to ensure
that the default clause was evaluated if and only if the initial expression
failed.


> rebased, many variable names have been renamed, comments adjusted.


The new SAFE option on user defined cast functions looks good to me.

I am concerned that adding _safe overhead to all cast functions will be
received poorly, but if it is poorly received then reverting isn't that
hard.

I'm going to re-review the whole patch set, but I wanted to say that I like
the main points of the changes so far.

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<div dir=3D"ltr"><div class=3D"gmail_quote gmail_quote_container"><blockquo=
te class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px =
solid rgb(204,204,204);padding-left:1ex">
&gt; +=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0/*<br>
&gt; +=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 * Here, we ca=
nnot deparsing cast_expr directly, since<br>
&gt; +=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 * transformTy=
peSafeCast may have folded it into a simple<br>
&gt; +=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 * constant or=
 NULL. Instead, we use source_expr and<br>
&gt; +=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 * default_exp=
r to reconstruct the CAST DEFAULT clause.<br>
&gt; +=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 */<br>
&gt;<br>
&gt; I am wondering how other places handle expression deparsing; do they<b=
r>
&gt; hold the original expression along with the transformed expression?<br=
></blockquote><div><br></div><div>In my initial implementation of this, I m=
odified CoalesceExpr to ensure that the default clause was evaluated if and=
 only if the initial expression failed.</div><div></div><div><br></div><div=
>=C2=A0</div><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px =
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
rebased, many variable names have been renamed, comments adjusted.</blockqu=
ote><div><br></div><div>The new SAFE option on user defined cast functions =
looks good to me.<br><br>I am concerned that adding _safe overhead to all c=
ast functions will be received poorly, but if it is poorly received then re=
verting isn&#39;t that hard.</div><div><br></div><div>I&#39;m going to re-r=
eview the whole patch set, but I wanted to say that I like the main points =
of the changes so far.</div></div></div>

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