Re: CAST(... ON DEFAULT) - WIP build on top of Error-Safe User Functions

On Fri, Oct 10, 2025 at 8:23 PM jian he <jian.universality@gmail.com> wrote:
> After applying the attached v7 patch patchset,
> the below are cast functions that I didn't refactor to error safe yet.
>
> select pc.castsource::regtype,
>        pc.casttarget::regtype, castfunc::regproc, pp.prosrc
> from pg_cast pc join pg_proc pp on pp.oid = pc.castfunc
> join pg_type pt on pt.oid = castsource
> join pg_type pt1 on pt1.oid = casttarget
> and pc.castfunc > 0 and pt.typnamespace = 'pg_catalog'::regnamespace
> and pt1.typnamespace = 'pg_catalog'::regnamespace and not pc.casterrorsafe;
>
>  castsource | casttarget |       castfunc       |    prosrc
> ------------+------------+----------------------+--------------
>  bigint     | money      | pg_catalog.money     | int8_cash
>  integer    | money      | pg_catalog.money     | int4_cash
>  numeric    | money      | pg_catalog.money     | numeric_cash
>  money      | numeric    | pg_catalog."numeric" | cash_numeric
> (4 rows)
>
> The reason I don't refactor these cast functions related to money data
> type  is because
> 1. I am not sure if the PGLC_localeconv() function is error safe or not.
> 2. refactoring such ``DirectFunctionCall1(numeric_int8, amount));``
> requires more effort.
>
> please check the attached v7 patch set:
> 01-error-safe-for-casting-bytea-to-other-types
> 02-error-safe-for-casting-bit-varbit-to-other-types
> 03-error-safe-for-casting-character-to-other-types
> 04-error-safe-for-casting-text-to-other-types
> 05-error-safe-for-casting-character-varying-to-other-types
> 06-error-safe-for-casting-inet-to-other-types
> 07-error-safe-for-casting-macaddr8-to-other-types
> 08-error-safe-for-casting-integer-to-other-types
> 09-error-safe-for-casting-bigint-to-other-types
> 10-error-safe-for-casting-numeric-to-other-types
> 11-error-safe-for-casting-float4-to-other-types
> 12-error-safe-for-casting-float8-to-other-types
> 13-error-safe-for-casting-date-to-other-types
> 14-error-safe-for-casting-interval-to-other-types
> 15-error-safe-for-casting-timestamptz-to-other-types
> 16-error-safe-for-casting-timestamp-to-other-types
> 17-error-safe-for-casting-jsonb-to-other-types
> 18-error-safe-for-casting-geometry-data-types
> 19-invent_some_error_safe_function.patch
> 20-CAST-expr-AS-newtype-DEFAULT-ON-ERROR.patch
>
> Each patch includes a commit message explaining which function is being
> refactored to be error-safe.
>

Summary of what this patch set is doing:
To implement the syntax:
CAST(source_expr AS target_type DEFAULT def_expr ON CONVERSION ERROR)

we need to ensure that the transformed cast expression is error-safe.
A transformed cast expression can be either a CoerceViaIO or a FuncExpr.
Since CoerceViaIO is already error-safe but FuncExpr cannot be
rewritten as CoerceViaIO
one of the example: SELECT ('11.1'::numeric::int)

So we need to refactor how pg_cast.castfunc works to make it error-safe.
We also need to query pg_cast to determine whether a given pg_cast.castfunc is
error-safe.  For this, a new field casterrorsafe is added to pg_cast.

Patches 01–18: Refactor all pg_cast.castfunc entries (except those with the
money data type) to be error-safe.
Patches 19–20: Implement support for CAST(... AS ... DEFAULT def_expr ON
CONVERSION ERROR)

Please check the attached v8.

It includes minor changes compared to v7:
mainly a small mistake fix in src/backend/jit/llvm/llvmjit_expr.c.
Additionally, one occurrence of NO_XML_SUPPORT(); was replaced with
errsave(escontext, …).