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

On Tue, Dec 9, 2025 at 11:39 AM jian he <jian.universality@gmail.com> wrote:
>
> On Mon, Dec 1, 2025 at 1:41 PM Corey Huinker <corey.huinker@gmail.com> wrote:
> >>
> > No, I meant implementing the syntax for being able to declare a custom CAST function as safe (or not). Basically
addingthe [SAFE] to 
> >
> > CREATE CAST (source_type AS target_type)
> >     WITH [SAFE] FUNCTION function_name [ (argument_type [, ...]) ]
> >
> > I'm not tied to this syntax choice, but this one seemed the most obvious and least invasive.
> >

hi.
please see the attached v15.
the primary implementation of CAST DEFAULT is contained in V15-0021.

changes compared to v14.
1. separate patch (v15-0017) for float error.
-pg_noreturn extern void float_overflow_error(void);
-pg_noreturn extern void float_underflow_error(void);
-pg_noreturn extern void float_zero_divide_error(void);
+extern void float_overflow_error(struct Node *escontext);
+extern void float_underflow_error(struct Node *escontext);
+extern void float_zero_divide_error(struct Node *escontext);

2. separate patch (v15-0018) for newly added float8 functions:
float8_pl_safe
float8_mi_safe
float8_mul_safe
float8_div_safe
refactoring existing functions is too invasive, I choose not to.

3. refactor point_dt (v15-0019). This is necessary for making geometry data type
error-safe, separate from the main patch (v15-0020). I hope to make it easier to
review.
-static inline float8 point_dt(Point *pt1, Point *pt2);
+static inline float8 point_dt(Point *pt1, Point *pt2, Node *escontext);

4. skip compile DEFAULT expression (ExecInitExprRec) for binary coercion cast,
as mentioned before.  See ExecInitSafeTypeCastExpr.

5.  Support user-defined type cast error-safe, see v15-0022.
user-defined error-safe cast syntax:
CREATE CAST (source_type AS target_type)
    WITH [SAFE] FUNCTION function_name [ (argument_type [, ...]) ]
    [ AS ASSIGNMENT | AS IMPLICIT ]

this only adds a new keyword SAFE.
This works for C and internal language functions only now.
To make it really usable, I have made citext, hstore module castfunc error safe.
A new column: pg_cast.casterrorsafe was added, this is needed for
CREATE CAST WITH SAFE FUNCTION.

+select CAST(ARRAY['a','g','b','h',null,'i'] AS hstore
+       DEFAULT NULL ON CONVERSION ERROR);
+ array
+-------
+
+(1 row)
+

6. slightly polished the doc.


--
jian
https://www.enterprisedb.com/