error safe for casting interval to other types per pg_cast

select castsource::regtype, casttarget::regtype, castfunc,
castcontext,castmethod, pp.prosrc, pp.proname from pg_cast pc join pg_proc pp on
pp.oid = pc.castfunc and pc.castfunc > 0
and castsource::regtype = 'interval'::regtype
order by castsource::regtype;

 castsource |       casttarget       | castfunc | castcontext | castmethod |     prosrc     | proname
------------+------------------------+----------+-------------+------------+----------------+----------
 interval   | time without time zone |     1419 | a           | f          | interval_time  | time
 interval   | interval               |     1200 | i           | f          | interval_scale | interval
(2 rows)

discussion: https://postgr.es/m/CADkLM=fv1JfY4Ufa-jcwwNbjQixNViskQ8jZu3Tz_p656i_4hQ@mail.gmail.com

Author: jianhe-fun

src/backend/utils/adt/date.c

@@ -2106,7 +2106,7 @@ interval_time(PG_FUNCTION_ARGS)
 	TimeADT		result;
 
 	if (INTERVAL_NOT_FINITE(span))
-		ereport(ERROR,
+		ereturn(fcinfo->context, (Datum) 0,
 				(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
 				 errmsg("cannot convert infinite interval to time")));
 

src/backend/utils/adt/timestamp.c

@@ -1334,7 +1334,8 @@ interval_scale(PG_FUNCTION_ARGS)
 	result = palloc(sizeof(Interval));
 	*result = *interval;
 
-	AdjustIntervalForTypmod(result, typmod, NULL);
+	if (!AdjustIntervalForTypmod(result, typmod, fcinfo->context))
+		PG_RETURN_NULL();
 
 	PG_RETURN_INTERVAL_P(result);
 }