SQL/JSON: Always coerce JsonExpr result at runtime

Instead of looking up casts at parse time for converting the result
of JsonPath* query functions to the specified or the default
RETURNING type, always perform the conversion at runtime using either
the target type's input function or the function
json_populate_type().

There are two motivations for this change:

1. json_populate_type() coerces to types with typmod such that any
   string values that exceed length limit cause an error instead of
   silent truncation, which is necessary to be standard-conforming.

2. It was possible to end up with a cast expression that doesn't
   support soft handling of errors causing bugs in the of handling
   ON ERROR clause.

JsonExpr.coercion_expr which would store the cast expression is no
longer necessary, so remove.

Bump catversion because stored rules change because of the above
removal.

Reported-by: Alvaro Herrera <alvherre@alvh.no-ip.org>
Reviewed-by: Jian He <jian.universality@gmail.com>
Discussion: Discussion: https://postgr.es/m/202405271326.5a5rprki64aw%40alvherre.pgsql

1 files changed, 2 insertions, 3 deletions

diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 8bc421e7c05..b62c96f2064 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -1052,9 +1052,8 @@ typedef struct JsonExprState
 
 	/*
 	 * Address of the step to coerce the result value of jsonpath evaluation
-	 * to the RETURNING type using JsonExpr.coercion_expr.  -1 if no coercion
-	 * is necessary or if either JsonExpr.use_io_coercion or
-	 * JsonExpr.use_json_coercion is true.
+	 * to the RETURNING type.  -1 if no coercion if JsonExpr.use_io_coercion
+	 * is true.
 	 */
 	int			jump_eval_coercion;