error safe for casting jsonb 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 = 'jsonb'::regtype
order by castsource::regtype;

 castsource |    casttarget    | castfunc | castcontext | castmethod |    prosrc     | proname
------------+------------------+----------+-------------+------------+---------------+---------
 jsonb      | boolean          |     3556 | e           | f          | jsonb_bool    | bool
 jsonb      | numeric          |     3449 | e           | f          | jsonb_numeric | numeric
 jsonb      | smallint         |     3450 | e           | f          | jsonb_int2    | int2
 jsonb      | integer          |     3451 | e           | f          | jsonb_int4    | int4
 jsonb      | bigint           |     3452 | e           | f          | jsonb_int8    | int8
 jsonb      | real             |     3453 | e           | f          | jsonb_float4  | float4
 jsonb      | double precision |     2580 | e           | f          | jsonb_float8  | float8
(7 rows)

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

Author: jianhe-fun

src/backend/utils/adt/jsonb.c

@@ -2005,7 +2005,7 @@ JsonbExtractScalar(JsonbContainer *jbc, JsonbValue *res)
  * Emit correct, translatable cast error message
  */
 static void
-cannotCastJsonbValue(enum jbvType type, const char *sqltype)
+cannotCastJsonbValue(enum jbvType type, const char *sqltype, Node *escontext)
 {
 	static const struct
 	{
@@ -2026,9 +2026,12 @@ cannotCastJsonbValue(enum jbvType type, const char *sqltype)
 
 	for (i = 0; i < lengthof(messages); i++)
 		if (messages[i].type == type)
-			ereport(ERROR,
+		{
+			errsave(escontext,
 					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 					 errmsg(messages[i].msg, sqltype)));
+			return;
+		}
 
 	/* should be unreachable */
 	elog(ERROR, "unknown jsonb type: %d", (int) type);
@@ -2041,7 +2044,11 @@ jsonb_bool(PG_FUNCTION_ARGS)
 	JsonbValue	v;
 
 	if (!JsonbExtractScalar(&in->root, &v))
-		cannotCastJsonbValue(v.type, "boolean");
+	{
+		cannotCastJsonbValue(v.type, "boolean", fcinfo->context);
+
+		PG_RETURN_NULL();
+	}
 
 	if (v.type == jbvNull)
 	{
@@ -2050,7 +2057,11 @@ jsonb_bool(PG_FUNCTION_ARGS)
 	}
 
 	if (v.type != jbvBool)
-		cannotCastJsonbValue(v.type, "boolean");
+	{
+		cannotCastJsonbValue(v.type, "boolean", fcinfo->context);
+
+		PG_RETURN_NULL();
+	}
 
 	PG_FREE_IF_COPY(in, 0);
 
@@ -2065,7 +2076,11 @@ jsonb_numeric(PG_FUNCTION_ARGS)
 	Numeric		retValue;
 
 	if (!JsonbExtractScalar(&in->root, &v))
-		cannotCastJsonbValue(v.type, "numeric");
+	{
+		cannotCastJsonbValue(v.type, "numeric", fcinfo->context);
+
+		PG_RETURN_NULL();
+	}
 
 	if (v.type == jbvNull)
 	{
@@ -2074,7 +2089,11 @@ jsonb_numeric(PG_FUNCTION_ARGS)
 	}
 
 	if (v.type != jbvNumeric)
-		cannotCastJsonbValue(v.type, "numeric");
+	{
+		cannotCastJsonbValue(v.type, "numeric", fcinfo->context);
+
+		PG_RETURN_NULL();
+	}
 
 	/*
 	 * v.val.numeric points into jsonb body, so we need to make a copy to
@@ -2095,7 +2114,11 @@ jsonb_int2(PG_FUNCTION_ARGS)
 	Datum		retValue;
 
 	if (!JsonbExtractScalar(&in->root, &v))
-		cannotCastJsonbValue(v.type, "smallint");
+	{
+		cannotCastJsonbValue(v.type, "smallint", fcinfo->context);
+
+		PG_RETURN_NULL();
+	}
 
 	if (v.type == jbvNull)
 	{
@@ -2104,7 +2127,11 @@ jsonb_int2(PG_FUNCTION_ARGS)
 	}
 
 	if (v.type != jbvNumeric)
-		cannotCastJsonbValue(v.type, "smallint");
+	{
+		cannotCastJsonbValue(v.type, "smallint", fcinfo->context);
+
+		PG_RETURN_NULL();
+	}
 
 	retValue = DirectFunctionCall1(numeric_int2,
 								   NumericGetDatum(v.val.numeric));
@@ -2122,7 +2149,11 @@ jsonb_int4(PG_FUNCTION_ARGS)
 	Datum		retValue;
 
 	if (!JsonbExtractScalar(&in->root, &v))
-		cannotCastJsonbValue(v.type, "integer");
+	{
+		cannotCastJsonbValue(v.type, "integer", fcinfo->context);
+
+		PG_RETURN_NULL();
+	}
 
 	if (v.type == jbvNull)
 	{
@@ -2131,7 +2162,11 @@ jsonb_int4(PG_FUNCTION_ARGS)
 	}
 
 	if (v.type != jbvNumeric)
-		cannotCastJsonbValue(v.type, "integer");
+	{
+		cannotCastJsonbValue(v.type, "integer", fcinfo->context);
+
+		PG_RETURN_NULL();
+	}
 
 	retValue = DirectFunctionCall1(numeric_int4,
 								   NumericGetDatum(v.val.numeric));
@@ -2149,7 +2184,11 @@ jsonb_int8(PG_FUNCTION_ARGS)
 	Datum		retValue;
 
 	if (!JsonbExtractScalar(&in->root, &v))
-		cannotCastJsonbValue(v.type, "bigint");
+	{
+		cannotCastJsonbValue(v.type, "bigint", fcinfo->context);
+
+		PG_RETURN_NULL();
+	}
 
 	if (v.type == jbvNull)
 	{
@@ -2158,7 +2197,11 @@ jsonb_int8(PG_FUNCTION_ARGS)
 	}
 
 	if (v.type != jbvNumeric)
-		cannotCastJsonbValue(v.type, "bigint");
+	{
+		cannotCastJsonbValue(v.type, "bigint", fcinfo->context);
+
+		PG_RETURN_NULL();
+	}
 
 	retValue = DirectFunctionCall1(numeric_int8,
 								   NumericGetDatum(v.val.numeric));
@@ -2176,7 +2219,11 @@ jsonb_float4(PG_FUNCTION_ARGS)
 	Datum		retValue;
 
 	if (!JsonbExtractScalar(&in->root, &v))
-		cannotCastJsonbValue(v.type, "real");
+	{
+		cannotCastJsonbValue(v.type, "real", fcinfo->context);
+
+		PG_RETURN_NULL();
+	}
 
 	if (v.type == jbvNull)
 	{
@@ -2185,7 +2232,11 @@ jsonb_float4(PG_FUNCTION_ARGS)
 	}
 
 	if (v.type != jbvNumeric)
-		cannotCastJsonbValue(v.type, "real");
+	{
+		cannotCastJsonbValue(v.type, "real", fcinfo->context);
+
+		PG_RETURN_NULL();
+	}
 
 	retValue = DirectFunctionCall1(numeric_float4,
 								   NumericGetDatum(v.val.numeric));
@@ -2203,7 +2254,11 @@ jsonb_float8(PG_FUNCTION_ARGS)
 	Datum		retValue;
 
 	if (!JsonbExtractScalar(&in->root, &v))
-		cannotCastJsonbValue(v.type, "double precision");
+	{
+		cannotCastJsonbValue(v.type, "double precision", fcinfo->context);
+
+		PG_RETURN_NULL();
+	}
 
 	if (v.type == jbvNull)
 	{
@@ -2212,7 +2267,11 @@ jsonb_float8(PG_FUNCTION_ARGS)
 	}
 
 	if (v.type != jbvNumeric)
-		cannotCastJsonbValue(v.type, "double precision");
+	{
+		cannotCastJsonbValue(v.type, "double precision", fcinfo->context);
+
+		PG_RETURN_NULL();
+	}
 
 	retValue = DirectFunctionCall1(numeric_float8,
 								   NumericGetDatum(v.val.numeric));