BUG #15071: Error in PostgreSQL-specific :: type cast

The following bug has been logged on the website:

Bug reference: 15071
Logged by: Yuriy Beliy
Email address: whiteman(dot)kr(at)gmail(dot)com
PostgreSQL version: 10.1
Operating system: Windows 10
Description:

PostgreSQL-specific :: type casts for lowest values of integer types are
produce "Out of range" errors:

SELECT -32768::smallint
^ERROR: smallint out of range

SELECT -2147483648::integer
^ERROR: integer out of range

SELECT -9223372036854775808::bigint
^ERROR: bigint out of range

Standard-syntax type casts are workes correctly:

SELECT cast(-32768 as smallint)
^Ok

SELECT cast(-2147483648 as integer)
^Ok

SELECT cast(-9223372036854775808 as bigint)
^Ok

For highest values (+32767, +2147483647, +9223372036854775807) - :: type
cast works correctly.