Regression in MySQL `auto_increment`

This configuration file fails:

LOAD DATABASE FROM {{MYSQL_URL}} INTO {{PSQL_URL}}
CAST type bigint with extra auto_increment to bigserial

❯ curl -L -o pgloader.jar \
    https://github.com/dimitri/pgloader/releases/download/v4-dev/pgloader.jar
❯ java -jar pgloader.jar test.load --dry-run
09:32:21.040 INFO  [main] pgloader.cli - DRY RUN — no data will be copied
09:32:21.044 INFO  [main] pgloader.cli - Parsing commands from file test.load
Error: Parse error at line 6, column 32:
    type bigint with extra auto_increment to bigserial
                               ^
Expected one of:
#"\s+" (followed by end-of-string)
:end-of-string
;
#"\s+"
DECODING
DISTRIBUTE
AFTER
BEFORE
EXCLUDING
INCLUDING
MATERIALIZE
ALTER
CAST
SET
WITH
,
#"\s+"

However, this succeeds. Note the removal of the underscore on line 2.

LOAD DATABASE FROM {{MYSQL_URL}} INTO {{PSQL_URL}}
CAST type bigint with extra auto increment to bigserial

The documentation uses the underscored auto_increment form exclusively and in many places.

I discovered this behavior while trying to figure out why my schema was losing all auto-incrementing primary keys. Removing the underscore allows the rest of the load to succeed, but the resulting database has no auto-incrementing primary keys, or sequences, identity, or serial.

Start with the test.load reproduction and run the documented pgloader.jar dry-run command, comparing auto_increment with auto increment in the CAST clause. Trace the CAST parser and the MySQL-to-PostgreSQL handling for bigint extras; done means the underscored form parses and migrated primary keys retain auto-increment behavior, sequences, serial, or identity.