Steps to reproduce

Add a gin index on a colum with a name position.

add_index :players, :position, using: :gin, opclass: :gin_trgm_ops, name: 'gin_index_position_on_players'
add_index :players, :name, using: :gin, opclass: :gin_trgm_ops, name: 'gin_index_name_on_players'

At the moment, I have only encountered the problem on column with position as name.

Expected behavior

This should dump properly the index the schema.rb.
Something like
t.index ["position"], name: "gin_index_position_on_players", opclass: :gin_trgm_ops, using: :gin

Actual behavior

It creates an index wihtout an opclass in the db/schema.rb. Here is what is created:
t.index ["position"], name: "gin_index_position_on_positions", using: :gin

Investigations done on my own

Creating indexes seems fine.
However, while checking the created indexes in db using

select *
from pg_indexes
where tablename = 'players';

The indexdef of the index related to the position column is different. The colum name is wrapped with double quotes.
indexdef:CREATE INDEX gin_index_position_on_players ON public.players USING gin ("position" gin_trgm_ops)

I did not find out why this particular word is wrapped up (other postgres reserved words are not wrapped up, other built-in functions are not wrapped up).

The issue occurs while parsing the indexdef in activerecord-5.2.1/lib/active_record/connection_adapters/postgresql/schema_statements.rb:127.

It could be fixed by adding this edge case to the regexp.

Why does this occurs
After deeper explanations, I land on https://www.postgresql.org/docs/current/sql-keywords-appendix.html and it seems that this behavior happens on the non reserved (cannot be function or type) keyword.

System configuration

Rails version: 5.2.1

Ruby version: 2.5.3