Deprecate supports_migrations? on connection adapters

[kamipo]

supports_migrations? was added at 4160b51 to determine if schema
statements (create_table, drop_table, etc) are implemented in the
adapter. But all tested databases has been supported migrations since
a4fc93c at least.

[pixeltrix]

@kamipo are we sure that all the major third-party adapters support migrations too? Also are there any schema-less databases with AR adapters that might make use of this?

[kamipo]

are we sure that all the major third-party adapters support migrations too?

Most adapters (firebird, frontbase, mysql, oracle, postgresql, sqlite, sqlserver, sybase) were true at least as of Rails 1.2.

https://github.com/rails/rails/blob/1-2-stable/activerecord/lib/active_record/connection_adapters/firebird_adapter.rb#L286-L288
https://github.com/rails/rails/blob/1-2-stable/activerecord/lib/active_record/connection_adapters/frontbase_adapter.rb#L270-L272
https://github.com/rails/rails/blob/1-2-stable/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb#L159-L161
https://github.com/rails/rails/blob/1-2-stable/activerecord/lib/active_record/connection_adapters/oracle_adapter.rb#L133-L135
https://github.com/rails/rails/blob/1-2-stable/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb#L106-L108
https://github.com/rails/rails/blob/1-2-stable/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb#L101-L103
https://github.com/rails/rails/blob/1-2-stable/activerecord/lib/active_record/connection_adapters/sqlserver_adapter.rb#L215-L217
https://github.com/rails/rails/blob/1-2-stable/activerecord/lib/active_record/connection_adapters/sybase_adapter.rb#L340-L342

db2 and openbase adapters were false, but looks like that create_table, drop_table, add_column, remove_column, add_index, and remove_index works at least.

supports_migrations? was used for two purposes.

1. to determine if schema statements (create_table, drop_table, etc) are implemented in the adapter in tests. But since a4fc93c any adapter never be able to run tests without create_table and drop_table are implemented at least (and supports_migrations? condition in migration_test.rb was removed at 2158a70).

2. to determine to allow migration (rake db:migrate) to the adapter. I think that disallowing migration is unneeded because not only schema statements can be used in migration.

[pixeltrix]

I think that disallowing migration is unneeded because not only schema statements can be used in migration.

Definitely - you could write all your migrations use execute

[pixeltrix]

Thanks for the additional research @kamipo 👍