Redmine

ActiveRecord uses db/schema.rb when ActiveRecord::Base.schema_format is :ruby and db/structure.sql when ActiveRecord::Base.schema_format is :sql.

:sql is needed to use SQL that isn't supported by Active Record's migration API.
For example, WITH of PostgreSQL's CREATE INDEX isn't supported.

I'm using SQL that isn't supported by Active Record's migration API in https://github.com/clear-code/redmine_full_text_search .

db:migrate in Rails supports :ruby and :sql.
https://github.com/rails/rails/blob/master/activerecord/lib/active_record/railties/databases.rake#L91-L93

So it's better that redmine:plugins:migrate also supports :ruby and :sql.