New cop rule: IrreversibleMigration

[AlasdairWallaceMackie]

Should resolve this issue: #30

According to the Sequel documentation, only certain methods should be placed inside a change block in a migration file. Other methods could make the migration irreversible.

This new cop will warn the user under the following conditions inside a change block:

• They use a method that's not listed in the documentation
• They use the method #add_primary_key with an array argument instead of a symbol

[AlasdairWallaceMackie]

Had to make this change due to failed CI build

[tt]

This introduced an issue where change blocks outside of Sequel migrations are also being detected. See #44 for context.

[soumyaray]

The IrreversibleMigration rule disallows using primary_key and String for create_table in a change block. However, the Sequel documentation example for how to use change in lieu of up/down blocks uses primary_key and String methods for a create_table in a change block. I'm a bit confused here as to why these are not allowed by IrreversibleMigration? Would this new cop also fail the example in the documentation?

Sequel.migration do
  change do
    create_table(:artists) do
      primary_key :id
      String :name, null: false
    end
  end
end

[AlasdairWallaceMackie]

@soumyaray Thanks for bringing this to my attention, the cop should be ignoring all methods within a create_table block. I will work on a fix for this

[soumyaray]

@soumyaray Thanks for bringing this to my attention, the cop should be ignoring all methods within a create_table block. I will work on a fix for this

Thank you so much for your quick handling of this -- really appreciate the work on this gem.