bring over command recorder remove_index :if_exists that was in schem…

…a_plus_foreign_key

(or should it go in schema_plus_indexes?)

lib/schema_plus/auto_foreign_keys.rb

@@ -1,5 +1,6 @@
 require 'schema_plus/foreign_keys'
 
+require_relative 'auto_foreign_keys/active_record/migration/command_recorder'
 require_relative 'auto_foreign_keys/middleware/migration'
 require_relative 'auto_foreign_keys/middleware/schema'
 

lib/schema_plus/auto_foreign_keys/active_record/migration/command_recorder.rb

@@ -0,0 +1,14 @@
+module SchemaAutoForeignKeys
+  module ActiveRecord
+    module Migration
+      module CommandRecorder
+
+        # overrides to add if_exists option
+        def invert_add_index(args)
+          table, columns, options = *args
+          [:remove_index, [table, (options||{}).merge(column: columns, if_exists: true)]]
+        end
+      end
+    end
+  end
+end