[Fix rubocop#6330] Fix an error for Rails/ReversibleMigration

Fixes rubocop#6330 and follow up of rubocop#6198.

This PR fixes an error for `Rails/ReversibleMigration`
when using variable assignment.

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## master (unreleased)
 
+### Bug fixes
+
+* [#6330](https://github.com/rubocop-hq/rubocop/issues/6330): Fix an error for `Rails/ReversibleMigration` when using variable assignment. ([@koic][], [@scottmatthewman][])
+
 ## 0.59.2 (2018-09-24)
 
 ### Bug fixes

lib/rubocop/cop/rails/reversible_migration.rb

@@ -246,6 +246,8 @@ def check_change_table_node(node, block)
         end
 
         def check_change_table_offense(receiver, node)
+          return unless node.send_type?
+
           method_name = node.method_name
           return if receiver != node.receiver &&
                     !IRREVERSIBLE_CHANGE_TABLE_CALLS.include?(method_name)

spec/rubocop/cop/rails/reversible_migration_spec.rb

@@ -61,6 +61,18 @@ def change
     RUBY
   end
 
+  context 'when using variable assignment' do
+    it_behaves_like 'accepts', 'create_table', <<-RUBY
+      def change
+        change_table :invoices do |t|
+          decimals_params = {precision: 10, scale: 2}
+
+          t.decimal :total_discount, decimals_params
+        end
+      end
+    RUBY
+  end
+
   context 'within #reversible' do
     it_behaves_like 'accepts', 'execute', <<-RUBY
       reversible do |dir|