Fix a false positive for Rails/ReversibleMigration

The `change_table` method is reversible when using `change_default` with
the :from and :to options.
However, RuboCop detects `Rails/ReversibleMigration` incorrectly, so it fixes.

CHANGELOG.md

@@ -9,6 +9,7 @@
 ### Bug fixes
 
 * [#120](https://github.com/rubocop-hq/rubocop-rails/issues/120): Fix message for `Rails/SaveBang` when the save is in the body of a conditional. ([@jas14][])
+* [#136](https://github.com/rubocop-hq/rubocop-rails/pull/136): Fix a false positive for `Rails/ReversibleMigration` when using `change_default` with the :from and :to options. ([@sinsoku][])
 
 ## 2.3.2 (2019-09-01)
 
@@ -90,3 +91,4 @@
 [@MaximeLaurenty]: https://github.com/MaximeLaurenty
 [@eugeneius]: https://github.com/eugeneius
 [@jas14]: https://github.com/jas14
+[@sinsoku]: https://github.com/sinsoku

lib/rubocop/cop/rails/reversible_migration.rb

@@ -128,7 +128,7 @@ module Rails
       class ReversibleMigration < Cop
         MSG = '%<action>s is not reversible.'
         IRREVERSIBLE_CHANGE_TABLE_CALLS = %i[
-          change change_default remove
+          change remove
         ].freeze
 
         def_node_matcher :irreversible_schema_statement_call, <<-PATTERN
@@ -244,14 +244,20 @@ def check_change_table_node(node, block)
         def check_change_table_offense(receiver, node)
           method_name = node.method_name
           return if receiver != node.receiver &&
-                    !IRREVERSIBLE_CHANGE_TABLE_CALLS.include?(method_name)
+                    !IRREVERSIBLE_CHANGE_TABLE_CALLS.include?(method_name) &&
+                    !irreversible_change_default?(node)
 
           add_offense(
             node,
             message: format(MSG, action: "change_table(with #{method_name})")
           )
         end
 
+        def irreversible_change_default?(node)
+          node.method_name == :change_default &&
+            !all_hash_key?(node.arguments.last, :from, :to)
+        end
+
         def within_change_method?(node)
           node.each_ancestor(:def).any? do |ancestor|
             ancestor.method?(:change)

spec/rubocop/cop/rails/reversible_migration_spec.rb

@@ -165,6 +165,13 @@ def change
       end
     RUBY
 
+    it_behaves_like 'accepts',
+                    'change_table(with reversible change_default)', <<-RUBY
+      change_table :users do |t|
+        t.change_default :authorized, from: nil, to: 1
+      end
+    RUBY
+
     it_behaves_like 'offense', 'change_table(with change_default)', <<-RUBY
       change_table :users do |t|
         t.change_default :authorized, 1