Fix autocorrection for Rails/IndexWith when the value is a hash literal without braces

Author: eugeneius

changelog/fix_index_with_hash_literal_without_braces.md

@@ -0,0 +1 @@
+* [#1405](https://github.com/rubocop/rubocop-rails/pull/1405): Fix autocorrection for `Rails/IndexWith` when the value is a hash literal without braces. ([@koic][], [@eugeneius][])

lib/rubocop/cop/mixin/index_method.rb

@@ -161,7 +161,10 @@ def set_new_arg_name(transformed_argname, corrector)
         end
 
         def set_new_body_expression(transforming_body_expr, corrector)
-          corrector.replace(block_node.body, transforming_body_expr.source)
+          body_source = transforming_body_expr.source
+          body_source = "{ #{body_source} }" if transforming_body_expr.hash_type? && !transforming_body_expr.braces?
+
+          corrector.replace(block_node.body, body_source)
         end
       end
     end

spec/rubocop/cop/rails/index_with_spec.rb

@@ -101,6 +101,32 @@
       end
     end
 
+    context 'when the value is a hash literal with braces' do
+      it 'registers an offense for `to_h { ... }`' do
+        expect_offense(<<~RUBY)
+          x.map { |el| [el, { value: el }] }.to_h
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Prefer `index_with` over `map { ... }.to_h`.
+        RUBY
+
+        expect_correction(<<~RUBY)
+          x.index_with { |el| { value: el } }
+        RUBY
+      end
+    end
+
+    context 'when the value is a hash literal without braces' do
+      it 'registers an offense for `to_h { ... }`' do
+        expect_offense(<<~RUBY)
+          x.map { |el| [el, value: el] }.to_h
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Prefer `index_with` over `map { ... }.to_h`.
+        RUBY
+
+        expect_correction(<<~RUBY)
+          x.index_with { |el| { value: el } }
+        RUBY
+      end
+    end
+
     context 'when to_h is not called on the result' do
       it 'does not register an offense for `map { ... }.to_h`' do
         expect_no_offenses('x.map { |el| [el, el.to_sym] }')