Fixes Rails/IndexBy correction when .to_h is separated by a newline

CHANGELOG.md

@@ -9,6 +9,7 @@
 ### Bug fixes
 
 * [#12](https://github.com/rubocop-hq/rubocop-rails/issues/12): Fix a false positive for `Rails/SkipsModelValidations` when passing a boolean literal to `touch`. ([@eugeneius][])
+* [#238](https://github.com/rubocop-hq/rubocop-rails/issues/238): Fix auto correction for `Rails/IndexBy` when the `.to_h` invocation is separated in multiple lines. ([@diogoosorio][])
 
 ### Changes
 
@@ -183,3 +184,4 @@
 [@sunny]: https://github.com/sunny
 [@hoshinotsuyoshi]: https://github.com/hoshinotsuyoshi
 [@tejasbubane]: https://github.com/tejasbubane
+[@diogoosorio]: https://github.com/diogoosorio

lib/rubocop/cop/mixin/index_method.rb

@@ -112,7 +112,14 @@ def self.from_each_with_object(node, match)
         end
 
         def self.from_map_to_h(node, match)
-          strip_trailing_chars = node.parent&.block_type? ? 0 : '.to_h'.length
+          strip_trailing_chars = 0
+
+          unless node.parent&.block_type?
+            map_range = node.children.first.source_range
+            node_range = node.source_range
+            strip_trailing_chars = node_range.end_pos - map_range.end_pos
+          end
+
           new(match, node.children.first, 0, strip_trailing_chars)
         end
 

spec/rubocop/cop/rails/index_by_spec.rb

@@ -94,6 +94,34 @@
     end
   end
 
+  context 'when `to_h` is on a different line' do
+    it 'registers an offense for `map { ... }.to_h`' do
+      expect_offense(<<~RUBY)
+        x.map { |el| [el.to_sym, el] }.
+        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Prefer `index_by` over `map { ... }.to_h`.
+          to_h
+      RUBY
+
+      expect_correction(<<~RUBY)
+        x.index_by { |el| el.to_sym }
+      RUBY
+    end
+  end
+
+  context 'when `.to_h` is on a different line' do
+    it 'registers an offense for `map { ... }.to_h`' do
+      expect_offense(<<~RUBY)
+        x.map { |el| [el.to_sym, el] }
+        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Prefer `index_by` over `map { ... }.to_h`.
+          .to_h
+      RUBY
+
+      expect_correction(<<~RUBY)
+        x.index_by { |el| el.to_sym }
+      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.to_sym, el] }')