[Fix rubocop#6936] Fix MultilineMethodArgumentLineBreaks when bracket…

… hash assignment on multiple lines

CHANGELOG.md

@@ -6,6 +6,10 @@
 
 * [#5976](https://github.com/rubocop-hq/rubocop/issues/5976): Warn for Rails Cops. ([@koic][])
 
+### Bug fixes
+
+* [#6936](https://github.com/rubocop-hq/rubocop/issues/6936): Fix `Layout/MultilineMethodArgumentLineBreaks` when bracket hash assignment on multiple lines. ([@maxh][])
+
 ## 0.70.0 (2019-05-21)
 
 ### New features

lib/rubocop/cop/layout/multiline_method_argument_line_breaks.rb

@@ -26,6 +26,8 @@ class MultilineMethodArgumentLineBreaks < Cop
           'on a separate line.'
 
         def on_send(node)
+          return if node.method_name == :[]=
+
           args = node.arguments
 
           # If there is a trailing hash arg without explicit braces, like this:

spec/rubocop/cop/layout/multiline_method_argument_line_breaks_spec.rb

@@ -13,6 +13,33 @@
     end
   end
 
+  context 'when bracket hash assignment on multiple lines' do
+    it 'does not add any offenses' do
+      expect_no_offenses(
+        <<-RUBY
+          class Thing
+            def call
+              bar['foo'] = ::Time.zone.at(
+                             huh['foo'],
+                           )
+            end
+          end
+        RUBY
+      )
+    end
+  end
+
+  context 'when bracket hash assignment key on multiple lines' do
+    it 'does not add any offenses' do
+      expect_no_offenses(
+        <<-RUBY
+          a['b',
+              'c', 'd'] = e
+        RUBY
+      )
+    end
+  end
+
   context 'when two arguments are on next line' do
     it 'does not add any offenses' do
       expect_no_offenses(