rubocop_5643_message_fix.diff

diff --git a/lib/rubocop/cop/style/unpack_first.rb b/lib/rubocop/cop/style/unpack_first.rb
index c1d4af411..da0a2e221 100644
--- a/lib/rubocop/cop/style/unpack_first.rb
+++ b/lib/rubocop/cop/style/unpack_first.rb
@@ -28,16 +28,23 @@ module RuboCop
 
         def_node_matcher :unpack_and_first_element?, <<-PATTERN
           {
-            (send (send (...) :unpack (...)) :first)
-            (send (send (...) :unpack (...)) {:[] :slice :at} (int 0))
-            (send (send (...) :unpack (...)) :take (int 1))
+            (send $(send (...) :unpack $(...)) :first)
+            (send $(send (...) :unpack $(...)) {:[] :slice :at} (int 0))
+            (send $(send (...) :unpack $(...)) :take (int 1))
           }
         PATTERN
 
         def on_send(node)
-          return unless unpack_and_first_element?(node)
-
-          add_offense(node)
+          unpack_and_first_element?(node) do |unpack_call, unpack_arg|
+            range =
+              Parser::Source::Range.new(node.loc.expression.source_buffer,
+                                        unpack_call.loc.expression.end_pos,
+                                        node.loc.expression.end_pos)
+            message = format(MSG,
+                             format: unpack_arg.source,
+                             method: range.source)
+            add_offense(node, message: message)
+          end
         end
 
         def autocorrect(node)
@@ -47,22 +54,6 @@ module RuboCop
             corrector.replace(node.children[0].loc.selector, 'unpack1')
           end
         end
-
-        private
-
-        def message(node)
-          format_arg = node.receiver.first_argument.source
-          accessor_method = case node.method_name
-                            when :first
-                              '.first'
-                            when :[]
-                              '[0]'
-                            else
-                              ".#{node.method_name}(#{node.arguments.first.source})"
-                            end
-
-          format(MSG, format: format_arg, method: accessor_method)
-        end
       end
     end
   end
diff --git a/spec/rubocop/cop/style/unpack_first_spec.rb b/spec/rubocop/cop/style/unpack_first_spec.rb
index 7550a3f17..015a603a5 100644
--- a/spec/rubocop/cop/style/unpack_first_spec.rb
+++ b/spec/rubocop/cop/style/unpack_first_spec.rb
@@ -22,7 +22,7 @@ RSpec.describe RuboCop::Cop::Style::UnpackFirst, :config do
       it 'when using `#unpack` with dot and square brackets' do
         expect_offense(<<-RUBY.strip_indent)
         ''.unpack(y).[](0)
-        ^^^^^^^^^^^^^^^^^^ Use `String#unpack1(y)` instead of `String#unpack(y)[0]`.
+        ^^^^^^^^^^^^^^^^^^ Use `String#unpack1(y)` instead of `String#unpack(y).[](0)`.
         RUBY
       end