Update the message for Style/OptionalBooleanParameter.

lib/rubocop/cop/style/optional_boolean_parameter.rb

@@ -37,20 +37,26 @@ module Style
       class OptionalBooleanParameter < Base
         include AllowedMethods
 
-        MSG = 'Use keyword arguments when defining method with boolean argument.'
-        BOOLEAN_TYPES = %i[true false].freeze
+        MSG = 'Prefer keyword arguments for arguments with a boolean default value; ' \
+              'use `%<replacement>s` instead of `%<original>s`.'
 
         def on_def(node)
           return if allowed_method?(node.method_name)
 
           node.arguments.each do |arg|
             next unless arg.optarg_type?
 
-            _name, value = *arg
-            add_offense(arg) if BOOLEAN_TYPES.include?(value.type)
+            add_offense(arg, message: format_message(arg)) if arg.default_value.boolean_type?
           end
         end
         alias on_defs on_def
+
+        private
+
+        def format_message(argument)
+          source = argument.source
+          format(MSG, original: source, replacement: source.sub(/\s+=/, ':'))
+        end
       end
     end
   end

spec/rubocop/cop/style/optional_boolean_parameter_spec.rb

@@ -6,24 +6,24 @@
   it 'registers an offense when defining method with optional boolean arg' do
     expect_offense(<<~RUBY)
       def some_method(bar = false)
-                      ^^^^^^^^^^^ Use keyword arguments when defining method with boolean argument.
+                      ^^^^^^^^^^^ Prefer keyword arguments for arguments with a boolean default value; use `bar: false` instead of `bar = false`.
       end
     RUBY
   end
 
   it 'registers an offense when defining class method with optional boolean arg' do
     expect_offense(<<~RUBY)
       def self.some_method(bar = false)
-                           ^^^^^^^^^^^ Use keyword arguments when defining method with boolean argument.
+                           ^^^^^^^^^^^ Prefer keyword arguments for arguments with a boolean default value; use `bar: false` instead of `bar = false`.
       end
     RUBY
   end
 
   it 'registers an offense when defining method with multiple optional boolean args' do
     expect_offense(<<~RUBY)
       def some_method(foo = true, bar = 1, baz = false, quux: true)
-                      ^^^^^^^^^^ Use keyword arguments when defining method with boolean argument.
-                                           ^^^^^^^^^^^ Use keyword arguments when defining method with boolean argument.
+                      ^^^^^^^^^^ Prefer keyword arguments for arguments with a boolean default value; use `foo: true` instead of `foo = true`.
+                                           ^^^^^^^^^^^ Prefer keyword arguments for arguments with a boolean default value; use `baz: false` instead of `baz = false`.
       end
     RUBY
   end