[Fix #10186] Explicit block arg is not counted for Metrics/ParameterLists

changelog/change_explicit_block_arg_is_not_counted_for_metrics_parameter_lists.md

@@ -0,0 +1 @@
+* [#10186](https://github.com/rubocop/rubocop/issues/10186): Explicit block arg is not counted for `Metrics/ParameterLists`. ([@koic][])

lib/rubocop/cop/metrics/parameter_lists.rb

@@ -9,6 +9,9 @@ module Metrics
       # Keyword arguments can optionally be excluded from the total count,
       # as they add less complexity than positional or optional parameters.
       #
+      # NOTE: Explicit block argument `&block` is not counted to prevent
+      #       erroneous change that is avoided by making block argument implicit.
+      #
       # @example Max: 3
       #   # good
       #   def foo(a, b, c = 1)
@@ -94,9 +97,9 @@ def on_args(node)
 
         def args_count(node)
           if count_keyword_args?
-            node.children.size
+            node.children.count { |a| !a.blockarg_type? }
           else
-            node.children.count { |a| !NAMED_KEYWORD_TYPES.include?(a.type) }
+            node.children.count { |a| !NAMED_KEYWORD_TYPES.include?(a.type) && !a.blockarg_type? }
           end
         end
 

spec/rubocop/cop/metrics/parameter_lists_spec.rb

@@ -82,4 +82,18 @@ def foo(a, b = 2, c = 3, d = 4)
       end
     RUBY
   end
+
+  it 'does not register an offense when method has allowed amount of args with block arg' do
+    expect_no_offenses(<<~RUBY)
+      def foo(a, b, c, d, &block)
+      end
+    RUBY
+  end
+
+  it 'does not register an offense when method has no args' do
+    expect_no_offenses(<<~RUBY)
+      def foo
+      end
+    RUBY
+  end
 end