[Fix #12873] Fix an error for Metrics/BlockLength

changelog/fix_an_error_for_metrics_block_length.md

@@ -0,0 +1 @@
+* [#12873](https://github.com/rubocop/rubocop/issues/12873): Fix an error for `Metrics/BlockLength` when the `CountAsOne` config is invalid. ([@koic][])

lib/rubocop/cop/metrics/utils/code_length_calculator.rb

@@ -51,8 +51,8 @@ def build_foldable_checks(types) # rubocop:disable Metrics/MethodLength
               when :method_call
                 ->(node) { node.call_type? }
               else
-                raise ArgumentError, "Unknown foldable type: #{type.inspect}. " \
-                                     "Valid foldable types are: #{FOLDABLE_TYPES.join(', ')}."
+                raise Warning, "Unknown foldable type: #{type.inspect}. " \
+                               "Valid foldable types are: #{FOLDABLE_TYPES.join(', ')}."
               end
             end
           end

spec/rubocop/cop/metrics/block_length_spec.rb

@@ -72,6 +72,25 @@
     RUBY
   end
 
+  context 'when the `CountAsOne` config is invalid' do
+    before do
+      cop_config['CountAsOne'] = 'config'
+    end
+
+    let(:source) { <<~RUBY }
+      something do
+      ^^^^^^^^^^^^ Block has too many lines. [3/2]
+        a = 1
+        a = 2
+        a = 3
+      end
+    RUBY
+
+    it 'raises `RuboCop::Warning`' do
+      expect { expect_offense(source) }.to raise_error(RuboCop::Warning)
+    end
+  end
+
   context 'when using numbered parameter', :ruby27 do
     it 'rejects a block with more than 5 lines' do
       expect_offense(<<~RUBY)

spec/rubocop/cop/metrics/utils/code_length_calculator_spec.rb

@@ -469,7 +469,7 @@ def test
 
       expect do
         described_class.new(source.ast, source, foldable_types: %i[unknown]).calculate
-      end.to raise_error(ArgumentError, /Unknown foldable type/)
+      end.to raise_error(RuboCop::Warning, /Unknown foldable type/)
     end
   end
 end