[Fix rubocop#11535] Fix a false positive for `Style/NumberedParameter…

…sLimit` Fixes rubocop#11535. This PR fixes a false positive for `Style/NumberedParametersLimit` when only `_2` or higher numbered parameter is used.
koic · Feb 3, 2023 · afaa604 · afaa604
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diff --git a/changelog/fix_a_false_positive_for_style_numbered_parameters_limit.md b/changelog/fix_a_false_positive_for_style_numbered_parameters_limit.md
@@ -0,0 +1 @@
+* [#11535](https://github.com/rubocop/rubocop/issues/11535): Fix a false positive for `Style/NumberedParametersLimit` when only `_2` or higher numbered parameter is used. ([@koic][])
diff --git a/lib/rubocop/cop/style/numbered_parameters_limit.rb b/lib/rubocop/cop/style/numbered_parameters_limit.rb
@@ -12,10 +12,11 @@ module Style
       #
       # @example Max: 1 (default)
       #   # bad
-      #   foo { _1.call(_2, _3, _4) }
+      #   use_multiple_numbered_parameters { _1.call(_2, _3, _4) }
       #
       #   # good
-      #   foo { do_something(_1) }
+      #   array.each { use_array_element_as_numbered_parameter(_1) }
+      #   hash.each { use_only_hash_value_as_numbered_parameter(_2) }
       class NumberedParametersLimit < Base
         extend TargetRubyVersion
         extend ExcludeLimit
@@ -26,9 +27,10 @@ class NumberedParametersLimit < Base
         exclude_limit 'Max'
 
         MSG = 'Avoid using more than %<max>i numbered %<parameter>s; %<count>i detected.'
+        NUMBERED_PARAMETER_PATTERN = /\A_[1-9]\z/.freeze
 
         def on_numblock(node)
-          _send_node, param_count, * = *node
+          param_count = numbered_parameter_nodes(node).uniq.count
           return if param_count <= max_count
 
           parameter = max_count > 1 ? 'parameters' : 'parameter'
@@ -38,6 +40,12 @@ def on_numblock(node)
 
         private
 
+        def numbered_parameter_nodes(node)
+          node.each_descendant(:lvar).select do |lvar_node|
+            lvar_node.source.match?(NUMBERED_PARAMETER_PATTERN)
+          end
+        end
+
         def max_count
           max = cop_config.fetch('Max', DEFAULT_MAX_VALUE)
 

diff --git a/spec/rubocop/cop/style/numbered_parameters_limit_spec.rb b/spec/rubocop/cop/style/numbered_parameters_limit_spec.rb
@@ -54,6 +54,31 @@
     context 'when Max is 1' do
       let(:max) { 1 }
 
+      it 'does not register an offense when only numbered parameter `_1` is used once' do
+        expect_no_offenses(<<~RUBY)
+          foo { do_something(_1) }
+        RUBY
+      end
+
+      it 'does not register an offense when only numbered parameter `_1` is used twice' do
+        expect_no_offenses(<<~RUBY)
+          foo { do_something(_1, _1) }
+        RUBY
+      end
+
+      it 'does not register an offense when only numbered parameter `_9` is used once' do
+        expect_no_offenses(<<~RUBY)
+          foo { do_something(_9) }
+        RUBY
+      end
+
+      it 'does not register an offense when using numbered parameter with underscored local variable' do
+        expect_no_offenses(<<~RUBY)
+          _lvar = 42
+          foo { do_something(_2, _lvar) }
+        RUBY
+      end
+
       it 'uses the right offense message' do
         expect_offense(<<~RUBY)
           foo { do_something(_1, _2, _3, _4, _5) }