[Fix #10927] Fix a false positive for Style/HashTransformKeys and `…

…Style/HashTransformValues`

Fixes #10927.

This PR fixes a false positive for `Style/HashTransformKeys` and `Style/HashTransformValues`
when not using transformed block argument.

changelog/fix_a_false_positive_for_style_hash_transform_values.md

@@ -0,0 +1 @@
+* [#10927](https://github.com/rubocop/rubocop/issues/10927): Fix a false positive for `Style/HashTransformKeys` and `Style/HashTransformValues` when not using transformed block argument. ([@koic][])

lib/rubocop/cop/mixin/hash_transform_method.rb

@@ -68,6 +68,8 @@ def handle_possible_offense(node, match, match_desc)
         # `transform_values` if value transformation uses key.
         return if captures.transformation_uses_both_args?
 
+        return unless captures.use_transformed_argname?
+
         message = "Prefer `#{new_method_name}` over `#{match_desc}`."
         add_offense(node, message: message) do |corrector|
           correction = prepare_correction(node)
@@ -113,11 +115,7 @@ def execute_correction(corrector, node, correction)
       end
 
       # Internal helper class to hold match data
-      Captures = Struct.new(
-        :transformed_argname,
-        :transforming_body_expr,
-        :unchanged_body_expr
-      ) do
+      Captures = Struct.new(:transformed_argname, :transforming_body_expr, :unchanged_body_expr) do
         def noop_transformation?
           transforming_body_expr.lvar_type? &&
             transforming_body_expr.children == [transformed_argname]
@@ -126,6 +124,12 @@ def noop_transformation?
         def transformation_uses_both_args?
           transforming_body_expr.descendants.include?(unchanged_body_expr)
         end
+
+        def use_transformed_argname?
+          transforming_body_expr.each_descendant(:lvar).any? do |node|
+            node.source == transformed_argname.to_s
+          end
+        end
       end
 
       # Internal helper class to hold autocorrect data

spec/rubocop/cop/style/hash_transform_keys_spec.rb

@@ -156,6 +156,12 @@
       expect_no_offenses('Hash[x.map {|k, v| [k.to_sym, foo(v)]}]')
     end
 
+    it 'does not flag _.map {...}.to_h when key block argument is unused' do
+      expect_no_offenses(<<~RUBY)
+        x.map {|_k, v| [v, v]}.to_h
+      RUBY
+    end
+
     it 'does not flag key transformation in the absence of to_h' do
       expect_no_offenses('x.map {|k, v| [k.to_sym, v]}')
     end
@@ -274,6 +280,12 @@
       RUBY
     end
 
+    it 'does not flag _.to_h {...} when key block argument is unused' do
+      expect_no_offenses(<<~RUBY)
+        x.to_h {|_k, v| [v, v]}
+      RUBY
+    end
+
     it 'does not flag `_.to_h{...}` when its receiver is an array literal' do
       expect_no_offenses(<<~RUBY)
         [1, 2, 3].to_h { |k, v| [k.to_sym, v] }

spec/rubocop/cop/style/hash_transform_values_spec.rb

@@ -156,6 +156,12 @@
       expect_no_offenses('Hash[x.map {|k, v| [k.to_sym, foo(v)]}]')
     end
 
+    it 'does not flag _.map {...}.to_h when value block argument is unused' do
+      expect_no_offenses(<<~RUBY)
+        x.map {|k, _v| [k, k]}.to_h
+      RUBY
+    end
+
     it 'does not flag value transformation in the absence of to_h' do
       expect_no_offenses('x.map {|k, v| [k, foo(v)]}')
     end
@@ -260,6 +266,12 @@
       RUBY
     end
 
+    it 'does not flag _.to_h {...} when value block argument is unused' do
+      expect_no_offenses(<<~RUBY)
+        x.to_h {|k, _v| [k, k]}
+      RUBY
+    end
+
     it 'does not flag `_.to_h{...}` when its receiver is an array literal' do
       expect_no_offenses(<<~RUBY)
         [1, 2, 3].to_h { |k, v| [k, foo(v)] }