From 9d32b6230b5b932d4b7221ce1f31728186734555 Mon Sep 17 00:00:00 2001
From: Koichi ITO <koic.ito@gmail.com>
Date: Sat, 24 Feb 2024 16:36:38 +0900
Subject: [PATCH] Fix false negative for `Style/RedundantAssignment`

This PR fixes false negative for `Style/RedundantAssignment`
when using pattern matching.
---
 ...negative_for_style_redundant_assignment.md |  1 +
 lib/rubocop/cop/style/redundant_assignment.rb | 12 ++++-
 .../cop/style/redundant_assignment_spec.rb    | 53 +++++++++++++++++++
 3 files changed, 64 insertions(+), 2 deletions(-)
 create mode 100644 changelog/fix_false_negative_for_style_redundant_assignment.md

diff --git a/changelog/fix_false_negative_for_style_redundant_assignment.md b/changelog/fix_false_negative_for_style_redundant_assignment.md
new file mode 100644
index 000000000000..85a4aaee2773
--- /dev/null
+++ b/changelog/fix_false_negative_for_style_redundant_assignment.md
@@ -0,0 +1 @@
+* [#12706](https://github.com/rubocop/rubocop/pull/12706): Fix false negative for `Style/RedundantAssignment` when using pattern matching. ([@koic][])
diff --git a/lib/rubocop/cop/style/redundant_assignment.rb b/lib/rubocop/cop/style/redundant_assignment.rb
index ba006fead64b..20fc0e13aafa 100644
--- a/lib/rubocop/cop/style/redundant_assignment.rb
+++ b/lib/rubocop/cop/style/redundant_assignment.rb
@@ -54,12 +54,14 @@ def on_def(node)
 
         private
 
+        # rubocop:disable Metrics/CyclomaticComplexity
         def check_branch(node)
           return unless node
 
           case node.type
-          when :case   then check_case_node(node)
-          when :if     then check_if_node(node)
+          when :case       then check_case_node(node)
+          when :case_match then check_case_match_node(node)
+          when :if         then check_if_node(node)
           when :rescue, :resbody
             check_rescue_node(node)
           when :ensure then check_ensure_node(node)
@@ -67,12 +69,18 @@ def check_branch(node)
             check_begin_node(node)
           end
         end
+        # rubocop:enable Metrics/CyclomaticComplexity
 
         def check_case_node(node)
           node.when_branches.each { |when_node| check_branch(when_node.body) }
           check_branch(node.else_branch)
         end
 
+        def check_case_match_node(node)
+          node.in_pattern_branches.each { |in_pattern_node| check_branch(in_pattern_node.body) }
+          check_branch(node.else_branch)
+        end
+
         def check_if_node(node)
           return if node.modifier_form? || node.ternary?
 
diff --git a/spec/rubocop/cop/style/redundant_assignment_spec.rb b/spec/rubocop/cop/style/redundant_assignment_spec.rb
index 1bacfa50d310..14c0357d9a7c 100644
--- a/spec/rubocop/cop/style/redundant_assignment_spec.rb
+++ b/spec/rubocop/cop/style/redundant_assignment_spec.rb
@@ -180,6 +180,59 @@ def func
     RUBY
   end
 
+  context 'when inside an `in` branch' do
+    it 'registers an offense and autocorrects' do
+      expect_offense(<<~RUBY)
+        def func
+          some_preceding_statements
+          case x
+          in y
+            res = 1
+            ^^^^^^^ Redundant assignment before returning detected.
+            res
+          in z
+            2
+          in q
+          else
+            res = 3
+            ^^^^^^^ Redundant assignment before returning detected.
+            res
+          end
+        end
+      RUBY
+
+      expect_correction(<<~RUBY)
+        def func
+          some_preceding_statements
+          case x
+          in y
+            1
+           #{trailing_whitespace}
+          in z
+            2
+          in q
+          else
+            3
+           #{trailing_whitespace}
+          end
+        end
+      RUBY
+    end
+  end
+
+  it 'accepts empty `in` nodes' do
+    expect_no_offenses(<<~RUBY)
+      def func
+        case x
+        in y then 1
+        in z # do nothing
+        else
+          3
+        end
+      end
+    RUBY
+  end
+
   it 'accepts empty method body' do
     expect_no_offenses(<<~RUBY)
       def func