Merge pull request #11336 from fatkodima/identical_conditional_branch…

…es-last-child

Fix `Style/IdenticalConditionalBranches` to ignore identical leading lines when branch has single child and is used in return context

changelog/fix_identical_conditional_branches_ignore_empty_left_branches.md

@@ -0,0 +1 @@
+* [#10858](https://github.com/rubocop/rubocop/issues/10858): Fix `Style/IdenticalConditionalBranches` to ignore identical leading lines when branch has single child and is used in return context. ([@fatkodima][])

lib/rubocop/cop/style/identical_conditional_branches.rb

@@ -136,6 +136,7 @@ def on_case_match(node)
 
         private
 
+        # rubocop:disable Metrics/CyclomaticComplexity, Metrics/PerceivedComplexity
         def check_branches(node, branches)
           # return if any branch is empty. An empty branch can be an `if`
           # without an `else` or a branch that contains only comments.
@@ -144,9 +145,13 @@ def check_branches(node, branches)
           tails = branches.map { |branch| tail(branch) }
           check_expressions(node, tails, :after_condition) if duplicated_expressions?(node, tails)
 
+          return if last_child_of_parent?(node) &&
+                    branches.any? { |branch| single_child_branch?(branch) }
+
           heads = branches.map { |branch| head(branch) }
           check_expressions(node, heads, :before_condition) if duplicated_expressions?(node, heads)
         end
+        # rubocop:enable Metrics/CyclomaticComplexity, Metrics/PerceivedComplexity
 
         def duplicated_expressions?(node, expressions)
           unique_expressions = expressions.uniq
@@ -180,6 +185,16 @@ def check_expressions(node, expressions, insert_position) # rubocop:disable Metr
           end
         end
 
+        def last_child_of_parent?(node)
+          return true unless (parent = node.parent)
+
+          parent.child_nodes.last == node
+        end
+
+        def single_child_branch?(branch_node)
+          !branch_node.begin_type? || branch_node.children.size == 1
+        end
+
         def message(node)
           format(MSG, source: node.source)
         end

spec/rubocop/cop/style/identical_conditional_branches_spec.rb

@@ -72,6 +72,31 @@
     end
   end
 
+  context 'on if..else with identical leading lines, single child branch and last node of the parent' do
+    it "doesn't register an offense" do
+      expect_no_offenses(<<~RUBY)
+        def foo
+          if something
+            do_x
+          else
+            do_x
+            1 + 2 + 3
+          end
+        end
+
+        def bar
+          y = if something
+                do_x
+              else
+                do_x
+                1 + 2 + 3
+              end
+          do_something_else
+        end
+      RUBY
+    end
+  end
+
   context 'on if..elsif with no else' do
     it "doesn't register an offense" do
       expect_no_offenses(<<~RUBY)
@@ -219,6 +244,39 @@
     end
   end
 
+  context 'on case with identical leading lines, single child branch and last node of the parent' do
+    it "doesn't register an offense" do
+      expect_no_offenses(<<~RUBY)
+        def foo
+          case something
+          when :a
+            do_x
+          when :b
+            do_x
+            x2
+          else
+            do_x
+            x3
+          end
+        end
+
+        def bar
+          x = case something
+              when :a
+                do_x
+              when :b
+                do_x
+                x2
+              else
+                do_x
+                x3
+              end
+          do_something
+        end
+      RUBY
+    end
+  end
+
   context 'on case without else' do
     it "doesn't register an offense" do
       expect_no_offenses(<<~RUBY)
@@ -388,6 +446,39 @@
       end
     end
 
+    context 'on case-match with identical leading lines, single child branch and last node of the parent' do
+      it "doesn't register an offense" do
+        expect_no_offenses(<<~RUBY)
+          def foo
+            case something
+            in :a
+              do_x
+            in :b
+              do_x
+              x2
+            else
+              do_x
+              x3
+            end
+          end
+
+          def bar
+            y = case something
+                in :a
+                  do_x
+                in :b
+                  do_x
+                  x2
+                else
+                  do_x
+                  x3
+                end
+            do_something
+          end
+        RUBY
+      end
+    end
+
     context 'on case-match without else' do
       it "doesn't register an offense" do
         expect_no_offenses(<<~RUBY)