[Fix #12249] Fix a false positive Style/IdenticalConditionalBranches

Fixes #12249.

This PR fixes a false positive `Style/IdenticalConditionalBranches`
when `if`..`else` with identical leading lines and assign to condition value.

changelog/fix_a_false_positive_for_style_identical_conditional_branches.md

@@ -0,0 +1 @@
+* [#12249](https://github.com/rubocop/rubocop/issues/12249): Fix a false positive `Style/IdenticalConditionalBranches` when `if`..`else` with identical leading lines and assign to condition value. ([@koic][])

lib/rubocop/cop/style/identical_conditional_branches.rb

@@ -136,7 +136,7 @@ def on_case_match(node)
 
         private
 
-        # rubocop:disable Metrics/CyclomaticComplexity, Metrics/PerceivedComplexity
+        # rubocop:disable Metrics/AbcSize, 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.
@@ -149,9 +149,15 @@ def check_branches(node, branches)
                     branches.any? { |branch| single_child_branch?(branch) }
 
           heads = branches.map { |branch| head(branch) }
-          check_expressions(node, heads, :before_condition) if duplicated_expressions?(node, heads)
+
+          return unless duplicated_expressions?(node, heads)
+
+          condition_variable = assignable_condition_value(node)
+          return if heads.first.assignment? && condition_variable == heads.first.name.to_s
+
+          check_expressions(node, heads, :before_condition)
         end
-        # rubocop:enable Metrics/CyclomaticComplexity, Metrics/PerceivedComplexity
+        # rubocop:enable Metrics/AbcSize, Metrics/CyclomaticComplexity, Metrics/PerceivedComplexity
 
         def duplicated_expressions?(node, expressions)
           unique_expressions = expressions.uniq
@@ -164,6 +170,14 @@ def duplicated_expressions?(node, expressions)
           node.condition.child_nodes.none? { |n| n.source == lhs.source if n.variable? }
         end
 
+        def assignable_condition_value(node)
+          if node.condition.call_type?
+            (receiver = node.condition.receiver) ? receiver.source : node.condition.source
+          elsif node.condition.variable?
+            node.condition.source
+          end
+        end
+
         # rubocop:disable Metrics/CyclomaticComplexity, Metrics/MethodLength, Metrics/PerceivedComplexity
         def check_expressions(node, expressions, insert_position)
           return if expressions.any?(&:nil?)

spec/rubocop/cop/style/identical_conditional_branches_spec.rb

@@ -72,6 +72,103 @@
     end
   end
 
+  context 'on if..else with identical leading lines and assign to condition value of method call receiver' do
+    it "doesn't register an offense" do
+      expect_no_offenses(<<~RUBY)
+        if x.condition
+          x = do_something
+          foo
+        else
+          x = do_something
+          bar
+        end
+      RUBY
+    end
+  end
+
+  context 'on if..else with identical leading lines and assign to condition value of safe navigation call receiver' do
+    it "doesn't register an offense" do
+      expect_no_offenses(<<~RUBY)
+        if x&.condition
+          x = do_something
+          foo
+        else
+          x = do_something
+          bar
+        end
+      RUBY
+    end
+  end
+
+  context 'on if..else with identical leading lines and assign to condition value of method call' do
+    it "doesn't register an offense" do
+      expect_no_offenses(<<~RUBY)
+        if x
+          x = do_something
+          foo
+        else
+          x = do_something
+          bar
+        end
+      RUBY
+    end
+  end
+
+  context 'on if..else with identical leading lines and assign to condition local variable' do
+    it "doesn't register an offense" do
+      expect_no_offenses(<<~RUBY)
+        x = 42
+
+        if x
+          x = do_something
+          foo
+        else
+          x = do_something
+          bar
+        end
+      RUBY
+    end
+  end
+
+  context 'on if..else with identical leading lines and assign to condition instance variable' do
+    it "doesn't register an offense" do
+      expect_no_offenses(<<~RUBY)
+        if @x
+          @x = do_something
+          foo
+        else
+          @x = do_something
+          bar
+        end
+      RUBY
+    end
+  end
+
+  context 'on if..else with identical trailing lines and assign to condition value' do
+    it 'registers and corrects an offense' do
+      expect_offense(<<~RUBY)
+        if x.condition
+          foo
+          x = do_something
+          ^^^^^^^^^^^^^^^^ Move `x = do_something` out of the conditional.
+        else
+          bar
+          x = do_something
+          ^^^^^^^^^^^^^^^^ Move `x = do_something` out of the conditional.
+        end
+      RUBY
+
+      expect_correction(<<~RUBY)
+        if x.condition
+          foo
+        else
+          bar
+        end
+        x = do_something
+      RUBY
+    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)