[Fix rubocop#10011] Fix a false positive for `Style/RedundantSelfAssi…

…gnmentBranch`

Fixes rubocop#10011.

This PR fixes a false positive for `Style/RedundantSelfAssignmentBranch`
when using instance variable, class variable, and global variable.

changelog/fix_false_positive_for_style_redundant_self_assignment_branch.md

@@ -0,0 +1 @@
+* [#10011](https://github.com/rubocop/rubocop/issues/10011): Fix a false positive for `Style/RedundantSelfAssignmentBranch` when using instance variable, class variable, and global variable. ([@koic][])

lib/rubocop/cop/style/redundant_self_assignment_branch.rb

@@ -5,6 +5,9 @@ module Cop
     module Style
       # This cop checks for places where conditional branch makes redundant self-assignment.
       #
+      # It only detects local variable because it may replace state of instance variable,
+      # class variable, and global variable that have state across methods with `nil`.
+      #
       # @example
       #
       #   # bad
@@ -45,10 +48,6 @@ def on_lvasgn(node)
           end
         end
 
-        alias on_ivasgn on_lvasgn
-        alias on_cvasgn on_lvasgn
-        alias on_gvasgn on_lvasgn
-
         private
 
         def self_assign?(variable, branch)

spec/rubocop/cop/style/redundant_self_assignment_branch_spec.rb

@@ -125,36 +125,21 @@
     RUBY
   end
 
-  it 'registers and corrects an offense when self-assigning redundant else ternary branch for ivar' do
-    expect_offense(<<~RUBY)
+  it 'does not register an offense when self-assigning redundant else ternary branch for ivar' do
+    expect_no_offenses(<<~RUBY)
       @foo = condition ? @bar : @foo
-                                ^^^^ Remove the self-assignment branch.
-    RUBY
-
-    expect_correction(<<~RUBY)
-      @foo = @bar if condition
     RUBY
   end
 
-  it 'registers and corrects an offense when self-assigning redundant else ternary branch for cvar' do
-    expect_offense(<<~RUBY)
+  it 'does not register an offense when self-assigning redundant else ternary branch for cvar' do
+    expect_no_offenses(<<~RUBY)
       @@foo = condition ? @@bar : @@foo
-                                  ^^^^^ Remove the self-assignment branch.
-    RUBY
-
-    expect_correction(<<~RUBY)
-      @@foo = @@bar if condition
     RUBY
   end
 
-  it 'registers and corrects an offense when self-assigning redundant else ternary branch for gvar' do
-    expect_offense(<<~RUBY)
+  it 'does not register an offense when self-assigning redundant else ternary branch for gvar' do
+    expect_no_offenses(<<~RUBY)
       $foo = condition ? $bar : $foo
-                                ^^^^ Remove the self-assignment branch.
-    RUBY
-
-    expect_correction(<<~RUBY)
-      $foo = $bar if condition
     RUBY
   end