From 4addf0987af65c8129d2b19c0385de02bb01f044 Mon Sep 17 00:00:00 2001
From: Koichi ITO <koic.ito@gmail.com>
Date: Fri, 13 Aug 2021 20:21:23 +0900
Subject: [PATCH] [Fix #10011] Fix a false positive for
 `Style/RedundantSelfAssignmentBranch`

Fixes #10011.

This PR fixes a false positive for `Style/RedundantSelfAssignmentBranch`
when using instance variable, class variable, and global variable.
---
 ..._style_redundant_self_assignment_branch.md |  1 +
 .../style/redundant_self_assignment_branch.rb |  7 +++--
 .../redundant_self_assignment_branch_spec.rb  | 27 +++++--------------
 3 files changed, 10 insertions(+), 25 deletions(-)
 create mode 100644 changelog/fix_false_positive_for_style_redundant_self_assignment_branch.md

diff --git a/changelog/fix_false_positive_for_style_redundant_self_assignment_branch.md b/changelog/fix_false_positive_for_style_redundant_self_assignment_branch.md
new file mode 100644
index 00000000000..a3c599b1f04
--- /dev/null
+++ b/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][])
diff --git a/lib/rubocop/cop/style/redundant_self_assignment_branch.rb b/lib/rubocop/cop/style/redundant_self_assignment_branch.rb
index c9083cd3178..d8a9dd8c670 100644
--- a/lib/rubocop/cop/style/redundant_self_assignment_branch.rb
+++ b/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)
diff --git a/spec/rubocop/cop/style/redundant_self_assignment_branch_spec.rb b/spec/rubocop/cop/style/redundant_self_assignment_branch_spec.rb
index 09e8955bc9f..bc88cc7050e 100644
--- a/spec/rubocop/cop/style/redundant_self_assignment_branch_spec.rb
+++ b/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