Merge pull request #9363 from uplus/add-new-cop-or_assignment_to_cons…

…tant

Add new cop `Lint/OrAssignmentToConstant`

CHANGELOG.md

@@ -5366,3 +5366,4 @@
 [@ohbarye]: https://github.com/ohbarye
 [@magneland]: https://github.com/magneland
 [@k-karen]: https://github.com/k-karen
+[@uplus]: https://github.com/uplus

changelog/new_add_new_cop_lintorassignmenttoconstant.md

@@ -0,0 +1 @@
+* [#9363](https://github.com/rubocop-hq/rubocop/pull/9363): Add new cop `Lint/OrAssignmentToConstant`. ([@uplus][])

config/default.yml

@@ -1811,6 +1811,12 @@ Lint/NumberedParameterAssignment:
   Enabled: pending
   VersionAdded: '<<next>>'
 
+Lint/OrAssignmentToConstant:
+  Description: 'Checks unintended or-assignment to constant.'
+  Enabled: pending
+  Safe: false
+  VersionAdded: '<<next>>'
+
 Lint/OrderedMagicComments:
   Description: 'Checks the proper ordering of magic comments and whether a magic comment is not placed before a shebang.'
   Enabled: true

lib/rubocop.rb

@@ -313,6 +313,7 @@
 require_relative 'rubocop/cop/lint/non_local_exit_from_iterator'
 require_relative 'rubocop/cop/lint/number_conversion'
 require_relative 'rubocop/cop/lint/numbered_parameter_assignment'
+require_relative 'rubocop/cop/lint/or_assignment_to_constant'
 require_relative 'rubocop/cop/lint/ordered_magic_comments'
 require_relative 'rubocop/cop/lint/out_of_range_regexp_ref'
 require_relative 'rubocop/cop/lint/parentheses_as_grouped_expression'

lib/rubocop/cop/lint/or_assignment_to_constant.rb

@@ -0,0 +1,39 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Lint
+      # This cop checks for unintended or-assignment to a constant.
+      #
+      # Constants should always be assigned in the same location. And its value
+      # should always be the same. If constants are assigned in multiple
+      # locations, the result may vary depending on the order of `require`.
+      #
+      # Also, if you already have such an implementation, auto-correction may
+      # change the result.
+      #
+      # @example
+      #
+      #   # bad
+      #   CONST ||= 1
+      #
+      #   # good
+      #   CONST = 1
+      #
+      class OrAssignmentToConstant < Base
+        extend AutoCorrector
+
+        MSG = 'Avoid using or-assignment with constants.'
+
+        def on_or_asgn(node)
+          lhs, _rhs = *node
+          return unless lhs&.casgn_type?
+
+          add_offense(node.loc.operator) do |corrector|
+            corrector.replace(node.loc.operator, '=')
+          end
+        end
+      end
+    end
+  end
+end

spec/rubocop/cop/lint/or_assignment_to_constant_spec.rb

@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Lint::OrAssignmentToConstant, :config do
+  subject(:cop) { described_class.new(config) }
+
+  it 'registers an offense with or-assignment to a constant' do
+    expect_offense(<<~RUBY)
+      CONST ||= 1
+            ^^^ Avoid using or-assignment with constants.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      CONST = 1
+    RUBY
+  end
+
+  it 'does not register an offense with plain assignment to a constant' do
+    expect_no_offenses(<<~RUBY)
+      CONST = 1
+    RUBY
+  end
+
+  [
+    ['a local variable', 'var'],
+    ['an instance variable', '@var'],
+    ['a class variable', '@@var'],
+    ['a global variable', '$var'],
+    ['an attribute', 'self.var']
+  ].each do |type, var|
+    it "does not register an offense with or-assignment to #{type}" do
+      expect_no_offenses(<<~RUBY)
+        #{var} ||= 1
+      RUBY
+    end
+  end
+end