[Fix rubocop#9328] Honour shareable_constant_value magic comment

CHANGELOG.md

@@ -5812,3 +5812,4 @@
 [@AirWick219]: https://github.com/AirWick219
 [@markburns]: https://github.com/markburns
 [@gregfletch]: https://github.com/gregfletch
+[@thearjunmdas]: https://github.com/thearjunmdas

changelog/change_recognize_shareable_constant_value_magic.md

@@ -0,0 +1 @@
+* [#9328](https://github.com/rubocop/rubocop/issues/9328): Recognize shareable_constant_value magic comment. ([@thearjunmdas][], [@caalberts][])

lib/rubocop/cop/style/mutable_constant.rb

@@ -14,6 +14,11 @@ module Style
       # positives. Luckily, there is no harm in freezing an already
       # frozen object.
       #
+      # From Ruby 3.0, this cop honours the magic comment
+      # 'shareable_constant_value'. When this magic comment is set to any
+      # acceptable value other than none, it will suppress the offenses
+      # raised by this cop. It enforces frozen state.
+      #
       # NOTE: Regexp and Range literals are frozen objects since Ruby 3.0.
       #
       # @example EnforcedStyle: literals (default)
@@ -53,6 +58,43 @@ module Style
       #     end
       #   end.freeze
       class MutableConstant < Base
+        # Handles magic comment shareable_constant_value with O(n ^ 2) complexity
+        # n - number of lines in the source
+        # Iterates over all lines before a CONSTANT
+        # until it reaches shareable_constant_value
+        module ShareableConstantValue
+          module_function
+
+          def recent_shareable_value?(node)
+            shareable_constant_comment = magic_comment_in_scope node
+            return false if shareable_constant_comment.nil?
+
+            shareable_constant_value = MagicComment.parse(shareable_constant_comment)
+                                                   .shareable_constant_value
+            shareable_constant_value_enabled? shareable_constant_value
+          end
+
+          # Identifies the most recent magic comment with valid shareable constant values
+          # thats in scope for this node
+          def magic_comment_in_scope(node)
+            processed_source_till_node(node).reverse_each.find do |line|
+              MagicComment.parse(line).valid_shareable_constant_value?
+            end
+          end
+
+          private
+
+          def processed_source_till_node(node)
+            processed_source.lines[0..(node.last_line - 1)]
+          end
+
+          def shareable_constant_value_enabled?(value)
+            %w[literal experimental_everything experimental_copy].include? value
+          end
+        end
+        private_constant :ShareableConstantValue
+
+        include ShareableConstantValue
         include FrozenStringLiteral
         include ConfigurableEnforcedStyle
         extend AutoCorrector
@@ -85,18 +127,18 @@ def strict_check(value)
           return if immutable_literal?(value)
           return if operation_produces_immutable_object?(value)
           return if frozen_string_literal?(value)
+          return if shareable_constant_value?(value)
 
           add_offense(value) { |corrector| autocorrect(corrector, value) }
         end
 
         def check(value)
           range_enclosed_in_parentheses = range_enclosed_in_parentheses?(value)
-
           return unless mutable_literal?(value) ||
                         target_ruby_version <= 2.7 && range_enclosed_in_parentheses
-
           return if FROZEN_STRING_LITERAL_TYPES.include?(value.type) &&
                     frozen_string_literals_enabled?
+          return if shareable_constant_value?(value)
 
           add_offense(value) { |corrector| autocorrect(corrector, value) }
         end
@@ -130,6 +172,12 @@ def frozen_string_literal?(node)
           FROZEN_STRING_LITERAL_TYPES.include?(node.type) && frozen_string_literals_enabled?
         end
 
+        def shareable_constant_value?(node)
+          return false if target_ruby_version < 3.0
+
+          recent_shareable_value? node
+        end
+
         def frozen_regexp_or_range_literals?(node)
           target_ruby_version >= 3.0 && (node.regexp_type? || node.range_type?)
         end

spec/rubocop/cop/style/mutable_constant_spec.rb

@@ -43,6 +43,43 @@
     end
   end
 
+  shared_examples 'literals that are frozen' do |o|
+    let(:prefix) { o }
+
+    it_behaves_like 'immutable objects', '[1, 2, 3]'
+    it_behaves_like 'immutable objects', '%w(a b c)'
+    it_behaves_like 'immutable objects', '{ a: 1, b: 2 }'
+    it_behaves_like 'immutable objects', "'str'"
+    it_behaves_like 'immutable objects', '"top#{1 + 2}"'
+    it_behaves_like 'immutable objects', '1'
+    it_behaves_like 'immutable objects', '1.5'
+    it_behaves_like 'immutable objects', ':sym'
+    it_behaves_like 'immutable objects', 'FOO + BAR'
+    it_behaves_like 'immutable objects', 'FOO - BAR'
+    it_behaves_like 'immutable objects', "'foo' + 'bar'"
+    it_behaves_like 'immutable objects', "ENV['foo']"
+    it_behaves_like 'immutable objects', "::ENV['foo']"
+  end
+
+  shared_examples 'literals that are not frozen' do |o|
+    let(:prefix) { o }
+
+    it_behaves_like 'mutable objects', '[1, 2, 3]'
+    it_behaves_like 'mutable objects', '%w(a b c)'
+    it_behaves_like 'mutable objects', '{ a: 1, b: 2 }'
+    it_behaves_like 'mutable objects', "'str'"
+    it_behaves_like 'mutable objects', '"top#{1 + 2}"'
+
+    it_behaves_like 'immutable objects', '1'
+    it_behaves_like 'immutable objects', '1.5'
+    it_behaves_like 'immutable objects', ':sym'
+    it_behaves_like 'immutable objects', 'FOO + BAR'
+    it_behaves_like 'immutable objects', 'FOO - BAR'
+    it_behaves_like 'immutable objects', "'foo' + 'bar'"
+    it_behaves_like 'immutable objects', "ENV['foo']"
+    it_behaves_like 'immutable objects', "::ENV['foo']"
+  end
+
   context 'Strict: false' do
     let(:cop_config) { { 'EnforcedStyle' => 'literals' } }
 
@@ -157,6 +194,34 @@
           RUBY
         end
       end
+
+      context 'when using shareable_constant_value' do
+        it_behaves_like 'literals that are frozen', '# shareable_constant_value: literal'
+        it_behaves_like 'literals that are frozen', '# shareable_constant_value: experimental_everything'
+        it_behaves_like 'literals that are frozen', '# shareable_constant_value: experimental_copy'
+        it_behaves_like 'literals that are not frozen', '# shareable_constant_value: none'
+      end
+
+      it 'raises offense when shareable_constant_value is specified as an inline comment' do
+        expect_offense(<<~RUBY)
+          X = [1, 2, 3] # shareable_constant_value: literal
+              ^^^^^^^^^ Freeze mutable objects assigned to constants.
+          Y = [4, 5, 6]
+              ^^^^^^^^^ Freeze mutable objects assigned to constants.
+        RUBY
+      end
+
+      it 'raises offense only for shareable_constant_value as none when set in the order of: literal, none and experimental_everything' do
+        expect_offense(<<~RUBY)
+          # shareable_constant_value: literal
+          X = [1, 2, 3]
+          # shareable_constant_value: none
+          Y = [4, 5, 6]
+              ^^^^^^^^^ Freeze mutable objects assigned to constants.
+          # shareable_constant_value: experimental_everything
+          Z = [7, 8, 9]
+        RUBY
+      end
     end
 
     context 'Ruby 2.7 or lower', :ruby27 do
@@ -220,6 +285,13 @@
           RUBY
         end
       end
+
+      context 'when using shareable_constant_values' do
+        it_behaves_like 'literals that are not frozen', '# shareable_constant_value: literal'
+        it_behaves_like 'literals that are not frozen', '# shareable_constant_value: experimental_everything'
+        it_behaves_like 'literals that are not frozen', '# shareable_constant_value: experimental_copy'
+        it_behaves_like 'literals that are not frozen', '# shareable_constant_value: none'
+      end
     end
 
     context 'when the constant is a frozen string literal' do

spec/rubocop/magic_comment_spec.rb

@@ -4,6 +4,7 @@
   shared_examples 'magic comment' do |comment, expectations = {}|
     encoding = expectations[:encoding]
     frozen_string = expectations[:frozen_string_literal]
+    shareable_constant_value = expectations[:shareable_constant_value]
 
     it "returns #{encoding.inspect} for encoding when comment is #{comment}" do
       expect(described_class.parse(comment).encoding).to eql(encoding)
@@ -12,6 +13,12 @@
     it "returns #{frozen_string.inspect} for frozen_string_literal when comment is #{comment}" do
       expect(described_class.parse(comment).frozen_string_literal).to eql(frozen_string)
     end
+
+    it "returns #{shareable_constant_value.inspect} for shareable_constant_value " \
+       "when comment is #{comment}" do
+      expect(described_class.parse(comment)
+                            .shareable_constant_value).to eql(shareable_constant_value)
+    end
   end
 
   include_examples 'magic comment', '#'
@@ -46,6 +53,34 @@
 
   include_examples 'magic comment', '# fRoZeN-sTrInG_lItErAl: true', frozen_string_literal: true
 
+  include_examples 'magic comment', '# shareable_constant_value: literal', shareable_constant_value: 'literal'
+
+  include_examples 'magic comment', '# shareable_constant_value:literal', shareable_constant_value: 'literal'
+
+  include_examples 'magic comment', '# shareable-constant-value: literal', shareable_constant_value: 'literal'
+
+  include_examples 'magic comment', '# SHAREABLE-CONSTANT-VALUE: literal', shareable_constant_value: 'literal'
+
+  include_examples 'magic comment', '# sHaReaBLE-CoNstANT-ValUE: literal', shareable_constant_value: 'literal'
+
+  include_examples 'magic comment', '# shareable_constant_value: none', shareable_constant_value: 'none'
+
+  include_examples 'magic comment', '# xyz shareable_constant_value: literal'
+
+  include_examples 'magic comment', '# xyz shareable_constant_value: literal xyz'
+
+  include_examples(
+    'magic comment',
+    '# shareable_constant_value: experimental_everything',
+    shareable_constant_value: 'experimental_everything'
+  )
+
+  include_examples(
+    'magic comment',
+    '# shareable_constant_value: experimental_copy',
+    shareable_constant_value: 'experimental_copy'
+  )
+
   include_examples 'magic comment',
                    '# -*- frozen-string-literal: true -*-',
                    frozen_string_literal: true