[Fix #10070] Fix a false positive for Style/MutableConstant

changelog/fix_false_positive_for_style_mutable_constant.md

@@ -0,0 +1 @@
+* [#10070](https://github.com/rubocop/rubocop/issues/10070): Fix a false positive for `Style/MutableConstant` when using non-interpolated heredoc in Ruby 3.0. ([@koic][])

lib/rubocop/cop/mixin/frozen_string_literal.rb

@@ -9,9 +9,8 @@ module FrozenStringLiteral
       FROZEN_STRING_LITERAL = '# frozen_string_literal:'
       FROZEN_STRING_LITERAL_ENABLED = '# frozen_string_literal: true'
       FROZEN_STRING_LITERAL_TYPES_RUBY27 = %i[str dstr].freeze
-      FROZEN_STRING_LITERAL_TYPES_RUBY30 = %i[str].freeze
 
-      private_constant :FROZEN_STRING_LITERAL_TYPES_RUBY27, :FROZEN_STRING_LITERAL_TYPES_RUBY30
+      private_constant :FROZEN_STRING_LITERAL_TYPES_RUBY27
 
       def frozen_string_literal_comment_exists?
         leading_comment_lines.any? { |line| MagicComment.parse(line).valid_literal_value? }
@@ -20,13 +19,19 @@ def frozen_string_literal_comment_exists?
       private
 
       def frozen_string_literal?(node)
-        literal_types = if target_ruby_version >= 3.0
-                          FROZEN_STRING_LITERAL_TYPES_RUBY30
+        frozen_string = if target_ruby_version >= 3.0
+                          node.str_type? || frozen_heredoc?(node)
                         else
-                          FROZEN_STRING_LITERAL_TYPES_RUBY27
+                          FROZEN_STRING_LITERAL_TYPES_RUBY27.include?(node.type)
                         end
 
-        literal_types.include?(node.type) && frozen_string_literals_enabled?
+        frozen_string && frozen_string_literals_enabled?
+      end
+
+      def frozen_heredoc?(node)
+        return false unless node.dstr_type? && node.heredoc?
+
+        node.children.all?(&:str_type?)
       end
 
       def frozen_string_literals_enabled?

spec/rubocop/cop/style/mutable_constant_spec.rb

@@ -115,6 +115,23 @@
         let(:prefix) { '# frozen_string_literal: true' }
 
         it_behaves_like 'mutable objects', '"#{a}"'
+        it_behaves_like 'immutable objects', <<~'RUBY'
+          <<~HERE
+            foo
+            bar
+          HERE
+        RUBY
+        it 'registers an offense when using interpolated heredoc constant' do
+          expect_offense(<<~'RUBY')
+            # frozen_string_literal: true
+
+            CONST = <<~HERE
+                    ^^^^^^^ Freeze mutable objects assigned to constants.
+              foo #{use_interpolation}
+              bar
+            HERE
+          RUBY
+        end
       end
 
       context 'when the frozen string literal comment is false' do
@@ -133,6 +150,22 @@
         let(:prefix) { '# frozen_string_literal: true' }
 
         it_behaves_like 'immutable objects', '"#{a}"'
+        it_behaves_like 'immutable objects', <<~'RUBY'
+          <<~HERE
+            foo
+            bar
+          HERE
+        RUBY
+        it 'does not register an offense when using interpolated heredoc constant' do
+          expect_no_offenses(<<~'RUBY')
+            # frozen_string_literal: true
+
+            CONST = <<~HERE
+              foo #{use_interpolation}
+              bar
+            HERE
+          RUBY
+        end
       end
 
       context 'when the frozen string literal comment is false' do