[Fix rubocop#7929] Accept frozen_string_literal anywhere in leading c…

…omment lines

The frozen_string_literal comment can exist anywhere in the
"leading comment lines" (i.e. before the first line of ruby
code). If it appears after any ruby code it is ignored which
does not cause an errors but could cause the absence of an
expected error which is bad.

The previous implementation was checking if this comment was
one of the first three comments which had two issues:
- The comments it was checking could be anywhere, even after
  ruby code
- Since it was only checking three comments, it's possible
  that you can have an appropriate frozen_string_literal but
  this cop would show an error.

This commit updates the logic to look at all leading comment
lines, which may be more or less than three depending on where
the first non-comment token is.

CHANGELOG.md

@@ -12,6 +12,7 @@
 
 ### Bug fixes
 
+* [#7929](https://github.com/rubocop-hq/rubocop/issues/7929): Fix `Style/FrozenStringLiteralComment` to accept frozen_string_literal anywhere in leading comment lines. ([@jeffcarbs][])
 * [#7882](https://github.com/rubocop-hq/rubocop/pull/7882): Fix `Style/CaseEquality` when `AllowOnConstant` is `true` and the method receiver is implicit. ([@rafaelfranca][])
 * [#7790](https://github.com/rubocop-hq/rubocop/issues/7790): Fix `--parallel` and `--ignore-parent-exclusion` combination. ([@jonas054][])
 * [#7881](https://github.com/rubocop-hq/rubocop/issues/7881): Fix `--parallel` and `--force-default-config` combination. ([@jonas054][])
@@ -4485,3 +4486,4 @@
 [@saurabhmaurya15]: https://github.com/saurabhmaurya15
 [@DracoAter]: https://github.com/DracoAter
 [@diogoosorio]: https://github.com/diogoosorio
+[@jeffcarbs]: https://github.com/jeffcarbs

lib/rubocop/cop/mixin/frozen_string_literal.rb

@@ -46,7 +46,16 @@ def frozen_string_literal_specified?
       end
 
       def leading_comment_lines
-        processed_source.comments.first(3).map(&:text)
+        first_non_comment_token = processed_source.tokens.find do |token|
+          !token.comment?
+        end
+
+        if first_non_comment_token
+          # `line` is 1-indexed so we need to subtract 1 to get the array index
+          processed_source.lines[0...first_non_comment_token.line - 1]
+        else
+          processed_source.lines
+        end
       end
     end
   end

spec/rubocop/cop/style/frozen_string_literal_comment_spec.rb

@@ -249,6 +249,39 @@
       RUBY
     end
 
+    it 'accepts a frozen string literal comment after other comments' do
+      expect_no_offenses(<<~RUBY)
+        #!/usr/bin/env ruby
+        # encoding: utf-8
+        #
+        # These are more comments
+        # frozen_string_literal: false
+        puts 1
+      RUBY
+    end
+
+    it 'registers an offense for having a frozen string literal comment ' \
+       'under ruby code' do
+      expect_offense(<<~RUBY)
+        # encoding: utf-8
+        ^ Missing frozen string literal comment.
+
+        puts 1
+        # frozen_string_literal: true
+      RUBY
+
+      # Since we're only looking at the leading comments, a
+      # `frozen_string_literal` comment elsewhere in the code is invisible
+      # to this cop so the autocorrect won't remove it.
+      expect_correction(<<~RUBY)
+        # encoding: utf-8
+        # frozen_string_literal: true
+
+        puts 1
+        # frozen_string_literal: true
+      RUBY
+    end
+
     it 'registers an offense for an extra first empty line' do
       pending 'There is a flaw that skips adding caret symbol in this case, ' \
               'making it impossible to use `expect_offense` matcher'
@@ -463,6 +496,36 @@
         puts 1
       RUBY
     end
+
+    it 'registers an offense for having a frozen string literal comment ' \
+       'after other comments' do
+      expect_offense(<<~RUBY)
+        #!/usr/bin/env ruby
+        # encoding: utf-8
+        #
+        # These are more comments
+        # frozen_string_literal: false
+        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Unnecessary frozen string literal comment.
+        puts 1
+      RUBY
+
+      expect_correction(<<~RUBY)
+        #!/usr/bin/env ruby
+        # encoding: utf-8
+        #
+        # These are more comments
+        puts 1
+      RUBY
+    end
+
+    it 'accepts a frozen string literal comment under ruby code' do
+      expect_no_offenses(<<~RUBY)
+        # encoding: utf-8
+
+        puts 1
+        # frozen_string_literal: true
+      RUBY
+    end
   end
 
   context 'always_true' do
@@ -959,6 +1022,61 @@
       RUBY
     end
 
+    it 'accepts a frozen string literal comment after other comments' do
+      expect_no_offenses(<<~RUBY)
+        #!/usr/bin/env ruby
+        # encoding: utf-8
+        #
+        # These are more comments
+        # frozen_string_literal: true
+        puts 1
+      RUBY
+    end
+
+    it 'registers an offense for a disabled frozen string literal comment ' \
+       'after other comments' do
+      expect_offense(<<~RUBY)
+        #!/usr/bin/env ruby
+        # encoding: utf-8
+        #
+        # These are more comments
+        # frozen_string_literal: false
+        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Frozen string literal comment must be set to `true`.
+        puts 1
+      RUBY
+
+      expect_correction(<<~RUBY)
+        #!/usr/bin/env ruby
+        # encoding: utf-8
+        #
+        # These are more comments
+        # frozen_string_literal: true
+        puts 1
+      RUBY
+    end
+
+    it 'registers an offense for having a frozen string literal comment ' \
+       'under ruby code' do
+      expect_offense(<<~RUBY)
+        # encoding: utf-8
+        ^ Missing magic comment `# frozen_string_literal: true`.
+
+        puts 1
+        # frozen_string_literal: true
+      RUBY
+
+      # Since we're only looking at the leading comments, a
+      # `frozen_string_literal` comment elsewhere in the code is invisible
+      # to this cop so the autocorrect won't remove it.
+      expect_correction(<<~RUBY)
+        # encoding: utf-8
+        # frozen_string_literal: true
+
+        puts 1
+        # frozen_string_literal: true
+      RUBY
+    end
+
     it 'registers an offense for a disabled frozen string literal comment ' \
        'under shebang with no other code' do
       expect_offense(<<~RUBY)