[Fix #6115] Fix a false positive for Lint/OrderedMagicComments

Fixes #6115.

This PR fixes a false positive for `Lint/OrderedMagicComments`
when using `encoding: Encoding::SJIS` Hash notation after
`frozen_string_literal` magic comment.

There was a false positive to misunderstanding the following
Hash notation as an encoding magic comment.

```ruby
# frozen_string_literal: true

x = { encoding: Encoding::SJIS }
puts x
```

This PR changes the pattern match of the magic encoding comment
so that beginning of line always starts with `#`.

CHANGELOG.md

@@ -15,6 +15,7 @@
 * [#6103](https://github.com/rubocop-hq/rubocop/pull/6103): Fix a false positive for `Layout/IndentationWidth` when multiple modifiers are used in a block and a method call is made at end of the block. ([@koic][])
 * [#6084](https://github.com/rubocop-hq/rubocop/issues/6084): Fix `Naming/MemoizedInstanceVariableName` cop to allow methods to have leading underscores. ([@kenman345][])
 * [#6098](https://github.com/rubocop-hq/rubocop/issues/6098): Fix an error for `Layout/ClassStructure` when there is a comment in the macro method to be auto-correct. ([@koic][])
+* [#6115](https://github.com/rubocop-hq/rubocop/issues/6115): Fix a false positive for `Lint/OrderedMagicComments` when using `{ encoding: Encoding::SJIS }` hash object after `frozen_string_literal` magic comment. ([@koic][])
 
 ## 0.58.1 (2018-07-10)
 

lib/rubocop/cop/mixin/frozen_string_literal.rb

@@ -34,7 +34,13 @@ def frozen_string_literals_enabled?
       end
 
       def leading_comment_lines
-        processed_source[0..2].compact
+        comments = processed_source.comments
+
+        comments.each_with_object([]) do |comment, leading_comments|
+          next if comment.loc.line > 3
+
+          leading_comments << comment.text
+        end
       end
     end
   end

lib/rubocop/magic_comment.rb

@@ -190,7 +190,7 @@ def frozen_string_literal; end
     class SimpleComment < MagicComment
       # Match `encoding` or `coding`
       def encoding
-        extract(/\#* \b(?:en)?coding: (#{TOKEN})/i)
+        extract(/\A\#.*\b(?:en)?coding: (#{TOKEN})/i)
       end
 
       private

spec/rubocop/cop/lint/ordered_magic_comments_spec.rb

@@ -70,6 +70,17 @@
     RUBY
   end
 
+  it 'does not register an offense when using ' \
+     '`encoding: Encoding::SJIS` Hash notation after' \
+     '`frozen_string_literal` magic comment' do
+    expect_no_offenses(<<-RUBY.strip_indent)
+      # frozen_string_literal: true
+
+      x = { encoding: Encoding::SJIS }
+      puts x
+    RUBY
+  end
+
   it 'autocorrects ordered magic comments' do
     new_source = autocorrect_source(<<-RUBY.strip_indent)
       # frozen_string_literal: true