Use cached Source instance even when extracting a single line

Author: yujinakayama

lib/rspec/core/formatters/snippet_extractor.rb

@@ -9,14 +9,15 @@ class SnippetExtractor
         NoSuchLineError = Class.new(StandardError)
 
         def self.extract_line_at(file_path, line_number)
-          raise_error_if_file_does_not_exist!(file_path)
-          line = File.readlines(file_path)[line_number - 1]
+          source = source_from_file(file_path)
+          line = source.lines[line_number - 1]
           raise NoSuchLineError unless line
-          line.chomp
+          line
         end
 
-        def self.raise_error_if_file_does_not_exist!(path)
+        def self.source_from_file(path)
           raise NoSuchFileError unless File.exist?(path)
+          RSpec.world.source_cache.source_from_file(path)
         end
 
         if RSpec::Support::RubyFeatures.ripper_supported?
@@ -40,11 +41,6 @@ def self.extract_expression_lines_at(file_path, beginning_line_number, max_line_
             end
           end
 
-          def self.source_from_file(path)
-            raise_error_if_file_does_not_exist!(path)
-            RSpec.world.source_cache.source_from_file(path)
-          end
-
           def initialize(source, beginning_line_number, max_line_count=nil)
             @source = source
             @beginning_line_number = beginning_line_number