Takes a different approach

lib/linguist/blob_helper.rb

@@ -241,8 +241,25 @@ module Linguist
     def lines
       @lines ||=
         if viewable? && data
-          newlines = Regexp.new("\r\n|\r|\n".encode(encoding))
-          data.force_encoding(encoding).split(newlines, -1)
+          # `data` is usually encoded as ASCII-8BIT even when the content has
+          # been detected as a different encoding. However, we are not allowed
+          # to change the encoding of `data` because we've made the implicit
+          # guarantee that each entry in `lines` is encoded the same way as
+          # `data`.
+          #
+          # Instead, we re-encode each possible newline sequence as the
+          # detected encoding, then force them back to the encoding of `data`
+          # (usually a binary encoding like ASCII-8BIT). This means that the
+          # byte sequence will match how newlines are likely encoded in the
+          # file, but we don't have to change the encoding of `data` as far as
+          # Ruby is concerned. This allows us to correctly parse out each line
+          # without changing the encoding of `data`, and
+          # also--importantly--without having to duplicate many (potentially
+          # large) strings.
+          encoded_newlines = ["\r\n", "\r", "\n"].
+            map { |nl| nl.encode(encoding).force_encoding(data.encoding) }
+
+          data.split(Regexp.union(encoded_newlines), -1)
         else
           []
         end
@@ -263,7 +280,7 @@ module Linguist
     #
     # Returns Integer
     def sloc
-      lines.grep(Regexp.new('\S'.encode(encoding || 'ASCII-8BIT'))).size
+      lines.grep(/\S/).size
     end
 
     # Public: Is the blob a generated file?

test/test_blob.rb

@@ -11,6 +11,17 @@ class TestBlob < Test::Unit::TestCase
 
   Lexer = Pygments::Lexer
 
+  def setup
+    # git blobs are normally loaded as ASCII-8BIT since they may contain data
+    # with arbitrary encoding not known ahead of time
+    @original_external = Encoding.default_external
+    Encoding.default_external = Encoding.find("ASCII-8BIT")
+  end
+
+  def teardown
+    Encoding.default_external = @original_external
+  end
+
   def samples_path
     File.expand_path("../../samples", __FILE__)
   end
@@ -67,6 +78,14 @@ class TestBlob < Test::Unit::TestCase
     assert_equal 475, blob("Emacs Lisp/ess-julia.el").lines.length
   end
 
+  def test_lines_maintains_original_encoding
+    # Even if the file's encoding is detected as something like UTF-16LE,
+    # earlier versions of the gem made implicit guarantees that the encoding of
+    # each `line` is in the same encoding as the file was originally read (in
+    # practice, UTF-8 or ASCII-8BIT)
+    assert_equal Encoding.default_external, blob("Text/utf16le.txt").lines.first.encoding
+  end
+
   def test_size
     assert_equal 15, blob("Ruby/foo.rb").size
   end