[ruby/error_highlight] Support a file that has no final newline

https://github.com/ruby/error_highlight/commit/9d671284cb

lib/error_highlight/base.rb

@@ -35,6 +35,7 @@ module ErrorHighlight
 
       @fetch = -> (lineno, last_lineno = lineno) do
         snippet = @node.script_lines[lineno - 1 .. last_lineno - 1].join("")
+        snippet += "\n" unless snippet.end_with?("\n")
 
         # It require some work to support Unicode (or multibyte) characters.
         # Tentatively, we stop highlighting if the code snippet has non-ascii characters.

test/error_highlight/test_error_highlight.rb

@@ -1016,4 +1016,20 @@ _ _ ^^^^^
       load tmp.path
     end
   end
+
+  def test_no_final_newline
+    tmp = Tempfile.new(["error_highlight_test", ".rb"])
+    tmp << "1.time {}"
+    tmp.close(false)
+
+    assert_error_message(NoMethodError, <<~END) do
+undefined method `time' for 1:Integer
+
+1.time {}
+ ^^^^^
+    END
+
+      load tmp.path
+    end
+  end
 end