Add documentation for DiffUtil.mkColoredLineDiff

Author: Duhemm

compiler/src/dotty/tools/dotc/util/DiffUtil.scala

@@ -59,11 +59,20 @@ object DiffUtil {
     (fnd, exp, totalChange.toDouble / (expected.length + found.length))
   }
 
+  /**
+   * Return a colored diff between the tokens of every line in `expected` and `actual`. Each line of
+   * output contains the expected value on the left and the actual value on the right.
+   *
+   * @param expected The expected lines
+   * @param actual   The actual lines
+   * @return A string with one element of `expected` and `actual` on each lines, where
+   *         differences are highlighted.
+   */
   def mkColoredLineDiff(expected: Seq[String], actual: Seq[String]): String = {
-    val expectedSize = DiffUtil.EOF.length max expected.map(_.length).max
+    val expectedSize = EOF.length max expected.map(_.length).max
     actual.padTo(expected.length, "").zip(expected.padTo(actual.length, "")).map { case (act, exp) =>
       mkColoredLineDiff(exp, act, expectedSize)
-    }.mkString("\n")
+    }.mkString(System.lineSeparator)
   }
 
   def mkColoredLineDiff(expected: String, actual: String, expectedSize: Int): String = {