1 files changed, 66 insertions, 0 deletions
diff --git a/src/dotty/tools/dotc/util/DiffUtil.scala b/src/dotty/tools/dotc/util/DiffUtil.scala
new file mode 100644
index 000000000..6718ccbf8
--- /dev/null
+++ b/src/dotty/tools/dotc/util/DiffUtil.scala
@@ -0,0 +1,66 @@
+package dotty.tools.dotc.util
+
+import scala.annotation.tailrec
+import difflib._
+
+object DiffUtil {
+
+  private final val ANSI_DEFAULT = "\u001B[0m"
+  private final val ANSI_RED = "\u001B[31m"
+  private final val ANSI_GREEN = "\u001B[32m"
+  private final val ANSI_YELLOW = "\u001B[33m"
+  private final val ANSI_MAGENTA = "\u001B[35m"
+
+  def mkColoredCodeDiff(code: String, lastCode: String, printDiffDel: Boolean): String = {
+    import scala.collection.JavaConversions._
+
+    @tailrec def split(str: String, acc: List[String]): List[String] = {
+      if (str == "") {
+        acc.reverse
+      } else {
+        val head = str.charAt(0)
+        val (token, rest) = if (Character.isAlphabetic(head) || Character.isDigit(head)) {
+          str.span(c => Character.isAlphabetic(c) || Character.isDigit(c))
+        } else if (Character.isMirrored(head) || Character.isWhitespace(head)) {
+          str.splitAt(1)
+        } else {
+          str.span { c =>
+            !Character.isAlphabetic(c) && !Character.isDigit(c) &&
+              !Character.isMirrored(c) && !Character.isWhitespace(c)
+          }
+        }
+        split(rest, token :: acc)
+      }
+    }
+
+    val lines = split(code, Nil).toArray
+    val diff = DiffUtils.diff(split(lastCode, Nil), lines.toList)
+
+    for (delta <- diff.getDeltas) {
+      val pos = delta.getRevised.getPosition
+      val endPos = pos + delta.getRevised.getLines.size - 1
+
+      delta.getType.toString match { // Issue #1355 forces us to use the toString
+        case "INSERT" =>
+          lines(pos) = ANSI_GREEN + lines(pos)
+          lines(endPos) = lines(endPos) + ANSI_DEFAULT
+
+        case "CHANGE" =>
+          val old = if (!printDiffDel) "" else
+            ANSI_MAGENTA + delta.getOriginal.getLines.mkString + ANSI_DEFAULT
+          lines(pos) = old + ANSI_YELLOW + lines(pos)
+          lines(endPos) = lines(endPos) + ANSI_DEFAULT
+
+        case "DELETE" if printDiffDel =>
+          val deleted = delta.getOriginal.getLines.mkString
+          if (!deleted.forall(Character.isWhitespace)) {
+            lines(pos) = ANSI_RED + deleted + ANSI_DEFAULT + lines(pos)
+          }
+
+        case _ =>
+      }
+    }
+
+    lines.mkString
+  }
+}