Fix #1405: Implement Xprint-diff without external libraries.

1 files changed, 105 insertions, 25 deletions

diff --git a/src/dotty/tools/dotc/util/DiffUtil.scala b/src/dotty/tools/dotc/util/DiffUtil.scala
index b28f36382..b7c77ad62 100644
--- a/src/dotty/tools/dotc/util/DiffUtil.scala
+++ b/src/dotty/tools/dotc/util/DiffUtil.scala
@@ -1,7 +1,7 @@
 package dotty.tools.dotc.util
 
 import scala.annotation.tailrec
-import difflib._
+import scala.collection.mutable
 
 object DiffUtil {
 
@@ -13,9 +13,8 @@ object DiffUtil {
   private final val ADDITION_COLOR = ANSI_GREEN
 
   def mkColoredCodeDiff(code: String, lastCode: String, printDiffDel: Boolean): String = {
-    import scala.collection.JavaConversions._
 
-    @tailrec def split(str: String, acc: List[String]): List[String] = {
+    @tailrec def splitTokens(str: String, acc: List[String] = Nil): List[String] = {
       if (str == "") {
         acc.reverse
       } else {
@@ -30,38 +29,119 @@ object DiffUtil {
               !Character.isMirrored(c) && !Character.isWhitespace(c)
           }
         }
-        split(rest, token :: acc)
+        splitTokens(rest, token :: acc)
       }
     }
 
-    val lines = split(code, Nil).toArray
-    val diff = DiffUtils.diff(split(lastCode, Nil), lines.toList)
+    val tokens = splitTokens(code, Nil).toArray
+    val lastTokens = splitTokens(lastCode, Nil).toArray
 
-    for (delta <- diff.getDeltas) {
-      val pos = delta.getRevised.getPosition
-      val endPos = pos + delta.getRevised.getLines.size - 1
+    val diff = hirschberg(lastTokens, tokens)
 
-      delta.getType.toString match { // Issue #1355 forces us to use the toString
-        case "INSERT" =>
-          lines(pos) = ADDITION_COLOR + lines(pos)
-          lines(endPos) = lines(endPos) + ANSI_DEFAULT
+    diff.collect {
+      case Unmodified(str) => str
+      case Inserted(str)                      => ADDITION_COLOR + str + ANSI_DEFAULT
+      case Modified(old, str) if printDiffDel => DELETION_COLOR + old + ADDITION_COLOR + str + ANSI_DEFAULT
+      case Modified(_, str)                   => ADDITION_COLOR + str + ANSI_DEFAULT
+      case Deleted(str) if printDiffDel       => DELETION_COLOR + str + ANSI_DEFAULT
+    }.mkString
+  }
 
-        case "CHANGE" =>
-          val old = if (!printDiffDel) "" else
-            DELETION_COLOR + delta.getOriginal.getLines.mkString + ANSI_DEFAULT
-          lines(pos) = old + ADDITION_COLOR + lines(pos)
-          lines(endPos) = lines(endPos) + ANSI_DEFAULT
+  private sealed trait Patch
+  private final case class Unmodified(str: String) extends Patch
+  private final case class Modified(original: String, str: String) extends Patch
+  private final case class Deleted(str: String) extends Patch
+  private final case class Inserted(str: String) extends Patch
 
-        case "DELETE" if printDiffDel =>
-          val deleted = delta.getOriginal.getLines.mkString
-          if (!deleted.forall(Character.isWhitespace)) {
-            lines(pos) = DELETION_COLOR + deleted + ANSI_DEFAULT + lines(pos)
-          }
+  private def hirschberg(a: Array[String], b: Array[String]): Array[Patch] = {
+    def build(x: Array[String], y: Array[String], builder: mutable.ArrayBuilder[Patch]): Unit = {
+      if (x.isEmpty) {
+        builder += Inserted(y.mkString)
+      } else if (y.isEmpty) {
+        builder += Deleted(x.mkString)
+      } else if (x.length == 1 || y.length == 1) {
+        needlemanWunsch(x, y, builder)
+      } else {
+        val xlen = x.length
+        val xmid = xlen / 2
+        val ylen = y.length
+
+        val (x1, x2) = x.splitAt(xmid)
+        val leftScore = nwScore(x1, y)
+        val rightScore = nwScore(x2.reverse, y.reverse)
+        val scoreSum = (leftScore zip rightScore.reverse).map {
+          case (left, right) => left + right
+        }
+        val max = scoreSum.max
+        val ymid = scoreSum.indexOf(max)
 
-        case _ =>
+        val (y1, y2) = y.splitAt(ymid)
+        build(x1, y1, builder)
+        build(x2, y2, builder)
       }
     }
+    val builder = Array.newBuilder[Patch]
+    build(a, b, builder)
+    builder.result()
+  }
+
+  private def nwScore(x: Array[String], y: Array[String]): Array[Int] = {
+    def ins(s: String) = -2
+    def del(s: String) = -2
+    def sub(s1: String, s2: String) = if (s1 == s2) 2 else -1
 
-    lines.mkString
+    val score = Array.fill(x.length + 1, y.length + 1)(0)
+    for (j <- 1 to y.length)
+      score(0)(j) = score(0)(j - 1) + ins(y(j - 1))
+    for (i <- 1 to x.length) {
+      score(i)(0) = score(i - 1)(0) + del(x(i - 1))
+      for (j <- 1 to y.length) {
+        val scoreSub = score(i - 1)(j - 1) + sub(x(i - 1), y(j - 1))
+        val scoreDel = score(i - 1)(j) + del(x(i - 1))
+        val scoreIns = score(i)(j - 1) + ins(y(j - 1))
+        score(i)(j) = scoreSub max scoreDel max scoreIns
+      }
+    }
+    Array.tabulate(y.length + 1)(j => score(x.length)(j))
   }
+
+  private def needlemanWunsch(x: Array[String], y: Array[String], builder: mutable.ArrayBuilder[Patch]): Unit = {
+    def similarity(a: String, b: String) = if (a == b) 2 else -1
+    val d = 1
+    val score = Array.tabulate(x.length + 1, y.length + 1) { (i, j) =>
+      if (i == 0) d * j
+      else if (j == 0) d * i
+      else 0
+    }
+    for (i <- 1 to x.length) {
+      for (j <- 1 to y.length) {
+        val mtch = score(i - 1)(j - 1) + similarity(x(i - 1), y(j - 1))
+        val delete = score(i - 1)(j) + d
+        val insert = score(i)(j - 1) + d
+        score(i)(j) = mtch max insert max delete
+      }
+    }
+
+    var alignment = List.empty[Patch]
+    var i = x.length
+    var j = y.length
+    while (i > 0 || j > 0) {
+      if (i > 0 && j > 0 && score(i)(j) == score(i - 1)(j - 1) + similarity(x(i - 1), y(j - 1))) {
+        val newHead =
+          if (x(i - 1) == y(j - 1)) Unmodified(x(i - 1))
+          else Modified(x(i - 1), y(j - 1))
+        alignment = newHead :: alignment
+        i = i - 1
+        j = j - 1
+      } else if (i > 0 && score(i)(j) == score(i - 1)(j) + d) {
+        alignment = Deleted(x(i - 1)) :: alignment
+        i = i - 1
+      } else {
+        alignment = Inserted(y(j - 1)) :: alignment
+        j = j - 1
+      }
+    }
+    builder ++= alignment
+  }
+
 }