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som-snytt · som-snytt · commit 7fe3dc9c1de2 · 2022-04-03T12:58:29.000-07:00
diff --git a/build.sbt b/build.sbt
@@ -444,6 +444,7 @@ lazy val compiler = configureAsSubproject(project)
     name := "scala-compiler",
     description := "Scala Compiler",
     libraryDependencies += asmDep,
+    libraryDependencies += diffUtilsDep,
     // These are only needed for the POM:
     // TODO: jline dependency is only needed for the REPL shell, which should move to its own jar
     libraryDependencies ++= jlineDeps,
@@ -454,7 +455,11 @@ lazy val compiler = configureAsSubproject(project)
     // (with strings) to deal with mutual recursion
     Compile / packageBin / products :=
       (Compile / packageBin / products).value ++
-        Seq((Compile / dependencyClasspath).value.find(_.get(moduleID.key).map(id => (id.organization, id.name, id.revision)).contains((asmDep.organization, asmDep.name, asmDep.revision))).get.data) ++
+        (Compile / dependencyClasspath).value.filter(_.get(moduleID.key).map(id => (id.organization, id.name, id.revision)) match {
+          case Some((diffUtilsDep.organization, diffUtilsDep.name, diffUtilsDep.revision)) => true
+          case Some((asmDep.organization, asmDep.name, asmDep.revision)) => true
+          case _ => false
+        }).map(_.data) ++
         (LocalProject("interactive")   / Compile / packageBin / products).value ++
         (LocalProject("scaladoc")      / Compile / packageBin / products).value ++
         (LocalProject("repl")          / Compile / packageBin / products).value ++
diff --git a/src/compiler/scala/tools/nsc/Global.scala b/src/compiler/scala/tools/nsc/Global.scala
@@ -210,11 +210,22 @@ class Global(var currentSettings: Settings, reporter0: Reporter)
       print(" // " + unit.source)
       if (unit.body == null) println(": tree is null")
       else {
-        val source = util.stringFromWriter(w => newTreePrinter(w) print unit.body)
+        val source = util.stringFromWriter(w => newTreePrinter(w).print(unit.body))
 
         // treePrinter show unit.body
         if (lastPrintedSource == source)
-          println(": tree is unchanged since " + lastPrintedPhase)
+          println(s": tree is unchanged since $lastPrintedPhase")
+        else if (settings.showTreeDiff) {
+          import scala.jdk.CollectionConverters._
+          import com.github.difflib.{DiffUtils, UnifiedDiffUtils}
+          val diff = DiffUtils.diff(lastPrintedSource.linesIterator.toList.asJava, source.linesIterator.toList.asJava)
+          val unified = UnifiedDiffUtils.generateUnifiedDiff(lastPrintedPhase.name, phase.prev.name, lastPrintedSource.linesIterator.toList.asJava, diff, 1).asScala
+          lastPrintedPhase = phase.prev
+          lastPrintedSource = source
+          println("")
+          unified.foreach(println)
+          println("")
+        }
         else {
           lastPrintedPhase = phase.prev // since we're running inside "exitingPhase"
           lastPrintedSource = source
diff --git a/src/compiler/scala/tools/nsc/settings/ScalaSettings.scala b/src/compiler/scala/tools/nsc/settings/ScalaSettings.scala
@@ -227,15 +227,16 @@ trait ScalaSettings extends StandardScalaSettings with Warnings { _: MutableSett
       name = "-Yprint-trees",
       helpArg = "style",
       descr = "How to print trees when -Vprint is enabled.",
-      choices = List("text", "compact", "format", "text+format"),
+      choices = List("text", "compact", "format", "text+format", "diff"),
       default = "text"
     ).withPostSetHook(pt => pt.value match {
-      case "text"        =>
       case "compact"     => XshowtreesCompact.value = true
       case "format"      => Xshowtrees.value = true
       case "text+format" => XshowtreesStringified.value = true
+      case _             =>
     })
 
+  def showTreeDiff: Boolean = YprintTrees.value == "diff"
   val Xshowtrees      = BooleanSetting    ("-Yshow-trees", "(Requires -Vprint:) Print detailed ASTs in formatted form.").internalOnly()
   val XshowtreesCompact
                       = BooleanSetting    ("-Yshow-trees-compact", "(Requires -Vprint:) Print detailed ASTs in compact form.").internalOnly()
