Support Scala 3

build.sbt

@@ -1,15 +1,17 @@
 import ReleaseTransformations._
+import Dependencies._
 
 lazy val baseSettings = Seq(
   scalaVersion := "2.13.10",
-  crossScalaVersions := Seq(scalaVersion.value),
+  crossScalaVersions := Seq(scalaVersion.value, "3.2.1"),
   organization := "com.madgag.scala-git",
   scmInfo := Some(ScmInfo(
     url("https://github.com/rtyley/scala-git"),
     "scm:git:git@github.com:rtyley/scala-git.git"
   )),
   licenses := Seq("Apache-2.0" -> url("http://www.apache.org/licenses/LICENSE-2.0")),
-  scalacOptions ++= Seq("-deprecation", "-unchecked")
+  scalacOptions ++= Seq("-deprecation", "-unchecked"),
+  libraryDependencies ++= Seq(madgagCompress % Test, scalatest % Test)
 )
 
 lazy val `scala-git` = project.settings(baseSettings: _*).dependsOn(`scala-git-test` % Test)

scala-git/src/main/scala/com/madgag/diff/MapDiff.scala

@@ -1,6 +1,6 @@
 package com.madgag.diff
 
-import com.madgag.scala.collection.decorators.MapDecorator
+import com.madgag.scala.collection.decorators._
 
 object MapDiff {
   def apply[K,V](before: Map[K,V], after: Map[K,V]): MapDiff[K,V] =
@@ -12,7 +12,7 @@ case class MapDiff[K, V](beforeAndAfter: Map[BeforeAndAfter, Map[K,V]]) {
   lazy val commonElements: Set[K] = beforeAndAfter.values.map(_.keySet).reduce(_ intersect _)
 
   lazy val only: Map[BeforeAndAfter, Map[K,V]] =
-    beforeAndAfter.mapV(_.view.filterKeys(!commonElements(_)).toMap)
+    beforeAndAfter.mapV(_.view.filterKeys(!commonElements(_)).toMap).toMap
 
   lazy val (unchanged, changed) =
     commonElements.partition(k => beforeAndAfter(Before)(k) == beforeAndAfter(After)(k))