diff --git a/build.mill b/build.mill
index 5e9f3e2a..5193be87 100644
--- a/build.mill
+++ b/build.mill
@@ -8,14 +8,16 @@ import mill._, scalalib._, scalanativelib._, publish._
 import mill.scalalib.api.ZincWorkerUtil
 import com.github.lolgab.mill.mima._
 import de.tobiasroeser.mill.vcs.version.VcsVersion
+import mill.scalalib.scalafmt.ScalafmtModule
+
 
 val communityBuildDottyVersion = sys.props.get("dottyVersion").toList
 
 val scala213Version = "2.13.14"
 
 val scalaVersions = Seq(
-  "3.3.1",
-  "2.12.17",
+  "3.3.3",
+  "2.12.19",
   scala213Version
 ) ++ communityBuildDottyVersion
 
@@ -26,6 +28,7 @@ object Deps {
   val sourcecode = ivy"com.lihaoyi::sourcecode::0.4.2"
   val utest = ivy"com.lihaoyi::utest::0.8.4"
   val expecty = ivy"com.eed3si9n.expecty::expecty::0.16.0"
+  val collectionCompact = ivy"org.scala-lang.modules::scala-collection-compat:2.12.0"
   def scalaReflect(scalaVersion: String) = ivy"org.scala-lang:scala-reflect:$scalaVersion"
   def scalaLibrary(version: String) = ivy"org.scala-lang:scala-library:${version}"
 }
@@ -39,7 +42,12 @@ trait AcyclicModule extends ScalaModule {
   }
   def compileIvyDeps = acyclicDep
   def scalacPluginIvyDeps = acyclicDep
-  def scalacOptions = super.scalacOptions() ++ acyclicOptions()
+  def scalacOptions = super.scalacOptions() ++ acyclicOptions() ++ Seq(
+    "-deprecation",
+    "-feature",
+    "-language:implicitConversions",
+    "-language:higherKinds",
+  )
 }
 
 trait SafeDeps extends ScalaModule {
@@ -111,8 +119,8 @@ trait OsLibModule
   }
 }
 
-trait OsModule extends OsLibModule { outer =>
-  def ivyDeps = Agg(Deps.geny)
+trait OsModule extends OsLibModule with ScalafmtModule { outer =>
+  def ivyDeps = Agg(Deps.geny, Deps.collectionCompact)
   override def compileIvyDeps = T {
     val scalaReflectOpt = Option.when(!ZincWorkerUtil.isDottyOrScala3(scalaVersion()))(
       Deps.scalaReflect(scalaVersion())
@@ -165,6 +173,7 @@ trait OsModule extends OsLibModule { outer =>
   }
 }
 
+
 object os extends Module {
 
   object jvm extends Cross[OsJvmModule](scalaVersions)
diff --git a/os/src/GlobInterpolator.scala b/os/src/GlobInterpolator.scala
index 73a11c0a..4c7f3edb 100644
--- a/os/src/GlobInterpolator.scala
+++ b/os/src/GlobInterpolator.scala
@@ -2,8 +2,8 @@ package os
 
 object GlobInterpolator {
   class Interped(parts: Seq[String]) {
-    def unapplySeq(s: String) = {
-      val Seq(head, tail @ _*) = parts.map(java.util.regex.Pattern.quote)
+    def unapplySeq(s: String): Option[List[String]] = {
+      val Seq(head, tail @ _*) = parts.map(java.util.regex.Pattern.quote): @unchecked
 
       val regex = head + tail.map("(.*)" + _).mkString
       regex.r.unapplySeq(s)
diff --git a/os/src/ListOps.scala b/os/src/ListOps.scala
index 05257407..5306b13e 100644
--- a/os/src/ListOps.scala
+++ b/os/src/ListOps.scala
@@ -17,7 +17,7 @@ import java.nio.file.attribute.BasicFileAttributes
 object list extends Function1[Path, IndexedSeq[Path]] {
   def apply(src: Path, sort: Boolean = true): IndexedSeq[Path] = {
     val arr = stream(src).toArray[Path]
-    if (sort) arr.sorted
+    if (sort) arr.sorted.toIndexedSeq
     else arr
   }
   def apply(src: Path): IndexedSeq[Path] = apply(src, true).toIndexedSeq
@@ -53,7 +53,7 @@ object list extends Function1[Path, IndexedSeq[Path]] {
  * saving time as compared to filtering them after the fact.
  *
  * By default, the paths are returned as a pre-order traversal: the enclosing
- * folder is occurs first before any of it's contents. You can pass in `preOrder =
+ * folder occurs first before any of its contents. You can pass in `preOrder =
  * false` to turn it into a post-order traversal, such that the enclosing folder
  * occurs last after all it's contents.
  *
@@ -76,12 +76,12 @@ object walk {
    *                 you want `preOrder` to be `true` so the folder gets
    *                 created first.
    *
-   * @param followLinks Whether or not to follow symlinks while walking; defaults
+   * @param followLinks Whether to follow symlinks while walking; defaults
    *                    to false
    *
    * @param maxDepth The max depth of the tree you wish to walk; defaults to unlimited
    *
-   * @param includeTarget Whether or not to include the given path as part of the walk.
+   * @param includeTarget Whether to include the given path as part of the walk.
    *                      If `true`, does not raise an error if the given path is a
    *                      simple file and not a folder
    */
@@ -109,12 +109,12 @@ object walk {
    *                 you want `preOrder` to be `true` so the folder gets
    *                 created first.
    *
-   * @param followLinks Whether or not to follow symlinks while walking; defaults
+   * @param followLinks Whether to follow symlinks while walking; defaults
    *                    to false
    *
    * @param maxDepth The max depth of the tree you wish to walk; defaults to unlimited
    *
-   * @param includeTarget Whether or not to include the given path as part of the walk.
+   * @param includeTarget Whether to include the given path as part of the walk.
    *                      If `true`, does not raise an error if the given path is a
    *                      simple file and not a folder
    */
@@ -145,12 +145,12 @@ object walk {
      *                 you want `preOrder` to be `true` so the folder gets
      *                 created first.
      *
-     * @param followLinks Whether or not to follow symlinks while walking; defaults
+     * @param followLinks Whether to follow symlinks while walking; defaults
      *                    to false
      *
      * @param maxDepth The max depth of the tree you wish to walk; defaults to unlimited
      *
-     * @param includeTarget Whether or not to include the given path as part of the walk.
+     * @param includeTarget Whether to include the given path as part of the walk.
      *                      If `true`, does not raise an error if the given path is a
      *                      simple file and not a folder
      */
@@ -179,12 +179,12 @@ object walk {
      *                 you want `preOrder` to be `true` so the folder gets
      *                 created first.
      *
-     * @param followLinks Whether or not to follow symlinks while walking; defaults
+     * @param followLinks Whether to follow symlinks while walking; defaults
      *                    to false
      *
      * @param maxDepth The max depth of the tree you wish to walk; defaults to unlimited
      *
-     * @param includeTarget Whether or not to include the given path as part of the walk.
+     * @param includeTarget Whether to include the given path as part of the walk.
      *                      If `true`, does not raise an error if the given path is a
      *                      simple file and not a folder
      */
@@ -228,7 +228,7 @@ object walk {
             // rather than relying on `walkFileTree`, because `walkFileTree`
             // does the unintuitive thing when the `path` being walked is a
             // symlink to a directory (it just returns the symlink path and
-            // does not walking)
+            // does not walk)
             val ds = Files.newDirectoryStream(pathNIO)
             val iter = ds.iterator()
             try {
diff --git a/os/src/Path.scala b/os/src/Path.scala
index e135c4c5..deb8acd7 100644
--- a/os/src/Path.scala
+++ b/os/src/Path.scala
@@ -2,7 +2,7 @@ package os
 
 import java.net.URI
 import java.nio.file.Paths
-import collection.JavaConverters._
+import scala.jdk.CollectionConverters._
 import scala.language.implicitConversions
 import acyclic.skipped
 import os.PathError.{InvalidSegment, NonCanonicalLiteral}
@@ -212,7 +212,7 @@ object BasePath {
     }
   }
   def chunkify(s: java.nio.file.Path) = {
-    import collection.JavaConverters._
+    import scala.jdk.CollectionConverters._
     s.iterator().asScala.map(_.toString).filter(_ != ".").filter(_ != "").toArray
   }
 }
diff --git a/os/src/ProcessOps.scala b/os/src/ProcessOps.scala
index 6175e87c..5bdc3124 100644
--- a/os/src/ProcessOps.scala
+++ b/os/src/ProcessOps.scala
@@ -1,6 +1,6 @@
 package os
 
-import collection.JavaConverters._
+import scala.jdk.CollectionConverters._
 import java.lang.ProcessBuilder.Redirect
 import os.SubProcess.InputStream
 import java.io.IOException
diff --git a/os/src/ReadWriteOps.scala b/os/src/ReadWriteOps.scala
index 62b8c0be..cffdc86b 100644
--- a/os/src/ReadWriteOps.scala
+++ b/os/src/ReadWriteOps.scala
@@ -56,7 +56,7 @@ object write {
   ) = {
     checker.value.onWrite(target)
 
-    import collection.JavaConverters._
+    import scala.jdk.CollectionConverters._
     val permArray: Array[FileAttribute[_]] =
       if (perms == null) Array.empty
       else Array(PosixFilePermissions.asFileAttribute(perms.toSet()))
diff --git a/os/src/SubProcess.scala b/os/src/SubProcess.scala
index 9f624819..680e077f 100644
--- a/os/src/SubProcess.scala
+++ b/os/src/SubProcess.scala
@@ -51,7 +51,7 @@ sealed trait ProcessLike extends java.lang.AutoCloseable {
 
   /**
    * Wait up to `millis` for the [[ProcessLike]] to terminate and all stdout and stderr
-   * from the subprocess to be handled. By default waits indefinitely; if a time
+   * from the subprocess to be handled. By default, waits indefinitely; if a time
    * limit is given, explicitly destroys the [[ProcessLike]] if it has not completed by
    * the time the timeout has occurred.
    *
@@ -152,7 +152,7 @@ class SubProcess(
    * @param async set this to `true` if you do not want to wait on the subprocess exiting
    * @param shutdownGracePeriod use this to override the default wait time for the subprocess
    *                            to gracefully exit before destroying it forcibly. Defaults to the `shutdownGracePeriod`
-   *                            that was used to spawned the process, but can be set to 0
+   *                            that was used to spawn the process, but can be set to 0
    *                            (i.e. force exit immediately) or -1 (i.e. never force exit)
    *                            or anything in between. Typically defaults to 100 milliseconds.
    */
@@ -183,7 +183,7 @@ class SubProcess(
   /**
    * Alias for [[destroy]]
    */
-  def close() = wrapped.destroy()
+  def close(): Unit = wrapped.destroy()
 
   /**
    * Wait up to `millis` for the subprocess to terminate, by default waits
@@ -296,7 +296,7 @@ object SubProcess {
       out.toByteArray
     }
 
-    override def close() = wrapped.close()
+    override def close(): Unit = wrapped.close()
   }
 }
 
@@ -314,7 +314,7 @@ class ProcessPipeline(
   /**
    * String representation of the pipeline.
    */
-  def commandString = processes.map(_.wrapped.toString).mkString(" | ")
+  def commandString: String = processes.map(_.wrapped.toString).mkString(" | ")
 
   private[os] val brokenPipeHandler: Option[Thread] = brokenPipeQueue.map { queue =>
     new Thread(
@@ -326,7 +326,7 @@ class ProcessPipeline(
             if (brokenPipeIndex == processes.length) { // Special case signaling finished pipeline
               pipelineRunning = false
             } else {
-              processes(brokenPipeIndex).destroyForcibly()
+              processes(brokenPipeIndex).destroy(shutdownGracePeriod = 0)
             }
           }
           new Thread(
@@ -354,9 +354,7 @@ class ProcessPipeline(
    */
   override def exitCode(): Int = {
     if (pipefail)
-      processes.map(_.exitCode())
-        .filter(_ != 0)
-        .headOption
+      processes.map(_.exitCode()).find(_ != 0)
         .getOrElse(0)
     else
       processes.last.exitCode()
@@ -383,7 +381,7 @@ class ProcessPipeline(
    * All processes in the pipeline are force-destroyed.
    */
   override def destroyForcibly(): Unit = {
-    processes.foreach(_.destroyForcibly())
+    processes.foreach(_.destroy(shutdownGracePeriod = 0))
   }
 
   /**
diff --git a/os/src/ZipOps.scala b/os/src/ZipOps.scala
index a62d7d49..968c2018 100644
--- a/os/src/ZipOps.scala
+++ b/os/src/ZipOps.scala
@@ -4,7 +4,8 @@ import java.net.URI
 import java.nio.file.{FileSystem, FileSystems, Files}
 import java.nio.file.attribute.{BasicFileAttributeView, FileTime, PosixFilePermissions}
 import java.util.zip.{ZipEntry, ZipFile, ZipInputStream, ZipOutputStream}
-import scala.collection.JavaConverters._
+import scala.jdk.CollectionConverters._
+
 import scala.util.matching.Regex
 
 object zip {
diff --git a/os/test/src-jvm/ZipOpJvmTests.scala b/os/test/src-jvm/ZipOpJvmTests.scala
index dfe4bad2..8ab629db 100644
--- a/os/test/src-jvm/ZipOpJvmTests.scala
+++ b/os/test/src-jvm/ZipOpJvmTests.scala
@@ -5,7 +5,7 @@ import utest._
 import java.nio.file.attribute.FileTime
 import java.nio.file.{Files, Paths}
 import java.util.zip.ZipFile
-import scala.collection.JavaConverters._
+import scala.jdk.CollectionConverters._
 
 object ZipOpJvmTests extends TestSuite {
 
diff --git a/os/watch/src/WatchServiceWatcher.scala b/os/watch/src/WatchServiceWatcher.scala
index 39f22b3d..ec731515 100644
--- a/os/watch/src/WatchServiceWatcher.scala
+++ b/os/watch/src/WatchServiceWatcher.scala
@@ -8,7 +8,7 @@ import java.nio.file.StandardWatchEventKinds.{ENTRY_CREATE, ENTRY_DELETE, ENTRY_
 import com.sun.nio.file.{ExtendedWatchEventModifier, SensitivityWatchEventModifier}
 
 import scala.collection.mutable
-import collection.JavaConverters._
+import scala.jdk.CollectionConverters._
 import scala.util.Properties.isWin
 
 class WatchServiceWatcher(