Enable -Werror option

io/src/main/scala/sbt/internal/io/ErrorHandling.scala

@@ -12,6 +12,7 @@
 package sbt.internal.io
 
 import java.io.IOException
+import scala.annotation.nowarn
 
 private[sbt] object ErrorHandling {
   def translate[T](msg: => String)(f: => T) =
@@ -22,6 +23,7 @@ private[sbt] object ErrorHandling {
       case e: Exception   => throw new TranslatedException(msg + e.toString, e)
     }
 
+  @nowarn("msg=ThreadDeath")
   def wideConvert[T](f: => T): Either[Throwable, T] =
     try {
       Right(f)

io/src/main/scala/sbt/internal/io/SourceModificationWatch.scala

@@ -24,6 +24,7 @@ import sbt.nio.file.{ AnyPath, FileAttributes, FileTreeView, Glob, RecursiveGlob
 import sbt.nio.file.Glob.GlobOps
 
 import scala.annotation.tailrec
+import scala.annotation.nowarn
 import scala.jdk.CollectionConverters._
 import scala.collection.{ immutable, mutable }
 import scala.concurrent.duration._
@@ -298,6 +299,7 @@ private[sbt] object WatchState {
     init
   }
 
+  @nowarn("msg=WatchState")
   def empty(globs: Seq[Glob]): WatchState = {
     val service = new WatchService {
       override def init(): Unit = {}

io/src/test/scala/sbt/io/IOSpec.scala

@@ -274,6 +274,6 @@ class IOSpec extends AnyFunSuite {
   }
 
   def normalizeForWindows(s: String): String = {
-    s.replaceAllLiterally("""\""", "/")
+    s.replace("""\""", "/")
   }
 }

project/HouseRulesPluglin.scala

@@ -13,21 +13,17 @@ object HouseRulesPlugin extends AutoPlugin {
     scalacOptions ++= Seq("-encoding", "utf8"),
     scalacOptions ++= Seq("-deprecation", "-feature", "-unchecked"),
     scalacOptions += "-language:implicitConversions",
-    scalacOptions ++= "-Werror"
-      .ifScala(v => {
-        sys.props.get("sbt.build.fatal") match {
-          case Some(_) => java.lang.Boolean.getBoolean("sbt.build.fatal")
-          case _       => v == 12
-        }
-      })
-      .value
-      .toList,
+    scalacOptions ++= Seq(
+      "-Wconf:msg=Compiler synthesis of Manifest and OptManifest is deprecated:silent",
+      "-Wconf:msg=type Traversable in package scala:silent",
+    ),
+    scalacOptions ++= {
+      sys.props.get("sbt.build.fatal") match {
+        case Some("false") =>
+          Nil
+        case _ =>
+          Seq("-Werror")
+      }
+    }
   )
-
-  private def scalaPartV = Def setting (CrossVersion partialVersion scalaVersion.value)
-
-  private implicit final class AnyWithIfScala[A](val __x: A) {
-    def ifScala(p: Long => Boolean) =
-      Def setting (scalaPartV.value collect { case (2, y) if p(y) => __x })
-  }
 }