use -Werror instead of -Xfatal-warnings

project/HouseRulesPlugin.scala

@@ -14,7 +14,7 @@ object HouseRulesPlugin extends AutoPlugin {
     scalacOptions += "-language:implicitConversions",
     scalacOptions ++= "-Xfuture".ifScala213OrMinus.value.toList,
     scalacOptions ++= "-Xlint".ifScala2.value.toList,
-    scalacOptions ++= "-Xfatal-warnings"
+    scalacOptions ++= "-Werror"
       .ifScala3x(_ => {
         sys.props.get("sbt.build.fatal") match {
           case Some(_) => java.lang.Boolean.getBoolean("sbt.build.fatal")

project/Utils.scala

@@ -31,7 +31,7 @@ object Utils {
 
   lazy val baseScalacOptions = Seq(
     Compile / doc / scalacOptions -= "-Xlint",
-    Compile / doc / scalacOptions -= "-Xfatal-warnings",
+    Compile / doc / scalacOptions -= "-Werror",
   )
 
   def projectComponent: Setting[?] =

sbt-app/src/sbt-test/actions/doc/build.sbt

@@ -7,7 +7,7 @@ lazy val root = (project in file("."))
     crossPaths := false,
     crossScalaVersions := Seq("2.12.20", "2.13.12"),
     scalaVersion := "2.12.20",
-    Compile / doc / scalacOptions += "-Xfatal-warnings",
+    Compile / doc / scalacOptions += "-Werror",
     commands += Command.command("excludeB") { s =>
       val impl = """val src = (Compile / sources).value; src.filterNot(_.getName.contains("B"))"""
       s"set Compile / doc / sources := { $impl }" :: s

sbt-app/src/sbt-test/plugins/unidoc/build.sbt

@@ -1,5 +1,5 @@
 scalaVersion := "2.12.20"
-scalacOptions += "-Xfatal-warnings" // required for the test
+scalacOptions += "-Werror" // required for the test
 
 enablePlugins(ScalaUnidocPlugin)
 autoAPIMappings := true

sbt-app/src/sbt-test/project1/sbt-plugin/build.sbt

@@ -2,5 +2,5 @@ lazy val root = project.in(file("."))
   .enablePlugins(SbtPlugin)
   .settings(
     scalaVersion := "2.12.20",
-    scalacOptions ++= Seq("-Xfatal-warnings", "-Xlint")
+    scalacOptions ++= Seq("-Werror", "-Xlint")
   )

sbt-app/src/sbt-test/project1/sbt-plugin/changes/oldSbtPlugin.sbt

@@ -2,5 +2,5 @@ lazy val root = project.in(file("."))
   .settings(
     scalaVersion := "2.12.20",
     sbtPlugin := true,
-    scalacOptions ++= Seq("-Xfatal-warnings", "-Xlint")
+    scalacOptions ++= Seq("-Werror", "-Xlint")
   )

sbt-app/src/sbt-test/project1/setting-macro/project/plugins.sbt

@@ -1 +1 @@
-Compile / scalacOptions += "-Xfatal-warnings"
+Compile / scalacOptions += "-Werror"

sbt-app/src/sbt-test/source-dependencies/sealed/test

@@ -1,4 +1,4 @@
-> 'set scalacOptions += "-Xfatal-warnings"'
+> 'set scalacOptions += "-Werror"'
 
 > compile
 

sbt-app/src/sbt-test/tests/arguments/test

@@ -25,7 +25,7 @@ $ touch failure3
 -> testQuick
 $ delete failure3
 
-> set Compile / scalacOptions += "-Xfatal-warnings"
+> set Compile / scalacOptions += "-Werror"
 
 > set foo += "an argument with spaces"