scala · som-snytt · Nov 7, 2025 · Nov 7, 2025 · Nov 7, 2025 · Nov 7, 2025
diff --git a/compiler/src/dotty/tools/dotc/config/ScalaSettings.scala b/compiler/src/dotty/tools/dotc/config/ScalaSettings.scala
@@ -146,8 +146,8 @@ private sealed trait PluginSettings:
 private sealed trait VerboseSettings:
   self: SettingGroup =>
   val Vhelp: Setting[Boolean] = BooleanSetting(VerboseSetting, "V", "Print a synopsis of verbose options.")
-  val Vprint: Setting[List[String]] = PhasesSetting(VerboseSetting, "Vprint", "Print out program after", aliases = List("-Xprint"))
-  val XshowPhases: Setting[Boolean] = BooleanSetting(VerboseSetting, "Vphases", "List compiler phases.", aliases = List("-Xshow-phases"))
+  val Vprint: Setting[List[String]] = PhasesSetting(VerboseSetting, "Vprint", "Print out program after", deprecatedAliases = List("-Xprint" -> Deprecation()))
+  val XshowPhases: Setting[Boolean] = BooleanSetting(VerboseSetting, "Vphases", "List compiler phases.", deprecatedAliases = List("-Xshow-phases" -> Deprecation()))
 
   val Vprofile: Setting[Boolean] = BooleanSetting(VerboseSetting, "Vprofile", "Show metrics about sources and internal representations to estimate compile-time complexity.")
   val VprofileSortedBy = ChoiceSetting(VerboseSetting, "Vprofile-sorted-by", "key", "Show metrics about sources and internal representations sorted by given column name", List("name", "path", "lines", "tokens", "tasty", "complexity"), "")
@@ -161,7 +161,7 @@ private sealed trait WarningSettings:
   self: SettingGroup =>
 
   val Whelp: Setting[Boolean] = BooleanSetting(WarningSetting, "W", "Print a synopsis of warning options.")
-  val Werror: Setting[Boolean] = BooleanSetting(WarningSetting, "Werror", "Fail the compilation if there are any warnings.", aliases = List("-Xfatal-warnings"))
+  val Werror: Setting[Boolean] = BooleanSetting(WarningSetting, "Werror", "Fail the compilation if there are any warnings.", deprecatedAliases = List("-Xfatal-warnings" -> Deprecation()))
   val Wall: Setting[Boolean] = BooleanSetting(WarningSetting, "Wall", "Enable all warning settings.")
   private val WvalueDiscard: Setting[Boolean] = BooleanSetting(WarningSetting, "Wvalue-discard", "Warn when non-Unit expression results are unused.")
   private val WNonUnitStatement = BooleanSetting(WarningSetting, "Wnonunit-statement", "Warn when block statements are non-Unit expressions.")

diff --git a/compiler/src/dotty/tools/dotc/config/Settings.scala b/compiler/src/dotty/tools/dotc/config/Settings.scala
diff --git a/compiler/src/dotty/tools/dotc/reporting/Reporter.scala b/compiler/src/dotty/tools/dotc/reporting/Reporter.scala
@@ -232,7 +232,7 @@ abstract class Reporter extends interfaces.ReporterResult {
 
   def finalizeReporting()(using Context) =
     if (hasWarnings && ctx.settings.Werror.value)
-      report(new Error("No warnings can be incurred under -Werror (or -Xfatal-warnings)", NoSourcePosition))
+      report(new Error("No warnings can be incurred under -Werror", NoSourcePosition))
 
   /** Summary of warnings and errors */
   def summary: String =

diff --git a/compiler/test/dotty/tools/dotc/config/ScalaSettingsTests.scala b/compiler/test/dotty/tools/dotc/config/ScalaSettingsTests.scala
@@ -306,4 +306,12 @@ class ScalaSettingsTests:
       assertEquals(0, result.warnings.length)
       assertEquals(1, result.errors.length)
 
+  @Test def `deprecated aliases warn`: Unit =
+    val settings = ScalaSettings
+    val args = "-Xfatal-warnings" :: "-Xprint" :: "typer" :: Nil
+    val result = settings.processArguments(args, processAll = true)
+    assertEquals(2, result.warnings.length)
+    assertEquals("Option -Xfatal-warnings is a deprecated alias: use -Werror instead", result.warnings.head)
+    assertEquals(0, result.errors.length)
+
 end ScalaSettingsTests
diff --git a/repl/test-resources/repl/rewrite-messages b/repl/test-resources/repl/rewrite-messages
@@ -4,7 +4,7 @@ scala> import scala.util._
 1 | import scala.util._
   |                   ^
   |         `_` is no longer supported for a wildcard import; use `*` instead
-No warnings can be incurred under -Werror (or -Xfatal-warnings)
+No warnings can be incurred under -Werror
 1 warning found
 1 error found
 scala> extension (x: Int) def foo(y: Int) = x + y
@@ -15,6 +15,6 @@ scala> 2 foo 4
   |   ^^^
   |Alphanumeric method foo is not declared infix; it should not be used as infix operator.
   |Instead, use method syntax .foo(...) or backticked identifier `foo`.
-No warnings can be incurred under -Werror (or -Xfatal-warnings)
+No warnings can be incurred under -Werror
 1 warning found
-1 error found
+1 error found
diff --git a/sbt-test/source-dependencies/changedTypeOfChildOfSealed/incOptions.properties b/sbt-test/source-dependencies/changedTypeOfChildOfSealed/incOptions.properties
@@ -1 +1 @@
-scalac.options = -Xfatal-warnings
+scalac.options = -Werror
diff --git a/sbt-test/source-dependencies/sealed-extends-sealed/project/DottyInjectedPlugin.scala b/sbt-test/source-dependencies/sealed-extends-sealed/project/DottyInjectedPlugin.scala
@@ -7,6 +7,6 @@ object DottyInjectedPlugin extends AutoPlugin {
 
   override val projectSettings = Seq(
     scalaVersion := sys.props("plugin.scalaVersion"),
-    scalacOptions ++= Seq("-source:3.0-migration", "-Xfatal-warnings")
+    scalacOptions ++= Seq("-source:3.0-migration", "-Werror")
   )
 }
diff --git a/sbt-test/source-dependencies/sealed/test b/sbt-test/source-dependencies/sealed/test
@@ -1,4 +1,4 @@
-> 'set scalacOptions += "-Xfatal-warnings"'
+> 'set scalacOptions += "-Werror"'
 
 > compile
 
@@ -8,4 +8,4 @@ $ copy-file changes/A.scala A.scala
 # D.scala needs recompiling because the pattern match in D
 # is no longer exhaustive, which should be a warning
 # there is no way to make warnings errors, so this has to be manually checked
--> compile
+-> compile
diff --git a/sbt-test/tasty-compat/add-overload/build.sbt b/sbt-test/tasty-compat/add-overload/build.sbt
@@ -16,7 +16,7 @@ lazy val `a-changes` = project.in(file("a-changes"))
 
 lazy val c = project.in(file("."))
   .settings(
-    scalacOptions ++= Seq("-from-tasty", "-Ycheck:readTasty", "-Xfatal-warnings"),
+    scalacOptions ++= Seq("-from-tasty", "-Ycheck:readTasty", "-Werror"),
     Compile / sources := Seq(new java.io.File("c-input/B.tasty")),
     Compile / unmanagedClasspath += (ThisBuild / baseDirectory).value / "c-input",
     Compile / classDirectory := (ThisBuild / baseDirectory).value / "c-output"

diff --git a/sbt-test/tasty-compat/add-param-unroll/build.sbt b/sbt-test/tasty-compat/add-param-unroll/build.sbt
@@ -29,7 +29,7 @@ lazy val c = project.in(file("c"))
   .settings(commonSettings)
   .settings(printSettings)
   .settings(
-    // scalacOptions ++= Seq("-from-tasty", "-Ycheck:readTasty", "-Xfatal-warnings", "-Vprint:readTasty", "-Xprint-types"),
+    // scalacOptions ++= Seq("-from-tasty", "-Ycheck:readTasty", "-Werror", "-Vprint:readTasty", "-Xprint-types"),
     // Compile / sources := Seq(new java.io.File("c-input/B.tasty")),
     Compile / unmanagedClasspath += (ThisBuild / baseDirectory).value / "c-input",
     Compile / classDirectory := (ThisBuild / baseDirectory).value / "c-output"

diff --git a/tests/disabled/macro/pos/t8013/inpervolated_2.scala b/tests/disabled/macro/pos/t8013/inpervolated_2.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -Xlint
+//> using options -Werror -Xlint
 package t8013
 
 // unsuspecting user of perverse macro

diff --git a/tests/disabled/partest/neg/t5663-badwarneq.scala b/tests/disabled/partest/neg/t5663-badwarneq.scala
@@ -24,7 +24,7 @@ final case class ValueClass3(val value: Int) extends AnyVal
 
 /* It's not possible to run partest without -deprecation.
  * Since detecting the warnings requires a neg test with
- * -Xfatal-warnings, and deprecation terminates the compile,
+ * -Werror and deprecation terminates the compile,
  * we'll just comment out the nasty part.  The point was
  * just to show there's nothing special about a trait
  * that extends a case class, which is only permitted

diff --git a/tests/explicit-nulls/neg-patmat/match-pat.scala b/tests/explicit-nulls/neg-patmat/match-pat.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 class Foo {
 

diff --git a/tests/explicit-nulls/pos/match-pat.scala b/tests/explicit-nulls/pos/match-pat.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 // Ensure we don't get "the type test for argType cannot be checked at runtime" warning
 

diff --git a/tests/explicit-nulls/pos/unsafe-match-null-pat.scala b/tests/explicit-nulls/pos/unsafe-match-null-pat.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 import scala.language.unsafeNulls
 

diff --git a/tests/neg-custom-args/captures/capt-wf.scala b/tests/neg-custom-args/captures/capt-wf.scala
@@ -1,4 +1,4 @@
-//> using options -language:experimental.captureChecking -Xfatal-warnings
+//> using options -language:experimental.captureChecking -Werror
 import caps.cap
 class C
 type Cap = C^
@@ -35,4 +35,4 @@ def test(c: Cap, other: String): Unit =
   val y3: String^{ev} = ??? // error cs is empty
 
   ()
-// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
+// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
diff --git a/tests/neg-custom-args/sourcepath2/hi/A.check b/tests/neg-custom-args/sourcepath2/hi/A.check
@@ -4,4 +4,4 @@
   |      class Hello is in the wrong directory.
   |      It was declared to be in package <empty>
   |      But it is found in directory     hi
-No warnings can be incurred under -Werror (or -Xfatal-warnings)
+No warnings can be incurred under -Werror
diff --git a/tests/neg-custom-args/wildcards.scala b/tests/neg-custom-args/wildcards.scala
@@ -1,6 +1,6 @@
-//> using options -source future -deprecation -Xfatal-warnings
+//> using options -source future -deprecation -Werror
 
 object Test {
   val xs: List[_] = List(1, 2, 3)  // error
   val ys: Map[_ <: AnyRef, _ >: Null] = Map() // error // error
-}
+}
diff --git a/tests/neg-deep-subtype/i17435.scala b/tests/neg-deep-subtype/i17435.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 import scala.collection.mutable
 

diff --git a/tests/neg-deep-subtype/i5495.scala b/tests/neg-deep-subtype/i5495.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 class A
 class B

diff --git a/tests/neg-deep-subtype/i5826b.scala b/tests/neg-deep-subtype/i5826b.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 class Foo {
   def test1[A]: List[Int] | A => Int = {

diff --git a/tests/neg-deep-subtype/patmat-applied.scala b/tests/neg-deep-subtype/patmat-applied.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 class A[-T]
 class B[T] extends A[T]

diff --git a/tests/neg-macros/i9570.check b/tests/neg-macros/i9570.check
@@ -2,4 +2,4 @@
 15 |        case '{HCons(_,$t)} => // warn (in .check file)
    |                     ^
    |             Use of `_` for lambda in quoted pattern. Use explicit lambda instead or use `$_` to match any term.
-No warnings can be incurred under -Werror (or -Xfatal-warnings)
+No warnings can be incurred under -Werror
diff --git a/tests/neg-macros/i9570.scala b/tests/neg-macros/i9570.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 import scala.quoted.*
 
@@ -25,4 +25,4 @@ object Macros {
   }
 }
 
-// nopos-error No warnings can be incurred under -Werror (or -Xfatal-warnings)
+// nopos-error No warnings can be incurred under -Werror
diff --git a/tests/neg-macros/macro-deprecation.check b/tests/neg-macros/macro-deprecation.check
@@ -2,4 +2,4 @@
 5 |inline def f = ${ impl } // warn (in .check file)
   |                  ^^^^
   |                  method impl is deprecated
-No warnings can be incurred under -Werror (or -Xfatal-warnings)
+No warnings can be incurred under -Werror
diff --git a/tests/neg-macros/macro-deprecation.scala b/tests/neg-macros/macro-deprecation.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -deprecation
+//> using options -Werror -deprecation
 
 import scala.quoted.*
 

diff --git a/tests/neg-scalajs/enumeration-warnings.check b/tests/neg-scalajs/enumeration-warnings.check
@@ -58,4 +58,4 @@
    |                               ^^^^^^^^^^^^
    |                 Passing null as name to a constructor of scala.Enumeration.Val requires reflection at run-time.
    |                 The resulting program is unlikely to function properly.
-No warnings can be incurred under -Werror (or -Xfatal-warnings)
+No warnings can be incurred under -Werror
diff --git a/tests/neg-scalajs/enumeration-warnings.scala b/tests/neg-scalajs/enumeration-warnings.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 class UnableToTransformValue extends Enumeration {
   val a = {

diff --git a/tests/neg/IsInstanceOfClassTag.scala b/tests/neg/IsInstanceOfClassTag.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 import scala.reflect.ClassTag
 

diff --git a/tests/neg/adhoc-extension/B.scala b/tests/neg/adhoc-extension/B.scala
@@ -1,4 +1,4 @@
-//> using options -source future -feature -Xfatal-warnings
+//> using options -source future -feature -Werror
 
 package adhoc
 class B extends A  // warn: adhoc-extension (under -strict -feature -Xfatal-warnings)
@@ -8,4 +8,4 @@ object O {
   val a = new A {}  // warn
   object E extends A  // warn
 }
-// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
+// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
diff --git a/tests/neg/classtag-typetest/3_1-migration.scala b/tests/neg/classtag-typetest/3_1-migration.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 import scala.language.`future-migration`
 import scala.reflect.ClassTag

diff --git a/tests/neg/classtag-typetest/3_1.scala b/tests/neg/classtag-typetest/3_1.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 import scala.language.future
 import scala.reflect.ClassTag

diff --git a/tests/neg/enum-variance.scala b/tests/neg/enum-variance.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 enum View[-T]:
   case Refl(f: T => T) // error: enum case Refl requires explicit declaration of type T

diff --git a/tests/neg/filtering-fors.scala b/tests/neg/filtering-fors.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 object Test {
 
@@ -31,4 +31,4 @@ object Test {
   for (case (x: String) <- xs; case (y, z) <- xs) do ()   // OK
 
   for (case (x, y) <- pairs) yield (y, x) // OK
-}
+}
diff --git a/tests/neg/i1050.scala b/tests/neg/i1050.scala
@@ -1,4 +1,4 @@
-//> using options -source future -deprecation -Xfatal-warnings
+//> using options -source future -deprecation -Werror
 
 // i1050 checks failing at posttyper
 trait A { type L <: Nothing }

diff --git a/tests/neg/i12188/Test.scala b/tests/neg/i12188/Test.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 sealed trait P
 case class PC1(a: String) extends P
@@ -10,4 +10,4 @@ def foo(x: P): Unit =
   x match           // warn
   case _: PC1 =>
 
-// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
+// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
diff --git a/tests/neg/i13946/BadPrinter.scala b/tests/neg/i13946/BadPrinter.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -feature
+//> using options -Werror -feature
 
 // in BadPrinter.scala
 import language.future

diff --git a/tests/neg/i15474b.check b/tests/neg/i15474b.check
@@ -3,4 +3,4 @@
   |                                   ^^^^^^^^^^
   |                                   Infinite loop in function body
   |                                   Test1.c.apply(from).toInt
-No warnings can be incurred under -Werror (or -Xfatal-warnings)
+No warnings can be incurred under -Werror
diff --git a/tests/neg/i15474b.scala b/tests/neg/i15474b.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 import scala.language.implicitConversions
 

diff --git a/tests/neg/i16092.scala b/tests/neg/i16092.scala
@@ -1,4 +1,4 @@
-//> using options -source future -deprecation -Xfatal-warnings
+//> using options -source future -deprecation -Werror
 
 trait X {
   type T

diff --git a/tests/neg/i16876/Test.scala b/tests/neg/i16876/Test.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -Wunused:all
+//> using options -Werror -Wunused:all
 
 object Foo {
   private def myMethod(a: Int, b: Int, c: Int) = adder // ok
@@ -7,4 +7,4 @@ object Foo {
   private def myMethodFailing(a: Int, b: Int, c: Int) = a + 0 // warn // warn
   myMethodFailing(1, 2, 3)
 }
-// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
+// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
diff --git a/tests/neg/i17335.scala b/tests/neg/i17335.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -Wunused:all
+//> using options -Werror -Wunused:all
 
 def aMethod() =
   doStuff { (x) => x } // error
diff --git a/tests/neg/i17612b.check b/tests/neg/i17612b.check
@@ -30,4 +30,4 @@
 41 |	class UnderDerived(x: Int, y: Int, z: Int) extends Derived(x, 1, y, z) // warn // warn // warn
    |	                                   ^
    |	                                   value z in class UnderDerived shadows field z inherited from trait Base
-No warnings can be incurred under -Werror (or -Xfatal-warnings)
+No warnings can be incurred under -Werror
diff --git a/tests/neg/i17612b/i17612b.scala b/tests/neg/i17612b/i17612b.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings -Wshadow:private-shadow -source:3.3
+//> using options -Werror -Wshadow:private-shadow -source:3.3
 
 object i17612b:
 
@@ -42,4 +42,4 @@ object i17612b:
 
 	def main(args: Array[String]) =
 		val derived = new Derived(1, 1, 1, 1)
-// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
+// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
diff --git a/tests/neg/i17613b.check b/tests/neg/i17613b.check
@@ -58,4 +58,4 @@
 42 |				class InnerCl[ImClassR] // warn
    |				              ^^^^^^^^
    |				              Type parameter ImClassR for class InnerCl shadows an explicitly renamed type : ImClassR
-No warnings can be incurred under -Werror (or -Xfatal-warnings)
+No warnings can be incurred under -Werror
diff --git a/tests/neg/i17613b/i17613b.scala b/tests/neg/i17613b/i17613b.scala
@@ -1,4 +1,4 @@
-//> using options -Wshadow:type-parameter-shadow -Xfatal-warnings
+//> using options -Wshadow:type-parameter-shadow -Werror
 
 object i17613b:
 	import importTry._

diff --git a/tests/neg/i18632.check b/tests/neg/i18632.check
@@ -2,4 +2,4 @@
 12 |  bar // warn
    |  ^^^
    |  unused value of type String
-No warnings can be incurred under -Werror (or -Xfatal-warnings)
+No warnings can be incurred under -Werror
diff --git a/tests/neg/i4986d.scala b/tests/neg/i4986d.scala
@@ -1,4 +1,4 @@
-//> using options -Xfatal-warnings
+//> using options -Werror
 
 trait Foo[A]
 
@@ -22,4 +22,4 @@ trait Bar[A]
 type Barable[A] = {
   def bar(implicit ev: Bar[A]): Any // ok
 }
-// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
+// nopos-error: No warnings can be incurred under -Werror (or -Xfatal-warnings)
Original file line number	Diff line number	Diff line change
		@@ -1 +1 @@
		scalac.options = -Xfatal-warnings
		scalac.options = -Werror