Enable experimental mode when experimental feature is imported

compiler/src/dotty/tools/dotc/Driver.scala

@@ -80,7 +80,6 @@ class Driver {
     val ictx = rootCtx.fresh
     val summary = command.distill(args, ictx.settings)(ictx.settingsState)(using ictx)
     ictx.setSettings(summary.sstate)
-    Feature.checkExperimentalSettings(using ictx)
     MacroClassLoader.init(ictx)
     Positioned.init(using ictx)
 

compiler/src/dotty/tools/dotc/config/Feature.scala

@@ -34,6 +34,11 @@ object Feature:
   val captureChecking = experimental("captureChecking")
   val into = experimental("into")
 
+  def experimentalAutoEnableFeatures(using Context): List[TermName] =
+    defn.languageExperimentalFeatures
+      .map(sym => experimental(sym.name))
+      .filterNot(_ == captureChecking) // TODO is this correct?
+
   /** Is `feature` enabled by by a command-line setting? The enabling setting is
    *
    *       -language:<prefix>feature
@@ -157,18 +162,19 @@ object Feature:
   private def experimentalUseSite(which: String): String =
     s"""Experimental $which may only be used under experimental mode:
        |  1. in a definition marked as @experimental, or
-       |  2. compiling with the -experimental compiler flag, or
-       |  3. with a nightly or snapshot version of the compiler.
+       |  2. an experimental feature is imported at the package level, or
+       |  3. compiling with the -experimental compiler flag.
        |""".stripMargin
 
-  /** Check that experimental compiler options are only set for snapshot or nightly compiler versions. */
-  def checkExperimentalSettings(using Context): Unit =
-    for setting <- ctx.settings.language.value
-        if setting.startsWith("experimental.") && setting != "experimental.macros"
-    do checkExperimentalFeature(s"feature $setting", NoSourcePosition)
-
   def isExperimentalEnabled(using Context): Boolean =
-    (Properties.unstableExperimentalEnabled && !ctx.settings.YnoExperimental.value) || ctx.settings.experimental.value
+    ctx.settings.experimental.value ||
+    experimentalAutoEnableFeatures.exists(enabled)
+
+  def experimentalEnabledByLanguageSetting(using Context): Option[TermName] =
+    experimentalAutoEnableFeatures.find(enabledBySetting)
+
+  def isExperimentalEnabledByImport(using Context): Boolean =
+    experimentalAutoEnableFeatures.exists(enabledByImport)
 
   /** Handle language import `import language.<prefix>.<imported>` if it is one
    *  of the global imports `pureFunctions` or `captureChecking`. In this case

compiler/src/dotty/tools/dotc/config/Properties.scala

@@ -84,12 +84,6 @@ trait PropertiesTrait {
    */
   val versionString: String = "version " + simpleVersionString
 
-  /** Whether the current version of compiler is experimental
-   *
-   *  Snapshot, nightly releases and non-bootstrapped compiler are experimental.
-   */
-  val unstableExperimentalEnabled: Boolean = versionString.contains("SNAPSHOT") || versionString.contains("NIGHTLY") || versionString.contains("nonbootstrapped")
-
   /** Whether the current version of compiler supports research plugins. */
   val researchPluginEnabled: Boolean = versionString.contains("SNAPSHOT") || versionString.contains("NIGHTLY") || versionString.contains("nonbootstrapped")
 

compiler/src/dotty/tools/dotc/config/ScalaSettings.scala

@@ -406,7 +406,6 @@ private sealed trait YSettings:
   val YretainTrees: Setting[Boolean] = BooleanSetting(ForkSetting, "Yretain-trees", "Retain trees for top-level classes, accessible from ClassSymbol#tree")
   val YshowTreeIds: Setting[Boolean] = BooleanSetting(ForkSetting, "Yshow-tree-ids", "Uniquely tag all tree nodes in debugging output.")
   val YfromTastyIgnoreList: Setting[List[String]] = MultiStringSetting(ForkSetting, "Yfrom-tasty-ignore-list", "file", "List of `tasty` files in jar files that will not be loaded when using -from-tasty.")
-  val YnoExperimental: Setting[Boolean] = BooleanSetting(ForkSetting, "Yno-experimental", "Disable experimental language features by default in NIGHTLY/SNAPSHOT versions of the compiler.")
   val YlegacyLazyVals: Setting[Boolean] = BooleanSetting(ForkSetting, "Ylegacy-lazy-vals", "Use legacy (pre 3.3.0) implementation of lazy vals.")
   val YcompileScala2Library: Setting[Boolean] = BooleanSetting(ForkSetting, "Ycompile-scala2-library", "Used when compiling the Scala 2 standard library.")
   val YoutputOnlyTasty: Setting[Boolean] = BooleanSetting(ForkSetting, "Youtput-only-tasty", "Used to only generate the TASTy file without the classfiles")

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -2008,6 +2008,13 @@ class Definitions {
     CapabilityAnnot, RequiresCapabilityAnnot,
     RetainsAnnot, RetainsCapAnnot, RetainsByNameAnnot)
 
+  /** Experimental language features defined in `scala.runtime.stdLibPatches.language.experimental`.
+   *
+   *  This list does not include `scala.language.experimental.macros`.
+   */
+  @tu lazy val languageExperimentalFeatures: List[TermSymbol] =
+    LanguageExperimentalModule.moduleClass.info.decls.toList.filter(_.isAllOf(Lazy | Module)).map(_.asTerm)
+
   // ----- primitive value class machinery ------------------------------------------
 
   class PerRun[T](generate: Context ?=> T) {

compiler/src/dotty/tools/dotc/transform/PostTyper.scala

@@ -417,7 +417,7 @@ class PostTyper extends MacroTransform with InfoTransformer { thisPhase =>
             )
           }
         case tree: ValDef =>
-          annotateExperimental(tree.symbol)
+          annotateExperimentalCompanion(tree.symbol)
           registerIfHasMacroAnnotations(tree)
           checkErasedDef(tree)
           Checking.checkPolyFunctionType(tree.tpt)
@@ -426,7 +426,6 @@ class PostTyper extends MacroTransform with InfoTransformer { thisPhase =>
             checkStableSelection(tree.rhs)
           processValOrDefDef(super.transform(tree1))
         case tree: DefDef =>
-          annotateExperimental(tree.symbol)
           registerIfHasMacroAnnotations(tree)
           checkErasedDef(tree)
           Checking.checkPolyFunctionType(tree.tpt)
@@ -438,7 +437,7 @@ class PostTyper extends MacroTransform with InfoTransformer { thisPhase =>
           val sym = tree.symbol
           if (sym.isClass)
             VarianceChecker.check(tree)
-            annotateExperimental(sym)
+            annotateExperimentalCompanion(sym)
             checkMacroAnnotation(sym)
             if sym.isOneOf(GivenOrImplicit) then
               sym.keepAnnotationsCarrying(thisPhase, Set(defn.CompanionClassMetaAnnot), orNoneOf = defn.MetaAnnots)
@@ -546,8 +545,8 @@ class PostTyper extends MacroTransform with InfoTransformer { thisPhase =>
       }
 
     override def transformStats[T](trees: List[Tree], exprOwner: Symbol, wrapResult: List[Tree] => Context ?=> T)(using Context): T =
-      try super.transformStats(trees, exprOwner, wrapResult)
-      finally Checking.checkExperimentalImports(trees)
+      Checking.checkAndAdaptExperimentalImports(trees)
+      super.transformStats(trees, exprOwner, wrapResult)
 
     /** Transforms the rhs tree into a its default tree if it is in an `erased` val/def.
      *  Performed to shrink the tree that is known to be erased later.
@@ -584,14 +583,9 @@ class PostTyper extends MacroTransform with InfoTransformer { thisPhase =>
         else if tpe.derivesFrom(defn.NullClass) then
           report.error("`erased` definition cannot be implemented with en expression of type Null", tree.srcPos)
 
-    private def annotateExperimental(sym: Symbol)(using Context): Unit =
-      def isTopLevelDefinitionInSource(sym: Symbol) =
-        !sym.is(Package) && !sym.name.isPackageObjectName &&
-        (sym.owner.is(Package) || (sym.owner.isPackageObject && !sym.isConstructor))
+    private def annotateExperimentalCompanion(sym: Symbol)(using Context): Unit =
       if sym.is(Module) then
         ExperimentalAnnotation.copy(sym.companionClass).foreach(sym.addAnnotation)
-      if !sym.hasAnnotation(defn.ExperimentalAnnot) && ctx.settings.experimental.value && isTopLevelDefinitionInSource(sym) then
-        sym.addAnnotation(ExperimentalAnnotation("Added by -experimental", sym.span))
 
     // It needs to run at the phase of the postTyper --- otherwise, the test of the symbols will use
     // the transformed denotation with added `Serializable` and `AbstractFunction1`.

compiler/src/dotty/tools/dotc/typer/Checking.scala

@@ -42,6 +42,7 @@ import cc.{isCaptureChecking, isRetainsLike}
 
 import collection.mutable
 import reporting.*
+import Annotations.ExperimentalAnnotation
 
 object Checking {
   import tpd.*
@@ -797,50 +798,57 @@ object Checking {
     tree
 
   /** Check that experimental language imports in `trees`
-   *  are done only in experimental scopes, or in a top-level
-   *  scope with only @experimental definitions.
+   *  are done only in experimental scopes. For top-level
+   *  experimental imports, all top-level definitions are transformed
+   *  to @experimental definitions.
+   *
    */
-  def checkExperimentalImports(trees: List[Tree])(using Context): Unit =
-
-    def nonExperimentalStat(trees: List[Tree]): Tree = trees match
-      case (_: Import | EmptyTree) :: rest =>
-        nonExperimentalStat(rest)
-      case (tree @ TypeDef(_, impl: Template)) :: rest if tree.symbol.isPackageObject =>
-        nonExperimentalStat(impl.body).orElse(nonExperimentalStat(rest))
-      case (tree: PackageDef) :: rest =>
-        nonExperimentalStat(tree.stats).orElse(nonExperimentalStat(rest))
-      case (tree: MemberDef) :: rest =>
-        if tree.symbol.isExperimental || tree.symbol.is(Synthetic) then
-          nonExperimentalStat(rest)
-        else
-          tree
-      case tree :: rest =>
-        tree
-      case Nil =>
-        EmptyTree
-
-    for case imp @ Import(qual, selectors) <- trees do
+  def checkAndAdaptExperimentalImports(trees: List[Tree])(using Context): Unit =
+    def nonExperimentalTopLevelDefs(pack: Symbol): Iterator[Symbol] =
+      def isNonExperimentalTopLevelDefinition(sym: Symbol) =
+        !sym.isExperimental
+        && sym.source == ctx.compilationUnit.source
+        && !sym.isConstructor // not constructor of package object
+        && !sym.is(Package) && !sym.name.isPackageObjectName
+
+      pack.info.decls.toList.iterator.flatMap: sym =>
+        if sym.isClass && (sym.is(Package) || sym.isPackageObject) then
+          nonExperimentalTopLevelDefs(sym)
+        else if isNonExperimentalTopLevelDefinition(sym) then
+          sym :: Nil
+        else Nil
+
+    def unitExperimentalLanguageImports =
       def isAllowedImport(sel: untpd.ImportSelector) =
         val name = Feature.experimental(sel.name)
         name == Feature.scala2macros
-        || name == Feature.erasedDefinitions
         || name == Feature.captureChecking
+      trees.filter {
+        case Import(qual, selectors) =>
+          languageImport(qual) match
+            case Some(nme.experimental) =>
+              !selectors.forall(isAllowedImport) && !ctx.owner.isInExperimentalScope
+            case _ => false
+        case _ => false
+      }
 
-      languageImport(qual) match
-        case Some(nme.experimental)
-        if !ctx.owner.isInExperimentalScope && !selectors.forall(isAllowedImport) =>
-          def check(stable: => String) =
-            Feature.checkExperimentalFeature("features", imp.srcPos,
-              s"\n\nNote: the scope enclosing the import is not considered experimental because it contains the\nnon-experimental $stable")
-          if ctx.owner.is(Package) then
-            // allow top-level experimental imports if all definitions are @experimental
-            nonExperimentalStat(trees) match
-              case EmptyTree =>
-              case tree: MemberDef => check(i"${tree.symbol}")
-              case tree => check(i"expression ${tree}")
-          else Feature.checkExperimentalFeature("features", imp.srcPos)
+    if ctx.owner.is(Package) || ctx.owner.name.startsWith(str.REPL_SESSION_LINE) then
+      def markTopLevelDefsAsExperimental(why: String): Unit =
+        for sym <- nonExperimentalTopLevelDefs(ctx.owner) do
+          sym.addAnnotation(ExperimentalAnnotation(s"Added by $why", sym.span))
+
+      unitExperimentalLanguageImports match
+        case imp :: _ => markTopLevelDefsAsExperimental(i"top level $imp")
         case _ =>
-  end checkExperimentalImports
+          Feature.experimentalEnabledByLanguageSetting match
+            case Some(sel) => markTopLevelDefsAsExperimental(i"-language:experimental.$sel")
+            case _ if ctx.settings.experimental.value => markTopLevelDefsAsExperimental(i"-experimental")
+            case _ =>
+    else
+      for imp <- unitExperimentalLanguageImports do
+        Feature.checkExperimentalFeature("feature local import", imp.srcPos)
+
+  end checkAndAdaptExperimentalImports
 
   /** Checks that PolyFunction only have valid refinements.
    *

compiler/src/dotty/tools/dotc/typer/CrossVersionChecks.scala

@@ -132,12 +132,14 @@ class CrossVersionChecks extends MiniPhase:
   }
 
   override def transformOther(tree: Tree)(using Context): Tree =
-    tree.foreachSubTree { // Find references in type trees and imports
-      case tree: Ident => transformIdent(tree)
-      case tree: Select => transformSelect(tree)
-      case tree: TypeTree => transformTypeTree(tree)
-      case _ =>
-    }
+    val inPackage = ctx.owner.is(Package) || ctx.owner.isPackageObject
+    if !(inPackage && tree.isInstanceOf[ImportOrExport] && Feature.isExperimentalEnabledByImport) then
+      tree.foreachSubTree { // Find references in type trees and imports
+        case tree: Ident => transformIdent(tree)
+        case tree: Select => transformSelect(tree)
+        case tree: TypeTree => transformTypeTree(tree)
+        case _ =>
+      }
     tree
 
 end CrossVersionChecks

compiler/test/dotty/tools/backend/jvm/PublicInBinaryTests.scala

@@ -42,7 +42,6 @@ class PublicInBinaryTests extends DottyBytecodeTest {
   override def initCtx =
     val ctx0 = super.initCtx
     ctx0.setSetting(ctx0.settings.experimental, true)
-    ctx0.setSetting(ctx0.settings.YnoExperimental, true)
 
   @Test
   def publicInBinaryDef(): Unit = {

docs/_docs/reference/other-new-features/experimental-defs.md

@@ -265,8 +265,7 @@ Experimental definitions can only be referenced in an experimental scope. Experi
 
    </details>
 
-6. Any code compiled using a [_Nightly_](https://search.maven.org/artifact/org.scala-lang/scala3-compiler_3) or _Snapshot_ version of the compiler is considered to be in an experimental scope.
-Can use the `-Yno-experimental` compiler flag to disable it and run as a proper release.
+6. An experimental language feature is imported in at the package level. All top-level definitions will be marked as `@experimental`.
 
 In any other situation, a reference to an experimental definition will cause a compilation error.
 

project/Build.scala

@@ -1083,7 +1083,6 @@ object Build {
       Compile / doc / scalacOptions += "-Ydocument-synthetic-types",
       scalacOptions += "-Ycompile-scala2-library",
       scalacOptions += "-Yscala2Unpickler:never",
-      scalacOptions += "-Yno-experimental",
       scalacOptions -= "-Xfatal-warnings",
       Compile / compile / logLevel.withRank(KeyRanks.Invisible) := Level.Error,
       ivyConfigurations += SourceDeps.hide,
@@ -1757,6 +1756,9 @@ object Build {
       SourceLinksIntegrationTest / scalaSource := baseDirectory.value / "test-source-links",
       SourceLinksIntegrationTest / test:= ((SourceLinksIntegrationTest / test) dependsOn generateScalaDocumentation.toTask("")).value,
     ).
+    settings(
+      scalacOptions += "-experimental" // workaround use of experimental .info in Scaladoc2AnchorCreator
+    ).
     settings(
       Compile / resourceGenerators ++= Seq(
         generateStaticAssetsTask.taskValue,
@@ -2170,9 +2172,6 @@ object Build {
           settings(
             versionScheme := Some("semver-spec"),
             libraryDependencies += "org.scala-lang" % "scala-library" % stdlibVersion,
-            // Make sure we do not refer to experimental features outside an experimental scope.
-            // In other words, disable NIGHTLY/SNAPSHOT experimental scope.
-            scalacOptions += "-Yno-experimental",
           ).
           settings(dottyLibrarySettings)
       if (mode == Bootstrapped) {

scaladoc-testcases/src/tests/hugetype.scala

@@ -31,7 +31,7 @@ trait E:
   @deprecated
   protected implicit def same[A](a: A): A
 
-trait XD extends E:
+@experimental trait XD extends E:
   /**
    * Some important information :o
    *

scaladoc-testcases/src/tests/methodsAndConstructors.scala

@@ -1,5 +1,7 @@
 package tests.methodsAndConstructors
 
+import scala.language.experimental.clauseInterleaving
+
 class A
 class B extends A
 class C
@@ -60,8 +62,6 @@ class Methods:
  def withImplicitParam2(v: String)(implicit ab: Double, a: Int, b: String): String
  = ???
 
- import scala.language.experimental.clauseInterleaving
-
  def clauseInterleaving[T](x: T)[U](y: U)(using (T, U)): (T, U)
  = ???
 

scaladoc/src/dotty/tools/scaladoc/snippets/SnippetCompiler.scala

@@ -27,7 +27,6 @@ class SnippetCompiler(
   object SnippetDriver extends Driver:
     val currentCtx =
       val rootCtx = initCtx.fresh.addMode(Mode.ReadPositions).addMode(Mode.Interactive)
-      rootCtx.setSetting(rootCtx.settings.YnoExperimental, true)
       rootCtx.setSetting(rootCtx.settings.experimental, true)
       rootCtx.setSetting(rootCtx.settings.YretainTrees, true)
       rootCtx.setSetting(rootCtx.settings.YcookComments, true)

tests/init-global/pos/global-region1.scala

@@ -1,4 +1,4 @@
-//> using options -experimental -Yno-experimental
+//> using options -experimental
 
 import scala.annotation.init.region
 

tests/init-global/warn/i18628_3.scala

@@ -1,4 +1,4 @@
-//> using options -experimental -Yno-experimental
+//> using options -experimental
 
 import scala.annotation.init.widen
 

tests/neg-macros/i18677-a/Macro_1.scala

@@ -1,4 +1,4 @@
-//> using options -experimental -Yno-experimental
+//> using options -experimental
 
 import annotation.MacroAnnotation
 import quoted.*

tests/neg-macros/i18677-a/Test_2.scala

@@ -1,4 +1,4 @@
-//> using options -experimental -Yno-experimental
+//> using options -experimental
 
 @extendFoo
 class AFoo // error

tests/neg-macros/i18677-b/Macro_1.scala

@@ -1,4 +1,4 @@
-//> using options -experimental -Yno-experimental
+//> using options -experimental
 
 import annotation.MacroAnnotation
 import quoted.*

tests/neg-macros/i18677-b/Test_2.scala

@@ -1,4 +1,4 @@
-//> using options -experimental -Yno-experimental
+//> using options -experimental
 
 @extendFoo
 class AFoo // error

tests/neg-macros/i19676/Macro_1.scala

@@ -1,4 +1,4 @@
-//> using options -experimental -Yno-experimental
+//> using options -experimental
 
 import scala.annotation.MacroAnnotation
 import scala.quoted.*

tests/neg-macros/i19676/Test_2.scala

@@ -1,4 +1,4 @@
-//> using options -experimental -Yno-experimental
+//> using options -experimental
 
 @buggy // error
 case class Foo()

tests/neg-macros/i19842-a/Macro.scala

@@ -1,4 +1,4 @@
-//> using options -experimental -Yno-experimental
+//> using options -experimental
 
 import scala.annotation.{experimental, targetName}
 import scala.quoted.*