Refactor ScopeAxis to use enum

main-settings/src/main/scala/sbt/DelegateIndex.scala

@@ -8,6 +8,8 @@
 
 package sbt
 
+import ScopeAxis.{ Select, zero }
+
 sealed trait DelegateIndex {
   def project(ref: ProjectRef): Seq[ScopeAxis[ResolvedReference]]
   def config(ref: ProjectRef, conf: ConfigKey): Seq[ScopeAxis[ConfigKey]]
@@ -23,9 +25,9 @@ private final class DelegateIndex0(refs: Map[ProjectRef, ProjectDelegates]) exte
       case Some(pd) =>
         pd.confs.get(conf) match {
           case Some(cs) => cs
-          case None => (Select(conf): ScopeAxis[ConfigKey]) :: (Zero: ScopeAxis[ConfigKey]) :: Nil
+          case None     => Select(conf) :: zero[ConfigKey] :: Nil
         }
-      case None => (Select(conf): ScopeAxis[ConfigKey]) :: (Zero: ScopeAxis[ConfigKey]) :: Nil
+      case None => Select(conf) :: zero[ConfigKey] :: Nil
     }
 }
 private final class ProjectDelegates(

main-settings/src/main/scala/sbt/Previous.scala

@@ -11,6 +11,7 @@ package sbt
 import sbt.Def.{ Initialize, ScopedKey }
 import sbt.Previous._
 import sbt.Scope.Global
+import sbt.ScopeAxis.Select
 import sbt.SlashSyntax0.given
 import sbt.internal.util._
 import sbt.std.TaskExtra._

main-settings/src/main/scala/sbt/Project.scala

@@ -11,6 +11,7 @@ import java.io.File
 import java.util.Locale
 import sbt.librarymanagement.Configuration
 import sbt.Def.{ Initialize, ScopedKey, Setting }
+import sbt.ScopeAxis.Select
 import sbt.internal.util.Dag
 import sbt.internal.util.complete.Parser
 import sbt.internal.util.complete.DefaultParsers

main-settings/src/main/scala/sbt/Reference.scala

@@ -14,6 +14,7 @@ import java.net.URI
 import sbt.internal.util.AttributeKey
 import sbt.io.IO
 import sbt.librarymanagement.Configuration
+import sbt.ScopeAxis.{ Select, This }
 import sbt.SlashSyntax.RichConfiguration
 
 // in all of these, the URI must be resolved and normalized before it is definitive

main-settings/src/main/scala/sbt/Scope.scala

@@ -12,6 +12,7 @@ import java.net.URI
 
 import sbt.internal.util.{ AttributeKey, AttributeMap, Dag }
 import sbt.internal.util.Util._
+import sbt.ScopeAxis.{ Select, This, Zero }
 
 import sbt.io.IO
 import scala.collection.concurrent.TrieMap

main-settings/src/main/scala/sbt/ScopeAxis.scala

@@ -8,46 +8,51 @@
 
 package sbt
 
-import sbt.internal.util.Util._
+import sbt.internal.util.Util.*
 
-sealed trait ScopeAxis[+S] {
-  def foldStrict[T](f: S => T, ifZero: T, ifThis: T): T = fold(f, ifZero, ifThis)
-  def fold[T](f: S => T, ifZero: => T, ifThis: => T): T = this match {
+enum ScopeAxis[+A1]:
+  /**
+   * Select is a type constructor that is used to wrap type `S`
+   * to make a scope component, equivalent of Some in Option.
+   */
+  case Select(axis: A1) extends ScopeAxis[A1]
+
+  /**
+   * This is a scope component that represents not being
+   * scoped by the user, which later could be further scoped automatically
+   * by sbt.
+   */
+  case This extends ScopeAxis[Nothing]
+
+  /**
+   * Zero is a scope component that represents not scoping.
+   * It is a universal fallback component that is strictly weaker
+   * than any other values on a scope axis.
+   */
+  case Zero extends ScopeAxis[Nothing]
+
+  def isSelect: Boolean = this match
+    case Select(_) => true
+    case _         => false
+
+  def foldStrict[A2](f: A1 => A2, ifZero: A2, ifThis: A2): A2 = fold(f, ifZero, ifThis)
+
+  def fold[A2](f: A1 => A2, ifZero: => A2, ifThis: => A2): A2 = this match
     case This      => ifThis
     case Zero      => ifZero
     case Select(s) => f(s)
-  }
-  def toOption: Option[S] = foldStrict(Option(_), none, none)
-  def map[T](f: S => T): ScopeAxis[T] =
-    foldStrict(s => Select(f(s)): ScopeAxis[T], Zero: ScopeAxis[T], This: ScopeAxis[T])
-  def isSelect: Boolean = false
-}
 
-/**
- * This is a scope component that represents not being
- * scoped by the user, which later could be further scoped automatically
- * by sbt.
- */
-case object This extends ScopeAxis[Nothing]
+  def toOption: Option[A1] = foldStrict(Option(_), none, none)
 
-/**
- * Zero is a scope component that represents not scoping.
- * It is a universal fallback component that is strictly weaker
- * than any other values on a scope axis.
- */
-case object Zero extends ScopeAxis[Nothing]
+  def map[A2](f: A1 => A2): ScopeAxis[A2] =
+    foldStrict(s => Select(f(s)): ScopeAxis[A2], Zero: ScopeAxis[A2], This: ScopeAxis[A2])
+end ScopeAxis
 
-/**
- * Select is a type constructor that is used to wrap type `S`
- * to make a scope component, equivalent of Some in Option.
- */
-final case class Select[S](s: S) extends ScopeAxis[S] {
-  override def isSelect = true
-}
+object ScopeAxis:
+  def `this`[A1]: ScopeAxis[A1] = ScopeAxis.This
+  def zero[A1]: ScopeAxis[A1] = ScopeAxis.Zero
 
-object ScopeAxis {
-  def fromOption[T](o: Option[T]): ScopeAxis[T] = o match {
-    case Some(v) => Select(v)
-    case None    => Zero
-  }
-}
+  def fromOption[A1](o: Option[A1]): ScopeAxis[A1] = o match
+    case Some(v) => ScopeAxis.Select(v)
+    case None    => ScopeAxis.Zero
+end ScopeAxis

main-settings/src/main/scala/sbt/SlashSyntax.scala

@@ -10,6 +10,7 @@ package sbt
 
 import sbt.librarymanagement.Configuration
 import sbt.internal.util.AttributeKey
+import sbt.ScopeAxis.{ Select, This }
 
 /**
  * SlashSyntax implements the slash syntax to scope keys for build.sbt DSL.

main-settings/src/main/scala/sbt/Structure.scala

@@ -16,6 +16,7 @@ import sbt.internal.util.TupleMapExtension.*
 import sbt.util.OptJsonWriter
 import sbt.ConcurrentRestrictions.Tag
 import sbt.Def.{ Initialize, ScopedKey, Setting, setting }
+import sbt.ScopeAxis.Select
 import std.TaskMacro
 import std.TaskExtra.{ task => mktask, _ }
 import scala.reflect.ClassTag

main-settings/src/test/scala/sbt/BuildSettingsInstances.scala

@@ -14,6 +14,7 @@ import hedgehog.*
 import scala.annotation.nowarn
 import scala.reflect.ClassTag
 import _root_.sbt.io.IO
+import _root_.sbt.ScopeAxis.{ Select, This, Zero }
 import _root_.sbt.Scoped.ScopingSetting
 import _root_.sbt.librarymanagement.syntax.*
 import _root_.sbt.internal.util.{ AttributeKey, AttributeMap }

main-settings/src/test/scala/sbt/SlashSyntaxSpec.scala

@@ -12,6 +12,7 @@ package test
 import hedgehog.*
 import hedgehog.runner.*
 import Scope.{ Global, ThisScope }
+import ScopeAxis.{ Select, This, Zero }
 import SlashSyntax0.given
 import BuildSettingsInstances.given
 import _root_.sbt.internal.util.AttributeKey
@@ -19,6 +20,7 @@ import _root_.sbt.internal.util.AttributeKey
 object SlashSyntaxSpec extends Properties:
   override def tests: List[Test] = List(
     property("Global / key", propGlobalKey),
+    example("Zero / compile", zeroCompile),
     property("Reference / key", propReferenceKey),
     property("Reference / Config / key", propReferenceConfigKey),
     property("Reference / task.key / key", propReferenceAttrKeyKey),
@@ -42,6 +44,7 @@ object SlashSyntaxSpec extends Properties:
   )
 
   def gen[A1: Gen]: Gen[A1] = summon[Gen[A1]]
+  lazy val compile: TaskKey[Unit] = TaskKey[Unit]("compile", "compile")
 
   def propGlobalKey: Property =
     for
@@ -58,6 +61,10 @@ object SlashSyntaxSpec extends Properties:
          else true)
     )
 
+  def zeroCompile: Result =
+    val actual = Zero / compile
+    Result.assert(actual.scope.project == Zero && actual.key == compile.key)
+
   def propReferenceKey: Property =
     for
       ref <- gen[Reference].forAll

main-settings/src/test/scala/sbt/SlashSyntaxTest.scala

@@ -12,9 +12,10 @@ import java.io.File
 import sjsonnew._
 import sbt.Def.{ Setting, inputKey, settingKey, taskKey }
 import sbt.Scope.Global
+import sbt.ScopeAxis.Zero
 import sbt.librarymanagement.ModuleID
 import sbt.librarymanagement.syntax._
-import sbt.{ LocalProject, ProjectReference, ThisBuild, Zero }
+import sbt.{ LocalProject, ProjectReference, ThisBuild }
 
 object SlashSyntaxTest extends sbt.SlashSyntax {
   final case class Proj(id: String)

main/src/main/scala/sbt/Cross.scala

@@ -12,6 +12,7 @@ import java.io.File
 import sbt.Def.{ ScopedKey, Setting }
 import sbt.Keys._
 import sbt.ProjectExtra.extract
+import sbt.ScopeAxis.{ Select, Zero }
 import sbt.SlashSyntax0.given
 import sbt.internal.Act
 import sbt.internal.CommandStrings._

main/src/main/scala/sbt/Defaults.scala

@@ -32,6 +32,7 @@ import sbt.Project.{
 }
 import sbt.ProjectExtra.*
 import sbt.Scope.{ GlobalScope, ThisBuildScope, ThisScope, fillTaskAxis }
+import sbt.ScopeAxis.{ Select, This, Zero }
 import sbt.State.StateOpsImpl
 import sbt.coursierint._
 import sbt.internal.CommandStrings.ExportStream

main/src/main/scala/sbt/Extracted.scala

@@ -10,6 +10,7 @@ package sbt
 
 import sbt.internal.{ Load, BuildStructure, Act, Aggregation, SessionSettings }
 import Scope.GlobalScope
+import sbt.ScopeAxis.This
 import Def.{ ScopedKey, Setting }
 import sbt.internal.util.complete.Parser
 import sbt.util.Show

main/src/main/scala/sbt/Main.scala

@@ -18,6 +18,7 @@ import java.util.concurrent.atomic.AtomicBoolean
 
 import sbt.Project.LoadAction
 import sbt.ProjectExtra.*
+import sbt.ScopeAxis.Select
 import sbt.internal.Aggregation.AnyKeys
 import sbt.internal._
 import sbt.internal.client.BspClient

main/src/main/scala/sbt/PluginCross.scala

@@ -13,6 +13,7 @@ import DefaultParsers._
 import sbt.Keys._
 import Scope.GlobalScope
 import Def.ScopedKey
+import sbt.ScopeAxis.Select
 import sbt.SlashSyntax0.given
 import sbt.internal.Load
 import sbt.internal.CommandStrings._

main/src/main/scala/sbt/ProjectExtra.scala

@@ -37,6 +37,7 @@ import Keys.{
 }
 import Project.LoadAction
 import Scope.{ Global, ThisScope }
+import sbt.ScopeAxis.Select
 import sbt.SlashSyntax0.given
 import Def.{ Flattened, Initialize, ScopedKey, Setting }
 import sbt.internal.{

main/src/main/scala/sbt/RemoteCache.scala

@@ -21,6 +21,7 @@ import sbt.Keys._
 import sbt.Project.{ inConfig => _, * }
 import sbt.ProjectExtra.*
 import sbt.ScopeFilter.Make._
+import sbt.ScopeAxis.Select
 import sbt.SlashSyntax0.given
 import sbt.coursierint.LMCoursier
 import sbt.internal.inc.{ HashUtil, JarUtils }

main/src/main/scala/sbt/ScopeFilter.scala

@@ -13,6 +13,7 @@ import sbt.internal.util.{ AttributeKey, Dag }
 import sbt.librarymanagement.{ ConfigRef, Configuration }
 import sbt.internal.util.Types.const
 import Def.Initialize
+import sbt.ScopeAxis.{ Select, Zero }
 import java.net.URI
 
 sealed abstract class ScopeFilter { self =>

main/src/main/scala/sbt/internal/Act.scala

@@ -15,6 +15,7 @@ import sbt.internal.util.complete.{ DefaultParsers, Parser }
 import Aggregation.{ KeyValue, Values }
 import DefaultParsers._
 import sbt.internal.util.Types.idFun
+import sbt.ScopeAxis.{ Select, Zero }
 import sbt.ProjectExtra.{ failure => _, * }
 import java.net.URI
 import sbt.internal.CommandStrings.{ MultiTaskCommand, ShowCommand, PrintCommand }

main/src/main/scala/sbt/internal/Aggregation.scala

@@ -14,6 +14,7 @@ import java.text.DateFormat
 import sbt.Def.{ ScopedKey, Settings }
 import sbt.Keys.{ showSuccess, showTiming, timingFormat }
 import sbt.ProjectExtra.*
+import sbt.ScopeAxis.{ Select, Zero }
 import sbt.SlashSyntax0.given
 import sbt.internal.util.complete.Parser
 import sbt.internal.util.complete.Parser.{ failure, seq, success }

main/src/main/scala/sbt/internal/BuildStructure.scala

@@ -16,6 +16,7 @@ import java.net.URI
 import Def.{ ScopeLocal, ScopedKey, Setting, displayFull }
 import BuildPaths.outputDirectory
 import Scope.GlobalScope
+import sbt.ScopeAxis.{ Select, This, Zero }
 import sbt.SlashSyntax0.given
 import BuildStreams.Streams
 import sbt.io.syntax._

main/src/main/scala/sbt/internal/Clean.scala

@@ -16,6 +16,7 @@ import sbt.Def._
 import sbt.Keys._
 // import sbt.Project.richInitializeTask
 import sbt.ProjectExtra.*
+import sbt.ScopeAxis.Zero
 import sbt.SlashSyntax0.given
 import sbt.io.syntax._
 import sbt.nio.Keys._

main/src/main/scala/sbt/internal/CrossJava.scala

@@ -18,6 +18,7 @@ import sbt.io.syntax._
 import sbt.Cross._
 import sbt.Def.{ ScopedKey, Setting }
 import sbt.ProjectExtra.extract
+import sbt.ScopeAxis.{ Select, Zero }
 import sbt.SlashSyntax0.given
 import sbt.internal.util.complete.DefaultParsers._
 import sbt.internal.util.AttributeKey

main/src/main/scala/sbt/internal/FileChangesMacro.scala

@@ -11,6 +11,7 @@ package internal
 
 import java.nio.file.{ Path => NioPath }
 
+import sbt.ScopeAxis.Select
 import sbt.nio.Keys._
 import sbt.nio.{ FileChanges, FileStamp }
 
@@ -100,6 +101,6 @@ object FileChangesMacro:
   private def getTaskScope[A: Type](in: Expr[TaskKey[A]])(using qctx: Quotes): Expr[sbt.Scope] =
     '{
       if $in.scope.task.toOption.isDefined then $in.scope
-      else $in.scope.copy(task = sbt.Select($in.key))
+      else $in.scope.copy(task = Select($in.key))
     }
 end FileChangesMacro

main/src/main/scala/sbt/internal/Load.scala

@@ -15,6 +15,7 @@ import sbt.Keys._
 import sbt.Project.inScope
 import sbt.ProjectExtra.{ prefixConfigs, setProject, showLoadingKey, structure }
 import sbt.Scope.GlobalScope
+import sbt.ScopeAxis.{ Select, Zero }
 import sbt.SlashSyntax0.given
 import sbt.internal.BuildStreams._
 import sbt.internal.inc.classpath.ClasspathUtil

main/src/main/scala/sbt/internal/LogManager.scala

@@ -13,6 +13,7 @@ import sbt.Def.ScopedKey
 import sbt.Keys._
 import sbt.ProjectExtra.showContextKey
 import sbt.Scope.Global
+import sbt.ScopeAxis.{ Select, Zero }
 import sbt.SlashSyntax0.given
 import sbt.internal.util.MainAppender._
 import sbt.internal.util.{ Terminal => ITerminal, _ }

main/src/main/scala/sbt/internal/Resolve.scala

@@ -10,6 +10,7 @@ package sbt
 package internal
 
 import sbt.internal.util.AttributeKey
+import sbt.ScopeAxis.{ Select, This, Zero }
 
 object Resolve {
   def apply(

main/src/main/scala/sbt/internal/SettingCompletions.scala

@@ -16,6 +16,7 @@ import sbt.librarymanagement.Configuration
 import ProjectExtra.{ relation }
 import Def.{ ScopedKey, Setting }
 import Scope.Global
+import sbt.ScopeAxis.{ Select, This, Zero }
 import sbt.SlashSyntax0.given
 import complete._
 import DefaultParsers._

main/src/main/scala/sbt/internal/WatchTransitiveDependencies.scala

@@ -13,6 +13,7 @@ import sbt.Def._
 import sbt.Keys._
 // import sbt.Project.richInitializeTask
 import sbt.ProjectExtra.*
+import sbt.ScopeAxis.Zero
 import sbt.SlashSyntax0.given
 import sbt.internal.io.Source
 import sbt.internal.nio.Globs

main/src/main/scala/sbt/nio/Settings.scala

@@ -13,6 +13,7 @@ import java.nio.file.{ Files, Path }
 import java.util.concurrent.ConcurrentHashMap
 
 import sbt.Keys._
+import sbt.ScopeAxis.{ Select, Zero }
 import sbt.SlashSyntax0.given
 import sbt.internal.Clean.ToSeqPath
 import sbt.internal.Continuous.FileStampRepository

main/src/test/scala/Delegates.scala

@@ -10,6 +10,7 @@ package sbt
 
 import sbt.internal.util.Types.idFun
 import sbt.internal.TestBuild._
+import sbt.ScopeAxis.{ Select, This, Zero }
 import hedgehog._
 import hedgehog.Result.{ all, assert, failure, success }
 import hedgehog.runner._

main/src/test/scala/ParseKeySpec.scala

@@ -12,6 +12,7 @@ import sbt.internal.TestBuild._
 import sbt.internal.util.complete.Parser
 import sbt.internal.{ Resolve, TestBuild }
 import sbt.ProjectExtra.equalKeys
+import sbt.ScopeAxis.{ Select, Zero }
 import hedgehog._
 import hedgehog.core.{ ShrinkLimit, SuccessCount }
 import hedgehog.runner._

main/src/test/scala/ParserSpec.scala

@@ -10,6 +10,7 @@ package sbt
 import java.net.URI
 
 import sbt.Def._
+import sbt.ScopeAxis.{ Select, Zero }
 import sbt.internal.TestBuild
 import sbt.internal.TestBuild._
 import sbt.internal.util.AttributeKey

main/src/test/scala/sbt/internal/TestBuild.scala

@@ -10,6 +10,7 @@ package sbt
 package internal
 
 import Def.{ ScopedKey, Setting }
+import sbt.ScopeAxis.{ Select, Zero }
 import sbt.internal.util.{ AttributeKey, Relation }
 import sbt.internal.util.Types.{ const, some }
 import sbt.internal.util.complete.Parser

main/src/test/scala/testpkg/CompletionSpec.scala

@@ -10,6 +10,7 @@ package testpkg
 import java.net.URI
 
 import sbt.{ Result => _, _ }
+import sbt.ScopeAxis.{ Select, Zero }
 import sbt.Def._
 import sbt.internal.TestBuild
 import sbt.internal.TestBuild._

sbt-app/src/main/scala/sbt/Import.scala

@@ -34,6 +34,9 @@ trait Import {
   type ClasspathDependency = ClasspathDep.ClasspathDependency
   val ResolvedClasspathDependency = ClasspathDep.ResolvedClasspathDependency
   type ResolvedClasspathDependency = ClasspathDep.ResolvedClasspathDependency
+  val Select = ScopeAxis.Select
+  val This = ScopeAxis.This
+  val Zero = ScopeAxis.Zero
   // sbt.testing
   type TestResult = sbt.protocol.testing.TestResult
   val TestResult = sbt.protocol.testing.TestResult