Add Matchable trait

History of squashed individual commits:

Fix scala3doc Hierarchy test and CompilationTest

Also, drop code that's no longer needed since we made Matchable an empty trait
Re-enable tasty-interpreter test

Since no more casts are inserted, this means tasty-interpreter runs as before.
Make Matchable an empty marker trait
Revert getClass changes

Move getClass back to Any. This is needed to make zio pass.
Make Matchable a trait
Rename Scrutable => Matchable
Re-enable utest

zio is still broken with failures at runtime.
Check nesteded scrutinees for scrutability
Disable zio
Move isInstanceOf to Scrutable
Avoid reloading `AnyVal`
Widen before checking types in assumedCanEqual
Require scrutinees to be Scrutable
Add test
Rename Classable -> Scrutable
Move getClass to Classable
Avoid duplication in TreeInfo and Inliner
Disable utest
Trial: Towards a parametric top type

Author: odersky

compiler/src/dotty/tools/dotc/ast/TreeInfo.scala

@@ -397,17 +397,14 @@ trait TypedTreeInfo extends TreeInfo[Type] { self: Trees.Instance[Type] =>
     case TypeApply(fn, _) =>
       if (fn.symbol.is(Erased) || fn.symbol == defn.QuotedTypeModule_of || fn.symbol == defn.Predef_classOf) Pure else exprPurity(fn)
     case Apply(fn, args) =>
-      def isKnownPureOp(sym: Symbol) =
-        sym.owner.isPrimitiveValueClass
-        || sym.owner == defn.StringClass
-        || defn.pureMethods.contains(sym)
-      if (tree.tpe.isInstanceOf[ConstantType] && isKnownPureOp(tree.symbol) // A constant expression with pure arguments is pure.
-          || (fn.symbol.isStableMember && !fn.symbol.is(Lazy))) // constructors of no-inits classes are stable
+      if isPureApply(tree, fn) then
         minOf(exprPurity(fn), args.map(exprPurity)) `min` Pure
-      else if (fn.symbol.is(Erased)) Pure
-      else if (fn.symbol.isStableMember) /* && fn.symbol.is(Lazy) */
+      else if fn.symbol.is(Erased) then
+        Pure
+      else if fn.symbol.isStableMember /* && fn.symbol.is(Lazy) */ then
         minOf(exprPurity(fn), args.map(exprPurity)) `min` Idempotent
-      else Impure
+      else
+        Impure
     case Typed(expr, _) =>
       exprPurity(expr)
     case Block(stats, expr) =>
@@ -440,6 +437,17 @@ trait TypedTreeInfo extends TreeInfo[Type] { self: Trees.Instance[Type] =>
 
   def isPureBinding(tree: Tree)(using Context): Boolean = statPurity(tree) >= Pure
 
+  /** Is the application `tree` with function part `fn` known to be pure?
+   *  Function value and arguments can still be impure.
+   */
+  def isPureApply(tree: Tree, fn: Tree)(using Context): Boolean =
+    def isKnownPureOp(sym: Symbol) =
+      sym.owner.isPrimitiveValueClass
+      || sym.owner == defn.StringClass
+      || defn.pureMethods.contains(sym)
+    tree.tpe.isInstanceOf[ConstantType] && isKnownPureOp(tree.symbol) // A constant expression with pure arguments is pure.
+    || fn.symbol.isStableMember && !fn.symbol.is(Lazy)  // constructors of no-inits classes are stable
+
   /** The purity level of this reference.
    *  @return
    *    PurePath        if reference is (nonlazy and stable)

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

@@ -259,10 +259,19 @@ class Definitions {
    */
   @tu lazy val AnyClass: ClassSymbol = completeClass(enterCompleteClassSymbol(ScalaPackageClass, tpnme.Any, Abstract, Nil), ensureCtor = false)
   def AnyType: TypeRef = AnyClass.typeRef
-  @tu lazy val AnyValClass: ClassSymbol = completeClass(enterCompleteClassSymbol(ScalaPackageClass, tpnme.AnyVal, Abstract, List(AnyClass.typeRef)))
+  @tu lazy val MatchableClass: ClassSymbol = completeClass(enterCompleteClassSymbol(ScalaPackageClass, tpnme.Matchable, Trait, AnyType :: Nil), ensureCtor = false)
+  def MatchableType: TypeRef = MatchableClass.typeRef
+  @tu lazy val AnyValClass: ClassSymbol =
+    val res = completeClass(enterCompleteClassSymbol(ScalaPackageClass, tpnme.AnyVal, Abstract, List(AnyType, MatchableType)))
+    // Mark companion as absent, so that class does not get re-completed
+    val companion = ScalaPackageVal.info.decl(nme.AnyVal).symbol
+    companion.moduleClass.markAbsent()
+    companion.markAbsent()
+    res
+
   def AnyValType: TypeRef = AnyValClass.typeRef
 
-    @tu lazy val Any_== : TermSymbol           = enterMethod(AnyClass, nme.EQ, methOfAny(BooleanType), Final)
+    @tu lazy val Any_== : TermSymbol          = enterMethod(AnyClass, nme.EQ, methOfAny(BooleanType), Final)
     @tu lazy val Any_!= : TermSymbol          = enterMethod(AnyClass, nme.NE, methOfAny(BooleanType), Final)
     @tu lazy val Any_equals: TermSymbol       = enterMethod(AnyClass, nme.equals_, methOfAny(BooleanType))
     @tu lazy val Any_hashCode: TermSymbol     = enterMethod(AnyClass, nme.hashCode_, MethodType(Nil, IntType))
@@ -288,7 +297,7 @@ class Definitions {
   @tu lazy val ObjectClass: ClassSymbol = {
     val cls = requiredClass("java.lang.Object")
     assert(!cls.isCompleted, "race for completing java.lang.Object")
-    cls.info = ClassInfo(cls.owner.thisType, cls, AnyClass.typeRef :: Nil, newScope)
+    cls.info = ClassInfo(cls.owner.thisType, cls, List(AnyType, MatchableType), newScope)
     cls.setFlag(NoInits | JavaDefined)
 
     // The companion object doesn't really exist, so it needs to be marked as
@@ -444,7 +453,7 @@ class Definitions {
       MethodType(List(ThrowableType), NothingType))
 
   @tu lazy val NothingClass: ClassSymbol = enterCompleteClassSymbol(
-    ScalaPackageClass, tpnme.Nothing, AbstractFinal, List(AnyClass.typeRef))
+    ScalaPackageClass, tpnme.Nothing, AbstractFinal, List(AnyType))
   def NothingType: TypeRef = NothingClass.typeRef
   @tu lazy val NullClass: ClassSymbol = {
     val parent = if (ctx.explicitNulls) AnyType else ObjectType
@@ -520,7 +529,7 @@ class Definitions {
     // but does not define it as an explicit class.
     enterCompleteClassSymbol(
       ScalaPackageClass, tpnme.Singleton, PureInterfaceCreationFlags | Final,
-      List(AnyClass.typeRef), EmptyScope)
+      List(AnyType), EmptyScope)
   @tu lazy val SingletonType: TypeRef = SingletonClass.typeRef
 
   @tu lazy val CollectionSeqType: TypeRef = requiredClassRef("scala.collection.Seq")
@@ -1144,6 +1153,8 @@ class Definitions {
 
   // ----- Symbol sets ---------------------------------------------------
 
+  @tu lazy val topClasses: Set[Symbol] = Set(AnyClass, MatchableClass, ObjectClass, AnyValClass)
+
   @tu lazy val AbstractFunctionType: Array[TypeRef] = mkArityArray("scala.runtime.AbstractFunction", MaxImplementedFunctionArity, 0)
   val AbstractFunctionClassPerRun: PerRun[Array[Symbol]] = new PerRun(AbstractFunctionType.map(_.symbol.asClass))
   def AbstractFunctionClass(n: Int)(using Context): Symbol = AbstractFunctionClassPerRun()(using ctx)(n)
@@ -1372,7 +1383,7 @@ class Definitions {
   @tu lazy val ShadowableImportNames: Set[TermName] = Set("Predef".toTermName)
 
   /** Class symbols for which no class exist at runtime */
-  @tu lazy val NotRuntimeClasses: Set[Symbol] = Set(AnyClass, AnyValClass, NullClass, NothingClass)
+  @tu lazy val NotRuntimeClasses: Set[Symbol] = Set(AnyClass, MatchableClass, AnyValClass, NullClass, NothingClass)
 
   @tu lazy val SpecialClassTagClasses: Set[Symbol] = Set(UnitClass, AnyClass, AnyValClass)
 
@@ -1672,6 +1683,7 @@ class Definitions {
   @tu lazy val specialErasure: SimpleIdentityMap[Symbol, ClassSymbol] =
     SimpleIdentityMap.empty[Symbol]
       .updated(AnyClass, ObjectClass)
+      .updated(MatchableClass, ObjectClass)
       .updated(AnyValClass, ObjectClass)
       .updated(SingletonClass, ObjectClass)
       .updated(TupleClass, ProductClass)
@@ -1683,6 +1695,7 @@ class Definitions {
   @tu lazy val syntheticScalaClasses: List[TypeSymbol] = {
     val synth = List(
       AnyClass,
+      MatchableClass,
       AnyRefAlias,
       AnyKindClass,
       andType,

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

@@ -297,7 +297,7 @@ class OrderingConstraint(private val boundsMap: ParamBounds,
   /** If `inst` is a TypeBounds, make sure it does not contain toplevel
    *  references to `param` (see `Constraint#occursAtToplevel` for a definition
    *  of "toplevel").
-   *  Any such references are replace by `Nothing` in the lower bound and `Any`
+   *  Any such references are replaced by `Nothing` in the lower bound and `Any`
    *  in the upper bound.
    *  References can be direct or indirect through instantiations of other
    *  parameters in the constraint.

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

@@ -387,6 +387,7 @@ object StdNames {
     val Ref: N                  = "Ref"
     val RootPackage: N          = "RootPackage"
     val RootClass: N            = "RootClass"
+    val Matchable: N            = "Matchable"
     val Select: N               = "Select"
     val Shape: N                = "Shape"
     val StringContext: N        = "StringContext"

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

@@ -2246,9 +2246,7 @@ object SymDenotations {
           if (pcls.isCompleting) recur(pobjs1, acc)
           else
             val pobjMembers = pcls.nonPrivateMembersNamed(name).filterWithPredicate { d =>
-              // Drop members of `Any` and `Object`
-              val owner = d.symbol.maybeOwner
-              (owner ne defn.AnyClass) && (owner ne defn.ObjectClass)
+              !defn.topClasses.contains(d.symbol.maybeOwner) // Drop members of top classes
             }
             recur(pobjs1, acc.union(pobjMembers))
         case nil =>

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

@@ -209,6 +209,10 @@ object Types {
     def isAnyRef(using Context): Boolean  = isRef(defn.ObjectClass, skipRefined = false)
     def isAnyKind(using Context): Boolean = isRef(defn.AnyKindClass, skipRefined = false)
 
+    def isTopType(using Context): Boolean = dealias match
+      case tp: TypeRef => defn.topClasses.contains(tp.symbol)
+      case _ => false
+
     /** Is this type exactly Nothing (no vars, aliases, refinements etc allowed)? */
     def isExactlyNothing(using Context): Boolean = this match {
       case tp: TypeRef =>
@@ -512,6 +516,20 @@ object Types {
       case _ =>
         false
 
+    /** Same as hasClassSmbol(MatchableClass), except that we also follow the constraint
+     *  bounds of type variables in the constraint.
+     */
+    def isMatchableBound(using Context): Boolean = dealias match
+      case tp: TypeRef => tp.symbol == defn.MatchableClass
+      case tp: TypeParamRef =>
+        ctx.typerState.constraint.entry(tp) match
+          case bounds: TypeBounds => bounds.hi.isMatchableBound
+          case _ => false
+      case tp: TypeProxy => tp.underlying.isMatchableBound
+      case tp: AndType => tp.tp1.isMatchableBound || tp.tp2.isMatchableBound
+      case tp: OrType => tp.tp1.isMatchableBound && tp.tp2.isMatchableBound
+      case _ => false
+
     /** The term symbol associated with the type */
     @tailrec final def termSymbol(using Context): Symbol = this match {
       case tp: TermRef => tp.symbol
@@ -3812,10 +3830,6 @@ object Types {
 
     def unapply(tl: PolyType): Some[(List[LambdaParam], Type)] =
       Some((tl.typeParams, tl.resType))
-
-    def any(n: Int)(using Context): PolyType =
-      apply(syntheticParamNames(n))(
-        pt => List.fill(n)(TypeBounds.empty), pt => defn.AnyType)
   }
 
   private object DepStatus {

compiler/src/dotty/tools/dotc/reporting/messages.scala

@@ -266,10 +266,7 @@ import transform.SymUtils._
       val postScript = addenda.find(!_.isEmpty) match
         case Some(p) => p
         case None =>
-          if expected.isAny
-             || expected.isAnyRef
-             || expected.isRef(defn.AnyValClass)
-             || found.isBottomType
+          if expected.isTopType || found.isBottomType
           then ""
           else ctx.typer.importSuggestionAddendum(ViewProto(found.widen, expected))
       val (where, printCtx) = Formatting.disambiguateTypes(found2, expected2)

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

@@ -61,8 +61,8 @@ class Erasure extends Phase with DenotTransformer {
         // After erasure, all former Any members are now Object members
         val ClassInfo(pre, _, ps, decls, selfInfo) = ref.info
         val extendedScope = decls.cloneScope
-        for (decl <- defn.AnyClass.classInfo.decls)
-          if (!decl.isConstructor) extendedScope.enter(decl)
+        for decl <- defn.AnyClass.classInfo.decls do
+          if !decl.isConstructor then extendedScope.enter(decl)
         ref.copySymDenotation(
           info = transformInfo(ref.symbol,
               ClassInfo(pre, defn.ObjectClass, ps, extendedScope, selfInfo))
@@ -71,11 +71,12 @@ class Erasure extends Phase with DenotTransformer {
       else {
         val oldSymbol = ref.symbol
         val newSymbol =
-          if ((oldSymbol.owner eq defn.AnyClass) && oldSymbol.isConstructor)
+          if ((oldSymbol.owner eq defn.AnyClass) && oldSymbol.isConstructor) then
+            //assert(false)
             defn.ObjectClass.primaryConstructor
           else oldSymbol
         val oldOwner = ref.owner
-        val newOwner = if (oldOwner eq defn.AnyClass) defn.ObjectClass else oldOwner
+        val newOwner = if oldOwner == defn.AnyClass then defn.ObjectClass else oldOwner
         val oldName = ref.name
         val newName = ref.targetName
         val oldInfo = ref.info

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

@@ -1158,6 +1158,7 @@ trait Applications extends Compatibility {
   def typedUnApply(tree: untpd.Apply, selType: Type)(using Context): Tree = {
     record("typedUnApply")
     val Apply(qual, args) = tree
+    checkMatchable(selType, tree.srcPos, pattern = true)
 
     def notAnExtractor(tree: Tree): Tree =
       // prefer inner errors

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

@@ -1246,6 +1246,11 @@ trait Checking {
         if preExisting.exists || seen.contains(tname) then
           report.error(em"@targetName annotation ${'"'}$tname${'"'} clashes with other definition in same scope", stat.srcPos)
         if stat.isDef then seen += tname
+
+  def checkMatchable(tp: Type, pos: SrcPos, pattern: Boolean)(using Context): Unit =
+    if !tp.derivesFrom(defn.MatchableClass) && sourceVersion.isAtLeast(`3.1-migration`) then
+      val kind = if pattern then "pattern selector " else ""
+      report.warning(em"${kind}type $tp should not be scrutinized", pos)
 }
 
 trait ReChecking extends Checking {
@@ -1256,6 +1261,7 @@ trait ReChecking extends Checking {
   override def checkFullyAppliedType(tree: Tree)(using Context): Unit = ()
   override def checkEnumCaseRefsLegal(cdef: TypeDef, enumCtx: Context)(using Context): Unit = ()
   override def checkAnnotApplicable(annot: Tree, sym: Symbol)(using Context): Boolean = true
+  override def checkMatchable(tp: Type, pos: SrcPos, pattern: Boolean)(using Context): Unit = ()
 }
 
 trait NoChecking extends ReChecking {

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

@@ -898,6 +898,8 @@ trait Implicits:
             case TypeBounds(lo, hi) if lo.ne(hi) && !t.symbol.is(Opaque) => apply(hi)
             case _ => t
           }
+        case t: SingletonType =>
+          apply(t.widen)
         case t: RefinedType =>
           apply(t.parent)
         case _ =>

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

@@ -545,10 +545,6 @@ class Inliner(call: tpd.Tree, rhsToInline: tpd.Tree)(using Context) {
       case TypeApply(fn, _) =>
         if (fn.symbol.is(Erased) || fn.symbol == defn.QuotedTypeModule_of) true else apply(fn)
       case Apply(fn, args) =>
-        def isKnownPureOp(sym: Symbol) =
-          sym.owner.isPrimitiveValueClass
-          || sym.owner == defn.StringClass
-          || defn.pureMethods.contains(sym)
         val isCaseClassApply = {
           val cls = tree.tpe.classSymbol
           val meth = fn.symbol
@@ -557,8 +553,7 @@ class Inliner(call: tpd.Tree, rhsToInline: tpd.Tree)(using Context) {
           meth.owner.linkedClass.is(Case) &&
           cls.isNoInitsRealClass
         }
-        if (tree.tpe.isInstanceOf[ConstantType] && isKnownPureOp(tree.symbol) // A constant expression with pure arguments is pure.
-            || (fn.symbol.isStableMember && !fn.symbol.is(Lazy))) // constructors of no-inits classes are stable
+        if isPureApply(tree, fn) then
           apply(fn) && args.forall(apply)
         else if (isCaseClassApply)
           args.forall(apply)

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

@@ -141,4 +141,4 @@ class ReTyper extends Typer with ReChecking {
   override protected def addAccessorDefs(cls: Symbol, body: List[Tree])(using Context): List[Tree] = body
   override protected def checkEqualityEvidence(tree: tpd.Tree, pt: Type)(using Context): Unit = ()
   override protected def matchingApply(methType: MethodOrPoly, pt: FunProto)(using Context): Boolean = true
-}
+}

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

@@ -62,7 +62,7 @@ class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
             val arg :: Nil = args
             val t = arg.tpe & tp2
             If(
-              arg.select(defn.Any_isInstanceOf).appliedToType(tp2),
+              arg.isInstance(tp2),
               ref(defn.SomeClass.companionModule.termRef).select(nme.apply)
                 .appliedToType(t)
                 .appliedTo(arg.select(nme.asInstanceOf_).appliedToType(t)),

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

@@ -682,7 +682,10 @@ class Typer extends Namer
       case templ: untpd.Template =>
         import untpd._
         var templ1 = templ
-        def isEligible(tp: Type) = tp.exists && !tp.typeSymbol.is(Final) && !tp.isRef(defn.AnyClass)
+        def isEligible(tp: Type) =
+        	tp.exists
+        	&& !tp.typeSymbol.is(Final)
+        	&& (!tp.isTopType || tp.isAnyRef) // Object is the only toplevel class that can be instantiated
         if (templ1.parents.isEmpty &&
             isFullyDefined(pt, ForceDegree.flipBottom) &&
             isSkolemFree(pt) &&
@@ -769,6 +772,7 @@ class Typer extends Namer
       def handlePattern: Tree = {
         val tpt1 = typedTpt
         if (!ctx.isAfterTyper && pt != defn.ImplicitScrutineeTypeRef)
+          checkMatchable(pt, tree.srcPos, pattern = true)
           withMode(Mode.GadtConstraintInference) {
             TypeComparer.constrainPatternType(tpt1.tpe, pt)
           }
@@ -1320,7 +1324,7 @@ class Typer extends Namer
           typed(desugar.makeCaseLambda(tree.cases, checkMode, protoFormals.length).withSpan(tree.span), pt)
         }
       case _ =>
-        if (tree.isInline) checkInInlineContext("inline match", tree.srcPos)
+        if tree.isInline then checkInInlineContext("inline match", tree.srcPos)
         val sel1 = typedExpr(tree.selector)
         val selType = fullyDefinedType(sel1.tpe, "pattern selector", tree.span).widen
 
@@ -3527,6 +3531,13 @@ class Typer extends Namer
         case _ =>
       }
 
+      // try an Any -> Matchable conversion
+      if pt.isMatchableBound && !wtp.derivesFrom(defn.MatchableClass) then
+        checkMatchable(wtp, tree.srcPos, pattern = false)
+        val target = AndType(tree.tpe.widenExpr, defn.MatchableType)
+        if target <:< pt then
+          return readapt(tree.cast(target))
+
       // try an implicit conversion
       val prevConstraint = ctx.typerState.constraint
       def recover(failure: SearchFailureType) =

compiler/src/dotty/tools/repl/ReplDriver.scala

@@ -291,9 +291,7 @@ class ReplDriver(settings: Array[String],
         info.bounds.hi.finalResultType
           .membersBasedOnFlags(required = Method, excluded = Accessor | ParamAccessor | Synthetic | Private)
           .filterNot { denot =>
-            denot.symbol.owner == defn.AnyClass ||
-            denot.symbol.owner == defn.ObjectClass ||
-            denot.symbol.isConstructor
+            defn.topClasses.contains(denot.symbol.owner) || denot.symbol.isConstructor
           }
 
       val vals =

compiler/src/scala/quoted/runtime/impl/QuotesImpl.scala

@@ -2513,6 +2513,7 @@ class QuotesImpl private (using val ctx: Context) extends Quotes, QuoteUnpickler
       def ScalaPackage: Symbol = dotc.core.Symbols.defn.ScalaPackageVal
       def ScalaPackageClass: Symbol = dotc.core.Symbols.defn.ScalaPackageClass
       def AnyClass: Symbol = dotc.core.Symbols.defn.AnyClass
+      def MatchableClass: Symbol = dotc.core.Symbols.defn.MatchableClass
       def AnyValClass: Symbol = dotc.core.Symbols.defn.AnyValClass
       def ObjectClass: Symbol = dotc.core.Symbols.defn.ObjectClass
       def AnyRefClass: Symbol = dotc.core.Symbols.defn.AnyRefAlias

compiler/test/dotty/tools/dotc/BootstrappedOnlyCompilationTests.scala

@@ -137,8 +137,9 @@ class BootstrappedOnlyCompilationTests extends ParallelTesting {
       compileFilesInDir("tests/run-custom-args/tasty-inspector", withTastyInspectorOptions)
     )
     val tests =
-      if (scala.util.Properties.isWin) basicTests
+      if scala.util.Properties.isWin then basicTests
       else compileDir("tests/run-custom-args/tasty-interpreter", withTastyInspectorOptions) :: basicTests
+
     aggregateTests(tests: _*).checkRuns()
   }
 

compiler/test/dotty/tools/dotc/CompilationTests.scala

@@ -164,6 +164,8 @@ class CompilationTests {
       compileFile("tests/neg-custom-args/typeclass-derivation2.scala", defaultOptions.and("-Yerased-terms")),
       compileFile("tests/neg-custom-args/i5498-postfixOps.scala", defaultOptions withoutLanguageFeature "postfixOps"),
       compileFile("tests/neg-custom-args/deptypes.scala", defaultOptions.and("-language:experimental.dependent")),
+      compileFile("tests/neg-custom-args/matchable.scala", defaultOptions.and("-Xfatal-warnings", "-source", "3.1")),
+      compileFile("tests/neg-custom-args/i7314.scala", defaultOptions.and("-Xfatal-warnings", "-source", "3.1"))
     ).checkExpectedErrors()
   }