cleaner way to extract class or tuple proxy

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

@@ -689,7 +689,9 @@ class TypeErasure(sourceLanguage: SourceLanguage, semiEraseVCs: Boolean, isConst
   }
 
   private def erasePair(tp: Type)(using Context): Type = {
-    val arity = tp.tupleArity
+    // NOTE: `tupleArity` does not consider TypeRef(EmptyTuple$) equivalent to EmptyTuple.type,
+    // we fix this for printers, but type erasure should be preserved.
+    val arity = tp.tupleArity()
     if (arity < 0) defn.ProductClass.typeRef
     else if (arity <= Definitions.MaxTupleArity) defn.TupleType(arity).nn
     else defn.TupleXXLClass.typeRef

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

@@ -40,13 +40,23 @@ import scala.annotation.internal.sharable
 import scala.annotation.threadUnsafe
 
 import dotty.tools.dotc.transform.SymUtils._
+import dotty.tools.dotc.transform.TypeUtils.*
 
 object Types {
 
   @sharable private var nextId = 0
 
   implicit def eqType: CanEqual[Type, Type] = CanEqual.derived
 
+  object GenericTupleType:
+    def unapply(tp: Type)(using Context): Option[List[Type]] = tp match
+      case tp @ AppliedType(r: TypeRef, _) if r.isRef(defn.PairClass) && tp.tupleArity(relaxEmptyTuple = true) > 0 =>
+        Some(tp.tupleElementTypes)
+      case AppliedType(_: TypeRef, args) if defn.isTupleNType(tp) =>
+        Some(args)
+      case _ =>
+        None
+
   /** Main class representing types.
    *
    *  The principal subclasses and sub-objects are as follows:

compiler/src/dotty/tools/dotc/printing/RefinedPrinter.scala

@@ -218,7 +218,7 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
         val cls = tycon.typeSymbol
         if tycon.isRepeatedParam then toTextLocal(args.head) ~ "*"
         else if defn.isFunctionClass(cls) then toTextFunction(args, cls.name.isContextFunction, cls.name.isErasedFunction)
-        else if tp.tupleArity >= 2 && !printDebug then toTextTuple(tp.tupleElementTypes)
+        else if tp.tupleArity(relaxEmptyTuple = true) >= 2 && !printDebug then toTextTuple(tp.tupleElementTypes)
         else if isInfixType(tp) then
           val l :: r :: Nil = args: @unchecked
           val opName = tyconName(tycon)

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

@@ -248,7 +248,7 @@ object GenericSignatures {
               case _ => jsig(elemtp)
 
         case RefOrAppliedType(sym, pre, args) =>
-          if (sym == defn.PairClass && tp.tupleArity > Definitions.MaxTupleArity)
+          if (sym == defn.PairClass && tp.tupleArity() > Definitions.MaxTupleArity)
             jsig(defn.TupleXXLClass.typeRef)
           else if (isTypeParameterInSig(sym, sym0)) {
             assert(!sym.isAliasType, "Unexpected alias type: " + sym)

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

@@ -51,14 +51,16 @@ object TypeUtils {
 
     /** The arity of this tuple type, which can be made up of EmptyTuple, TupleX and `*:` pairs,
      *  or -1 if this is not a tuple type.
+     *
+     *  @param relaxEmptyTuple if true then TypeRef(EmptyTuple$) =:= EmptyTuple.type
      */
-    def tupleArity(using Context): Int = self match {
+    def tupleArity(relaxEmptyTuple: Boolean = false)(using Context): Int = self match {
       case AppliedType(tycon, _ :: tl :: Nil) if tycon.isRef(defn.PairClass) =>
-        val arity = tl.tupleArity
+        val arity = tl.tupleArity(relaxEmptyTuple)
         if (arity < 0) arity else arity + 1
       case self: SingletonType =>
         if self.termSymbol == defn.EmptyTupleModule then 0 else -1
-      case self: TypeRef if self.classSymbol == defn.EmptyTupleModule.moduleClass =>
+      case self: TypeRef if relaxEmptyTuple && self.classSymbol == defn.EmptyTupleModule.moduleClass =>
         0
       case self if defn.isTupleClass(self.classSymbol) =>
         self.dealias.argInfos.length

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

@@ -279,36 +279,81 @@ class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
         case t => mapOver(t)
     monoMap(mirroredType.resultType)
 
-  private def productMirror(mirroredType: Type, formal: Type, span: Span)(using Context): TreeWithErrors =
+  private[Synthesizer] enum MirrorSource:
+    case ClassSymbol(cls: Symbol)
+    case GenericTuple(tuplArity: Int, tpArgs: List[Type])
+
+    def isGenericTuple: Boolean = this.isInstanceOf[GenericTuple]
+
+    /** tuple arity, works for TupleN classes and generic tuples */
+    final def arity(using Context): Int = this match
+      case GenericTuple(arity, _) => arity
+      case ClassSymbol(cls) if defn.isTupleClass(cls) => cls.typeParams.length
+      case _ => -1
+
+    def equiv(that: MirrorSource)(using Context): Boolean = (this.arity, that.arity) match
+      case (n, m) if n > 0 || m > 0 =>
+        // we shortcut when at least one was a tuple.
+        // This protects us from comparing classes for two TupleXXL with different arities.
+        n == m
+      case _ => this.asClass eq that.asClass // class equality otherwise
+
+    def isSub(that: MirrorSource)(using Context): Boolean = (this.arity, that.arity) match
+      case (n, m) if n > 0 || m > 0 =>
+        // we shortcut when at least one was a tuple.
+        // This protects us from comparing classes for two TupleXXL with different arities.
+        n == m
+      case _ => this.asClass isSubClass that.asClass
+
+    def asClass(using Context): Symbol = this match
+      case ClassSymbol(cls) => cls
+      case GenericTuple(arity, _) =>
+        if arity <= Definitions.MaxTupleArity then defn.TupleType(arity).nn.classSymbol
+        else defn.TupleXXLClass
+
+  object MirrorSource:
+    def tuple(tps: List[Type]): MirrorSource.GenericTuple = MirrorSource.GenericTuple(tps.size, tps)
+
+  end MirrorSource
 
-    var isSafeGenericTuple = Option.empty[(Symbol, List[Type])]
+  private def productMirror(mirroredType: Type, formal: Type, span: Span)(using Context): TreeWithErrors =
 
-    /** do all parts match the class symbol? Or can we extract a generic tuple type out? */
-    def acceptable(tp: Type, cls: Symbol): Boolean =
-      var genericTupleParts = List.empty[(Symbol, List[Type])]
+    extension (msrc: MirrorSource) def isGenericProd(using Context) =
+      msrc.isGenericTuple || msrc.asClass.isGenericProduct && canAccessCtor(msrc.asClass)
 
-      def acceptableGenericTuple(tp: AppliedType): Boolean =
-        val tupleArgs = tp.tupleElementTypes
-        val arity = tupleArgs.size
-        val isOk = arity <= Definitions.MaxTupleArity
-        if isOk then
-          genericTupleParts ::= {
-            val cls = defn.TupleType(arity).nn.classSymbol
-            (cls, tupleArgs)
-          }
-        isOk
+    /** Follows `classSymbol`, but instead reduces to a proxy of a generic tuple (or a scala.TupleN class).
+     *
+     *  Does not need to consider AndType, as that is already stripped.
+     */
+    def tupleProxy(tp: Type)(using Context): Option[MirrorSource] = tp match
+      case tp: TypeRef => if tp.symbol.isClass then None else tupleProxy(tp.superType)
+      case GenericTupleType(args) => Some(MirrorSource.tuple(args))
+      case tp: TypeProxy =>
+        tupleProxy(tp.underlying)
+      case tp: OrType =>
+        if tp.tp1.hasClassSymbol(defn.NothingClass) then
+          tupleProxy(tp.tp2)
+        else if tp.tp2.hasClassSymbol(defn.NothingClass) then
+          tupleProxy(tp.tp1)
+        else tupleProxy(tp.join)
+      case _ =>
+        None
 
-      def inner(tp: Type, cls: Symbol): Boolean = tp match
-        case tp: HKTypeLambda if tp.resultType.isInstanceOf[HKTypeLambda] => false
-        case tp @ AppliedType(cons: TypeRef, _) if cons.isRef(defn.PairClass) => acceptableGenericTuple(tp)
-        case tp: TypeProxy    => inner(tp.underlying, cls)
-        case OrType(tp1, tp2) => inner(tp1, cls) && inner(tp2, cls)
-        case _                => tp.classSymbol eq cls
+    def mirrorSource(tp: Type)(using Context): Option[MirrorSource] =
+      val fromClass = tp.classSymbol
+      if fromClass.exists then // test if it could be reduced to a generic tuple
+        if fromClass.isSubClass(defn.TupleClass) && !defn.isTupleClass(fromClass) then tupleProxy(tp)
+        else Some(MirrorSource.ClassSymbol(fromClass))
+      else None
 
-      val classPartsMatch = inner(tp, cls)
-      classPartsMatch && genericTupleParts.map((cls, _) => cls).distinct.sizeIs <= 1 &&
-        { isSafeGenericTuple = genericTupleParts.headOption ; true }
-    end acceptable
+    /** do all parts match the class symbol? */
+    def acceptable(tp: Type, msrc: MirrorSource): Boolean = tp match
+      case tp: HKTypeLambda if tp.resultType.isInstanceOf[HKTypeLambda] => false
+      case OrType(tp1, tp2) => acceptable(tp1, msrc) && acceptable(tp2, msrc)
+      case GenericTupleType(args) if args.size <= Definitions.MaxTupleArity =>
+        MirrorSource.tuple(args).equiv(msrc)
+      case tp: TypeProxy    => acceptable(tp.underlying, msrc)
+      case _                => mirrorSource(tp).exists(_.equiv(msrc))
 
     /** for a case class, if it will have an anonymous mirror,
      *  check that its constructor can be accessed
@@ -326,13 +371,13 @@ class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
     def genAnonyousMirror(cls: Symbol): Boolean =
       cls.is(Scala2x) || cls.linkedClass.is(Case)
 
-    def makeProductMirror(cls: Symbol): TreeWithErrors =
-      val mirroredClass = isSafeGenericTuple.fold(cls)((cls, _) => cls)
+    def makeProductMirror(msrc: MirrorSource): TreeWithErrors =
+      val mirroredClass = msrc.asClass
       val accessors = mirroredClass.caseAccessors.filterNot(_.isAllOf(PrivateLocal))
       val elemLabels = accessors.map(acc => ConstantType(Constant(acc.name.toString)))
-      val nestedPairs = isSafeGenericTuple.map((_, tps) => TypeOps.nestedPairs(tps)).getOrElse {
-        TypeOps.nestedPairs(accessors.map(mirroredType.resultType.memberInfo(_).widenExpr))
-      }
+      val nestedPairs = msrc match
+        case MirrorSource.GenericTuple(_, args) => TypeOps.nestedPairs(args)
+        case _ => TypeOps.nestedPairs(accessors.map(mirroredType.resultType.memberInfo(_).widenExpr))
       val (monoType, elemsType) = mirroredType match
         case mirroredType: HKTypeLambda =>
           (mkMirroredMonoType(mirroredType), mirroredType.derivedLambdaType(resType = nestedPairs))
@@ -342,25 +387,30 @@ class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
       checkRefinement(formal, tpnme.MirroredElemTypes, elemsType, span)
       checkRefinement(formal, tpnme.MirroredElemLabels, elemsLabels, span)
       val mirrorType =
-        mirrorCore(defn.Mirror_ProductClass, monoType, mirroredType, cls.name, formal)
+        mirrorCore(defn.Mirror_ProductClass, monoType, mirroredType, mirroredClass.name, formal)
           .refinedWith(tpnme.MirroredElemTypes, TypeAlias(elemsType))
           .refinedWith(tpnme.MirroredElemLabels, TypeAlias(elemsLabels))
       val mirrorRef =
         if genAnonyousMirror(mirroredClass) then
-          anonymousMirror(monoType, ExtendsProductMirror, isSafeGenericTuple.map(_(1).size), span)
+          val arity = msrc match
+            case MirrorSource.GenericTuple(arity, _) => Some(arity)
+            case _ => None
+          anonymousMirror(monoType, ExtendsProductMirror, arity, span)
         else companionPath(mirroredType, span)
       withNoErrors(mirrorRef.cast(mirrorType))
     end makeProductMirror
 
-    def getError(cls: Symbol): String =
+    def getError(msrc: MirrorSource): String =
       val reason =
-        if !cls.isGenericProduct then
-          i"because ${cls.whyNotGenericProduct}"
-        else if !canAccessCtor(cls) then
-          i"because the constructor of $cls is innaccessible from the calling scope."
+        if !msrc.isGenericTuple then
+          if !msrc.asClass.isGenericProduct then
+            i"because ${msrc.asClass.whyNotGenericProduct}"
+          else if !canAccessCtor(msrc.asClass) then
+            i"because the constructor of ${msrc.asClass} is innaccessible from the calling scope."
+          else ""
         else
           ""
-      i"$cls is not a generic product $reason"
+      i"${msrc.asClass} is not a generic product $reason"
     end getError
 
     mirroredType match
@@ -378,13 +428,14 @@ class Synthesizer(typer: Typer)(using @constructorOnly c: Context):
             val mirrorType = mirrorCore(defn.Mirror_SingletonClass, mirroredType, mirroredType, module.name, formal)
             withNoErrors(modulePath.cast(mirrorType))
         else
-          val cls = mirroredType.classSymbol
-          if acceptable(mirroredType, cls)
-            && isSafeGenericTuple.isDefined || (cls.isGenericProduct && canAccessCtor(cls))
-          then
-            makeProductMirror(cls)
-          else
-            (EmptyTree, List(getError(cls)))
+          mirrorSource(mirroredType) match
+            case Some(msrc) =>
+              if acceptable(mirroredType, msrc) && msrc.isGenericProd then
+                makeProductMirror(msrc)
+              else
+                (EmptyTree, List(getError(msrc)))
+            case None =>
+              (EmptyTree, List(i"${mirroredType.show} does not reduce to a class or generic tuple type"))
   end productMirror
 
   private def sumMirror(mirroredType: Type, formal: Type, span: Span)(using Context): TreeWithErrors =

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

@@ -2766,7 +2766,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
       typed(desugar.smallTuple(tree).withSpan(tree.span), pt)
     else {
       val pts =
-        if (arity == pt.tupleArity) pt.tupleElementTypes
+        if (arity == pt.tupleArity()) pt.tupleElementTypes
         else List.fill(arity)(defn.AnyType)
       val elems = tree.trees.lazyZip(pts).map(
         if ctx.mode.is(Mode.Type) then typedType(_, _, mapPatternBounds = true)

tests/neg/i14127a.scala

@@ -2,4 +2,7 @@ import scala.deriving.Mirror
 
 // mixing arities is not supported
 
-val mT23 = summon[Mirror.Of[(Int *: Int *: EmptyTuple) | (Int *: Int *: Int *: EmptyTuple)]] // error
+val mT2Or2a = summon[Mirror.Of[(Int *: Int *: EmptyTuple) | (Int *: Int *: EmptyTuple)]] // ok, same arity
+val mT2Or2b = summon[Mirror.Of[(Int *: Int *: EmptyTuple) | Tuple2[Int, Int]]] // ok, same arity
+val mT2Or2c = summon[Mirror.Of[Tuple2[Int, Int] | (Int *: Int *: EmptyTuple)]] // ok, same arity
+val mT2Or3 = summon[Mirror.Of[(Int *: Int *: EmptyTuple) | (Int *: Int *: Int *: EmptyTuple)]] // error