Merge pull request #8082 from dotty-staging/change-lambda-variance

Rework variances of higher-kinded types

Author: odersky

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

@@ -49,13 +49,13 @@ object DesugarEnums {
     val tparams = enumClass.typeParams
     def isGround(tp: Type) = tp.subst(tparams, tparams.map(_ => NoType)) eq tp
     val targs = tparams map { tparam =>
-      if (tparam.variance > 0 && isGround(tparam.info.bounds.lo))
+      if (tparam.is(Covariant) && isGround(tparam.info.bounds.lo))
         tparam.info.bounds.lo
-      else if (tparam.variance < 0 && isGround(tparam.info.bounds.hi))
+      else if (tparam.is(Contravariant) && isGround(tparam.info.bounds.hi))
         tparam.info.bounds.hi
       else {
         def problem =
-          if (tparam.variance == 0) "is non variant"
+          if (!tparam.isOneOf(VarianceFlags)) "is non variant"
           else "has bounds that depend on a type parameter in the same parameter list"
         errorType(i"""cannot determine type argument for enum parent $enumClass,
                      |type parameter $tparam $problem""", ctx.source.atSpan(span))

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

@@ -379,8 +379,9 @@ trait ConstraintHandling[AbstractContext] {
           case bounds: TypeBounds =>
             val lower = constraint.lower(param)
             val upper = constraint.upper(param)
-            if (lower.nonEmpty && !bounds.lo.isRef(defn.NothingClass) ||
-              upper.nonEmpty && !bounds.hi.isRef(defn.AnyClass)) constr_println(i"INIT*** $tl")
+            if lower.nonEmpty && !bounds.lo.isRef(defn.NothingClass)
+               || upper.nonEmpty && !bounds.hi.isAny
+            then constr_println(i"INIT*** $tl")
             lower.forall(addOneBound(_, bounds.hi, isUpper = true)) &&
               upper.forall(addOneBound(_, bounds.lo, isUpper = false))
           case _ =>

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

@@ -535,7 +535,7 @@ class Definitions {
   @tu lazy val StringModule: Symbol = StringClass.linkedClass
     @tu lazy val String_+ : TermSymbol = enterMethod(StringClass, nme.raw.PLUS, methOfAny(StringType), Final)
     @tu lazy val String_valueOf_Object: Symbol = StringModule.info.member(nme.valueOf).suchThat(_.info.firstParamTypes match {
-      case List(pt) => pt.isRef(AnyClass) || pt.isRef(ObjectClass)
+      case List(pt) => pt.isAny || pt.isAnyRef
       case _ => false
     }).symbol
 

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

@@ -775,7 +775,7 @@ object Denotations {
 
     def matchesImportBound(bound: Type)(implicit ctx: Context): Boolean =
       if bound.isRef(defn.NothingClass) then false
-      else if bound.isRef(defn.AnyClass) then true
+      else if bound.isAny then true
       else NoViewsAllowed.normalizedCompatible(info, bound, keepConstraint = false)
 
     // ------ Transformations -----------------------------------------

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

@@ -155,26 +155,8 @@ final class ProperGadtConstraint private(
           else if (isUpper) addLess(symTvar.origin, boundTvar.origin)
           else addLess(boundTvar.origin, symTvar.origin)
         case bound =>
-          val oldUpperBound = bounds(symTvar.origin)
-          // If we have bounds:
-          //     F >: [t] => List[t] <: [t] => Any
-          // and we want to record that:
-          //     F <: [+A] => List[A]
-          // we need to adapt the variance and instead record that:
-          //     F <: [A] => List[A]
-          // We cannot record the original bound, since it is false that:
-          //     [t] => List[t]  <:  [+A] => List[A]
-          //
-          // Note that the following code is accepted:
-          //     class Foo[F[t] >: List[t]]
-          //     type T = Foo[List]
-          // precisely because Foo[List] is desugared to Foo[[A] => List[A]].
-          //
-          // Ideally we'd adapt the bound in ConstraintHandling#addOneBound,
-          // but doing it there actually interferes with type inference.
-          val bound1 = bound.adaptHkVariances(oldUpperBound)
-          if (isUpper) addUpperBound(symTvar.origin, bound1)
-          else addLowerBound(symTvar.origin, bound1)
+          if (isUpper) addUpperBound(symTvar.origin, bound)
+          else addLowerBound(symTvar.origin, bound)
       }
     ).reporting({
       val descr = if (isUpper) "upper" else "lower"

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

@@ -6,7 +6,7 @@ import scala.util.hashing.{ MurmurHash3 => hashing }
 import annotation.tailrec
 
 object Hashable {
- 
+
   /** A null terminated list of BindingTypes. We use `null` here for efficiency */
   class Binders(val tp: BindingType, val next: Binders)
 
@@ -44,7 +44,7 @@ trait Hashable {
     avoidSpecialHashes(hashing.finalizeHash(hashCode, arity))
 
   final def typeHash(bs: Binders, tp: Type): Int =
-    if (bs == null || tp.stableHash) tp.hash else tp.computeHash(bs)
+    if (bs == null || tp.hashIsStable) tp.hash else tp.computeHash(bs)
 
   def identityHash(bs: Binders): Int = avoidSpecialHashes(System.identityHashCode(this))
 
@@ -80,7 +80,7 @@ trait Hashable {
     finishHash(bs, hashing.mix(seed, elemHash), arity + 1, tps)
   }
 
-  
+
   protected final def doHash(x: Any): Int =
     finishHash(hashing.mix(hashSeed, x.hashCode), 1)
 

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

@@ -338,11 +338,6 @@ object NameKinds {
     }
   }
 
-  /** The kind of names that also encode a variance: 0 for contravariance, 1 for covariance. */
-  val VariantName: NumberedNameKind = new NumberedNameKind(VARIANT, "Variant") {
-    def mkString(underlying: TermName, info: ThisInfo) = "-+"(info.num).toString + underlying
-  }
-
   /** Names of the form N_<outer>. Emitted by inliner, replaced by outer path
    *  in ExplicitOuter.
    */

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

@@ -139,32 +139,8 @@ object NameOps {
       name.replace { case ExpandedName(_, unexp) => unexp }
     }
 
-    /** Remove the variance from the name. */
-    def invariantName: N = likeSpacedN {
-      name.replace { case VariantName(invariant, _) => invariant }
-    }
-
     def errorName: N = likeSpacedN(name ++ nme.ERROR)
 
-    /** Map variance value -1, +1 to 0, 1 */
-    private def varianceToNat(v: Int) = (v + 1) / 2
-
-    /** Map 0, 1 to variance value -1, +1 */
-    private def natToVariance(n: Int) = n * 2 - 1
-
-    /** Name with variance prefix: `+` for covariant, `-` for contravariant */
-    def withVariance(v: Int): N = {
-      val underlying = name.exclude(VariantName)
-      likeSpacedN(
-          if (v == 0) underlying
-          else VariantName(underlying.toTermName, varianceToNat(v)))
-    }
-
-    /** The variance as implied by the variance prefix, or 0 if there is
-     *  no variance prefix.
-     */
-    def variance: Int = name.collect { case VariantName(_, n) => natToVariance(n) }.getOrElse(0)
-
     def freshened(implicit ctx: Context): N = likeSpacedN {
       name.toTermName match {
         case ModuleClassName(original) => ModuleClassName(original.freshened)

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

@@ -45,7 +45,6 @@ object NameTags extends TastyFormat.NameTags {
     case TRAITSETTER => "TRAITSETTER"
     case UNIQUE => "UNIQUE"
     case DEFAULTGETTER => "DEFAULTGETTER"
-    case VARIANT => "VARIANT"
     case OUTERSELECT => "OUTERSELECT"
 
     case SUPERACCESSOR => "SUPERACCESSOR"

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

@@ -3,6 +3,7 @@ package dotty.tools.dotc.core
 import Names.Name
 import Contexts.Context
 import Types.Type
+import Variances.{Variance, varianceToInt}
 
 /** A common super trait of Symbol and LambdaParam.
  *  Used to capture the attributes of type parameters which can be implemented as either.
@@ -35,7 +36,13 @@ trait ParamInfo {
   def paramInfoOrCompleter(implicit ctx: Context): Type
 
   /** The variance of the type parameter */
-  def paramVariance(implicit ctx: Context): Int
+  def paramVariance(implicit ctx: Context): Variance
+
+  /** The variance of the type parameter, as a number -1, 0, +1.
+   *  Bivariant is mapped to 1, i.e. it is treated like Covariant.
+   */
+  final def paramVarianceSign(implicit ctx: Context): Int =
+    varianceToInt(paramVariance)
 
   /** A type that refers to the parameter */
   def paramRef(implicit ctx: Context): Type