Merge pull request #9400 from dotty-staging/simplify-typecomparer

Simplify ConstraintHandling

Author: odersky

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

@@ -22,16 +22,12 @@ import reporting.trace
  * By comparison: Constraint handlers are parts of type comparers and can use their functionality.
  * Constraint handlers update the current constraint as a side effect.
  */
-trait ConstraintHandling[AbstractContext] {
+trait ConstraintHandling {
 
   def constr: config.Printers.Printer = config.Printers.constr
 
-  def comparerCtx(using AbstractContext): Context
-
-  given (using AbstractContext) as Context = comparerCtx
-
-  protected def isSubType(tp1: Type, tp2: Type)(implicit actx: AbstractContext): Boolean
-  protected def isSameType(tp1: Type, tp2: Type)(implicit actx: AbstractContext): Boolean
+  protected def isSub(tp1: Type, tp2: Type)(using Context): Boolean
+  protected def isSame(tp1: Type, tp2: Type)(using Context): Boolean
 
   protected def constraint: Constraint
   protected def constraint_=(c: Constraint): Unit
@@ -71,23 +67,23 @@ trait ConstraintHandling[AbstractContext] {
     case tp => tp
   }
 
-  def nonParamBounds(param: TypeParamRef)(implicit actx: AbstractContext): TypeBounds = constraint.nonParamBounds(param)
+  def nonParamBounds(param: TypeParamRef)(using Context): TypeBounds = constraint.nonParamBounds(param)
 
-  def fullLowerBound(param: TypeParamRef)(implicit actx: AbstractContext): Type =
+  def fullLowerBound(param: TypeParamRef)(using Context): Type =
     constraint.minLower(param).foldLeft(nonParamBounds(param).lo)(_ | _)
 
-  def fullUpperBound(param: TypeParamRef)(implicit actx: AbstractContext): Type =
+  def fullUpperBound(param: TypeParamRef)(using Context): Type =
     constraint.minUpper(param).foldLeft(nonParamBounds(param).hi)(_ & _)
 
   /** Full bounds of `param`, including other lower/upper params.
     *
     * Note that underlying operations perform subtype checks - for this reason, recursing on `fullBounds`
     * of some param when comparing types might lead to infinite recursion. Consider `bounds` instead.
     */
-  def fullBounds(param: TypeParamRef)(implicit actx: AbstractContext): TypeBounds =
+  def fullBounds(param: TypeParamRef)(using Context): TypeBounds =
     nonParamBounds(param).derivedTypeBounds(fullLowerBound(param), fullUpperBound(param))
 
-  protected def addOneBound(param: TypeParamRef, bound: Type, isUpper: Boolean)(using AbstractContext): Boolean =
+  protected def addOneBound(param: TypeParamRef, bound: Type, isUpper: Boolean)(using Context): Boolean =
     if !constraint.contains(param) then true
     else if !isUpper && param.occursIn(bound)
       // We don't allow recursive lower bounds when defining a type,
@@ -121,11 +117,11 @@ trait ConstraintHandling[AbstractContext] {
         || {
           constraint = c1
           val TypeBounds(lo, hi) = constraint.entry(param)
-          isSubType(lo, hi)
+          isSub(lo, hi)
         }
   end addOneBound
 
-  protected def addBoundTransitively(param: TypeParamRef, rawBound: Type, isUpper: Boolean)(implicit actx: AbstractContext): Boolean =
+  protected def addBoundTransitively(param: TypeParamRef, rawBound: Type, isUpper: Boolean)(using Context): Boolean =
 
     /** Adjust the bound `tp` in the following ways:
      *
@@ -172,7 +168,7 @@ trait ConstraintHandling[AbstractContext] {
         .reporting(i"added $description = $result$location", constr)
   end addBoundTransitively
 
-  protected def addLess(p1: TypeParamRef, p2: TypeParamRef)(implicit actx: AbstractContext): Boolean = {
+  protected def addLess(p1: TypeParamRef, p2: TypeParamRef)(using Context): Boolean = {
     def description = i"ordering $p1 <: $p2 to\n$constraint"
     val res =
       if (constraint.isLess(p2, p1)) unify(p2, p1)
@@ -195,7 +191,7 @@ trait ConstraintHandling[AbstractContext] {
   /** Make p2 = p1, transfer all bounds of p2 to p1
    *  @pre  less(p1)(p2)
    */
-  private def unify(p1: TypeParamRef, p2: TypeParamRef)(implicit actx: AbstractContext): Boolean = {
+  private def unify(p1: TypeParamRef, p2: TypeParamRef)(using Context): Boolean = {
     constr.println(s"unifying $p1 $p2")
     assert(constraint.isLess(p1, p2))
     val down = constraint.exclusiveLower(p2, p1)
@@ -204,16 +200,16 @@ trait ConstraintHandling[AbstractContext] {
     val bounds = constraint.nonParamBounds(p1)
     val lo = bounds.lo
     val hi = bounds.hi
-    isSubType(lo, hi) &&
+    isSub(lo, hi) &&
     down.forall(addOneBound(_, hi, isUpper = true)) &&
     up.forall(addOneBound(_, lo, isUpper = false))
   }
 
-  protected def isSubType(tp1: Type, tp2: Type, whenFrozen: Boolean)(implicit actx: AbstractContext): Boolean =
+  protected def isSubType(tp1: Type, tp2: Type, whenFrozen: Boolean)(using Context): Boolean =
     if (whenFrozen)
       isSubTypeWhenFrozen(tp1, tp2)
     else
-      isSubType(tp1, tp2)
+      isSub(tp1, tp2)
 
   inline final def inFrozenConstraint[T](op: => T): T = {
     val savedFrozen = frozenConstraint
@@ -227,16 +223,16 @@ trait ConstraintHandling[AbstractContext] {
     }
   }
 
-  final def isSubTypeWhenFrozen(tp1: Type, tp2: Type)(implicit actx: AbstractContext): Boolean = inFrozenConstraint(isSubType(tp1, tp2))
-  final def isSameTypeWhenFrozen(tp1: Type, tp2: Type)(implicit actx: AbstractContext): Boolean = inFrozenConstraint(isSameType(tp1, tp2))
+  final def isSubTypeWhenFrozen(tp1: Type, tp2: Type)(using Context): Boolean = inFrozenConstraint(isSub(tp1, tp2))
+  final def isSameTypeWhenFrozen(tp1: Type, tp2: Type)(using Context): Boolean = inFrozenConstraint(isSame(tp1, tp2))
 
   /** Test whether the lower bounds of all parameters in this
    *  constraint are a solution to the constraint.
    */
-  protected final def isSatisfiable(implicit actx: AbstractContext): Boolean =
+  protected final def isSatisfiable(using Context): Boolean =
     constraint.forallParams { param =>
       val TypeBounds(lo, hi) = constraint.entry(param)
-      isSubType(lo, hi) || {
+      isSub(lo, hi) || {
         report.log(i"sub fail $lo <:< $hi")
         false
       }
@@ -253,7 +249,7 @@ trait ConstraintHandling[AbstractContext] {
    *  @return the instantiating type
    *  @pre `param` is in the constraint's domain.
    */
-  final def approximation(param: TypeParamRef, fromBelow: Boolean)(implicit actx: AbstractContext): Type = {
+  final def approximation(param: TypeParamRef, fromBelow: Boolean)(using Context): Type = {
     val replaceWildcards = new TypeMap {
       override def stopAtStatic = true
       def apply(tp: Type) = mapOver {
@@ -317,7 +313,7 @@ trait ConstraintHandling[AbstractContext] {
    * At this point we also drop the @Repeated annotation to avoid inferring type arguments with it,
    * as those could leak the annotation to users (see run/inferred-repeated-result).
    */
-  def widenInferred(inst: Type, bound: Type)(implicit actx: AbstractContext): Type =
+  def widenInferred(inst: Type, bound: Type)(using Context): Type =
 
     def dropSuperTraits(tp: Type): Type =
       var kept: Set[Type] = Set()      // types to keep since otherwise bound would not fit
@@ -380,7 +376,7 @@ trait ConstraintHandling[AbstractContext] {
    *  a lower bound instantiation can be a singleton type only if the upper bound
    *  is also a singleton type.
    */
-  def instanceType(param: TypeParamRef, fromBelow: Boolean)(implicit actx: AbstractContext): Type = {
+  def instanceType(param: TypeParamRef, fromBelow: Boolean)(using Context): Type = {
     val approx = approximation(param, fromBelow).simplified
     if (fromBelow)
       val widened = widenInferred(approx, param)
@@ -408,7 +404,7 @@ trait ConstraintHandling[AbstractContext] {
    *  Both `c1` and `c2` are required to derive from constraint `pre`, without adding
    *  any new type variables but possibly narrowing already registered ones with further bounds.
    */
-  protected final def subsumes(c1: Constraint, c2: Constraint, pre: Constraint)(implicit actx: AbstractContext): Boolean =
+  protected final def subsumes(c1: Constraint, c2: Constraint, pre: Constraint)(using Context): Boolean =
     if (c2 eq pre) true
     else if (c1 eq pre) false
     else {
@@ -427,7 +423,7 @@ trait ConstraintHandling[AbstractContext] {
     }
 
   /** The current bounds of type parameter `param` */
-  def bounds(param: TypeParamRef)(implicit actx: AbstractContext): TypeBounds = {
+  def bounds(param: TypeParamRef)(using Context): TypeBounds = {
     val e = constraint.entry(param)
     if (e.exists) e.bounds
     else {
@@ -441,7 +437,7 @@ trait ConstraintHandling[AbstractContext] {
    *  and propagate all bounds.
    *  @param tvars   See Constraint#add
    */
-  def addToConstraint(tl: TypeLambda, tvars: List[TypeVar])(implicit actx: AbstractContext): Boolean =
+  def addToConstraint(tl: TypeLambda, tvars: List[TypeVar])(using Context): Boolean =
     checkPropagated(i"initialized $tl") {
       constraint = constraint.add(tl, tvars)
       tl.paramRefs.forall { param =>
@@ -470,7 +466,7 @@ trait ConstraintHandling[AbstractContext] {
    *  This holds if `TypeVarsMissContext` is set unless `param` is a part
    *  of a MatchType that is currently normalized.
    */
-  final def assumedTrue(param: TypeParamRef)(implicit actx: AbstractContext): Boolean =
+  final def assumedTrue(param: TypeParamRef)(using Context): Boolean =
     ctx.mode.is(Mode.TypevarsMissContext) && (caseLambda `ne` param.binder)
 
   /** Add constraint `param <: bound` if `fromBelow` is false, `param >: bound` otherwise.
@@ -480,7 +476,7 @@ trait ConstraintHandling[AbstractContext] {
    *  not be AndTypes and lower bounds may not be OrTypes. This is assured by the
    *  way isSubType is organized.
    */
-  protected def addConstraint(param: TypeParamRef, bound: Type, fromBelow: Boolean)(implicit actx: AbstractContext): Boolean =
+  protected def addConstraint(param: TypeParamRef, bound: Type, fromBelow: Boolean)(using Context): Boolean =
 
     /** When comparing lambdas we might get constraints such as
      *  `A <: X0` or `A = List[X0]` where `A` is a constrained parameter
@@ -514,7 +510,7 @@ trait ConstraintHandling[AbstractContext] {
         case _: TypeBounds =>
           if (fromBelow) addLess(bound, param) else addLess(param, bound)
         case tp =>
-          if (fromBelow) isSubType(bound, tp) else isSubType(tp, bound)
+          if (fromBelow) isSub(bound, tp) else isSub(tp, bound)
       }
 
     def kindCompatible(tp1: Type, tp2: Type): Boolean =
@@ -541,7 +537,7 @@ trait ConstraintHandling[AbstractContext] {
   end addConstraint
 
   /** Check that constraint is fully propagated. See comment in Config.checkConstraintsPropagated */
-  def checkPropagated(msg: => String)(result: Boolean)(implicit actx: AbstractContext): Boolean = {
+  def checkPropagated(msg: => String)(result: Boolean)(using Context): Boolean = {
     if (Config.checkConstraintsPropagated && result && addConstraintInvocations == 0)
       inFrozenConstraint {
         for (p <- constraint.domainParams) {

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

@@ -735,7 +735,7 @@ object Contexts {
     store = initialStore
       .updated(settingsStateLoc, settingsGroup.defaultState)
       .updated(notNullInfosLoc, Nil)
-    typeComparer = new TypeComparer(this)
+    typeComparer = new TypeComparer(using this)
     searchHistory = new SearchRoot
     gadt = EmptyGadtConstraint
   }

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

@@ -61,7 +61,7 @@ final class ProperGadtConstraint private(
   private var myConstraint: Constraint,
   private var mapping: SimpleIdentityMap[Symbol, TypeVar],
   private var reverseMapping: SimpleIdentityMap[TypeParamRef, Symbol],
-) extends GadtConstraint with ConstraintHandling[Context] {
+) extends GadtConstraint with ConstraintHandling {
   import dotty.tools.dotc.config.Printers.{gadts, gadtsConstr}
 
   def this() = this(
@@ -140,7 +140,7 @@ final class ProperGadtConstraint private(
       case tv: TypeVar => tv
       case inst =>
         gadts.println(i"instantiated: $sym -> $inst")
-        return if (isUpper) isSubType(inst , bound) else isSubType(bound, inst)
+        return if (isUpper) isSub(inst, bound) else isSub(bound, inst)
     }
 
     val internalizedBound = bound match {
@@ -217,13 +217,11 @@ final class ProperGadtConstraint private(
 
   // ---- Protected/internal -----------------------------------------------
 
-  override def comparerCtx(using Context): Context = ctx
-
   override protected def constraint = myConstraint
   override protected def constraint_=(c: Constraint) = myConstraint = c
 
-  override def isSubType(tp1: Type, tp2: Type)(using Context): Boolean = ctx.typeComparer.isSubType(tp1, tp2)
-  override def isSameType(tp1: Type, tp2: Type)(using Context): Boolean = ctx.typeComparer.isSameType(tp1, tp2)
+  override protected def isSub(tp1: Type, tp2: Type)(using Context): Boolean = ctx.typeComparer.isSubType(tp1, tp2)
+  override protected def isSame(tp1: Type, tp2: Type)(using Context): Boolean = ctx.typeComparer.isSameType(tp1, tp2)
 
    override def nonParamBounds(param: TypeParamRef)(using Context): TypeBounds =
      constraint.nonParamBounds(param) match {

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

@@ -24,16 +24,10 @@ import typer.Applications.productSelectorTypes
 import reporting.trace
 import NullOpsDecorator.NullOps
 
-final class AbsentContext
-object AbsentContext {
-  implicit val absentContext: AbsentContext = new AbsentContext
-}
-
 /** Provides methods to compare types.
  */
-class TypeComparer(initctx: Context) extends ConstraintHandling[AbsentContext] with PatternTypeConstrainer {
+class TypeComparer(using val comparerCtx: Context) extends ConstraintHandling with PatternTypeConstrainer {
   import TypeComparer._
-  def comparerCtx(using AbsentContext): Context = initctx
 
   val state = ctx.typerState
   def constraint: Constraint = state.constraint
@@ -175,7 +169,9 @@ class TypeComparer(initctx: Context) extends ConstraintHandling[AbsentContext] w
     }
   }
 
-  def isSubType(tp1: Type, tp2: Type)(implicit nc: AbsentContext): Boolean = isSubType(tp1, tp2, FreshApprox)
+  def isSubType(tp1: Type, tp2: Type): Boolean = isSubType(tp1, tp2, FreshApprox)
+
+  override protected def isSub(tp1: Type, tp2: Type)(using Context): Boolean = isSubType(tp1, tp2)
 
   /** The inner loop of the isSubType comparison.
    *  Recursive calls from recur should go to recur directly if the two types
@@ -1769,11 +1765,13 @@ class TypeComparer(initctx: Context) extends ConstraintHandling[AbsentContext] w
   // Type equality =:=
 
   /** Two types are the same if are mutual subtypes of each other */
-  def isSameType(tp1: Type, tp2: Type)(implicit nc: AbsentContext): Boolean =
+  def isSameType(tp1: Type, tp2: Type): Boolean =
     if (tp1 eq NoType) false
     else if (tp1 eq tp2) true
     else isSubType(tp1, tp2) && isSubType(tp2, tp1)
 
+  override protected def isSame(tp1: Type, tp2: Type)(using Context): Boolean = isSameType(tp1, tp2)
+
   /** Same as `isSameType` but also can be applied to overloaded TermRefs, where
    *  two overloaded refs are the same if they have pairwise equal alternatives
    */
@@ -2215,7 +2213,7 @@ class TypeComparer(initctx: Context) extends ConstraintHandling[AbsentContext] w
   }
 
   /** A new type comparer of the same type as this one, using the given context. */
-  def copyIn(ctx: Context): TypeComparer = new TypeComparer(ctx)
+  def copyIn(ctx: Context): TypeComparer = new TypeComparer(using ctx)
 
   // ----------- Diagnostics --------------------------------------------------
 
@@ -2469,7 +2467,7 @@ object TypeComparer {
 
   /** Show trace of comparison operations when performing `op` */
   def explaining[T](say: String => Unit)(op: Context ?=> T)(using Context): T = {
-    val nestedCtx = ctx.fresh.setTypeComparerFn(new ExplainingTypeComparer(_))
+    val nestedCtx = ctx.fresh.setTypeComparerFn(new ExplainingTypeComparer(using _))
     val res = try { op(using nestedCtx) } finally { say(nestedCtx.typeComparer.lastTrace()) }
     res
   }
@@ -2482,17 +2480,17 @@ object TypeComparer {
   }
 }
 
-class TrackingTypeComparer(initctx: Context) extends TypeComparer(initctx) {
+class TrackingTypeComparer(using Context) extends TypeComparer {
   import state.constraint
 
   val footprint: mutable.Set[Type] = mutable.Set[Type]()
 
-  override def bounds(param: TypeParamRef)(implicit nc: AbsentContext): TypeBounds = {
+  override def bounds(param: TypeParamRef)(using Context): TypeBounds = {
     if (param.binder `ne` caseLambda) footprint += param
     super.bounds(param)
   }
 
-  override def addOneBound(param: TypeParamRef, bound: Type, isUpper: Boolean)(implicit nc: AbsentContext): Boolean = {
+  override def addOneBound(param: TypeParamRef, bound: Type, isUpper: Boolean)(using Context): Boolean = {
     if (param.binder `ne` caseLambda) footprint += param
     super.addOneBound(param, bound, isUpper)
   }
@@ -2630,7 +2628,7 @@ class TrackingTypeComparer(initctx: Context) extends TypeComparer(initctx) {
 }
 
 /** A type comparer that can record traces of subtype operations */
-class ExplainingTypeComparer(initctx: Context) extends TypeComparer(initctx) {
+class ExplainingTypeComparer(using Context) extends TypeComparer {
   import TypeComparer._
 
   private var indent = 0
@@ -2678,12 +2676,12 @@ class ExplainingTypeComparer(initctx: Context) extends TypeComparer(initctx) {
       super.glb(tp1, tp2)
     }
 
-  override def addConstraint(param: TypeParamRef, bound: Type, fromBelow: Boolean)(implicit nc: AbsentContext): Boolean =
+  override def addConstraint(param: TypeParamRef, bound: Type, fromBelow: Boolean)(using Context): Boolean =
     traceIndented(i"add constraint $param ${if (fromBelow) ">:" else "<:"} $bound $frozenConstraint, constraint = ${ctx.typerState.constraint}") {
       super.addConstraint(param, bound, fromBelow)
     }
 
-  override def copyIn(ctx: Context): ExplainingTypeComparer = new ExplainingTypeComparer(ctx)
+  override def copyIn(using Context): ExplainingTypeComparer = new ExplainingTypeComparer
 
   override def lastTrace(): String = "Subtype trace:" + { try b.toString finally b.clear() }
 }

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

@@ -4283,7 +4283,7 @@ object Types {
     override def tryNormalize(using Context): Type = reduced.normalized
 
     def reduced(using Context): Type = {
-      val trackingCtx = ctx.fresh.setTypeComparerFn(new TrackingTypeComparer(_))
+      val trackingCtx = ctx.fresh.setTypeComparerFn(new TrackingTypeComparer(using _))
       val typeComparer = trackingCtx.typeComparer.asInstanceOf[TrackingTypeComparer]
 
       def contextInfo(tp: Type): Type = tp match {