Cleanup SmartGADTMap#ctx

Parameterised ConstraintHandling on what context it needs.

TypeComparer works by being manually cloned in Context#typeComparer
whenever Context notices that TypeComparer#ctx is different from itself.
Unlike TypeComparer, SmartGADTMap keeps its own internal variables,
so we cannot apply the same trick.

Author: Aleksander Boruch-Gruszecki

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

@@ -18,15 +18,15 @@ import config.Printers.{constr, typr}
  * 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 {
+trait ConstraintHandling[AbstractContext] {
 
   def constr_println(msg: => String): Unit = constr.println(msg)
   def typr_println(msg: => String): Unit = typr.println(msg)
 
-  implicit def ctx: Context
+  implicit def ctx(implicit ac: AbstractContext): Context
 
-  protected def isSubType(tp1: Type, tp2: Type): Boolean
-  protected def isSameType(tp1: Type, tp2: Type): Boolean
+  protected def isSubType(tp1: Type, tp2: Type)(implicit actx: AbstractContext): Boolean
+  protected def isSameType(tp1: Type, tp2: Type)(implicit actx: AbstractContext): Boolean
 
   protected def constraint: Constraint
   protected def constraint_=(c: Constraint): Unit
@@ -66,7 +66,7 @@ trait ConstraintHandling {
     case tp => tp
   }
 
-  protected def addOneBound(param: TypeParamRef, bound: Type, isUpper: Boolean): Boolean =
+  protected def addOneBound(param: TypeParamRef, bound: Type, isUpper: Boolean)(implicit actx: AbstractContext): Boolean =
     !constraint.contains(param) || {
       def occursIn(bound: Type): Boolean = {
         val b = bound.dealias
@@ -116,7 +116,7 @@ trait ConstraintHandling {
 
   private def location(implicit ctx: Context) = "" // i"in ${ctx.typerState.stateChainStr}" // use for debugging
 
-  protected def addUpperBound(param: TypeParamRef, bound: Type): Boolean = {
+  protected def addUpperBound(param: TypeParamRef, bound: Type)(implicit actx: AbstractContext): Boolean = {
     def description = i"constraint $param <: $bound to\n$constraint"
     if (bound.isRef(defn.NothingClass) && ctx.typerState.isGlobalCommittable) {
       def msg = s"!!! instantiated to Nothing: $param, constraint = ${constraint.show}"
@@ -132,7 +132,7 @@ trait ConstraintHandling {
     res
   }
 
-  protected def addLowerBound(param: TypeParamRef, bound: Type): Boolean = {
+  protected def addLowerBound(param: TypeParamRef, bound: Type)(implicit actx: AbstractContext): Boolean = {
     def description = i"constraint $param >: $bound to\n$constraint"
     constr_println(i"adding $description")
     val upper = constraint.upper(param)
@@ -143,7 +143,7 @@ trait ConstraintHandling {
     res
   }
 
-  protected def addLess(p1: TypeParamRef, p2: TypeParamRef): Boolean = {
+  protected def addLess(p1: TypeParamRef, p2: TypeParamRef)(implicit actx: AbstractContext): Boolean = {
     def description = i"ordering $p1 <: $p2 to\n$constraint"
     val res =
       if (constraint.isLess(p2, p1)) unify(p2, p1)
@@ -165,7 +165,7 @@ trait ConstraintHandling {
   /** Make p2 = p1, transfer all bounds of p2 to p1
    *  @pre  less(p1)(p2)
    */
-  private def unify(p1: TypeParamRef, p2: TypeParamRef): Boolean = {
+  private def unify(p1: TypeParamRef, p2: TypeParamRef)(implicit actx: AbstractContext): Boolean = {
     constr_println(s"unifying $p1 $p2")
     assert(constraint.isLess(p1, p2))
     val down = constraint.exclusiveLower(p2, p1)
@@ -180,7 +180,7 @@ trait ConstraintHandling {
   }
 
 
-  protected def isSubType(tp1: Type, tp2: Type, whenFrozen: Boolean): Boolean = {
+  protected def isSubType(tp1: Type, tp2: Type, whenFrozen: Boolean)(implicit actx: AbstractContext): Boolean = {
     if (whenFrozen)
       isSubTypeWhenFrozen(tp1, tp2)
     else
@@ -199,13 +199,13 @@ trait ConstraintHandling {
     }
   }
 
-  final def isSubTypeWhenFrozen(tp1: Type, tp2: Type): Boolean = inFrozenConstraint(isSubType(tp1, tp2))
-  final def isSameTypeWhenFrozen(tp1: Type, tp2: Type): Boolean = inFrozenConstraint(isSameType(tp1, tp2))
+  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))
 
   /** Test whether the lower bounds of all parameters in this
    *  constraint are a solution to the constraint.
    */
-  protected final def isSatisfiable: Boolean =
+  protected final def isSatisfiable(implicit actx: AbstractContext): Boolean =
     constraint.forallParams { param =>
       val TypeBounds(lo, hi) = constraint.entry(param)
       isSubType(lo, hi) || {
@@ -224,7 +224,7 @@ trait ConstraintHandling {
    *  @return the instantiating type
    *  @pre `param` is in the constraint's domain.
    */
-  final def approximation(param: TypeParamRef, fromBelow: Boolean): Type = {
+  final def approximation(param: TypeParamRef, fromBelow: Boolean)(implicit actx: AbstractContext): Type = {
     val avoidParam = new TypeMap {
       override def stopAtStatic = true
       def avoidInArg(arg: Type): Type =
@@ -278,7 +278,7 @@ trait ConstraintHandling {
    *   2. If `tp` is a union type, yet upper bound is not a union type,
    *      approximate the union type from above by an intersection of all common base types.
    */
-  def widenInferred(tp: Type, bound: Type): Type = {
+  def widenInferred(tp: Type, bound: Type)(implicit actx: AbstractContext): Type = {
     def isMultiSingleton(tp: Type): Boolean = tp.stripAnnots match {
       case tp: SingletonType => true
       case AndType(tp1, tp2) => isMultiSingleton(tp1) | isMultiSingleton(tp2)
@@ -311,7 +311,7 @@ trait ConstraintHandling {
    *  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): Type = {
+  def instanceType(param: TypeParamRef, fromBelow: Boolean)(implicit actx: AbstractContext): Type = {
     val inst = approximation(param, fromBelow).simplified
     if (fromBelow) widenInferred(inst, constraint.fullUpperBound(param)) else inst
   }
@@ -326,7 +326,7 @@ trait ConstraintHandling {
    *  Both `c1` and `c2` are required to derive from constraint `pre`, possibly
    *  narrowing it with further bounds.
    */
-  protected final def subsumes(c1: Constraint, c2: Constraint, pre: Constraint): Boolean =
+  protected final def subsumes(c1: Constraint, c2: Constraint, pre: Constraint)(implicit actx: AbstractContext): Boolean =
     if (c2 eq pre) true
     else if (c1 eq pre) false
     else {
@@ -340,7 +340,7 @@ trait ConstraintHandling {
     }
 
   /** The current bounds of type parameter `param` */
-  def bounds(param: TypeParamRef): TypeBounds = {
+  def bounds(param: TypeParamRef)(implicit actx: AbstractContext): TypeBounds = {
     val e = constraint.entry(param)
     if (e.exists) e.bounds
     else {
@@ -354,7 +354,7 @@ trait ConstraintHandling {
    *  and propagate all bounds.
    *  @param tvars   See Constraint#add
    */
-  def addToConstraint(tl: TypeLambda, tvars: List[TypeVar]): Boolean =
+  def addToConstraint(tl: TypeLambda, tvars: List[TypeVar])(implicit actx: AbstractContext): Boolean =
     checkPropagated(i"initialized $tl") {
       constraint = constraint.add(tl, tvars)
       tl.paramRefs.forall { param =>
@@ -382,7 +382,7 @@ trait ConstraintHandling {
    *  This holds if `TypeVarsMissContext` is set unless `param` is a part
    *  of a MatchType that is currently normalized.
    */
-  final def assumedTrue(param: TypeParamRef): Boolean =
+  final def assumedTrue(param: TypeParamRef)(implicit actx: AbstractContext): Boolean =
     ctx.mode.is(Mode.TypevarsMissContext) && (caseLambda `ne` param.binder)
 
   /** Add constraint `param <: bound` if `fromBelow` is false, `param >: bound` otherwise.
@@ -392,7 +392,7 @@ trait ConstraintHandling {
    *  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): Boolean = {
+  protected def addConstraint(param: TypeParamRef, bound: Type, fromBelow: Boolean)(implicit actx: AbstractContext): Boolean = {
     def description = i"constr $param ${if (fromBelow) ">:" else "<:"} $bound:\n$constraint"
     //checkPropagated(s"adding $description")(true) // DEBUG in case following fails
     checkPropagated(s"added $description") {
@@ -508,7 +508,7 @@ trait ConstraintHandling {
   }
 
   /** Instantiate `param` to `tp` if the constraint stays satisfiable */
-  protected def tryInstantiate(param: TypeParamRef, tp: Type): Boolean = {
+  protected def tryInstantiate(param: TypeParamRef, tp: Type)(implicit actx: AbstractContext): Boolean = {
     val saved = constraint
     constraint =
       if (addConstraint(param, tp, fromBelow = true) &&
@@ -518,7 +518,7 @@ trait ConstraintHandling {
   }
 
   /** Check that constraint is fully propagated. See comment in Config.checkConstraintsPropagated */
-  def checkPropagated(msg: => String)(result: Boolean): Boolean = {
+  def checkPropagated(msg: => String)(result: Boolean)(implicit actx: AbstractContext): Boolean = {
     if (Config.checkConstraintsPropagated && result && addConstraintInvocations == 0) {
       inFrozenConstraint {
         for (p <- constraint.domainParams) {

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

@@ -723,7 +723,7 @@ object Contexts {
     private[this] var reverseMapping: SimpleIdentityMap[TypeParamRef, Symbol],
     private[this] var boundCache: SimpleIdentityMap[Symbol, TypeBounds],
     private[this] var dirtyFlag: Boolean
-  ) extends GADTMap with ConstraintHandling {
+  ) extends GADTMap with ConstraintHandling[Context] {
     import dotty.tools.dotc.config.Printers.{gadts, gadtsConstr}
 
     def this() = this(
@@ -748,20 +748,13 @@ object Contexts {
 
     private[this] var checkInProgress = false
 
-    // TODO: clean up this dirty kludge
-    private[this] var myCtx: Context = null
-    implicit override def ctx = myCtx
-    @forceInline private[this] final def inCtx[T](_ctx: Context)(op: => T) = {
-      val savedCtx = myCtx
-      myCtx = _ctx
-      try op finally myCtx = savedCtx
-    }
+    implicit override def ctx(implicit ctx: Context): Context = ctx
 
     override protected def constraint = myConstraint
     override protected def constraint_=(c: Constraint) = myConstraint = c
 
-    override def isSubType(tp1: Type, tp2: Type): Boolean = ctx.typeComparer.isSubType(tp1, tp2)
-    override def isSameType(tp1: Type, tp2: Type): Boolean = ctx.typeComparer.isSameType(tp1, tp2)
+    override def isSubType(tp1: Type, tp2: Type)(implicit ctx: Context): Boolean = ctx.typeComparer.isSubType(tp1, tp2)
+    override def isSameType(tp1: Type, tp2: Type)(implicit ctx: Context): Boolean = ctx.typeComparer.isSameType(tp1, tp2)
 
     private[this] def tvar(sym: Symbol)(implicit ctx: Context): TypeVar = {
       mapping(sym) match {
@@ -788,7 +781,7 @@ object Contexts {
 
     override def addEmptyBounds(sym: Symbol)(implicit ctx: Context): Unit = tvar(sym)
 
-    override def addBound(sym: Symbol, bound: Type, isUpper: Boolean)(implicit ctx: Context): Boolean = try inCtx(ctx) {
+    override def addBound(sym: Symbol, bound: Type, isUpper: Boolean)(implicit ctx: Context): Boolean = try {
       dirtyFlag = true
       checkInProgress = true
       @annotation.tailrec def stripInst(tp: Type): Type = tp match {
@@ -799,8 +792,8 @@ object Contexts {
       }
 
       def cautiousSubtype(tp1: Type, tp2: Type, isSubtype: Boolean): Boolean = {
-        val externalizedTp1 = (new TypeVarRemovingMap)(tp1)
-        val externalizedTp2 = (new TypeVarRemovingMap)(tp2)
+        val externalizedTp1 = (new TypeVarRemovingMap()(ctx))(tp1)
+        val externalizedTp2 = (new TypeVarRemovingMap()(ctx))(tp2)
 
         def descr = {
           def op = s"frozen_${if (isSubtype) "<:<" else ">:>"}"
@@ -846,7 +839,7 @@ object Contexts {
         constraint = constraint.updateEntry(tv.origin, tp)
       }
 
-      val tvarBound = (new TypeVarInsertingMap)(bound)
+      val tvarBound = (new TypeVarInsertingMap()(ctx))(bound)
       val res = tvarBound match {
         case boundTvar: TypeVar =>
           doAddBound(boundTvar)
@@ -861,13 +854,13 @@ object Contexts {
       res
     } finally checkInProgress = false
 
-    override def bounds(sym: Symbol)(implicit ctx: Context): TypeBounds = inCtx(ctx) {
+    override def bounds(sym: Symbol)(implicit ctx: Context): TypeBounds = {
       mapping(sym) match {
         case null => null
         case tv =>
           def retrieveBounds: TypeBounds = {
             val tb = constraint.fullBounds(tv.origin)
-            (new TypeVarRemovingMap)(tb).asInstanceOf[TypeBounds]
+            (new TypeVarRemovingMap()(ctx))(tb).asInstanceOf[TypeBounds]
           }
           val res =
             if (checkInProgress || ctx.mode.is(Mode.GADTflexible)) retrieveBounds
@@ -900,7 +893,7 @@ object Contexts {
       dirtyFlag
     )
 
-    private final class TypeVarInsertingMap extends TypeMap {
+    private final class TypeVarInsertingMap(implicit ctx: Context) extends TypeMap {
       override def apply(tp: Type): Type = tp match {
         case tp: TypeRef =>
           val sym = tp.typeSymbol
@@ -910,7 +903,7 @@ object Contexts {
       }
     }
 
-    private final class TypeVarRemovingMap extends TypeMap {
+    private final class TypeVarRemovingMap(implicit ctx: Context) extends TypeMap {
       override def apply(tp: Type): Type = tp match {
         case tpr: TypeParamRef =>
           reverseMapping(tpr) match {

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

@@ -17,11 +17,16 @@ import scala.util.control.NonFatal
 import typer.ProtoTypes.constrained
 import reporting.trace
 
+final class AbsentContext
+object AbsentContext {
+  implicit val absentContext: AbsentContext = new AbsentContext
+}
+
 /** Provides methods to compare types.
  */
-class TypeComparer(initctx: Context) extends ConstraintHandling {
+class TypeComparer(initctx: Context) extends ConstraintHandling[AbsentContext] {
   import TypeComparer._
-  implicit val ctx: Context = initctx
+  implicit def ctx(implicit nc: AbsentContext): Context = initctx
 
   val state = ctx.typerState
   def constraint: Constraint = state.constraint
@@ -138,7 +143,7 @@ class TypeComparer(initctx: Context) extends ConstraintHandling {
     finally this.approx = saved
   }
 
-  def isSubType(tp1: Type, tp2: Type): Boolean = isSubType(tp1, tp2, NoApprox)
+  def isSubType(tp1: Type, tp2: Type)(implicit nc: AbsentContext): Boolean = isSubType(tp1, tp2, NoApprox)
 
   protected def recur(tp1: Type, tp2: Type): Boolean = trace(s"isSubType ${traceInfo(tp1, tp2)} $approx", subtyping) {
 
@@ -1323,7 +1328,7 @@ class TypeComparer(initctx: Context) extends ConstraintHandling {
   // Type equality =:=
 
   /** Two types are the same if are mutual subtypes of each other */
-  def isSameType(tp1: Type, tp2: Type): Boolean =
+  def isSameType(tp1: Type, tp2: Type)(implicit nc: AbsentContext): Boolean =
     if (tp1 eq NoType) false
     else if (tp1 eq tp2) true
     else isSubType(tp1, tp2) && isSubType(tp2, tp1)
@@ -1844,12 +1849,12 @@ class TrackingTypeComparer(initctx: Context) extends TypeComparer(initctx) {
 
   val footprint: mutable.Set[Type] = mutable.Set[Type]()
 
-  override def bounds(param: TypeParamRef): TypeBounds = {
+  override def bounds(param: TypeParamRef)(implicit nc: AbsentContext): TypeBounds = {
     if (param.binder `ne` caseLambda) footprint += param
     super.bounds(param)
   }
 
-  override def addOneBound(param: TypeParamRef, bound: Type, isUpper: Boolean): Boolean = {
+  override def addOneBound(param: TypeParamRef, bound: Type, isUpper: Boolean)(implicit nc: AbsentContext): Boolean = {
     if (param.binder `ne` caseLambda) footprint += param
     super.addOneBound(param, bound, isUpper)
   }
@@ -1960,7 +1965,7 @@ class ExplainingTypeComparer(initctx: Context) extends TypeComparer(initctx) {
       super.glb(tp1, tp2)
     }
 
-  override def addConstraint(param: TypeParamRef, bound: Type, fromBelow: Boolean): Boolean =
+  override def addConstraint(param: TypeParamRef, bound: Type, fromBelow: Boolean)(implicit nc: AbsentContext): Boolean =
     traceIndented(i"add constraint $param ${if (fromBelow) ">:" else "<:"} $bound $frozenConstraint, constraint = ${ctx.typerState.constraint}") {
       super.addConstraint(param, bound, fromBelow)
     }