Change : freeze bounds

src/dotty/tools/dotc/ast/tpd.scala

@@ -626,7 +626,7 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
           loop(from.owner, from :: froms, to :: tos)
         else {
           //println(i"change owner ${from :: froms}%, % ==> $tos of $tree")
-          new TreeTypeMap(oldOwners = from :: froms, newOwners = tos)(ctx.withMode(Mode.FutureDefsOK)).apply(tree)
+          new TreeTypeMap(oldOwners = from :: froms, newOwners = tos)(ctx.addMode(Mode.FutureDefsOK)).apply(tree)
         }
       }
       loop(from, Nil, to :: Nil)
@@ -652,7 +652,7 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
             traverseChildren(tree)
         }
       }
-      traverser.traverse(tree)(ctx.withMode(Mode.FutureDefsOK))
+      traverser.traverse(tree)(ctx.addMode(Mode.FutureDefsOK))
       tree
     }
 

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

@@ -23,6 +23,7 @@ trait ConstraintHandling {
   implicit val ctx: Context
 
   protected def isSubType(tp1: Type, tp2: Type): Boolean
+  protected def isSameType(tp1: Type, tp2: Type): Boolean
 
   val state: TyperState
   import state.constraint
@@ -104,13 +105,20 @@ trait ConstraintHandling {
     up.forall(addOneBound(_, lo, isUpper = false))
   }
 
-  protected final def isSubTypeWhenFrozen(tp1: Type, tp2: Type): Boolean = {
+  final def isSubTypeWhenFrozen(tp1: Type, tp2: Type): Boolean = {
     val saved = frozenConstraint
     frozenConstraint = true
     try isSubType(tp1, tp2)
     finally frozenConstraint = saved
   }
 
+  final def isSameTypeWhenFrozen(tp1: Type, tp2: Type): Boolean = {
+    val saved = frozenConstraint
+    frozenConstraint = true
+    try isSameType(tp1, tp2)
+    finally frozenConstraint = saved
+  }
+
   /** Test whether the lower bounds of all parameters in this
    *  constraint are a solution to the constraint.
    */

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

@@ -439,12 +439,12 @@ object Contexts {
   }
 
   implicit class ModeChanges(val c: Context) extends AnyVal {
-    final def withMode(mode: Mode): Context =
+    final def withModeBits(mode: Mode): Context =
       if (mode != c.mode) c.fresh.setMode(mode) else c
 
-    final def addMode(mode: Mode): Context = withMode(c.mode | mode)
-    final def maskMode(mode: Mode): Context = withMode(c.mode & mode)
-    final def retractMode(mode: Mode): Context = withMode(c.mode &~ mode)
+    final def addMode(mode: Mode): Context = withModeBits(c.mode | mode)
+    final def maskMode(mode: Mode): Context = withModeBits(c.mode & mode)
+    final def retractMode(mode: Mode): Context = withModeBits(c.mode &~ mode)
   }
 
   implicit class FreshModeChanges(val c: FreshContext) extends AnyVal {

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

@@ -339,8 +339,8 @@ object Denotations {
           val info1 = denot1.info
           val info2 = denot2.info
           val sameSym = sym1 eq sym2
-          if (sameSym && info1 <:< info2) denot2
-          else if (sameSym && info2 <:< info1) denot1
+          if (sameSym && (info1 frozen_<:< info2)) denot2
+          else if (sameSym && (info2 frozen_<:< info1)) denot1
           else {
             val jointSym =
               if (sameSym) sym1

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

@@ -129,7 +129,6 @@ class OrderingConstraint(private val boundsMap: ParamBounds,
 
   type This = OrderingConstraint
 
-
 // ----------- Basic indices --------------------------------------------------
 
   /** The number of type parameters in the given entry array */
@@ -576,4 +575,22 @@ class OrderingConstraint(private val boundsMap: ParamBounds,
       }
     Text.lines(List(header, uninstVarsText, constrainedText, boundsText, orderingText, ")"))
   }
+
+  override def toString: String = {
+    def entryText(tp: Type): String = tp match {
+      case tp: TypeBounds => tp.toString
+      case _ =>" := " + tp
+    }
+    val constrainedText =
+      " constrained types = " + domainPolys.mkString("\n")
+    val boundsText =
+      " bounds = " + {
+        val assocs =
+          for (param <- domainParams)
+          yield
+            param.binder.paramNames(param.paramNum) + ": " + entryText(entry(param))
+        assocs.mkString("\n")
+    }
+    constrainedText + "\n" + boundsText
+  }
 }

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

@@ -1587,6 +1587,7 @@ object SymDenotations {
               if (isCachable(tp)) baseTypeRefCache.put(tp, basetp)
               else baseTypeRefCache.remove(tp)
             } else if (basetp == NoPrefix) {
+              baseTypeRefCache.put(tp, null)
               throw CyclicReference(this)
             }
             basetp

src/dotty/tools/dotc/core/TypeApplications.scala

@@ -497,7 +497,7 @@ class TypeApplications(val self: Type) extends AnyVal {
       val boundss = new mutable.ListBuffer[TypeBounds]
       for (sym <- boundSyms) {
         val bounds = sym.info.bounds
-        if (!(TypeBounds.empty <:< bounds)) {
+        if (!(TypeBounds.empty frozen_<:< bounds)) {
           boundNames += sym.name
           boundss += bounds
         }
@@ -574,7 +574,7 @@ class TypeApplications(val self: Type) extends AnyVal {
                 // we have a binding T = Lambda$XYZ{...}.this.hk$i where hk$i names the current `tparam`.
                 val pcore = etaCore(tp.parent, otherParams)
                 val hkBounds = self.member(rname).info.bounds
-                if (TypeBounds.empty <:< hkBounds) pcore
+                if (TypeBounds.empty frozen_<:< hkBounds) pcore
                 else tp.derivedRefinedType(pcore, tp.refinedName, hkBounds)
               case _ =>
                 val pcore = etaCore(tp.parent, tparams)

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

@@ -154,24 +154,10 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
           case tp1: NamedType =>
             val sym1 = tp1.symbol
             (if ((sym1 ne NoSymbol) && (sym1 eq tp2.symbol))
-               ctx.erasedTypes || sym1.isStaticOwner ||
-               { // Implements: A # X  <:  B # X
-                 // if either A =:= B (i.e. A <: B and B <: A), or the following three conditions hold:
-                 //  1. X is a class type,
-                 //  2. B is a class type without abstract type members.
-                 //  3. A <: B.
-                 // Dealiasing is taken care of elsewhere.
-                 val pre1 = tp1.prefix
-                 val pre2 = tp2.prefix
-                 isSameType(pre1, pre2) ||
-                   sym1.isClass &&
-                   pre2.classSymbol.exists &&
-                   pre2.abstractTypeMembers.isEmpty &&
-                   isSubType(pre1, pre2)
-              }
+               ctx.erasedTypes || sym1.isStaticOwner || isSubType(tp1.prefix, tp2.prefix)
             else
               (tp1.name eq tp2.name) &&
-              isSameType(tp1.prefix, tp2.prefix) &&
+              isSubType(tp1.prefix, tp2.prefix) &&
               (tp1.signature == tp2.signature) &&
               !tp1.isInstanceOf[WithFixedSym] &&
               !tp2.isInstanceOf[WithFixedSym]
@@ -229,6 +215,9 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
       compareSuper
     case AndType(tp21, tp22) =>
       isSubType(tp1, tp21) && isSubType(tp1, tp22)
+    case OrType(tp21, tp22) =>
+      if (tp21.stripTypeVar eq tp22.stripTypeVar) isSubType(tp1, tp21)
+      else secondTry(tp1, tp2)
     case TypeErasure.ErasedValueType(cls2, underlying2) =>
       def compareErasedValueType = tp1 match {
         case TypeErasure.ErasedValueType(cls1, underlying1) =>
@@ -291,6 +280,9 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
       isSubType(tp1.ref, tp2)
     case tp1: AnnotatedType =>
       isSubType(tp1.tpe, tp2)
+    case AndType(tp11, tp12) =>
+      if (tp11.stripTypeVar eq tp12.stripTypeVar) isSubType(tp11, tp2)
+      else thirdTry(tp1, tp2)
     case OrType(tp11, tp12) =>
       isSubType(tp11, tp2) && isSubType(tp12, tp2)
     case ErrorType =>
@@ -353,6 +345,21 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
       }
       compareRefined
     case OrType(tp21, tp22) =>
+      // Rewrite T1 <: (T211 & T212) | T22 to T1 <: (T211 | T22) and T1 <: (T212 | T22)
+      // and analogously for T1 <: T21 | (T221 & T222)
+      // `|' types to the right of <: are problematic, because
+      // we have to choose one constraint set or another, which might cut off
+      // solutions. The rewriting delays the point where we have to choose.
+      tp21 match {
+        case AndType(tp211, tp212) =>
+          return isSubType(tp1, OrType(tp211, tp22)) && isSubType(tp1, OrType(tp212, tp22))
+        case _ =>
+      }
+      tp22 match {
+        case AndType(tp221, tp222) =>
+          return isSubType(tp1, OrType(tp21, tp221)) && isSubType(tp1, OrType(tp21, tp222))
+        case _ =>
+      }
       eitherIsSubType(tp1, tp21, tp1, tp22) || fourthTry(tp1, tp2)
     case tp2 @ MethodType(_, formals2) =>
       def compareMethod = tp1 match {
@@ -454,6 +461,21 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
        isNewSubType(tp1.parent, tp2) ||
          needsEtaLift(tp2, tp1) && tp2.testLifted(tp1.typeParams, isSubType(tp1, _), Nil)
     case AndType(tp11, tp12) =>
+      // Rewrite (T111 | T112) & T12 <: T2 to (T111 & T12) <: T2 and (T112 | T12) <: T2
+      // and analogously for T11 & (T121 | T122) & T12 <: T2
+      // `&' types to the left of <: are problematic, because
+      // we have to choose one constraint set or another, which might cut off
+      // solutions. The rewriting delays the point where we have to choose.
+      tp11 match {
+        case OrType(tp111, tp112) =>
+          return isSubType(AndType(tp111, tp12), tp2) && isSubType(AndType(tp112, tp12), tp2)
+        case _ =>
+      }
+      tp12 match {
+        case OrType(tp121, tp122) =>
+          return isSubType(AndType(tp11, tp121), tp2) && isSubType(AndType(tp11, tp122), tp2)
+        case _ =>
+      }
       eitherIsSubType(tp11, tp2, tp12, tp2)
     case JavaArrayType(elem1) =>
       def compareJavaArray = tp2 match {
@@ -693,7 +715,7 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
     case formal1 :: rest1 =>
       formals2 match {
         case formal2 :: rest2 =>
-          (isSameType(formal1, formal2)
+          (isSameTypeWhenFrozen(formal1, formal2)
             || isJava1 && (formal2 isRef ObjectClass) && (formal1 isRef AnyClass)
             || isJava2 && (formal1 isRef ObjectClass) && (formal2 isRef AnyClass)) &&
           matchingParams(rest1, rest2, isJava1, isJava2)
@@ -1067,7 +1089,7 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
     case tp1: ClassInfo =>
       tp2 match {
         case tp2: ClassInfo =>
-          isSubType(tp1.prefix, tp2.prefix) || (tp1.cls.owner derivesFrom tp2.cls.owner)
+          isSubTypeWhenFrozen(tp1.prefix, tp2.prefix) || (tp1.cls.owner derivesFrom tp2.cls.owner)
         case _ =>
           false
       }
@@ -1083,7 +1105,7 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
       tp2 match {
         case tp2: MethodType =>
           def asGoodParams(formals1: List[Type], formals2: List[Type]) =
-            (formals2 corresponds formals1)(isSubType)
+            (formals2 corresponds formals1)(isSubTypeWhenFrozen)
           asGoodParams(tp1.paramTypes, tp2.paramTypes) &&
           (!asGoodParams(tp2.paramTypes, tp1.paramTypes) ||
            isAsGood(tp1.resultType, tp2.resultType))

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

@@ -595,6 +595,11 @@ object Types {
       ctx.typeComparer.topLevelSubType(this, that)
     }
 
+    /** Is this type a subtype of that type? */
+    final def frozen_<:<(that: Type)(implicit ctx: Context): Boolean = track("frozen_<:<") {
+      ctx.typeComparer.isSubTypeWhenFrozen(this, that)
+    }
+
     /** Is this type the same as that type?
      *  This is the case iff `this <:< that` and `that <:< this`.
      */
@@ -625,9 +630,9 @@ object Types {
         case ExprType(_) | MethodType(Nil, _) => tp.resultType
         case _ => tp
       }
-      this <:< that || {
+      (this frozen_<:< that) || {
         val rthat = result(that)
-        (rthat ne that) && result(this) <:< rthat
+        (rthat ne that) && (result(this) frozen_<:< rthat)
       }
     }
 
@@ -801,12 +806,18 @@ object Types {
       case _ => NoType
     }
 
-    /** The chain of underlying types as long as type is a TypeProxy.
+    /** The iterator of underlying types as long as type is a TypeProxy.
      *  Useful for diagnostics
      */
-    def underlyingChain(implicit ctx: Context): List[Type] = this match {
-      case tp: TypeProxy => tp :: tp.underlying.underlyingChain
-      case _ => Nil
+    def underlyingIterator(implicit ctx: Context): Iterator[Type] = new Iterator[Type] {
+      var current = Type.this
+      var hasNext = true
+      def next = {
+        val res = current
+        hasNext = current.isInstanceOf[TypeProxy]
+        if (hasNext) current = current.asInstanceOf[TypeProxy].underlying
+        res
+      }
     }
 
     /** A prefix-less refined this or a termRef to a new skolem symbol
@@ -2652,13 +2663,13 @@ object Types {
     }
 
     def & (that: TypeBounds)(implicit ctx: Context): TypeBounds =
-      if (this.lo <:< that.lo && that.hi <:< this.hi) that
-      else if (that.lo <:< this.lo && this.hi <:< that.hi) this
+      if ((this.lo frozen_<:< that.lo) && (that.hi frozen_<:< this.hi)) that
+      else if ((that.lo frozen_<:< this.lo) && (this.hi frozen_<:< that.hi)) this
       else TypeBounds(this.lo | that.lo, this.hi & that.hi)
 
     def | (that: TypeBounds)(implicit ctx: Context): TypeBounds =
-      if (this.lo <:< that.lo && that.hi <:< this.hi) this
-      else if (that.lo <:< this.lo && this.hi <:< that.hi) that
+      if ((this.lo frozen_<:< that.lo) && (that.hi frozen_<:< this.hi)) this
+      else if ((that.lo frozen_<:< this.lo) && (this.hi frozen_<:< that.hi)) that
       else TypeBounds(this.lo & that.lo, this.hi | that.hi)
 
     override def & (that: Type)(implicit ctx: Context) = that match {

src/dotty/tools/dotc/printing/PlainPrinter.scala

@@ -166,7 +166,7 @@ class PlainPrinter(_ctx: Context) extends Printer {
         else {
           val constr = ctx.typerState.constraint
           val bounds =
-            if (constr.contains(tp)) constr.fullBounds(tp.origin)
+            if (constr.contains(tp)) constr.fullBounds(tp.origin)(ctx.addMode(Mode.Printing))
             else TypeBounds.empty
           "(" ~ toText(tp.origin) ~ "?" ~ toText(bounds) ~ ")"
         }

src/dotty/tools/dotc/reporting/Reporter.scala

@@ -149,16 +149,18 @@ trait Reporting { this: Context =>
     else traceIndented[T](s"==> $question?", (res: Any) => s"<== $question = ${resStr(res)}")(op)
   }
 
-  def traceIndented[T](leading: => String, trailing: Any => String)(op: => T): T = {
-    var finalized = false
-    var logctx = this
-    while (logctx.reporter.isInstanceOf[StoreReporter]) logctx = logctx.outer
-    def finalize(result: Any, note: String) =
-      if (!finalized) {
-        base.indent -= 1
-        logctx.log(s"${base.indentTab * base.indent}${trailing(result)}$note")
-        finalized = true
-      }
+  def traceIndented[T](leading: => String, trailing: Any => String)(op: => T): T =
+    if (ctx.mode.is(Mode.Printing)) op
+    else {
+      var finalized = false
+      var logctx = this
+      while (logctx.reporter.isInstanceOf[StoreReporter]) logctx = logctx.outer
+      def finalize(result: Any, note: String) =
+        if (!finalized) {
+          base.indent -= 1
+          logctx.log(s"${base.indentTab * base.indent}${trailing(result)}$note")
+          finalized = true
+        }
     try {
       logctx.log(s"${base.indentTab * base.indent}$leading")
       base.indent += 1

src/dotty/tools/dotc/transform/TreeChecker.scala

@@ -66,7 +66,7 @@ class TreeChecker extends Phase with SymTransformer {
     val cur = symd.linkedClass
     val prev = ctx.atPhase(ctx.phase.prev) {
       ct => {
-        implicit val ctx: Context = ct.withMode(Mode.FutureDefsOK)
+        implicit val ctx: Context = ct.addMode(Mode.FutureDefsOK)
         symd.symbol.linkedClass
       }
     }

test/test/DeSugarTest.scala

@@ -35,7 +35,7 @@ class DeSugarTest extends ParserTest {
     def transform(trees: List[Tree], mode: Mode)(implicit ctx: Context): List[Tree] = withMode(mode) { transform(trees) }
 
     override def transform(tree: Tree)(implicit ctx: Context): Tree = {
-      val tree1 = desugar(tree)(ctx.withMode(curMode))
+      val tree1 = desugar(tree)(ctx.withModeBits(curMode))
       tree1 match {
         case TypedSplice(t) =>
           tree1