Fix dependency checking in OrderingConstraint's replace

Author: odersky

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

@@ -11,6 +11,7 @@ import config.Config
 import config.Printers.constr
 import reflect.ClassTag
 import Constraint.ReverseDeps
+import Substituters.SubstParamMap
 import annotation.tailrec
 import annotation.internal.sharable
 import cc.{CapturingType, derivedCapturingType}
@@ -37,7 +38,7 @@ object OrderingConstraint {
     }
 
     /** The `current` constraint but with the entry for `param` updated to `entry`.
-     *  `current` is used linearly. If it is different from `prev` it is
+     *  `current` is used linearly. If it is different from `prev` then `current` is
      *  known to be dead after the call. Hence it is OK to update destructively
      *  parts of `current` which are not shared by `prev`.
      */
@@ -133,6 +134,7 @@ class OrderingConstraint(private val boundsMap: ParamBounds,
                          private val lowerMap : ParamOrdering,
                          private val upperMap : ParamOrdering,
                          private val hardVars : TypeVars) extends Constraint {
+  thisConstraint =>
 
   import UnificationDirection.*
 
@@ -243,7 +245,9 @@ class OrderingConstraint(private val boundsMap: ParamBounds,
         //.showing(i"outer depends on $tv with ${tvdeps.toList}%, % = $result")
     if co then test(coDeps, upperLens) else test(contraDeps, lowerLens)
 
-  private class Adjuster(srcParam: TypeParamRef)(using Context) extends TypeTraverser:
+  private class Adjuster(srcParam: TypeParamRef)(using Context)
+  extends TypeTraverser, ConstraintAwareTraversal:
+
     var add: Boolean = compiletime.uninitialized
     val seen = util.HashSet[LazyRef]()
 
@@ -411,7 +415,6 @@ class OrderingConstraint(private val boundsMap: ParamBounds,
     tvars.copyToArray(entries1, nparams)
     newConstraint(boundsMap = this.boundsMap.updated(poly, entries1))
       .init(poly)
-      .adjustDeps(poly, entries1, add = true)
   }
 
   /** Split dependent parameters off the bounds for parameters in `poly`.
@@ -433,7 +436,8 @@ class OrderingConstraint(private val boundsMap: ParamBounds,
         todos.dropInPlace(1)
       i += 1
     }
-    current.checkWellFormed()
+    current.adjustDeps(poly, current.boundsMap(poly).nn, add = true)
+      .checkWellFormed()
   }
 
 // ---------- Updates ------------------------------------------------------------
@@ -591,30 +595,33 @@ class OrderingConstraint(private val boundsMap: ParamBounds,
     if param == replacement then this.checkWellFormed()
     else
       assert(replacement.isValueTypeOrLambda)
-      var current =
-        if isRemovable(param.binder) then remove(param.binder)
-        else updateEntry(this, param, replacement)
 
-      def removeParam(ps: List[TypeParamRef]) = ps.filterConserve(param ne _)
+      val droppedTypeVar = typeVarOfParam(param)
 
-      def replaceParam(entry: Type, atPoly: TypeLambda, atIdx: Int): Type =
-        val pref = atPoly.paramRefs(atIdx)
-        val newEntry = current.ensureNonCyclic(pref, entry.substParam(param, replacement))
-        adjustDeps(newEntry, entry, pref)
-        newEntry
+      //println(i"replace $param, $droppedTypeVar with $replacement in $this")
+      val dropTypeVar = new TypeMap:
+        override def apply(t: Type): Type =
+          if t.exists && (t eq droppedTypeVar) then param else mapOver(t)
 
+      var current = this
+
+      def removeParam(ps: List[TypeParamRef]) = ps.filterConserve(param ne _)
       for lo <- lower(param) do
         current = upperLens.map(this, current, lo, removeParam)
       for hi <- upper(param) do
         current = lowerLens.map(this, current, hi, removeParam)
 
       current.foreachParam { (p, i) =>
-        current = boundsLens.map(this, current, p, i,
-          entry =>
-            val newEntry = replaceParam(entry, p, i)
-            adjustDeps(newEntry, entry, p.paramRefs(i))
-            newEntry)
+        val other = p.paramRefs(i)
+        if other != param then
+          val oldEntry = current.entry(other)
+          val newEntry = current.ensureNonCyclic(other, oldEntry.substParam(param, replacement))
+          current = updateEntryNoOrdering(current, other, newEntry, dropTypeVar(oldEntry))
       }
+
+      current =
+        if isRemovable(param.binder) then current.remove(param.binder)
+        else updateEntry(current, param, replacement)
       current.dropDeps(param)
       current.checkWellFormed()
   end replace

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

@@ -193,7 +193,7 @@ object Substituters:
     def apply(tp: Type): Type = substRecThis(tp, from, to, this)(using mapCtx)
   }
 
-  final class SubstParamMap(from: ParamRef, to: Type)(using Context) extends DeepTypeMap, IdempotentCaptRefMap {
+  class SubstParamMap(from: ParamRef, to: Type)(using Context) extends DeepTypeMap, IdempotentCaptRefMap {
     def apply(tp: Type): Type = substParam(tp, from, to, this)(using mapCtx)
   }
 

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

@@ -5497,8 +5497,21 @@ object Types {
         stop == StopAt.Static && tp.currentSymbol.isStatic && isStaticPrefix(tp.prefix)
         || stop == StopAt.Package && tp.currentSymbol.is(Package)
       }
+
+    protected def tyconTypeParams(tp: AppliedType)(using Context): List[ParamInfo] =
+      tp.tyconTypeParams
   end VariantTraversal
 
+  trait ConstraintAwareTraversal extends VariantTraversal:
+    override def tyconTypeParams(tp: AppliedType)(using Context): List[ParamInfo] =
+      tp.tycon match
+        case tycon: TypeParamRef =>
+          ctx.typerState.constraint.entry(tycon) match
+            case _: TypeBounds =>
+            case tp1 => if tp1.typeParams.nonEmpty then return tp1.typeParams
+        case _ =>
+      tp.tyconTypeParams
+
   /** A supertrait for some typemaps that are bijections. Used for capture checking.
    *  BiTypeMaps should map capture references to capture references.
    */
@@ -5614,7 +5627,7 @@ object Types {
             derivedSelect(tp, prefix1)
 
         case tp: AppliedType =>
-          derivedAppliedType(tp, this(tp.tycon), mapArgs(tp.args, tp.tyconTypeParams))
+          derivedAppliedType(tp, this(tp.tycon), mapArgs(tp.args, tyconTypeParams(tp)))
 
         case tp: LambdaType =>
           mapOverLambda(tp)
@@ -5941,7 +5954,7 @@ object Types {
               case nil =>
                 true
             }
-            if (distributeArgs(args, tp.tyconTypeParams))
+            if (distributeArgs(args, tyconTypeParams(tp)))
               range(tp.derivedAppliedType(tycon, loBuf.toList),
                     tp.derivedAppliedType(tycon, hiBuf.toList))
             else if tycon.isLambdaSub || args.exists(isRangeOfNonTermTypes) then
@@ -6087,7 +6100,7 @@ object Types {
             }
             foldArgs(acc, tparams.tail, args.tail)
           }
-        foldArgs(this(x, tycon), tp.tyconTypeParams, args)
+        foldArgs(this(x, tycon), tyconTypeParams(tp), args)
 
       case _: BoundType | _: ThisType => x