Drop traces of previous dependency checking which was based on levels

Author: odersky

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

@@ -188,16 +188,6 @@ abstract class Constraint extends Showable {
    */
   def dependsOn(tv: TypeVar, except: TypeVars, co: Boolean)(using Context): Boolean
 
-  /** If the type variable `tv` would be instantiated to a larger type, the
-   *  constraint over outer type variables would be narrowed.
-   */
-  def outerDependsCovariantlyOn(tv: TypeVar)(using Context): Boolean
-
-  /** If the type variable `tv` would be instantiated to a smaller type, the
-   *  constraint over outer type variables would be narrowed.
-   */
-  def outerDependsContravariantlyOn(tv: TypeVar)(using Context): Boolean
-
   /** Check that no constrained parameter contains itself as a bound */
   def checkNonCyclic()(using Context): this.type
 

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

@@ -227,28 +227,6 @@ class OrderingConstraint(private val boundsMap: ParamBounds,
 
   var coDeps, contraDeps: TypeVarDeps = SimpleIdentityMap.empty
 
-  private def outerDependsOn(tv: TypeVar, nestingLevel: Int, deps: TypeVarDeps, lens: ConstraintLens[List[TypeParamRef]], seen: TypeVars)(using Context): Boolean =
-
-    def qualifies(tp: Type): Boolean = tp match
-      case tv1: TypeVar =>
-        tv1.nestingLevel < tv.nestingLevel
-        || tv1.nestingLevel == tv.nestingLevel && tv.origin.paramName.is(DepParamName)
-            // dependent parameters get created at the same nesting level as the current constraint,
-            // but are logically nested inside the variables of the expected result type.
-        || outerDependsOn(tv1, nestingLevel, deps, lens, seen + tv)
-      case tp: TypeParamRef =>
-        qualifies(typeVarOfParam(tp))
-      case _ =>
-        false
-
-    val tvdeps = deps(tv)
-    null != tvdeps
-    && !seen.contains(tv)
-    && (tvdeps.exists(qualifies)
-        || lens(this, tv.origin.binder, tv.origin.paramNum).exists(qualifies))
-      //.showing(i"outer depends on $tv ${tv.initNestingLevel} with ${tvdeps.toList.map(_.initNestingLevel)}%, % = $result")
-  end outerDependsOn
-
   def dependsOn(tv: TypeVar, except: TypeVars, co: Boolean)(using Context): Boolean =
     def test(deps: TypeVarDeps, lens: ConstraintLens[List[TypeParamRef]]) =
       val tvdeps = deps(tv)
@@ -258,12 +236,6 @@ 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)
 
-  def outerDependsCovariantlyOn(tv: TypeVar)(using Context) =
-    outerDependsOn(tv, tv.nestingLevel, coDeps, upperLens, SimpleIdentitySet.empty)
-
-  def outerDependsContravariantlyOn(tv: TypeVar)(using Context) =
-    outerDependsOn(tv, tv.nestingLevel, contraDeps, lowerLens, SimpleIdentitySet.empty)
-
   private class Adjuster(tvar: TypeVar)(using Context) extends TypeTraverser:
     var add: Boolean = compiletime.uninitialized
 

compiler/src/dotty/tools/dotc/typer/Inferencing.scala

@@ -6,17 +6,15 @@ import core._
 import ast._
 import Contexts._, Types._, Flags._, Symbols._
 import ProtoTypes._
-import NameKinds.{AvoidNameKind, UniqueName}
+import NameKinds.UniqueName
 import util.Spans._
-import util.{Stats, SimpleIdentityMap, SrcPos}
+import util.{Stats, SimpleIdentityMap, SimpleIdentitySet, SrcPos}
 import Decorators._
 import config.Printers.{gadts, typr}
 import annotation.tailrec
 import reporting._
 import collection.mutable
-
 import scala.annotation.internal.sharable
-import dotty.tools.dotc.util.SimpleIdentitySet
 
 object Inferencing {
 
@@ -629,22 +627,6 @@ trait Inferencing { this: Typer =>
             // instantiated `tvar` through unification.
             val v = vs(tvar)
             if v == null then
-              // Even though `tvar` is non-occurring in `v`, the specific
-              // instantiation we pick still matters because `tvar` might appear
-              // in the bounds of a non-`qualifying` type variable in the
-              // constraint.
-              // In particular, if `tvar` was created as the upper or lower
-              // bound of an existing variable by `LevelAvoidMap`, we
-              // instantiate it in the direction corresponding to the
-              // original variable which might be further constrained later.
-              // Otherwise, we simply rely on `hasLowerBound`.
-              //val name = tvar.origin.paramName
-              //val fromBelow =
-              //  if name.is(AvoidNameKind.UpperBound) then true
-              //  else if name.is(AvoidNameKind.LowerBound) then false
-              //  else if constraint.outerDependsCovariantlyOn(tvar) then true
-              //  else if constraint.outerDependsContravariantlyOn(tvar) then false
-              //  else tvar.hasLowerBound
               toInstantiate += ((tvar, 0))
             else if v.intValue != 0 then
               toInstantiate += ((tvar, v.intValue))
@@ -699,23 +681,8 @@ trait Inferencing { this: Typer =>
                 if v == 0 then
                   val aboveOK = !constraint.dependsOn(tvar, varsToInstantiate, co = true)
                   val belowOK = !constraint.dependsOn(tvar, varsToInstantiate, co = false)
-                  val now =
-                    if aboveOK == belowOK then tvar.hasLowerBound
-                    else belowOK
-/*
-                  val was =
-                    val name = tvar.origin.paramName
-                    val depCo = constraint.outerDependsCovariantlyOn(tvar)
-                    val depContra = constraint.outerDependsContravariantlyOn(tvar)
-                    if name.is(AvoidNameKind.UpperBound) then true
-                    else if name.is(AvoidNameKind.LowerBound) then false
-                    else if constraint.outerDependsCovariantlyOn(tvar) then true
-                    else if constraint.outerDependsContravariantlyOn(tvar) then false
-                    else tvar.hasLowerBound
-                  if now != was then
-                    println(i"diff for $tvar, was $was, aboveOK = $aboveOK, belowOK = $belowOK, depCo = $depCo, depContra = $depContra")
-*/
-                  now
+                  if aboveOK == belowOK then tvar.hasLowerBound
+                  else belowOK
                 else
                   v == 1
               typr.println(