Merge pull request #2045 from dotty-staging/fix-hlist-hmap

Fix type inference for HLists and HMaps

7 files changed, 48 insertions, 30 deletions

diff --git a/compiler/src/dotty/tools/dotc/core/Constraint.scala b/compiler/src/dotty/tools/dotc/core/Constraint.scala
index c99b748b7..50136a26c 100644
--- a/compiler/src/dotty/tools/dotc/core/Constraint.scala
+++ b/compiler/src/dotty/tools/dotc/core/Constraint.scala
@@ -111,12 +111,6 @@ abstract class Constraint extends Showable {
    */
   def replace(param: PolyParam, tp: Type)(implicit ctx: Context): This
 
-  /** Narrow one of the bounds of type parameter `param`
-   *  If `isUpper` is true, ensure that `param <: `bound`, otherwise ensure
-   *  that `param >: bound`.
-   */
-  def narrowBound(param: PolyParam, bound: Type, isUpper: Boolean)(implicit ctx: Context): This
-
   /** Is entry associated with `pt` removable? This is the case if
    *  all type parameters of the entry are associated with type variables
    *  which have their `inst` fields set.
diff --git a/compiler/src/dotty/tools/dotc/core/ConstraintHandling.scala b/compiler/src/dotty/tools/dotc/core/ConstraintHandling.scala
index b3c50fb71..2a1f4ee6e 100644
--- a/compiler/src/dotty/tools/dotc/core/ConstraintHandling.scala
+++ b/compiler/src/dotty/tools/dotc/core/ConstraintHandling.scala
@@ -44,6 +44,13 @@ trait ConstraintHandling {
     try op finally alwaysFluid = saved
   }
 
+  /** If set, align arguments `S1`, `S2`when taking the glb
+   *  `T1 { X = S1 } & T2 { X = S2 }` of a constraint upper bound for some type parameter.
+   *  Aligning means computing `S1 =:= S2` which may change the current constraint.
+   *  See note in TypeComparer#distributeAnd.
+   */
+  protected var homogenizeArgs = false
+
   /** We are currently comparing polytypes. Used as a flag for
    *  optimization: when `false`, no need to do an expensive `pruneLambdaParams`
    */
@@ -64,7 +71,8 @@ trait ConstraintHandling {
       }
       if (Config.checkConstraintsSeparated)
         assert(!occursIn(bound), s"$param occurs in $bound")
-      val c1 = constraint.narrowBound(param, bound, isUpper)
+      val newBound = narrowedBound(param, bound, isUpper)
+      val c1 = constraint.updateEntry(param, newBound)
       (c1 eq constraint) || {
         constraint = c1
         val TypeBounds(lo, hi) = constraint.entry(param)
@@ -72,6 +80,20 @@ trait ConstraintHandling {
       }
     }
 
+  /** Narrow one of the bounds of type parameter `param`
+   *  If `isUpper` is true, ensure that `param <: `bound`, otherwise ensure
+   *  that `param >: bound`.
+   */
+  def narrowedBound(param: PolyParam, bound: Type, isUpper: Boolean)(implicit ctx: Context): TypeBounds = {
+    val oldBounds @ TypeBounds(lo, hi) = constraint.nonParamBounds(param)
+    val saved = homogenizeArgs
+    homogenizeArgs = Config.alignArgsInAnd
+    try
+      if (isUpper) oldBounds.derivedTypeBounds(lo, hi & bound)
+      else oldBounds.derivedTypeBounds(lo | bound, hi)
+    finally homogenizeArgs = saved
+  }
+
   protected def addUpperBound(param: PolyParam, bound: Type): Boolean = {
     def description = i"constraint $param <: $bound to\n$constraint"
     if (bound.isRef(defn.NothingClass) && ctx.typerState.isGlobalCommittable) {
diff --git a/compiler/src/dotty/tools/dotc/core/Definitions.scala b/compiler/src/dotty/tools/dotc/core/Definitions.scala
index 1be47c1da..4d4350f98 100644
--- a/compiler/src/dotty/tools/dotc/core/Definitions.scala
+++ b/compiler/src/dotty/tools/dotc/core/Definitions.scala
@@ -355,6 +355,7 @@ class Definitions {
     enterCompleteClassSymbol(
       ScalaPackageClass, tpnme.Singleton, PureInterfaceCreationFlags | Final,
       List(AnyClass.typeRef), EmptyScope)
+  def SingletonType = SingletonClass.typeRef
 
   lazy val SeqType: TypeRef = ctx.requiredClassRef("scala.collection.Seq")
   def SeqClass(implicit ctx: Context) = SeqType.symbol.asClass
diff --git a/compiler/src/dotty/tools/dotc/core/OrderingConstraint.scala b/compiler/src/dotty/tools/dotc/core/OrderingConstraint.scala
index 72c7a8e51..61dd5a445 100644
--- a/compiler/src/dotty/tools/dotc/core/OrderingConstraint.scala
+++ b/compiler/src/dotty/tools/dotc/core/OrderingConstraint.scala
@@ -354,14 +354,6 @@ class OrderingConstraint(private val boundsMap: ParamBounds,
     updateEntry(p1, p1Bounds).replace(p2, p1)
   }
 
-  def narrowBound(param: PolyParam, bound: Type, isUpper: Boolean)(implicit ctx: Context): This = {
-    val oldBounds @ TypeBounds(lo, hi) = nonParamBounds(param)
-    val newBounds =
-      if (isUpper) oldBounds.derivedTypeBounds(lo, hi & bound)
-      else oldBounds.derivedTypeBounds(lo | bound, hi)
-    updateEntry(param, newBounds)
-  }
-
 // ---------- Removals ------------------------------------------------------------
 
   /** A new constraint which is derived from this constraint by removing
diff --git a/compiler/src/dotty/tools/dotc/core/StdNames.scala b/compiler/src/dotty/tools/dotc/core/StdNames.scala
index 766e3733f..5b7dc3d1d 100644
--- a/compiler/src/dotty/tools/dotc/core/StdNames.scala
+++ b/compiler/src/dotty/tools/dotc/core/StdNames.scala
@@ -97,6 +97,7 @@ object StdNames {
     val EMPTY: N                      = ""
     val EMPTY_PACKAGE: N              = Names.EMPTY_PACKAGE.toString
     val EVIDENCE_PARAM_PREFIX: N      = "evidence$"
+    val DEP_PARAM_PREFIX              = "<param>"
     val EXCEPTION_RESULT_PREFIX: N    = "exceptionResult"
     val EXPAND_SEPARATOR: N           = "$$"
     val IMPL_CLASS_SUFFIX: N          = "$class"
diff --git a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
index b97dfe684..b61fccf31 100644
--- a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
+++ b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
@@ -1300,23 +1300,28 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
     case tp1: RefinedType =>
       tp2 match {
         case tp2: RefinedType if tp1.refinedName == tp2.refinedName =>
-          // Given two refinements `T1 { X = S1 }` and `T2 { X = S2 }`, if `S1 =:= S2`
-          // (possibly by instantiating type parameters), rewrite to `T1 & T2 { X = S1 }`.
-          // Otherwise rewrite to `T1 & T2 { X B }` where `B` is the conjunction of
-          // the bounds of `X` in `T1` and `T2`.
-          // The first rule above is contentious because it cuts the constraint set.
-          // But without it we would replace the two aliases by
-          // `T { X >: S1 | S2 <: S1 & S2 }`, which looks weird and is probably
-          // not what's intended.
+          // Given two refinements `T1 { X = S1 }` and `T2 { X = S2 }` rewrite to
+          // `T1 & T2 { X B }` where `B` is the conjunction of the bounds of `X` in `T1` and `T2`.
+          //
+          // However, if `homogenizeArgs` is set, and both aliases `X = Si` are
+          // nonvariant, and `S1 =:= S2` (possibly by instantiating type parameters),
+          // rewrite instead to `T1 & T2 { X = S1 }`. This rule is contentious because
+          // it cuts the constraint set. On the other hand, without it we would replace
+          // the two aliases by `T { X >: S1 | S2 <: S1 & S2 }`, which looks weird
+          // and is probably not what's intended.
           val rinfo1 = tp1.refinedInfo
           val rinfo2 = tp2.refinedInfo
           val parent = tp1.parent & tp2.parent
-          val rinfo =
-            if (rinfo1.isAlias && rinfo2.isAlias && isSameType(rinfo1, rinfo2))
-              rinfo1
-            else
-              rinfo1 & rinfo2
-          tp1.derivedRefinedType(parent, tp1.refinedName, rinfo)
+
+          def isNonvariantAlias(tp: Type) = tp match {
+            case tp: TypeAlias => tp.variance == 0
+            case _ => false
+          }
+          if (homogenizeArgs &&
+              isNonvariantAlias(rinfo1) && isNonvariantAlias(rinfo2))
+            isSameType(rinfo1, rinfo2) // establish new constraint
+
+          tp1.derivedRefinedType(parent, tp1.refinedName, rinfo1 & rinfo2)
         case _ =>
           NoType
       }
diff --git a/compiler/src/dotty/tools/dotc/core/Types.scala b/compiler/src/dotty/tools/dotc/core/Types.scala
index cb462af45..546473b68 100644
--- a/compiler/src/dotty/tools/dotc/core/Types.scala
+++ b/compiler/src/dotty/tools/dotc/core/Types.scala
@@ -1681,7 +1681,10 @@ object Types {
           }
         else newLikeThis(prefix)
       }
-      else newLikeThis(prefix)
+      else prefix match {
+        case _: WildcardType => WildcardType
+        case _ => newLikeThis(prefix)
+      }
 
     /** Create a NamedType of the same kind as this type, but with a new prefix.
      */