Merge pull request #1482 from dotty-staging/fix-asapplicable-safe

More tweaks to type inference

5 files changed, 65 insertions, 25 deletions

diff --git a/src/dotty/tools/dotc/core/Constraint.scala b/src/dotty/tools/dotc/core/Constraint.scala
index 436b035dc..99b4af0a9 100644
--- a/src/dotty/tools/dotc/core/Constraint.scala
+++ b/src/dotty/tools/dotc/core/Constraint.scala
@@ -143,6 +143,9 @@ abstract class Constraint extends Showable {
   /** The uninstantiated typevars of this constraint */
   def uninstVars: collection.Seq[TypeVar]
 
+  /** The weakest constraint that subsumes both this constraint and `other` */
+  def & (other: Constraint)(implicit ctx: Context): Constraint
+
   /** Check that no constrained parameter contains itself as a bound */
   def checkNonCyclic()(implicit ctx: Context): Unit
 
diff --git a/src/dotty/tools/dotc/core/OrderingConstraint.scala b/src/dotty/tools/dotc/core/OrderingConstraint.scala
index b0170b67c..e7e388be9 100644
--- a/src/dotty/tools/dotc/core/OrderingConstraint.scala
+++ b/src/dotty/tools/dotc/core/OrderingConstraint.scala
@@ -15,11 +15,13 @@ import annotation.tailrec
 
 object OrderingConstraint {
 
+  type ArrayValuedMap[T] = SimpleMap[GenericType, Array[T]]
+
   /** The type of `OrderingConstraint#boundsMap` */
-  type ParamBounds = SimpleMap[GenericType, Array[Type]]
+  type ParamBounds = ArrayValuedMap[Type]
 
   /** The type of `OrderingConstraint#lowerMap`, `OrderingConstraint#upperMap` */
-  type ParamOrdering = SimpleMap[GenericType, Array[List[PolyParam]]]
+  type ParamOrdering = ArrayValuedMap[List[PolyParam]]
 
   /** A new constraint with given maps */
   private def newConstraint(boundsMap: ParamBounds, lowerMap: ParamOrdering, upperMap: ParamOrdering)(implicit ctx: Context) : OrderingConstraint = {
@@ -495,6 +497,44 @@ class OrderingConstraint(private val boundsMap: ParamBounds,
       }
     }
 
+  def & (other: Constraint)(implicit ctx: Context) = {
+    def merge[T](m1: ArrayValuedMap[T], m2: ArrayValuedMap[T], join: (T, T) => T): ArrayValuedMap[T] = {
+      var merged = m1
+      def mergeArrays(xs1: Array[T], xs2: Array[T]) = {
+        val xs = xs1.clone
+        for (i <- xs.indices) xs(i) = join(xs1(i), xs2(i))
+        xs
+      }
+      m2.foreachBinding { (poly, xs2) =>
+        merged = merged.updated(poly,
+            if (m1.contains(poly)) mergeArrays(m1(poly), xs2) else xs2)
+      }
+      merged
+    }
+
+    def mergeParams(ps1: List[PolyParam], ps2: List[PolyParam]) =
+      (ps1 /: ps2)((ps1, p2) => if (ps1.contains(p2)) ps1 else p2 :: ps1)
+
+    def mergeEntries(e1: Type, e2: Type): Type = e1 match {
+        case e1: TypeBounds =>
+          e2 match {
+            case e2: TypeBounds => e1 & e2
+            case _ if e1 contains e2 => e2
+            case _ => mergeError
+          }
+        case _ if e1 eq e2 => e1
+        case _ => mergeError
+    }
+
+    def mergeError = throw new AssertionError(i"cannot merge $this with $other")
+
+    val that = other.asInstanceOf[OrderingConstraint]
+    new OrderingConstraint(
+        merge(this.boundsMap, that.boundsMap, mergeEntries),
+        merge(this.lowerMap, that.lowerMap, mergeParams),
+        merge(this.upperMap, that.upperMap, mergeParams))
+  }
+
   override def checkClosed()(implicit ctx: Context): Unit = {
     def isFreePolyParam(tp: Type) = tp match {
       case PolyParam(binder: GenericType, _) => !contains(binder)
diff --git a/src/dotty/tools/dotc/core/TyperState.scala b/src/dotty/tools/dotc/core/TyperState.scala
index 69c35faf5..7b8867ccc 100644
--- a/src/dotty/tools/dotc/core/TyperState.scala
+++ b/src/dotty/tools/dotc/core/TyperState.scala
@@ -59,18 +59,10 @@ class TyperState(r: Reporter) extends DotClass with Showable {
   /** Commit state so that it gets propagated to enclosing context */
   def commit()(implicit ctx: Context): Unit = unsupported("commit")
 
-  /** The typer state has already been committed */
-  def isCommitted: Boolean = false
-
-  /** Optionally, if this is a mutable typerstate, it's creator state */
-  def parent: Option[TyperState] = None
-
   /** The closest ancestor of this typer state (including possibly this typer state itself)
    *  which is not yet committed, or which does not have a parent.
    */
-  def uncommittedAncestor: TyperState =
-    if (!isCommitted || !parent.isDefined) this
-    else parent.get.uncommittedAncestor
+  def uncommittedAncestor: TyperState = this
 
   /** Make type variable instances permanent by assigning to `inst` field if
    *  type variable instantiation cannot be retracted anymore. Then, remove
@@ -96,7 +88,8 @@ extends TyperState(r) {
 
   override def reporter = myReporter
 
-  private var myConstraint: Constraint = previous.constraint
+  private val previousConstraint = previous.constraint
+  private var myConstraint: Constraint = previousConstraint
 
   override def constraint = myConstraint
   override def constraint_=(c: Constraint)(implicit ctx: Context) = {
@@ -109,7 +102,6 @@ extends TyperState(r) {
   override def ephemeral = myEphemeral
   override def ephemeral_=(x: Boolean): Unit = { myEphemeral = x }
 
-
   override def fresh(isCommittable: Boolean): TyperState =
     new MutableTyperState(this, new StoreReporter(reporter), isCommittable)
 
@@ -120,6 +112,11 @@ extends TyperState(r) {
     isCommittable &&
     (!previous.isInstanceOf[MutableTyperState] || previous.isGlobalCommittable)
 
+  private var isCommitted = false
+
+  override def uncommittedAncestor: TyperState =
+    if (isCommitted) previous.uncommittedAncestor else this
+
   /** Commit typer state so that its information is copied into current typer state
    *  In addition (1) the owning state of undetermined or temporarily instantiated
    *  type variables changes from this typer state to the current one. (2) Variables
@@ -128,25 +125,20 @@ extends TyperState(r) {
    */
   override def commit()(implicit ctx: Context) = {
     val targetState = ctx.typerState
-    assert(targetState eq previous)
     assert(isCommittable)
-    targetState.constraint = constraint
+    targetState.constraint =
+      if (targetState.constraint eq previousConstraint) constraint
+      else targetState.constraint & constraint
     constraint foreachTypeVar { tvar =>
       if (tvar.owningState eq this)
         tvar.owningState = targetState
     }
-    targetState.ephemeral = ephemeral
+    targetState.ephemeral |= ephemeral
     targetState.gc()
     reporter.flush()
-    myIsCommitted = true
+    isCommitted = true
   }
 
-  private var myIsCommitted = false
-
-  override def isCommitted: Boolean = myIsCommitted
-
-  override def parent = Some(previous)
-
   override def gc()(implicit ctx: Context): Unit = {
     val toCollect = new mutable.ListBuffer[GenericType]
     constraint foreachTypeVar { tvar =>
diff --git a/src/dotty/tools/dotc/typer/Inferencing.scala b/src/dotty/tools/dotc/typer/Inferencing.scala
index 7c61f8c23..719e8d7fc 100644
--- a/src/dotty/tools/dotc/typer/Inferencing.scala
+++ b/src/dotty/tools/dotc/typer/Inferencing.scala
@@ -78,7 +78,8 @@ object Inferencing {
     def apply(x: Boolean, tp: Type): Boolean = tp.dealias match {
       case _: WildcardType | _: ProtoType =>
         false
-      case tvar: TypeVar if !tvar.isInstantiated =>
+      case tvar: TypeVar
+      if !tvar.isInstantiated && ctx.typerState.constraint.contains(tvar) =>
         force.appliesTo(tvar) && {
           val direction = instDirection(tvar.origin)
           if (direction != 0) {
diff --git a/src/dotty/tools/dotc/typer/Typer.scala b/src/dotty/tools/dotc/typer/Typer.scala
index f0086b0ab..fdcfe347b 100644
--- a/src/dotty/tools/dotc/typer/Typer.scala
+++ b/src/dotty/tools/dotc/typer/Typer.scala
@@ -895,7 +895,11 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
   }
 
   def typedSeqLiteral(tree: untpd.SeqLiteral, pt: Type)(implicit ctx: Context): SeqLiteral = track("typedSeqLiteral") {
-    val proto1 = pt.elemType orElse WildcardType
+    val proto1 = pt.elemType match {
+      case NoType => WildcardType
+      case bounds: TypeBounds => WildcardType(bounds)
+      case elemtp => elemtp
+    }
     val elems1 = tree.elems mapconserve (typed(_, proto1))
     val proto2 = // the computed type of the `elemtpt` field
       if (!tree.elemtpt.isEmpty) WildcardType