Avoid hoisting local classes

The patch disables hoisting of classes local to a block into the
result type of the block.

Instead, we widen the result type of the block to one which reflects
all refinements made to the parents type of the local class.

Test cases in avoid.scala, t1569.scala.

The original t1569.scala no longer works. Why is explained in neg/t1569-failedAvoid.scala

2 files changed, 16 insertions, 11 deletions

diff --git a/src/dotty/tools/dotc/typer/TypeAssigner.scala b/src/dotty/tools/dotc/typer/TypeAssigner.scala
index ccf67b55b..cb6fefab1 100644
--- a/src/dotty/tools/dotc/typer/TypeAssigner.scala
+++ b/src/dotty/tools/dotc/typer/TypeAssigner.scala
@@ -49,7 +49,21 @@ trait TypeAssigner {
             case TypeAlias(ref) =>
               apply(ref)
             case info: ClassInfo =>
-              mapOver(info.instantiatedParents.reduceLeft(ctx.typeComparer.andType(_, _)))
+              val parentType = info.instantiatedParents.reduceLeft(ctx.typeComparer.andType(_, _))
+              def addRefinement(parent: Type, decl: Symbol) = {
+                val inherited = parentType.findMember(decl.name, info.cls.thisType, Private)
+                val inheritedInfo = inherited.atSignature(decl.info .signature).info
+                if (inheritedInfo.exists && decl.info <:< inheritedInfo && !(inheritedInfo <:< decl.info))
+                  typr.echo(
+                    i"add ref $parent $decl --> ",
+                    RefinedType(parent, decl.name, decl.info))
+                else
+                  parent
+              }
+              val refinableDecls = info.decls.filterNot(
+                sym => sym.is(TypeParamAccessor | Private) || sym.isConstructor)
+              val fullType = (parentType /: refinableDecls)(addRefinement)
+              mapOver(fullType)
             case _ =>
               mapOver(tp)
           }
diff --git a/src/dotty/tools/dotc/typer/Typer.scala b/src/dotty/tools/dotc/typer/Typer.scala
index 80eb5965c..1cab2fa46 100644
--- a/src/dotty/tools/dotc/typer/Typer.scala
+++ b/src/dotty/tools/dotc/typer/Typer.scala
@@ -415,17 +415,8 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
   def escapingRefs(block: Block)(implicit ctx: Context): collection.Set[NamedType] = {
     var hoisted: Set[Symbol] = Set()
     lazy val locals = localSyms(block.stats).toSet
-    def isLocal(sym: Symbol): Boolean =
-      (locals contains sym) && !isHoistableClass(sym)
-    def isHoistableClass(sym: Symbol) =
-      sym.isClass && {
-        (hoisted contains sym) || {
-          hoisted += sym
-          !classLeaks(sym.asClass)
-        }
-      }
     def leakingTypes(tp: Type): collection.Set[NamedType] =
-      tp namedPartsWith (tp => isLocal(tp.symbol))
+      tp namedPartsWith (tp => locals.contains(tp.symbol))
     def typeLeaks(tp: Type): Boolean = leakingTypes(tp).nonEmpty
     def classLeaks(sym: ClassSymbol): Boolean =
       (ctx.owner is Method) || // can't hoist classes out of method bodies