Corrects behavior of finalResultType.

The implementation had come to depend on finalResultType
accidentally doing things beyond its charter - in particular,
widening types. After hunting down and fixing the call sites
depending on the bugs, I was able to rewrite the method to do
only what it's supposed to do.

I threw in a different way of writing it entirely to suggest how
some correctness might be obtained in the future. It's a lot
harder for a method written like this to break.

7 files changed, 12 insertions, 11 deletions

diff --git a/src/compiler/scala/tools/nsc/ast/TreeDSL.scala b/src/compiler/scala/tools/nsc/ast/TreeDSL.scala
index d7a32c3be0..53304bee30 100644
--- a/src/compiler/scala/tools/nsc/ast/TreeDSL.scala
+++ b/src/compiler/scala/tools/nsc/ast/TreeDSL.scala
@@ -192,7 +192,7 @@ trait TreeDSL {
     }
 
     class DefSymStart(val sym: Symbol) extends SymVODDStart with DefCreator {
-      def symType  = sym.tpe.finalResultType
+      def symType  = sym.tpe_*.finalResultType
       def tparams  = sym.typeParams map TypeDef
       def vparamss = mapParamss(sym)(ValDef)
     }
diff --git a/src/compiler/scala/tools/nsc/transform/Erasure.scala b/src/compiler/scala/tools/nsc/transform/Erasure.scala
index c74fc620ca..48eb570654 100644
--- a/src/compiler/scala/tools/nsc/transform/Erasure.scala
+++ b/src/compiler/scala/tools/nsc/transform/Erasure.scala
@@ -268,7 +268,7 @@ abstract class Erasure extends AddInterfaces
             else abbrvTag(sym).toString
           }
           else if (sym.isDerivedValueClass) {
-            val unboxed     = sym.derivedValueClassUnbox.info.finalResultType
+            val unboxed     = sym.derivedValueClassUnbox.tpe_*.finalResultType
             val unboxedSeen = (tp memberType sym.derivedValueClassUnbox).finalResultType
             def unboxedMsg  = if (unboxed == unboxedSeen) "" else s", seen within ${sym.simpleName} as $unboxedSeen"
             logResult(s"Erasure of value class $sym (underlying type $unboxed$unboxedMsg) is") {
diff --git a/src/compiler/scala/tools/nsc/transform/ExtensionMethods.scala b/src/compiler/scala/tools/nsc/transform/ExtensionMethods.scala
index 1c32721444..ca8065b519 100644
--- a/src/compiler/scala/tools/nsc/transform/ExtensionMethods.scala
+++ b/src/compiler/scala/tools/nsc/transform/ExtensionMethods.scala
@@ -234,7 +234,7 @@ abstract class ExtensionMethods extends Transform with TypingTransformers {
             if (extensionBody.tpe <:< extensionMono.finalResultType)
               extensionBody
             else
-              gen.mkCastPreservingAnnotations(extensionBody, extensionMono.finalResultType) // SI-7818 e.g. mismatched existential skolems        
+              gen.mkCastPreservingAnnotations(extensionBody, extensionMono.finalResultType) // SI-7818 e.g. mismatched existential skolems
 
           // Record the extension method. Later, in `Extender#transformStats`, these will be added to the companion object.
           extensionDefs(companion) += atPos(tree.pos)(DefDef(extensionMeth, castBody))
diff --git a/src/compiler/scala/tools/nsc/transform/TailCalls.scala b/src/compiler/scala/tools/nsc/transform/TailCalls.scala
index 6f422fcc90..b471d16ddd 100644
--- a/src/compiler/scala/tools/nsc/transform/TailCalls.scala
+++ b/src/compiler/scala/tools/nsc/transform/TailCalls.scala
@@ -156,7 +156,7 @@ abstract class TailCalls extends Transform {
       private def mkLabel() = {
         val label     = method.newLabel(newTermName("_" + method.name), method.pos)
         val thisParam = method.newSyntheticValueParam(currentClass.typeOfThis)
-        label setInfo MethodType(thisParam :: method.tpe.params, method.tpe.finalResultType)
+        label setInfo MethodType(thisParam :: method.tpe.params, method.tpe_*.finalResultType)
         if (isEligible)
           label substInfo (method.tpe.typeParams, tparams)
 
diff --git a/src/compiler/scala/tools/nsc/transform/UnCurry.scala b/src/compiler/scala/tools/nsc/transform/UnCurry.scala
index 16c803e2e8..93a36f8f01 100644
--- a/src/compiler/scala/tools/nsc/transform/UnCurry.scala
+++ b/src/compiler/scala/tools/nsc/transform/UnCurry.scala
@@ -158,11 +158,12 @@ abstract class UnCurry extends InfoTransform
      */
     private def nonLocalReturnTry(body: Tree, key: Symbol, meth: Symbol) = {
       localTyper typed {
-        val extpe   = nonLocalReturnExceptionType(meth.tpe.finalResultType)
+        val restpe  = meth.tpe_*.finalResultType
+        val extpe   = nonLocalReturnExceptionType(restpe)
         val ex      = meth.newValue(nme.ex, body.pos) setInfo extpe
-        val argType = meth.tpe.finalResultType withAnnotation (AnnotationInfo marker UncheckedClass.tpe)
+        val argType = restpe withAnnotation (AnnotationInfo marker UncheckedClass.tpe)
         val pat     = gen.mkBindForCase(ex, NonLocalReturnControlClass, List(argType))
-        val rhs = (
+        val rhs     = (
           IF   ((ex DOT nme.key)() OBJ_EQ Ident(key))
           THEN ((ex DOT nme.value)())
           ELSE (Throw(Ident(ex)))
@@ -739,7 +740,7 @@ abstract class UnCurry extends InfoTransform
         case p if rpsymbols(p.symbol) => toArrayType(p.symbol.tpe)
         case p                        => p.symbol.tpe
       }
-      val forwresult = dd.symbol.tpe.finalResultType
+      val forwresult = dd.symbol.tpe_*.finalResultType
       val forwformsyms = map2(forwformals, flatparams)((tp, oldparam) =>
         currentClass.newValueParameter(oldparam.name, oldparam.symbol.pos).setInfo(tp)
       )
diff --git a/src/compiler/scala/tools/nsc/typechecker/MethodSynthesis.scala b/src/compiler/scala/tools/nsc/typechecker/MethodSynthesis.scala
index 263b5ad784..787c7ebf63 100644
--- a/src/compiler/scala/tools/nsc/typechecker/MethodSynthesis.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/MethodSynthesis.scala
@@ -413,7 +413,7 @@ trait MethodSynthesis {
         // starts compiling (instead of failing like it's supposed to) because the typer
         // expects to be able to identify escaping locals in typedDefDef, and fails to
         // spot that brand of them. In other words it's an artifact of the implementation.
-        val tpt = atPos(derivedSym.pos.focus)(derivedSym.tpe.finalResultType match {
+        val tpt = atPos(derivedSym.pos.focus)(derivedSym.tpe_*.finalResultType.widen match {
           case ExistentialType(_, _)  => TypeTree()
           case _ if mods.isDeferred   => TypeTree()
           case tp                     => TypeTree(tp)
diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index 629513ada3..1f5ad3534e 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -363,7 +363,7 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
           check(owner, scope, pt, tree setType tp1.typeSymbol.classBound)
         else if (owner == NoSymbol)
           tree setType packSymbols(hiddenSymbols.reverse, tp1)
-        else if (!phase.erasedTypes) { // privates
+        else if (!isPastTyper) { // privates
           val badSymbol = hiddenSymbols.head
           SymbolEscapesScopeError(tree, badSymbol)
         } else tree
@@ -2103,7 +2103,7 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
         case PolyType(_, restpe)        => paramssTypes(restpe)
         case _                          => Nil
       }
-      def resultType = meth.tpe.finalResultType
+      def resultType = meth.tpe_*.finalResultType
       def nthParamPos(n1: Int, n2: Int) =
         try ddef.vparamss(n1)(n2).pos catch { case _: IndexOutOfBoundsException => meth.pos }