Fix phase of context for denotation transformer

The phase is now always the phase on which the denotation transformer is defined.

Author: odersky

src/dotty/tools/dotc/core/Contexts.scala

@@ -280,6 +280,11 @@ object Contexts {
     final def withMode(mode: Mode): Context =
       if (mode != this.mode) fresh.withNewMode(mode) else this
 
+    def withPhase(phase: PhaseId): Context =
+      if (this.phaseId == phaseId) this else fresh.withPhase(phase)
+    def withPhase(phase: Phase): Context =
+      withPhase(phase.id)
+
     final def addMode(mode: Mode): Context = withMode(this.mode | mode)
     final def maskMode(mode: Mode): Context = withMode(this.mode & mode)
     final def retractMode(mode: Mode): Context = withMode(this.mode &~ mode)
@@ -324,8 +329,7 @@ object Contexts {
 
     def withProperty(prop: (String, Any)): this.type = withMoreProperties(moreProperties + prop)
 
-    def withPhase(pid: PhaseId): this.type = withPeriod(Period(runId, pid))
-    def withPhase(phase: Phase): this.type = withPhase(phase.id)
+    override def withPhase(pid: PhaseId): this.type = withPeriod(Period(runId, pid))
 
     def withSetting[T](setting: Setting[T], value: T): this.type =
       withSettings(setting.updateIn(sstate, value))

src/dotty/tools/dotc/core/Denotations.scala

@@ -524,7 +524,7 @@ object Denotations {
             val transformer = ctx.denotTransformers(nextTranformerId)
             //println(s"transforming with $transformer")
             if (currentPeriod.lastPhaseId > transformer.id)
-              next = transformer.transform(cur).syncWithParents
+              next = transformer.transform(cur)(ctx.withPhase(startPid)).syncWithParents
             if (next eq cur)
               startPid = cur.validFor.firstPhaseId
             else {