Catch stale references

If a NamedType was denoted a SymDenotation one run, but stops being defined in the next, throw a staleSymbol error.

3 files changed, 10 insertions, 7 deletions

diff --git a/src/dotty/tools/dotc/core/Denotations.scala b/src/dotty/tools/dotc/core/Denotations.scala
index e6d5023e5..90a6a373c 100644
--- a/src/dotty/tools/dotc/core/Denotations.scala
+++ b/src/dotty/tools/dotc/core/Denotations.scala
@@ -479,7 +479,7 @@ object Denotations {
           } while (d ne denot)
           initial.copyIfParentInvalid
         case _ =>
-          throw new Error(s"stale symbol; $this, defined in run ${valid.runId} is referred to in run ${currentPeriod.runId}")
+          staleSymbolError
       }
       if (valid.runId != currentPeriod.runId) bringForward.current
       else {
@@ -523,6 +523,9 @@ object Denotations {
       }
     }
 
+    def staleSymbolError(implicit ctx: Context) =
+      throw new Error(s"stale symbol; $this, defined in run ${myValidFor.runId} is referred to in run ${ctx.period.runId}")
+
     /** For ClassDenotations only:
      *  If caches influenced by parent classes are still valid, the denotation
      *  itself, otherwise a freshly initialized copy.
diff --git a/src/dotty/tools/dotc/core/Types.scala b/src/dotty/tools/dotc/core/Types.scala
index 2a6a5017f..28a7f9e67 100644
--- a/src/dotty/tools/dotc/core/Types.scala
+++ b/src/dotty/tools/dotc/core/Types.scala
@@ -1018,8 +1018,12 @@ object Types {
         case null =>
           val sym = lastSymbol
           if (sym == null) loadDenot else denotOfSym(sym)
-        case d: SymDenotation if ctx.stillValid(d) =>
-          d.current
+        case d: SymDenotation =>
+          if (ctx.stillValid(d)) d.current
+          else {
+            val newd = loadDenot
+            if (newd.exists) newd else d.staleSymbolError
+          }
         case d =>
           if (d.validFor.runId == ctx.period.runId) d.current
           else loadDenot
diff --git a/src/dotty/tools/dotc/typer/Inferencing.scala b/src/dotty/tools/dotc/typer/Inferencing.scala
index a153f9066..868276598 100644
--- a/src/dotty/tools/dotc/typer/Inferencing.scala
+++ b/src/dotty/tools/dotc/typer/Inferencing.scala
@@ -204,10 +204,6 @@ object Inferencing {
    */
   abstract case class ViewProto(argType: Type, override val resultType: Type)(implicit ctx: Context)
   extends CachedGroundType with ApplyingProto {
- //   def lookingForInfo = resultType match {
- //     case rt: SelectionProto => rt.name.toString == "info"
- //     case _ => false
- //   }
     def isMatchedBy(tp: Type)(implicit ctx: Context): Boolean = /*ctx.conditionalTraceIndented(lookingForInfo, i"?.info isMatchedBy $tp ${tp.getClass}")*/ {
   	  ctx.typer.isApplicable(tp, argType :: Nil, resultType)
     }