Merge pull request #4206 from dotty-staging/fix/checkedPeriod-cache

Fix denotation caching in NamedType

Author: smarter

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

@@ -1020,12 +1020,6 @@ object Denotations {
       interval
     }
 
-    /** For ClassDenotations only:
-     *  If caches influenced by parent classes are still valid, the denotation
-     *  itself, otherwise a freshly initialized copy.
-     */
-    def syncWithParents(implicit ctx: Context): SingleDenotation = this
-
     /** Show declaration string; useful for showing declarations
      *  as seen from subclasses.
      */

compiler/src/dotty/tools/dotc/core/Types.scala

@@ -1648,6 +1648,8 @@ object Types {
       }
 
     final def symbol(implicit ctx: Context): Symbol =
+      // We can rely on checkedPeriod (unlike in the definition of `denot` below)
+      // because SymDenotation#installAfter never changes the symbol
       if (checkedPeriod == ctx.period) lastSymbol else computeSymbol
 
     private def computeSymbol(implicit ctx: Context): Symbol =
@@ -1692,17 +1694,11 @@ object Types {
     /** The denotation currently denoted by this type */
     final def denot(implicit ctx: Context): Denotation = {
       val now = ctx.period
-      val lastd = lastDenotation
-      if (checkedPeriod == now) lastd else denotAt(lastd, now)
-    }
-
-    /** A first fall back to do a somewhat more expensive calculation in case the first
-     *  attempt in `denot` does not yield a denotation.
-     */
-    private def denotAt(lastd: Denotation, now: Period)(implicit ctx: Context): Denotation = {
-      if (checkedPeriod != Nowhere && lastd.validFor.contains(now)) {
+      // Even if checkedPeriod == now we still need to recheck lastDenotation.validFor
+      // as it may have been mutated by SymDenotation#installAfter
+      if (checkedPeriod != Nowhere && lastDenotation.validFor.contains(now)) {
         checkedPeriod = now
-        lastd
+        lastDenotation
       }
       else computeDenot
     }

compiler/src/dotty/tools/dotc/transform/ExtensionMethods.scala

@@ -108,7 +108,7 @@ class ExtensionMethods extends MiniPhase with DenotTransformer with FullParamete
           moduleClassSym
       }
     case ref: SymDenotation =>
-      if (isMethodWithExtension(ref) && ref.hasAnnotation(defn.TailrecAnnot)) {
+      if (isMethodWithExtension(ref.symbol) && ref.hasAnnotation(defn.TailrecAnnot)) {
         val ref1 = ref.copySymDenotation()
         ref1.removeAnnotation(defn.TailrecAnnot)
         ref1

compiler/src/dotty/tools/dotc/transform/ValueClasses.scala

@@ -21,12 +21,16 @@ object ValueClasses {
     !d.isPrimitiveValueClass
   }
 
-  def isMethodWithExtension(d: SymDenotation)(implicit ctx: Context) =
-    d.isRealMethod &&
+  def isMethodWithExtension(sym: Symbol)(implicit ctx: Context) =
+    ctx.atPhaseNotLaterThan(ctx.extensionMethodsPhase) { implicit ctx =>
+      val d = sym.denot
+      d.validFor.containsPhaseId(ctx.phaseId) &&
+      d.isRealMethod &&
       isDerivedValueClass(d.owner) &&
       !d.isConstructor &&
       !d.isSuperAccessor &&
       !d.is(Macro)
+    }
 
   /** The member of a derived value class that unboxes it. */
   def valueClassUnbox(d: ClassDenotation)(implicit ctx: Context): Symbol =