Make caseClassSynthesized idempotent

Author: nicolasstucki

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

@@ -1210,7 +1210,7 @@ class Definitions {
   val AbstractFunctionClassPerRun: PerRun[Array[Symbol]] = new PerRun(AbstractFunctionType.map(_.symbol.asClass))
   def AbstractFunctionClass(n: Int)(using Context): Symbol = AbstractFunctionClassPerRun()(using ctx)(n)
 
-  @tu lazy val caseClassSynthesized: Set[Symbol] = Set(
+  @tu lazy val caseClassSynthesized: List[Symbol] = List(
     Any_hashCode, Any_equals, Any_toString, Product_canEqual, Product_productArity,
     Product_productPrefix, Product_productElement, Product_productElementName)
 

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

@@ -63,7 +63,7 @@ class SyntheticMembers(thisPhase: DenotTransformer) {
   private def initSymbols(using Context) =
     if (myValueSymbols.isEmpty) {
       myValueSymbols = List(defn.Any_hashCode, defn.Any_equals)
-      myCaseSymbols = defn.caseClassSynthesized.toList
+      myCaseSymbols = defn.caseClassSynthesized
       myCaseModuleSymbols = myCaseSymbols.filter(_ ne defn.Any_equals)
       myEnumValueSymbols = List(defn.Product_productPrefix)
       myNonJavaEnumValueSymbols = myEnumValueSymbols :+ defn.Any_toString