Handle abstract apply and multiple applys

Author: liufengyun

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

@@ -34,22 +34,25 @@ class SpecializeFunctions extends MiniPhase with InfoTransformer {
       while (arity < 3) {
         val func = defn.FunctionClass(arity)
         if (sym.derivesFrom(func)) {
-          val baseType = tp.cls.typeRef.baseType(func)
-          val apply = baseType.member(nme.apply)
-
+          val baseType   = tp.cls.typeRef.baseType(func)
           val paramTypes = baseType.argInfos
-          val argTypes = paramTypes.init
-          val retType  = paramTypes.last
+          val argTypes   = paramTypes.init
+          val retType    = paramTypes.last
+
+          val apply = baseType.member(nme.apply)
+          val overrideApply = tp.decls.find {  sym =>
+            sym.is(Flags.Method) && sym.name == nme.apply && sym.info.matches(apply.info)
+          }
 
-          val isSpecializable = defn.isSpecializableFunction(sym.asClass, argTypes, retType)
+          def isSpecializable = defn.isSpecializableFunction(sym.asClass, argTypes, retType)
 
-          if (isSpecializable) {
+          if (overrideApply.exists && isSpecializable) {
             val specializedMethodName: Name = nme.apply.specializedFunction(retType, argTypes)
             val applySpecialized = newSymbol(
               sym,
               specializedMethodName,
-              Flags.Override | Flags.Method | Flags.Synthetic,
-              apply.info
+              overrideApply.flags | Flags.Synthetic,
+              overrideApply.info
             )
 
             newApplys += applySpecialized