Fix #24571: Handling nullable types in convertTo for adapting number constants to target number types

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

@@ -3,6 +3,7 @@ package dotc
 package core
 
 import Types.*, Symbols.*, Contexts.*
+import NullOpsDecorator.stripNull
 import printing.Printer
 import printing.Texts.Text
 
@@ -149,7 +150,7 @@ object Constants {
     /** Convert constant value to conform to given type.
      */
     def convertTo(pt: Type)(using Context): Constant | Null = {
-      def classBound(pt: Type): Type = pt.dealias.stripTypeVar match {
+      def classBound(pt: Type): Type = pt.dealias.stripTypeVar.stripNull() match {
         case tref: TypeRef if !tref.symbol.isClass && tref.info.exists =>
           classBound(tref.info.bounds.lo)
         case param: TypeParamRef =>

tests/pos/i24571.scala

@@ -0,0 +1,24 @@
+val n: Byte = 2
+val n2: Byte | Null = 2
+val n3: Int = 2
+val n4: Int | Null = 2222
+val n5: Int | Byte = 2
+val n6: Byte | Int = 10000
+
+val x: Option[Byte] = Option(2)
+val x2: Option[Byte] = Option[Byte](2)
+val x3: Option[Int] = Option(2)
+val x4: Option[Null] = Option(null)
+val x5: Option[Byte | Null] = Option(2)
+
+trait MyOption[+T]
+
+object MyOption:
+  def apply[T](x: T | Null): MyOption[T] = ???
+  def applyOld[T](x: T): MyOption[T] = ???
+
+val test1: MyOption[Byte] = MyOption(2)
+val test2: MyOption[Byte] = MyOption.applyOld(2)
+val test3: MyOption[Int] = MyOption(2)
+val test4: MyOption[Null] = MyOption(null)
+val test5: MyOption[Byte | Null] = MyOption(2)