Modification via a type alias failing on Scala 3

quicklens/src/main/scala-3/com/softwaremill/quicklens/QuicklensMacros.scala

@@ -141,16 +141,16 @@ object QuicklensMacros {
     }
 
     def termMethodByNameUnsafe(term: Term, name: String): Symbol = {
-      term.tpe.typeSymbol
+      term.tpe.widen.dealias.typeSymbol
         .memberMethod(name)
         .headOption
         .getOrElse(report.errorAndAbort(noSuchMember(term, name)))
     }
 
     def termAccessorMethodByNameUnsafe(term: Term, name: String): (Symbol, Int) = {
-      val caseParamNames = term.tpe.typeSymbol.primaryConstructor.paramSymss.flatten.filter(_.isTerm).map(_.name)
+      val caseParamNames = term.tpe.widen.dealias.typeSymbol.primaryConstructor.paramSymss.flatten.filter(_.isTerm).map(_.name)
       val idx = caseParamNames.indexOf(name)
-      term.tpe.typeSymbol.caseFields.find(_.name == name).getOrElse(report.errorAndAbort(noSuchMember(term, name)))
+      term.tpe.widen.dealias.typeSymbol.caseFields.find(_.name == name).getOrElse(report.errorAndAbort(noSuchMember(term, name)))
         -> (idx + 1)
     }
 
@@ -160,7 +160,7 @@ object QuicklensMacros {
         obj: Term,
         fields: Seq[(PathSymbol.Field, Seq[PathTree])]
     ): Term = {
-      val objSymbol = obj.tpe.typeSymbol
+      val objSymbol = obj.tpe.widen.dealias.typeSymbol
       if objSymbol.flags.is(Flags.Case) then {
         val copy = termMethodByNameUnsafe(obj, "copy")
         val argsMap: Map[Int, Term] = fields.map { (field, trees) =>
@@ -172,15 +172,15 @@ object QuicklensMacros {
           idx -> namedArg
         }.toMap
 
-        val fieldsIdxs = 1.to(obj.tpe.typeSymbol.primaryConstructor.paramSymss.flatten.filter(_.isTerm).length)
+        val fieldsIdxs = 1.to(objSymbol.primaryConstructor.paramSymss.flatten.filter(_.isTerm).length)
         val args = fieldsIdxs.map { i =>
           argsMap.getOrElse(
             i,
             Select(obj, termMethodByNameUnsafe(obj, "copy$default$" + i.toString))
           )
         }.toList
 
-        obj.tpe.widen match {
+        obj.tpe.widen.dealias match {
           // if the object's type is parametrised, we need to call .copy with the same type parameters
           case AppliedType(_, typeParams) => Apply(TypeApply(Select(obj, copy), typeParams.map(Inferred(_))), args)
           case _                          => Apply(Select(obj, copy), args)

quicklens/src/test/scala/com/softwaremill/quicklens/ModifyAliasTest.scala

@@ -0,0 +1,22 @@
+package com.softwaremill.quicklens
+
+import org.scalatest.flatspec.AnyFlatSpec
+import org.scalatest.matchers.should.Matchers
+
+import ModifyAliasTest._
+
+object ModifyAliasTest {
+
+  case class State(x: Int)
+
+  type S = State
+}
+
+class ModifyAliasTest extends AnyFlatSpec with Matchers {
+  it should "modify an object declared using type alias" in {
+    val s: S = State(0)
+    val modified = s.modify(_.x).setTo(1)
+
+    modified.x shouldBe 1
+  }
+}