Allow for using explicit copy methods in classes

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

@@ -34,8 +34,6 @@ object QuicklensMacros {
       focus: Expr[S => A],
       focusesExpr: Expr[Seq[S => A]]
   )(using Quotes): Expr[PathModify[S, A]] = {
-    import quotes.reflect.*
-
     val focuses = focusesExpr match {
       case Varargs(args) => focus +: args
     }
@@ -60,6 +58,9 @@ object QuicklensMacros {
     def noSuchMember(tpeStr: String, name: String) =
       s"$tpeStr has no member named $name"
 
+    def multipleMatchingMethods(tpeStr: String, name: String) =
+      s"Multiple methods named $name found in $tpeStr"
+
     def methodSupported(method: String) =
       Seq("at", "each", "eachWhere", "eachRight", "eachLeft", "atOrElse", "index", "when").contains(method)
 
@@ -148,90 +149,61 @@ object QuicklensMacros {
         case AndType(l, r) if r <:< l => r
         case _                        => tpe
       }
+
       def widenAll: TypeRepr =
         tpe.widen.dealias.poorMansLUB
+
       def matchingTypeSymbol: Symbol = tpe.widenAll match {
         case AndType(l, r) =>
           val lSym = l.matchingTypeSymbol
           if l.matchingTypeSymbol != Symbol.noSymbol then lSym else r.matchingTypeSymbol
         case tpe if isProduct(tpe.typeSymbol) || isSum(tpe.typeSymbol) =>
           tpe.typeSymbol
-        case tpe =>
+        case tpe if isProductLike(tpe.typeSymbol) =>
+          tpe.typeSymbol
+        case _ =>
           Symbol.noSymbol
       }
 
-    def symbolMethodByNameUnsafe(sym: Symbol, name: String): Symbol = {
-      sym
-        .methodMember(name)
-        .headOption
-        .getOrElse(report.errorAndAbort(noSuchMember(sym.name, name)))
+    def symbolAccessorByNameOrError(sym: Symbol, name: String): Symbol = {
+      val mem = sym.fieldMember(name)
+      if mem != Symbol.noSymbol then mem
+      else report.errorAndAbort(noSuchMember(sym.name, name))
     }
 
-    def termMethodByNameUnsafe(term: Term, name: String): Symbol = {
-      symbolMethodByNameUnsafe(term.tpe.widenAll.typeSymbol, name)
+    def symbolMethodByNameOrError(sym: Symbol, name: String): Symbol = {
+      sym.methodMember(name) match
+        case List(m) => m
+        case Nil => symbolAccessorByNameOrError(sym, name)
+        case _ => report.errorAndAbort(multipleMatchingMethods(sym.name, name))
     }
 
-    def termAccessorMethodByNameUnsafe(term: Term, name: String): (Symbol, Int) = {
-      val typeSymbol = term.tpe.widenAll.matchingTypeSymbol
-      val caseParamNames = typeSymbol.primaryConstructor.paramSymss.flatten.filter(_.isTerm).map(_.name)
-      val idx = caseParamNames.indexOf(name)
-      typeSymbol.caseFields.find(_.name == name).getOrElse(report.errorAndAbort(noSuchMember(term.tpe.show, name)))
-        -> (idx + 1)
+    def termMethodByNameUnsafe(term: Term, name: String): Symbol = {
+      val typeSymbol = term.tpe.widenAll.typeSymbol
+      symbolMethodByNameOrError(typeSymbol, name)
     }
 
     def isProduct(sym: Symbol): Boolean = {
       sym.flags.is(Flags.Case)
     }
 
     def isSum(sym: Symbol): Boolean = {
-      sym.flags.is(Flags.Enum) ||
+      (sym.flags.is(Flags.Enum) && !sym.flags.is(Flags.Case)) ||
       (sym.flags.is(Flags.Sealed) && (sym.flags.is(Flags.Trait) || sym.flags.is(Flags.Abstract)))
     }
 
+    def isProductLike(sym: Symbol): Boolean = {
+      sym.methodMember("copy").size == 1
+    }
+
     def caseClassCopy(
         owner: Symbol,
         mod: Expr[A => A],
         obj: Term,
         fields: Seq[(PathSymbol.Field, Seq[PathTree])]
     ): Term = {
       val objSymbol = obj.tpe.widenAll.matchingTypeSymbol
-      if isProduct(objSymbol) then {
-        val copy = symbolMethodByNameUnsafe(objSymbol, "copy")
-        val argsMap: Map[Int, Term] = fields.map { (field, trees) =>
-          val (fieldMethod, idx) = termAccessorMethodByNameUnsafe(obj, field.name)
-          val resTerm: Term = trees.foldLeft[Term](Select(obj, fieldMethod)) { (term, tree) =>
-            mapToCopy(owner, mod, term, tree)
-          }
-          val namedArg = NamedArg(field.name, resTerm)
-          idx -> namedArg
-        }.toMap
-
-        val typeParams = obj.tpe.widenAll match {
-          case AppliedType(_, typeParams) => Some(typeParams)
-          case _                          => None
-        }
-        val constructorTree: DefDef = objSymbol.primaryConstructor.tree.asInstanceOf[DefDef]
-        val firstParamListLength: Int = constructorTree.termParamss.headOption.map(_.params).toList.flatten.length
-        val fieldsIdxs = 1.to(firstParamListLength)
-        val args = fieldsIdxs.map { i =>
-          val defaultMethod = obj.select(symbolMethodByNameUnsafe(objSymbol, "copy$default$" + i.toString))
-          argsMap.getOrElse(
-            i,
-            typeParams.fold(defaultMethod)(defaultMethod.appliedToTypes)
-          )
-        }.toList
-
-        if constructorTree.termParamss.drop(1).exists(_.params.exists(!_.symbol.flags.is(Flags.Implicit))) then
-          report.errorAndAbort(
-            s"Implementation limitation: Only the first parameter list of the modified case classes can be non-implicit."
-          )
-
-        typeParams match {
-          // if the object's type is parametrised, we need to call .copy with the same type parameters
-          case Some(typeParams) => Apply(TypeApply(Select(obj, copy), typeParams.map(Inferred(_))), args)
-          case _                => Apply(Select(obj, copy), args)
-        }
-      } else if isSum(objSymbol) then {
+      if isSum(objSymbol) then {
         obj.tpe.widenAll match {
           case AndType(_, _) =>
             report.errorAndAbort(
@@ -260,6 +232,45 @@ object QuicklensMacros {
         ifThens.foldRight(elseThrow) { case ((ifCond, ifThen), ifElse) =>
           If(ifCond, ifThen, ifElse)
         }
+      } else if isProduct(objSymbol) || isProductLike(objSymbol) then {
+        val copy = symbolMethodByNameOrError(objSymbol, "copy")
+        val argsMap: Map[String, Term] = fields.map { (field, trees) =>
+          val fieldMethod = symbolMethodByNameOrError(objSymbol, field.name)
+          val resTerm: Term = trees.foldLeft[Term](Select(obj, fieldMethod)) { (term, tree) =>
+            mapToCopy(owner, mod, term, tree)
+          }
+          val namedArg = NamedArg(field.name, resTerm)
+          field.name -> namedArg
+        }.toMap
+
+        val typeParams = obj.tpe.widenAll match {
+          case AppliedType(_, typeParams) => Some(typeParams)
+          case _                          => None
+        }
+        val copyTree: DefDef = copy.tree.asInstanceOf[DefDef]
+        val copyParamNames: List[String] = copyTree.termParamss.headOption.map(_.params).toList.flatten.map(_.name)
+
+        val args = copyParamNames.zipWithIndex.map { (n, _i) =>
+          val i = _i + 1
+          val defaultMethod = obj.select(symbolMethodByNameOrError(objSymbol, "copy$default$" + i.toString))
+          // for extension methods, might need sth more like this: (or probably some weird implicit conversion)
+          // val defaultGetter = obj.select(symbolMethodByNameOrError(objSymbol, n))
+          argsMap.getOrElse(
+            n,
+            defaultMethod
+          )
+        }.toList
+
+        if copyTree.termParamss.drop(1).exists(_.params.exists(!_.symbol.flags.is(Flags.Implicit))) then
+          report.errorAndAbort(
+            s"Implementation limitation: Only the first parameter list of the modified case classes can be non-implicit."
+          )
+
+        typeParams match {
+          // if the object's type is parametrised, we need to call .copy with the same type parameters
+          case Some(typeParams) => Apply(TypeApply(Select(obj, copy), typeParams.map(Inferred(_))), args)
+          case _                => Apply(Select(obj, copy), args)
+        }
       } else
         report.errorAndAbort(s"Unsupported source object: must be a case class or sealed trait, but got: $objSymbol")
     }

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

@@ -1,6 +1,6 @@
 package com.softwaremill
 
-import scala.collection.{Factory, SortedMap}
+import scala.collection.SortedMap
 import scala.annotation.compileTimeOnly
 import com.softwaremill.quicklens.QuicklensMacros._
 import scala.reflect.ClassTag

quicklens/src/test/scala-3/com/softwaremill/quicklens/test/ExplicitCopyTest.scala

@@ -0,0 +1,25 @@
+package com.softwaremill.quicklens
+
+import org.scalatest.flatspec.AnyFlatSpec
+import org.scalatest.matchers.should.Matchers
+
+class ExplicitCopyTest extends AnyFlatSpec with Matchers {
+  it should "modify a class with an explicit copy method" in {
+    case class V(x: Double, y: Double)
+    class Vec(val v: V) {
+      def x: Double = v.x
+      def y: Double = v.y
+      def copy(x: Double = v.x, y: Double = v.y): Vec = new Vec(V(x, y)) {}
+      def show: String = s"Vec(${v.x}, ${v.y})"
+    }
+    object Vec {
+      def apply(x: Double, y: Double): Vec = new Vec(V(x, y)) {}
+    }
+
+    val vec = Vec(1, 2)
+    val modified = vec.modify(_.x).using(_ + 1)
+    val expected = Vec(2, 2)
+    modified.show shouldEqual expected.show
+  }
+
+}