Fix parameter untupling for named tuples (#23440)

Author: aherlihy

compiler/src/dotty/tools/dotc/typer/Applications.scala

@@ -153,16 +153,18 @@ object Applications {
 
   def tupleComponentTypes(tp: Type)(using Context): List[Type] =
     tp.widenExpr.dealias.normalized match
-    case tp: AppliedType =>
-      if defn.isTupleClass(tp.tycon.typeSymbol) then
-        tp.args
-      else if tp.tycon.derivesFrom(defn.PairClass) then
-        val List(head, tail) = tp.args
-        head :: tupleComponentTypes(tail)
-      else
+      case defn.NamedTuple(_, vals) =>
+        tupleComponentTypes(vals)
+      case tp: AppliedType =>
+        if defn.isTupleClass(tp.tycon.typeSymbol) then
+          tp.args
+        else if tp.tycon.derivesFrom(defn.PairClass) then
+          val List(head, tail) = tp.args
+          head :: tupleComponentTypes(tail)
+        else
+          Nil
+      case _ =>
         Nil
-    case _ =>
-      Nil
 
   def productArity(tp: Type, errorPos: SrcPos = NoSourcePosition)(using Context): Int =
     if (defn.isProductSubType(tp)) productSelectorTypes(tp, errorPos).size else -1
@@ -2585,7 +2587,7 @@ trait Applications extends Compatibility {
   /** Is `formal` a product type which is elementwise compatible with `params`? */
   def ptIsCorrectProduct(formal: Type, params: List[untpd.ValDef])(using Context): Boolean =
     isFullyDefined(formal, ForceDegree.flipBottom)
-    && defn.isProductSubType(formal)
+    && (defn.isProductSubType(formal) || formal.isNamedTupleType)
     && tupleComponentTypes(formal).corresponds(params): (argType, param) =>
          param.tpt.isEmpty || argType.widenExpr <:< typedAheadType(param.tpt).tpe
 

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -1943,8 +1943,9 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
       val firstFormal = protoFormals.head.loBound
       if ptIsCorrectProduct(firstFormal, params) then
         val isGenericTuple =
-          firstFormal.derivesFrom(defn.TupleClass)
-          && !defn.isTupleClass(firstFormal.typeSymbol)
+          firstFormal.isNamedTupleType
+          || (firstFormal.derivesFrom(defn.TupleClass)
+              && !defn.isTupleClass(firstFormal.typeSymbol))
         desugared = desugar.makeTupledFunction(params, fnBody, isGenericTuple)
     else if protoFormals.length > 1 && params.length == 1 then
       def isParamRef(scrut: untpd.Tree): Boolean = scrut match

tests/run/i23440.scala

@@ -0,0 +1,12 @@
+@main def Test: Unit =
+  List((42, "asdads")) match
+    case List((a, b)) => 1
+  List((a = 42, b = "asdads")) match
+    case List((a, b)) => 1
+  val tuple_list = List((42, "asdads"))
+  tuple_list.map((a, b) => println(s"$a $b"))
+  val named_tuple_list = List((a = 42, b = "asdads"))
+  named_tuple_list.foreach((a, b) => println(s"$a $b"))
+  named_tuple_list.foreach { case (a, b) => println(s"$a $b") }
+  val l = Seq.empty[(name: String, age: Int)]
+  l.map((name, i) => name + i)