Validate named patterns for case classes

compiler/src/dotty/tools/dotc/ast/Desugar.scala

@@ -1654,7 +1654,7 @@ object desugar {
       AppliedTypeTree(
         TypeTree(defn.throwsAlias.typeRef).withSpan(op.span), tpt :: excepts :: Nil)
 
-  private def checkWellFormedTupleElems(elems: List[Tree])(using Context): List[Tree] =
+  def checkWellFormedTupleElems(elems: List[Tree])(using Context): List[Tree] =
     val seen = mutable.Set[Name]()
     for case arg @ NamedArg(name, _) <- elems do
       if seen.contains(name) then

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

@@ -199,20 +199,22 @@ object Applications {
       else tp :: Nil
 
     private def productUnapplySelectors(tp: Type)(using Context): Option[List[Type]] =
+      val validatedTupleElements = desugar.checkWellFormedTupleElems(args)
+
       if defn.isProductSubType(tp) then
-        tryAdaptPatternArgs(args, tp) match
+        tryAdaptPatternArgs(validatedTupleElements, tp) match
           case Some(args1) if isProductMatch(tp, args1.length, pos) =>
             args = args1
             Some(productSelectorTypes(tp, pos))
           case _ => None
-        else tp.widen.normalized.dealias match
-          case tp @ defn.NamedTuple(_, tt) =>
-            tryAdaptPatternArgs(args, tp) match
-              case Some(args1) =>
-                args = args1
-                tt.tupleElementTypes
-              case _ => None
-          case _ => None
+      else tp.widen.normalized.dealias match
+        case tp @ defn.NamedTuple(_, tt) =>
+          tryAdaptPatternArgs(validatedTupleElements, tp) match
+            case Some(args1) =>
+              args = args1
+              tt.tupleElementTypes
+            case _ => None
+        case _ => None
 
     /** The computed argument types which will be the scutinees of the sub-patterns. */
     val argTypes: List[Type] =

tests/neg/named-tuples-4.check

@@ -0,0 +1,16 @@
+-- Error: tests/neg/named-tuples-4.scala:10:35 -------------------------------------------------------------------------
+10 |    case PersonCaseClass(name = n, age) => () // error
+   |                                   ^^^
+   |                                   Illegal combination of named and unnamed tuple elements
+-- Error: tests/neg/named-tuples-4.scala:11:31 -------------------------------------------------------------------------
+11 |    case PersonCaseClass(name, age = a) => () // error
+   |                               ^^^^^^^
+   |                               Illegal combination of named and unnamed tuple elements
+-- Error: tests/neg/named-tuples-4.scala:15:20 -------------------------------------------------------------------------
+15 |    case (name = n, age) => () // error
+   |                    ^^^
+   |                    Illegal combination of named and unnamed tuple elements
+-- Error: tests/neg/named-tuples-4.scala:16:16 -------------------------------------------------------------------------
+16 |    case (name, age = a) => () // error
+   |                ^^^^^^^
+   |                Illegal combination of named and unnamed tuple elements

tests/neg/named-tuples-4.scala

@@ -0,0 +1,16 @@
+import language.experimental.namedTuples
+import scala.annotation.experimental
+
+@experimental object Test:
+
+  case class PersonCaseClass(name: String, age: Int)
+
+  val personCaseClass = PersonCaseClass("Bob", 33)
+  personCaseClass match
+    case PersonCaseClass(name = n, age) => () // error
+    case PersonCaseClass(name, age = a) => () // error
+
+  val person = (name = "Bob", age = 33): (name: String, age: Int)
+  person match
+    case (name = n, age) => () // error
+    case (name, age = a) => () // error