Skip bypassing unapply for scala 2 case classes to allow for single-element named tuple in unapply

Author: aherlihy

compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala

@@ -343,7 +343,7 @@ object PatternMatcher {
               receiver.ensureConforms(defn.NonEmptyTupleTypeRef), // If scrutinee is a named tuple, cast to underlying tuple
               Literal(Constant(i)))
 
-        if (isSyntheticScala2Unapply(unapp.symbol) && caseAccessors.length == args.length)
+        if (isSyntheticScala2Unapply(unapp.symbol) && caseAccessors.length == args.length && args.length != 1)
           def tupleSel(sym: Symbol) =
             // If scrutinee is a named tuple, cast to underlying tuple, so that we can
             // continue to select with _1, _2, ...

tests/run/i23131.scala

@@ -0,0 +1,9 @@
+import scala.NamedTuple
+@main
+def Test =
+  Some((name = "Bob")) match {
+    case Some(name = a) => println(a)
+  }
+//  (name = "Bob") match { // works fine
+//    case (name = a) => println (a)
+//  }