Check for mismatched argument type length in PatternMatcher due to Named-Tuple :* syntax

Author: aherlihy

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

@@ -267,8 +267,14 @@ object PatternMatcher {
         def matchArgsPatternPlan(args: List[Tree], syms: List[Symbol]): Plan =
           args match {
             case arg :: args1 =>
-              val sym :: syms1 = syms: @unchecked
-              patternPlan(sym, arg, matchArgsPatternPlan(args1, syms1))
+              if (args.length != syms.length)
+                report.error(UnapplyInvalidNumberOfArguments(tree, tree.tpe :: Nil), arg.srcPos)
+                // Generate a throwaway but type-correct plan.
+                // This plan will never execute because it'll be guarded by a `NonNullTest`.
+                ResultPlan(tpd.Throw(tpd.nullLiteral))
+              else
+                val sym :: syms1 = syms: @unchecked
+                patternPlan(sym, arg, matchArgsPatternPlan(args1, syms1))
             case Nil =>
               assert(syms.isEmpty)
               onSuccess

tests/neg/i23155a.scala

@@ -0,0 +1,7 @@
+import scala.NamedTuple
+object Unpack_NT {
+  (1, 2) match {
+    case Unpack_NT(first, _) => first // error
+  }
+  def unapply(e: (Int, Int)): Some[NamedTuple.NamedTuple["x" *: "y" *: EmptyTuple, Int *: Int *: EmptyTuple]] = ???
+}

tests/neg/i23155b.scala

@@ -0,0 +1,6 @@
+object Unpack_T {
+  (1, 2) match {
+    case Unpack_T(first, _) => first // error
+  }
+  def unapply(e: (Int, Int)): Some[Int *: Int *: EmptyTuple] = ???
+}