For generic tuples, call Tuples.apply instead of _1/_2/..

Author: dwijnand

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

@@ -231,8 +231,8 @@ object PatternMatcher {
         case _ =>
           tree.tpe
 
-      /** Plan for matching `selectors` against argument patterns `args` */
-      def matchArgsPlan(selectors: List[Tree], args: List[Tree], onSuccess: Plan): Plan = {
+      /** Plan for matching `components` against argument patterns `args` */
+      def matchArgsPlan(components: List[Tree], args: List[Tree], onSuccess: Plan): Plan = {
         /* For a case with arguments that have some test on them such as
          * ```
          * case Foo(1, 2) => someCode
@@ -249,9 +249,9 @@ object PatternMatcher {
          * } else ()
          * ```
          */
-        def matchArgsSelectorsPlan(selectors: List[Tree], syms: List[Symbol]): Plan =
-          selectors match {
-            case selector :: selectors1 => letAbstract(selector, selector.avoidPatBoundType())(sym => matchArgsSelectorsPlan(selectors1, sym :: syms))
+        def matchArgsComponentsPlan(components: List[Tree], syms: List[Symbol]): Plan =
+          components match {
+            case component :: components1 => letAbstract(component, component.avoidPatBoundType())(sym => matchArgsComponentsPlan(components1, sym :: syms))
             case Nil => matchArgsPatternPlan(args, syms.reverse)
           }
         def matchArgsPatternPlan(args: List[Tree], syms: List[Symbol]): Plan =
@@ -263,7 +263,7 @@ object PatternMatcher {
               assert(syms.isEmpty)
               onSuccess
           }
-        matchArgsSelectorsPlan(selectors, Nil)
+        matchArgsComponentsPlan(components, Nil)
       }
 
       /** Plan for matching the sequence in `seqSym` against sequence elements `args`.
@@ -326,7 +326,15 @@ object PatternMatcher {
           sym.isAllOf(SyntheticCase) && sym.owner.is(Scala2x)
 
         if (isSyntheticScala2Unapply(unapp.symbol) && caseAccessors.length == args.length)
-          matchArgsPlan(caseAccessors.map(ref(scrutinee).select(_)), args, onSuccess)
+          def tupleSel(sym: Symbol) = ref(scrutinee).select(sym)
+          def tupleApp(i: Int) = // manually inlining the call to NonEmptyTuple#apply, because it's an inline method
+            ref(defn.RuntimeTuplesModule)
+              .select(defn.RuntimeTuples_apply)
+              .appliedTo(ref(scrutinee), Literal(Constant(i)))
+              .cast(args(i).tpe.widen)
+          val isGenericTuple = defn.isTupleClass(caseClass) && !defn.isTupleNType(tree.tpe)
+          val components = if isGenericTuple then caseAccessors.indices.toList.map(tupleApp) else caseAccessors.map(tupleSel)
+          matchArgsPlan(components, args, onSuccess)
         else if (unapp.tpe <:< (defn.BooleanType))
           TestPlan(GuardTest, unapp, unapp.span, onSuccess)
         else

tests/run/i13968.scala

@@ -0,0 +1,26 @@
+object Bar {
+  def unapply(x: Any): Option[Int *: Int *: EmptyTuple] = Some(1 *: 2 *: Tuple())
+}
+
+object Bar23 {
+  def unapply(x: Any): Option[
+      Int *: Int *: Int *: Int *: Int *: Int *: Int *: Int *: Int *: Int *:
+      Int *: Int *: Int *: Int *: Int *: Int *: Int *: Int *: Int *: Int *:
+      Int *: Int *: Int *: EmptyTuple
+  ] = Some(
+     1 *:  2 *:  3 *:  4 *:  5 *:  6 *:  7 *:  8 *:  9 *: 10 *:
+    11 *: 12 *: 13 *: 14 *: 15 *: 16 *: 17 *: 18 *: 19 *: 20 *:
+    21 *: 22 *: 23 *: Tuple()
+  )
+}
+
+@main def Test() =
+  "" match
+    case Bar((a, b)) => assert(a == 1 && b == 2, (a, b))
+
+  "" match
+    case Bar23((
+      u1, u2, u3, u4, u5, u6, u7, u8, u9, u10,
+      u11, u12, u13, u14, u15, u16, u17, u18, u19, u20,
+      u21, u22, u23
+    )) => assert(u1 == 1 && u23 == 23, (u1, u23))