From b1fb67cb188e237b143731f1f65178472b86016b Mon Sep 17 00:00:00 2001
From: Eugene Flesselle <eugene@flesselle.net>
Date: Wed, 6 Aug 2025 18:07:11 +0200
Subject: [PATCH] Fix auto-untupling for generic tuple types

This makes the behaviour of auto-untupling consistent between the usual and
generic tuples.

Related to https://github.com/scala/scala3/pull/23602
---
 compiler/src/dotty/tools/dotc/typer/Applications.scala | 2 +-
 tests/pos/generic-untupling.scala                      | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)
 create mode 100644 tests/pos/generic-untupling.scala

diff --git a/compiler/src/dotty/tools/dotc/typer/Applications.scala b/compiler/src/dotty/tools/dotc/typer/Applications.scala
index da6b20b75c29..2e9288dcd9be 100644
--- a/compiler/src/dotty/tools/dotc/typer/Applications.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Applications.scala
@@ -280,7 +280,7 @@ object Applications {
         case argType :: Nil
         if args.lengthCompare(1) > 0
             && Feature.autoTuplingEnabled
-            && defn.isTupleNType(argType) =>
+            && (defn.isTupleNType(argType) || argType.isSmallGenericTuple) =>
           untpd.Tuple(args) :: Nil
         case _ =>
           args
diff --git a/tests/pos/generic-untupling.scala b/tests/pos/generic-untupling.scala
new file mode 100644
index 000000000000..b6002301baec
--- /dev/null
+++ b/tests/pos/generic-untupling.scala
@@ -0,0 +1,8 @@
+
+def foo(x: Option[(Int, Boolean)]) = x match
+  case Some(a, b) => ??? // was ok
+  case None => ???
+
+def bar(x: Option[Int *: Boolean *: EmptyTuple]) = x match
+  case Some(a, b) => ??? // was error, now ok
+  case None => ???