From ad29ce89624470de6204b242f0c3ee75fde727a3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?S=C3=A9bastien=20Doeraene?= <sjrdoeraene@gmail.com>
Date: Fri, 11 Aug 2023 15:57:51 +0200
Subject: [PATCH] Fix #17115: Try to normalize while computing `typeSize`.

---
 compiler/src/dotty/tools/dotc/core/Types.scala | 4 +++-
 tests/pos/i17115.scala                         | 9 +++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)
 create mode 100644 tests/pos/i17115.scala

diff --git a/compiler/src/dotty/tools/dotc/core/Types.scala b/compiler/src/dotty/tools/dotc/core/Types.scala
index 576f9a6c64f6..c5f65c73f57c 100644
--- a/compiler/src/dotty/tools/dotc/core/Types.scala
+++ b/compiler/src/dotty/tools/dotc/core/Types.scala
@@ -6459,7 +6459,9 @@ object Types {
         seen += tp
         tp match {
           case tp: AppliedType =>
-            foldOver(n + 1, tp)
+            val tpNorm = tp.tryNormalize
+            if tpNorm.exists then apply(n, tpNorm)
+            else foldOver(n + 1, tp)
           case tp: RefinedType =>
             foldOver(n + 1, tp)
           case tp: TypeRef if tp.info.isTypeAlias =>
diff --git a/tests/pos/i17115.scala b/tests/pos/i17115.scala
new file mode 100644
index 000000000000..5a7cac5d0dc1
--- /dev/null
+++ b/tests/pos/i17115.scala
@@ -0,0 +1,9 @@
+trait A[T <: Tuple] { val x: Int }
+given empty: A[EmptyTuple] with { val x = 1 }
+given inductive[Tup <: NonEmptyTuple](using A[Tuple.Tail[Tup]]): A[Tup] with { val x = summon[A[Tuple.Tail[Tup]]].x + 1 }
+
+object Test:
+  def main(args: Array[String]): Unit =
+    println(summon[A[(String, String, String)]].x) //this line is fine
+    println(summon[A[(String, String, String, String)]].x) //this line gives error
+end Test