From b65f689af77e15fba5e36e1d943e818b34b75bb4 Mon Sep 17 00:00:00 2001
From: Dale Wijnand <dale.wijnand@gmail.com>
Date: Sat, 15 Jul 2023 13:39:23 +0100
Subject: [PATCH] Handle recursion in collectParts

---
 compiler/src/dotty/tools/dotc/typer/Implicits.scala |  3 ++-
 tests/neg/i18171.scala                              | 10 ++++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)
 create mode 100644 tests/neg/i18171.scala

diff --git a/compiler/src/dotty/tools/dotc/typer/Implicits.scala b/compiler/src/dotty/tools/dotc/typer/Implicits.scala
index d5dffff30afb..91d946ad1c63 100644
--- a/compiler/src/dotty/tools/dotc/typer/Implicits.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Implicits.scala
@@ -604,7 +604,7 @@ trait ImplicitRunInfo:
       private var parts: mutable.LinkedHashSet[Type] = _
       private val partSeen = util.HashSet[Type]()
 
-      def traverse(t: Type) =
+      def traverse(t: Type) = try
         if partSeen.contains(t) then ()
         else if implicitScopeCache.contains(t) then parts += t
         else
@@ -643,6 +643,7 @@ trait ImplicitRunInfo:
               traverse(mt)
             case t =>
               traverseChildren(t)
+      catch case ex: Throwable => handleRecursive("collectParts of", t.show, ex)
 
       def apply(tp: Type): collection.Set[Type] =
         parts = mutable.LinkedHashSet()
diff --git a/tests/neg/i18171.scala b/tests/neg/i18171.scala
new file mode 100644
index 000000000000..d269f70beb30
--- /dev/null
+++ b/tests/neg/i18171.scala
@@ -0,0 +1,10 @@
+type BAZ[T] = T match
+  case Any => DFVal[BAZREC[T]]
+
+type BAZREC[T] = T match
+  case NonEmptyTuple => Tuple.Map[T, BAZ]
+
+trait DFVal[T]
+
+def foo(relIdx: BAZ[Any]): Unit =
+  relIdx.bar // error