Handle recursion in collectParts (#18214)

Author: odersky

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()

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