Handle & avoid recursion in traverseTp2

Author: dwijnand

compiler/src/dotty/tools/dotc/core/TypeOps.scala

@@ -844,17 +844,17 @@ object TypeOps:
       val singletons = util.HashMap[Symbol, SingletonType]()
       val gadtSyms = new mutable.ListBuffer[Symbol]
 
-      def traverse(tp: Type) = {
+      def traverse(tp: Type) = try
         val tpd = tp.dealias
         if tpd ne tp then traverse(tpd)
         else tp match
-          case tp: ThisType if !tp.tref.symbol.isStaticOwner && !singletons.contains(tp.tref.symbol) =>
+          case tp: ThisType if !singletons.contains(tp.tref.symbol) && !tp.tref.symbol.isStaticOwner =>
             singletons(tp.tref.symbol) = tp
             traverseChildren(tp.tref)
           case tp: TermRef if tp.symbol.is(Param) =>
             singletons(tp.typeSymbol) = tp
             traverseChildren(tp)
-          case tp: TypeRef if tp.symbol.isAbstractOrParamType =>
+          case tp: TypeRef if !gadtSyms.contains(tp.symbol) && tp.symbol.isAbstractOrParamType =>
             gadtSyms += tp.symbol
             traverseChildren(tp)
             // traverse abstract type infos, to add any singletons
@@ -863,7 +863,7 @@ object TypeOps:
             traverseChildren(tp.info)
           case _ =>
             traverseChildren(tp)
-      }
+      catch case ex: Throwable => handleRecursive("traverseTp2", tp.show, ex)
     TraverseTp2.traverse(tp2)
     val singletons = TraverseTp2.singletons
     val gadtSyms   = TraverseTp2.gadtSyms.toList