Avoid more crashes in the presence of cyclic definitions

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

@@ -542,16 +542,17 @@ object Types {
      *  Inherited by all type proxies. Overridden for And and Or types.
      *  `Nil` for all other types.
      */
-    def baseClasses(using Context): List[ClassSymbol] = {
+    def baseClasses(using Context): List[ClassSymbol] =
       record("baseClasses")
-      this match {
-        case tp: TypeProxy =>
-          tp.underlying.baseClasses
-        case tp: ClassInfo =>
-          tp.cls.classDenot.baseClasses
-        case _ => Nil
-      }
-    }
+      try
+        this match
+          case tp: TypeProxy =>
+            tp.underlying.baseClasses
+          case tp: ClassInfo =>
+            tp.cls.classDenot.baseClasses
+          case _ => Nil
+      catch case ex: Throwable =>
+        handleRecursive("base classes of", this.show, ex)
 
 // ----- Member access -------------------------------------------------
 

compiler/src/dotty/tools/dotc/typer/Namer.scala

@@ -1345,8 +1345,11 @@ class Namer { typer: Typer =>
           // TODO: Look only at member of supertype instead?
           lazy val schema = paramFn(WildcardType)
           val site = sym.owner.thisType
-
-          sym.owner.info.baseClasses.tail.foldLeft(NoType: Type) { (tp, cls) =>
+          val bcs = sym.owner.info.baseClasses
+          if bcs.isEmpty then
+            assert(ctx.reporter.errorsReported)
+            NoType
+          else bcs.tail.foldLeft(NoType: Type) { (tp, cls) =>
             def instantiatedResType(info: Type, paramss: List[List[Symbol]]): Type = info match
               case info: PolyType =>
                 paramss match

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -1320,7 +1320,9 @@ class Typer extends Namer
                   EmptyTree
             }
           case tp =>
-            throw new java.lang.Error(i"internal error: closing over non-method $tp, pos = ${tree.span}")
+            if !tp.isErroneous then
+              throw new java.lang.Error(i"internal error: closing over non-method $tp, pos = ${tree.span}")
+            TypeTree(defn.AnyType)
         }
       else typed(tree.tpt)
     //println(i"typing closure $tree : ${meth1.tpe.widen}")

tests/neg/i9299.scala

@@ -0,0 +1,4 @@
+type F <: F = 1 match { // error
+  case _ => foo.foo // error // error
+}
+def foo(a: Int): Unit = ???

tests/neg/i9299a.scala

@@ -0,0 +1,4 @@
+type T <: foo.a = Int match { // error
+  case "" => foo.b // error
+}
+def foo(x: Int): Unit = ???