From f2b432e21676513a2b738dc225210fb0dcde6ce9 Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Wed, 25 Apr 2018 18:55:14 +0200
Subject: [PATCH] Harden IDE: Avoid ClassCastException in ThisType.cls

This was observed repeatedly as a PC crash.
---
 compiler/src/dotty/tools/dotc/core/Types.scala | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/compiler/src/dotty/tools/dotc/core/Types.scala b/compiler/src/dotty/tools/dotc/core/Types.scala
index b465510f1866..ecbd9e18dc68 100644
--- a/compiler/src/dotty/tools/dotc/core/Types.scala
+++ b/compiler/src/dotty/tools/dotc/core/Types.scala
@@ -2177,7 +2177,11 @@ object Types {
    *  do not survive runs whereas typerefs do.
    */
   abstract case class ThisType(tref: TypeRef) extends CachedProxyType with SingletonType {
-    def cls(implicit ctx: Context): ClassSymbol = tref.stableInRunSymbol.asClass
+    def cls(implicit ctx: Context): ClassSymbol = tref.stableInRunSymbol match {
+      case cls: ClassSymbol => cls
+      case _ if ctx.mode.is(Mode.Interactive) => defn.AnyClass // was observed to happen in IDE mode
+    }
+
     override def underlying(implicit ctx: Context): Type =
       if (ctx.erasedTypes) tref
       else cls.info match {