From dba4b94443a8066df23ee7ccdb890ad048a06a2c Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Sun, 13 Dec 2015 15:32:17 +0100
Subject: Avoid cycle when computing sets

The tightened subtyping algorithm led to a cycle in baseTypeRef when
compiling sets.scala. This commit fixes the problem.
---
 src/dotty/tools/dotc/core/Types.scala | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

(limited to 'src')

diff --git a/src/dotty/tools/dotc/core/Types.scala b/src/dotty/tools/dotc/core/Types.scala
index a7c457d8f..f65633595 100644
--- a/src/dotty/tools/dotc/core/Types.scala
+++ b/src/dotty/tools/dotc/core/Types.scala
@@ -447,7 +447,18 @@ object Types {
             if (rinfo.isAlias) rinfo
             else if (pdenot.info.isAlias) pdenot.info
             else if (ctx.pendingMemberSearches.contains(name)) safeAnd(pdenot.info, rinfo)
-            else pdenot.info & rinfo
+            else
+              try pdenot.info & rinfo
+              catch {
+                case ex: CyclicReference =>
+                  // happens for tests/pos/sets.scala. findMember is called from baseTypeRef.
+                  // The & causes a subtype check which calls baseTypeRef again with the same
+                  // superclass. In the observed case, the superclass was Any, and
+                  // the special shortcut for Any in derivesFrom was as yet absent. To reproduce,
+                  // remove the special treatment of Any in derivesFrom and compile
+                  // sets.scala.
+                  safeAnd(pdenot.info, rinfo)
+              }
           pdenot.asSingleDenotation.derivedSingleDenotation(pdenot.symbol, jointInfo)
         } else
           pdenot & (new JointRefDenotation(NoSymbol, rinfo, Period.allInRun(ctx.runId)), pre)
@@ -1562,6 +1573,15 @@ object Types {
       case _ =>
         false
     }
+
+    /* A version of toString which also prints aliases. Can be used for debugging
+    override def toString =
+      if (isTerm) s"TermRef($prefix, $name)"
+      else s"TypeRef($prefix, $name)${
+        if (lastDenotation != null && lastDenotation.infoOrCompleter.isAlias)
+          s"@@@ ${lastDenotation.infoOrCompleter.asInstanceOf[TypeAlias].hi}"
+        else ""}"
+    */
   }
 
   abstract case class TermRef(override val prefix: Type, name: TermName) extends NamedType with SingletonType {
-- 
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