Fail fast if LHS of subtype is Nothing

odersky · odersky · commit 40bd71cd03db · 2017-12-31T13:59:16.000+01:00
This is purely an optimization. It would have fixed by itself
the subtype loop in the first part of i3627.scala but not the
one in the second part.
diff --git a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
@@ -288,6 +288,7 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
           if (isSubType(info1.alias, tp2)) return true
           if (tp1.prefix.isStable) return false
         case _ =>
+          if (tp1 eq NothingType) return tp1 == tp2.bottomType
       }
       thirdTry(tp1, tp2)
     case tp1: TypeParamRef =>

Original file line number	Diff line number	Diff line change
`@@ -288,6 +288,7 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {`
`288`	`288`	`if (isSubType(info1.alias, tp2)) return true`
`289`	`289`	`if (tp1.prefix.isStable) return false`
`290`	`290`	`case _ =>`
	`291`	`+ if (tp1 eq NothingType) return tp1 == tp2.bottomType`
`291`	`292`	`}`
`292`	`293`	`thirdTry(tp1, tp2)`
`293`	`294`	`case tp1: TypeParamRef =>`