SI-2066 -Xsource:2.10: lenient treatment of variance in <:<, =:=

The soundness hole was exploited in Scalaz. They have fixed their
codebase correctly for Scalac 7.1.x, but have less freedom to
break source compatiblity in 7.0.x.

After this commit, they could choose to compile that branch with
-Xsource:2.10

3 files changed, 5 insertions, 2 deletions

diff --git a/src/reflect/scala/reflect/internal/settings/MutableSettings.scala b/src/reflect/scala/reflect/internal/settings/MutableSettings.scala
index 28afd18fe0..816916787e 100644
--- a/src/reflect/scala/reflect/internal/settings/MutableSettings.scala
+++ b/src/reflect/scala/reflect/internal/settings/MutableSettings.scala
@@ -51,6 +51,8 @@ abstract class MutableSettings extends AbsSettings {
 
   def Yrecursion: IntSetting
   def maxClassfileName: IntSetting
+
+  def isScala211: Boolean
 }
 
 object MutableSettings {
diff --git a/src/reflect/scala/reflect/internal/tpe/TypeComparers.scala b/src/reflect/scala/reflect/internal/tpe/TypeComparers.scala
index 3c4e93f11d..f9b10c90be 100644
--- a/src/reflect/scala/reflect/internal/tpe/TypeComparers.scala
+++ b/src/reflect/scala/reflect/internal/tpe/TypeComparers.scala
@@ -173,11 +173,11 @@ trait TypeComparers {
   // SI-2066 This prevents overrides with incompatible variance in higher order type parameters.
   private def methodHigherOrderTypeParamsSameVariance(sym1: Symbol, sym2: Symbol) = {
     def ignoreVariance(sym: Symbol) = !(sym.isHigherOrderTypeParameter && sym.logicallyEnclosingMember.isMethod)
-    ignoreVariance(sym1) || ignoreVariance(sym2) || sym1.variance == sym2.variance
+    !settings.isScala211 || ignoreVariance(sym1) || ignoreVariance(sym2) || sym1.variance == sym2.variance
   }
 
   private def methodHigherOrderTypeParamsSubVariance(low: Symbol, high: Symbol) =
-    methodHigherOrderTypeParamsSameVariance(low, high) || low.variance.isInvariant
+    !settings.isScala211 || methodHigherOrderTypeParamsSameVariance(low, high) || low.variance.isInvariant
 
   def isSameType2(tp1: Type, tp2: Type): Boolean = {
     def retry(lhs: Type, rhs: Type) = ((lhs ne tp1) || (rhs ne tp2)) && isSameType(lhs, rhs)
diff --git a/src/reflect/scala/reflect/runtime/Settings.scala b/src/reflect/scala/reflect/runtime/Settings.scala
index 11db83d7d5..de5ba99900 100644
--- a/src/reflect/scala/reflect/runtime/Settings.scala
+++ b/src/reflect/scala/reflect/runtime/Settings.scala
@@ -48,4 +48,5 @@ private[reflect] class Settings extends MutableSettings {
 
   val Yrecursion        = new IntSetting(0)
   val maxClassfileName  = new IntSetting(255)
+  def isScala211        = true
 }