Use symbol.owner

Author: OlivierBlanvillain

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

@@ -483,7 +483,6 @@ class Definitions {
   lazy val BoxedFloatModule   = ctx.requiredModule("java.lang.Float")
   lazy val BoxedDoubleModule  = ctx.requiredModule("java.lang.Double")
   lazy val BoxedUnitModule    = ctx.requiredModule("java.lang.Void")
-  lazy val SystemModule       = ctx.requiredModule("java.lang.System")
 
   lazy val ByNameParamClass2x = enterSpecialPolyClass(tpnme.BYNAME_PARAM_CLASS, Covariant, Seq(AnyType))
   lazy val EqualsPatternClass = enterSpecialPolyClass(tpnme.EQUALS_PATTERN, EmptyFlags, Seq(AnyType))
@@ -516,6 +515,9 @@ class Definitions {
   lazy val JavaSerializableClass     = ctx.requiredClass("java.io.Serializable")
   lazy val ComparableClass           = ctx.requiredClass("java.lang.Comparable")
 
+  lazy val SystemClass               = ctx.requiredClass("java.lang.System")
+  lazy val SystemModule              = SystemClass.linkedClass
+
   // in scalac modified to have Any as parent
 
   lazy val SerializableType: TypeRef       = ctx.requiredClassRef("scala.Serializable")

compiler/src/dotty/tools/dotc/transform/localopt/Simplify.scala

@@ -153,7 +153,7 @@ object Simplify {
    */
   def isEffectivelyMutable(t: Tree)(implicit ctx: Context): Boolean = t match {
     case _ if t.symbol.is(Mutable) => true
-    case s: Select => (s.symbol == defn.SystemModule)
+    case s: Select => s.symbol.owner == defn.SystemModule
     case i: Ident  => desugarIdent(i).exists(isEffectivelyMutable)
     case _ => false
   }