Class symbols can't be contravariant.

During development of the fix for SI-6666, I encountered:

    % test/files/pos/t4842.scala
    test/files/pos/t4842.scala:10: error: contravariant class Bar occurs in covariant position in type ()this.Bar of constructor Bar
         this(new { class Bar { println(Bar.this); new { println(Bar.this) } }; new Bar } ) // okay

I had incorrectly set the INCONSTRUCTOR flag on the class symbol
`Bar`. (It isn't directly in the self constructor call, as it
is nested an intervening anonymous class.)

But, this flag shares a slot with CONTRAVARIANT, and the variance
validation intepreted it as such.

ClassSymbol already has this code to resolve the ambiguous
flags for display purposes:

    override def resolveOverloadedFlag(flag: Long) = flag match {
      case INCONSTRUCTOR => "<inconstructor>" // INCONSTRUCTOR / CONTRAVARIANT / LABEL
      case EXISTENTIAL   => "<existential>"   // EXISTENTIAL / MIXEDIN
      case IMPLCLASS     => "<implclass>"     // IMPLCLASS / PRESUPER
      case _             => super.resolveOverloadedFlag(flag)
    }

This commit overrides `isContravariant` to reflect the same logic.

2 files changed, 4 insertions, 1 deletions

diff --git a/src/compiler/scala/tools/nsc/interpreter/IMain.scala b/src/compiler/scala/tools/nsc/interpreter/IMain.scala
index b46d28dec3..4b6466c079 100644
--- a/src/compiler/scala/tools/nsc/interpreter/IMain.scala
+++ b/src/compiler/scala/tools/nsc/interpreter/IMain.scala
@@ -262,7 +262,9 @@ class IMain(initialSettings: Settings, protected val out: JPrintWriter) extends
   protected def newCompiler(settings: Settings, reporter: Reporter): ReplGlobal = {
     settings.outputDirs setSingleOutput virtualDirectory
     settings.exposeEmptyPackage.value = true
-    new Global(settings, reporter) with ReplGlobal
+    new Global(settings, reporter) with ReplGlobal {
+      override def toString: String = "<global>"
+    }
   }
 
   /** Parent classloader.  Overridable. */
diff --git a/src/reflect/scala/reflect/internal/Symbols.scala b/src/reflect/scala/reflect/internal/Symbols.scala
index a4287fb181..923dac7498 100644
--- a/src/reflect/scala/reflect/internal/Symbols.scala
+++ b/src/reflect/scala/reflect/internal/Symbols.scala
@@ -2867,6 +2867,7 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
     final override def isNonClassType = false
     final override def isAbstractType = false
     final override def isAliasType = false
+    final override def isContravariant = false
 
     override def isAbstractClass           = this hasFlag ABSTRACT
     override def isCaseClass               = this hasFlag CASE