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.

1 files changed, 15 insertions, 0 deletions

diff --git a/test/files/run/class-symbol-contravariant.scala b/test/files/run/class-symbol-contravariant.scala
new file mode 100644
index 0000000000..6a84944e3b
--- /dev/null
+++ b/test/files/run/class-symbol-contravariant.scala
@@ -0,0 +1,15 @@
+import scala.tools.partest.ReplTest
+
+object Test extends ReplTest {
+  override def code = """
+  |:power
+  |val u = rootMirror.universe
+  |import u._, scala.reflect.internal.Flags
+  |class C
+  |val sym = u.typeOf[C].typeSymbol
+  |sym.isContravariant
+  |sym setFlag Flags.INCONSTRUCTOR
+  |sym.isClassLocalToConstructor
+  |sym.isContravariant // was true
+  |""".stripMargin.trim
+}
\ No newline at end of file