Fix for SI-3272.

"References to the type parameters in object-private or
 object-protected values, variables, or methods (§5.2) of
 the class are not checked for their variance position."

Review by @odersky.

4 files changed, 48 insertions, 23 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala b/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
index 045614e773..54b711cebc 100644
--- a/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
@@ -951,17 +951,20 @@ abstract class RefChecks extends InfoTransform with reflect.internal.transform.R
 
       override def traverse(tree: Tree) {
         tree match {
-          case ClassDef(_, _, _, _) |
-               TypeDef(_, _, _, _) =>
+          case ClassDef(_, _, _, _) | TypeDef(_, _, _, _) =>
             validateVariance(tree.symbol)
             super.traverse(tree)
           // ModuleDefs need not be considered because they have been eliminated already
           case ValDef(_, _, _, _) =>
-            validateVariance(tree.symbol)
+            if (!tree.symbol.hasLocalFlag)
+              validateVariance(tree.symbol)
           case DefDef(_, _, tparams, vparamss, _, _) =>
-            validateVariance(tree.symbol)
-            traverseTrees(tparams)
-            traverseTreess(vparamss)
+            // No variance check for object-private/protected methods/values.
+            if (!tree.symbol.hasLocalFlag) {
+              validateVariance(tree.symbol)
+              traverseTrees(tparams)
+              traverseTreess(vparamss)
+            }
           case Template(_, _, _) =>
             super.traverse(tree)
           case _ =>
diff --git a/test/files/neg/variances.check b/test/files/neg/variances.check
index dc72b05e1e..0643e533b7 100644
--- a/test/files/neg/variances.check
+++ b/test/files/neg/variances.check
@@ -1,16 +1,19 @@
 variances.scala:4: error: covariant type A occurs in contravariant position in type test.Vector[A] of value x
-  def append(x: Vector[A]): Vector[A] 
+  def append(x: Vector[A]): Vector[A]
              ^
-variances.scala:14: error: covariant type A occurs in contravariant position in type A of value a
-    private[this] def setA(a : A) = this.a = a 
-                           ^
-variances.scala:16: error: covariant type A occurs in invariant position in supertype test.C[A] of object Baz
+variances.scala:18: error: covariant type A occurs in contravariant position in type A of value a
+    private def setA3(a : A) = this.a = a
+                      ^
+variances.scala:19: error: covariant type A occurs in contravariant position in type A of value a
+    protected def setA4(a : A) = this.a = a
+                        ^
+variances.scala:21: error: covariant type A occurs in invariant position in supertype test.C[A] of object Baz
     object Baz extends C[A]
            ^
-variances.scala:63: error: covariant type A occurs in contravariant position in type => test.Covariant.T[A]{val m: A => A} of value x
+variances.scala:74: error: covariant type A occurs in contravariant position in type => test.Covariant.T[A]{val m: A => A} of value x
     val x: T[A] {
         ^
-variances.scala:79: error: covariant type T occurs in contravariant position in type => test.TestAlias.B[C.this.A] of method foo
+variances.scala:90: error: covariant type T occurs in contravariant position in type => test.TestAlias.B[C.this.A] of method foo
     def foo: B[A]
         ^
-5 errors found
+6 errors found
diff --git a/test/files/neg/variances.scala b/test/files/neg/variances.scala
index 726bc35270..10ca111cd0 100644
--- a/test/files/neg/variances.scala
+++ b/test/files/neg/variances.scala
@@ -1,7 +1,7 @@
 package test
 
 trait Vector[+A] {
-  def append(x: Vector[A]): Vector[A] 
+  def append(x: Vector[A]): Vector[A]
   private[this] def append3(x: Vector[A]): Vector[A] = append(x)
 }
 
@@ -11,19 +11,27 @@ object Covariant {
   class Foo[+A] {
     private[this] var a : A = _
     def getA : A = a
-    private[this] def setA(a : A) = this.a = a 
-    
+    // allowed
+    private[this] def setA1(a : A) = this.a = a
+    protected[this] def setA2(a : A) = this.a = a
+    // forbidden
+    private def setA3(a : A) = this.a = a
+    protected def setA4(a : A) = this.a = a
+
     object Baz extends C[A]
     trait Convert[B] {
       def b2a(b : B) : A
-      def doit(b : B) = setA(b2a(b))
+      def doit1(b : B) = setA1(b2a(b))
+      def doit2(b : B) = setA2(b2a(b))
+      def doit3(b : B) = setA3(b2a(b))
+      def doit4(b : B) = setA4(b2a(b))
     }
   }
   class Foo2[+A] {
     private[this] var a : A = _
     def getA : A = a
-    private[this] def setA(a : A) = this.a = a 
-    
+    private[this] def setA(a : A) = this.a = a
+
     {
       trait Convert[B] {
         def b2a(b : B) : A
@@ -35,8 +43,8 @@ object Covariant {
   class Foo3[+A] {
     private[this] var a : A = _
     def getA : A = a
-    private[this] def setA(a : A) = this.a = a 
-    
+    private[this] def setA(a : A) = this.a = a
+
     private[this] trait Convert[B] {
       def b2a(b : B) : A
       def doit(b : B) = setA(b2a(b))
@@ -54,7 +62,10 @@ object Covariant {
   }
   def main(args : Array[String]) {
     val test = new Test
-    test.c.doit(test.b)
+    test.c.doit1(test.b)
+    test.c.doit2(test.b)
+    test.c.doit3(test.b)
+    test.c.doit4(test.b)
     val x : java.lang.Character = test.a.getA
     Console.println("XXX " + x)
   }
diff --git a/test/files/pos/t3272.scala b/test/files/pos/t3272.scala
new file mode 100644
index 0000000000..8efd5ded2c
--- /dev/null
+++ b/test/files/pos/t3272.scala
@@ -0,0 +1,8 @@
+trait A {
+  trait C[+T] {
+    protected[this] def f(t: T) {}
+  }
+  trait D[T] extends C[T] {
+    def g(t: T) { f(t) }
+  }
+}