Do not suggest to add variance modifier if both in and out are possible

idea/src/org/jetbrains/kotlin/idea/inspections/AddVarianceModifierInspection.kt

@@ -56,8 +56,8 @@ class AddVarianceModifierInspection : AbstractKotlinInspection() {
                     val variances = listOf(Variance.IN_VARIANCE, Variance.OUT_VARIANCE).filter {
                         variancePossible(klass, parameterDescriptor, it, context)
                     }
-                    if (variances.isNotEmpty()) {
-                        val suggested = variances.joinToString(" or ") { "'$it'" }
+                    if (variances.size == 1) {
+                        val suggested = variances.first()
                         val fixes = variances.map { AddVarianceFix(it) }
                         holder.registerProblem(
                                 typeParameter,

idea/testData/inspections/addVarianceModifier/inspectionData/expected.xml

@@ -31,12 +31,4 @@
         <problem_class severity="WARNING" attribute_key="WARNING_ATTRIBUTES">Type parameter can have 'in' or 'out' variance</problem_class>
         <description>Type parameter can have 'in' variance</description>
     </problem>
-    <problem>
-        <file>test.kt</file>
-        <line>24</line>
-        <module>light_idea_test_case</module>
-        <entry_point TYPE="file" FQNAME="temp:///src/test.kt" />
-        <problem_class severity="WARNING" attribute_key="WARNING_ATTRIBUTES">Type parameter can have 'in' or 'out' variance</problem_class>
-        <description>Type parameter can have 'in' or 'out' variance</description>
-    </problem>
 </problems>

idea/testData/inspections/addVarianceModifier/test.kt

@@ -21,7 +21,7 @@ abstract class AbstractOut<T> {
 abstract class AbstractIn<T>(private val foo: T) {
     fun bar(arg: T) = foo == arg
 }
-interface Empty<T>
+interface Empty<T> // here we do not report anything to avoid ambiguity
 
 abstract class AbstractInv<T>(var foo: T)
 

idea/testData/quickfix/addVarianceModifier/emptyTest.kt

@@ -1,2 +1,3 @@
-// "Add 'out' variance" "true"
+// "Add 'out' variance" "false"
+// ACTION: Implement interface
 interface Empty<<caret>T>

idea/testData/quickfix/addVarianceModifier/emptyTest.kt.after

@@ -1,2 +0,0 @@
-// "Add 'out' variance" "true"
-interface Empty<out T>