test for fixed KT-1891

compiler/testData/codegen/regressions/kt1891.kt

@@ -0,0 +1,14 @@
+class MyList<T>() {
+    var value: T? = null
+
+    fun get(index: Int): T = value!!
+
+    fun set(index: Int, value: T) { this.value = value }
+}
+
+fun box(): String {
+    val list = MyList<Int>()
+    list[17] = 1
+    list[17] = list[18]++
+    return "OK"
+}

compiler/tests/org/jetbrains/jet/codegen/ClassGenTest.java

@@ -426,4 +426,9 @@ public class ClassGenTest extends CodegenTestCase {
         createEnvironmentWithMockJdkAndIdeaAnnotations(CompilerSpecialMode.JDK_HEADERS);
         blackBoxFile("regressions/kt1611.kt");
     }
+
+    public void testKt1891() {
+        createEnvironmentWithMockJdkAndIdeaAnnotations(CompilerSpecialMode.JDK_HEADERS);
+        blackBoxFile("regressions/kt1891.kt");
+    }
 }