Make JetReferenceExpression an interface

compiler/frontend/src/org/jetbrains/jet/lang/psi/JetArrayAccessExpression.java

@@ -29,7 +29,7 @@ import org.jetbrains.jet.lexer.JetTokens;
 import java.util.Collections;
 import java.util.List;
 
-public class JetArrayAccessExpression extends JetReferenceExpression {
+public class JetArrayAccessExpression extends JetExpressionImpl implements JetReferenceExpression {
     public JetArrayAccessExpression(@NotNull ASTNode node) {
         super(node);
     }

compiler/frontend/src/org/jetbrains/jet/lang/psi/JetCallExpression.java

@@ -27,7 +27,7 @@ import org.jetbrains.jet.lexer.JetTokens;
 import java.util.Collections;
 import java.util.List;
 
-public class JetCallExpression extends JetReferenceExpression implements JetCallElement {
+public class JetCallExpression extends JetExpressionImpl implements JetCallElement, JetReferenceExpression {
     public JetCallExpression(@NotNull ASTNode node) {
         super(node);
     }

compiler/frontend/src/org/jetbrains/jet/lang/psi/JetPackageDirective.java

@@ -29,7 +29,7 @@ import org.jetbrains.jet.lang.resolve.name.SpecialNames;
 import java.util.Collections;
 import java.util.List;
 
-public class JetPackageDirective extends JetReferenceExpression {
+public class JetPackageDirective extends JetExpressionImpl implements JetReferenceExpression {
     private String qualifiedNameCache = null;
 
     public JetPackageDirective(@NotNull ASTNode node) {

compiler/frontend/src/org/jetbrains/jet/lang/psi/JetReferenceExpression.java

@@ -16,11 +16,5 @@
 
 package org.jetbrains.jet.lang.psi;
 
-import com.intellij.lang.ASTNode;
+public interface JetReferenceExpression extends JetExpression {
-import org.jetbrains.annotations.NotNull;
-
-public abstract class JetReferenceExpression extends JetExpressionImpl {
-    public JetReferenceExpression(@NotNull ASTNode node) {
-        super(node);
-    }
 }

compiler/frontend/src/org/jetbrains/jet/lang/psi/JetSimpleNameExpression.java

@@ -29,7 +29,7 @@ import org.jetbrains.jet.lexer.JetTokens;
 
 import static org.jetbrains.jet.lexer.JetTokens.*;
 
-public abstract class JetSimpleNameExpression extends JetReferenceExpression {
+public abstract class JetSimpleNameExpression extends JetExpressionImpl implements JetReferenceExpression {
     public static final TokenSet REFERENCE_TOKENS = TokenSet.create(LABEL_IDENTIFIER, IDENTIFIER, FIELD_IDENTIFIER, THIS_KEYWORD, SUPER_KEYWORD);
 
     public JetSimpleNameExpression(@NotNull ASTNode node) {

compiler/frontend/src/org/jetbrains/jet/lang/psi/JetThisReferenceExpression.java

@@ -19,7 +19,7 @@ package org.jetbrains.jet.lang.psi;
 import com.intellij.lang.ASTNode;
 import org.jetbrains.annotations.NotNull;
 
-public class JetThisReferenceExpression extends JetReferenceExpression {
+public class JetThisReferenceExpression extends JetExpressionImpl implements JetReferenceExpression {
     public JetThisReferenceExpression(@NotNull ASTNode node) {
         super(node);
     }

compiler/frontend/src/org/jetbrains/jet/lang/psi/psiUtil/jetPsiUtil.kt

@@ -215,7 +215,7 @@ public fun PsiElement.parameterIndex(): Int {
  * ([[JetQualifiedExpression]] or [[JetUserType]] or original expression)
  */
 public fun JetSimpleNameExpression.getQualifiedElement(): JetElement {
-    val baseExpression = (getParent() as? JetCallExpression) ?: this
+    val baseExpression: JetElement = (getParent() as? JetCallExpression) ?: this
     val parent = baseExpression.getParent()
     return when (parent) {
         is JetQualifiedExpression -> if (parent.getSelectorExpression().isAncestor(baseExpression)) parent else baseExpression