JET-40 Check that 'else' entry is the last one in the list of 'when' entries

idea/src/org/jetbrains/jet/lang/cfg/JetControlFlowProcessor.java

@@ -622,11 +622,18 @@ public class JetControlFlowProcessor {
             Label doneLabel = builder.createUnboundLabel();
 
             Label nextLabel = builder.createUnboundLabel();
-            for (JetWhenEntry whenEntry : expression.getEntries()) {
+            for (Iterator<JetWhenEntry> iterator = expression.getEntries().iterator(); iterator.hasNext(); ) {
+                JetWhenEntry whenEntry = iterator.next();
                 if (whenEntry.getSubWhen() != null) throw new UnsupportedOperationException(); // TODO
 
                 if (whenEntry.isElseContinue()) throw new UnsupportedOperationException(); // TODO
 
+                if (whenEntry.isElse()) {
+                    if (iterator.hasNext()) {
+                        trace.getErrorHandler().genericError(whenEntry.getNode(), "'else' entry must be the last one in a when-expression");
+                    }
+                }
+
                 JetWhenCondition condition = whenEntry.getCondition();
                 if (condition != null) {
                     condition.accept(new JetVisitor() {

idea/testData/checker/When.jet

@@ -14,6 +14,7 @@ fun foo() {
       .<error>a</error> => 1
       .equals(1).<error>a</error> => 1
       <warning>?.</warning>equals(1) => 1
+      else => 1
     }
     when (<warning>x</warning>?:null) {
       <error>.</error>equals(1) => 1
@@ -46,6 +47,15 @@ fun test() {
     is boo @ (1, <error>"a"</error>, *) => 1
     is boo @ <error>(1, *)</error> => 1
   }
+
+  when (z) {
+    <error>else => 1</error>
+    (1, 1) => 2
+  }
+
+  when (z) {
+    else => 1
+  }
 }
 
 val (Int, Int).boo : (Int, Int, Int) = (1, 1, 1)