Fixed handling of empty keys in emitSWITCH.

The problem of emitSWITCH not handling empty
keys popped up when I tried to implement
unfolding of pattern alternatives in genicode
instead of in typers/explicitouter.

This change makes perfect sense in isolation
as bytecode allows LOOKUPSWITCHes that have
only default case. I actually verified that
this kind of bytecode is generated by javac
when one has switch statement with only
default case defined.

Review by @paulp or @dragos.

Author: gkossakowski

lib/fjbg.jar.desired.sha1

@@ -1 +1 @@
-9aa9c99b8032e454f1f85d27de31a88b3dec1045 ?fjbg.jar
+c3f9b576c91cb9761932ad936ccc4a71f33d2ef2 ?fjbg.jar

src/fjbg/ch/epfl/lamp/fjbg/JExtendedCode.java

@@ -596,6 +596,16 @@ public void emitSWITCH(int[] keys,
                            double minDensity) {
         assert keys.length == branches.length;
 
+        //The special case for empty keys. It makes sense to allow
+        //empty keys and generate LOOKUPSWITCH with defaultBranch
+        //only. This is exactly what javac does for switch statement
+        //that has only a default case.
+        if (keys.length == 0) {
+          emitLOOKUPSWITCH(keys, branches, defaultBranch);
+          return;
+        }
+        //the rest of the code assumes that keys.length > 0
+
         // sorting the tables
         // FIXME use quicksort
         for (int i = 1; i < keys.length; i++) {