Throw FallThroughError when we fall through a case in a switch statement. Fixes

frogsh

Index: frogsh
===================================================================
--- frogsh	(revision 858)
+++ frogsh	(working copy)
@@ -283,6 +283,11 @@
 TypeError.prototype.toString = function() {
   return ("Failed type check: type " + this.srcType + " is not assignable to type ") + ("" + this.dstType + " of " + this.dstName + " in " + this.url + " at line ") + ("" + this.line + ", column " + this.column + ".");
 }
+// ********** Code for FallThroughError **************
+function FallThroughError() {}
+FallThroughError.prototype.toString = function() {
+  return ("Switch case fall-through in " + this.url + " at line " + this.line + ".");
+}
 // ********** Code for Object **************
 Object.prototype.get$dynamic = function() {
   return this;
@@ -7272,6 +7277,7 @@
   else {
     this.writer.writeln(('return ' + this.visitValue(node.value).code + ';'));
   }
+  return true;
 }
 MethodGenerator.prototype.visitThrowStatement = function(node) {
   if (node.value != null) {
@@ -7288,6 +7294,7 @@
       this.writer.writeln(('throw ' + rethrow.code + ';'));
     }
   }
+  return true;
 }
 MethodGenerator.prototype.visitAssertStatement = function(node) {
   var test = this.visitValue(node.test);
@@ -7309,6 +7316,7 @@
   else {
     this.writer.writeln(('break ' + node.label.name + ';'));
   }
+  return true;
 }
 MethodGenerator.prototype.visitContinueStatement = function(node) {
   if (node.label == null) {
@@ -7317,15 +7325,18 @@
   else {
     this.writer.writeln(('continue ' + node.label.name + ';'));
   }
+  return true;
 }
 MethodGenerator.prototype.visitIfStatement = function(node) {
   var test = this.visitBool(node.test);
+  var return1, return2;
   this.writer.write(('if (' + test.code + ') '));
-  node.trueBranch.visit(this);
+  return1 = node.trueBranch.visit(this);
   if (node.falseBranch != null) {
     this.writer.write('else ');
-    node.falseBranch.visit(this);
+    return2 = node.falseBranch.visit(this);
   }
+  return (return1 && return2);
 }
 MethodGenerator.prototype.visitWhileStatement = function(node) {
   var test = this.visitBool(node.test);
@@ -7482,6 +7493,7 @@
 MethodGenerator.prototype.visitSwitchStatement = function(node) {
   var test = this.visitValue(node.test);
   this.writer.enterBlock(('switch (' + test.code + ') {'));
+  var allCasesReturn = true;
   var $list = node.cases;
   for (var $i = 0;$i < $list.length; $i++) {
     var case_ = $list.$index($i);
@@ -7493,6 +7505,9 @@
      i < case_.cases.length; i++) {
       var expr = case_.cases.$index(i);
       if (expr == null) {
+        if (i < case_.cases.length - 1) {
+          world.error('default clause must be the last case', case_.get$span());
+        }
         this.writer.writeln('default:');
       }
       else {
@@ -7501,26 +7516,35 @@
       }
     }
     this.writer.enterBlock('');
+    var caseReturns;
     var $list0 = case_.statements;
     for (var $i0 = case_.statements.iterator(); $i0.hasNext(); ) {
       var stmt = $i0.next();
-      stmt.visit(this);
+      caseReturns = stmt.visit(this);
     }
+    if ($ne(case_, node.cases.$index(node.cases.length - 1)) && !caseReturns) {
+      var span = case_.statements.$index(case_.statements.length - 1).get$span();
+      this.writer.writeln(('\$throw(new FallThroughError("' + span.file.filename + '",') + (' ' + span.file.getLine(span.start) + '))'));
+      allCasesReturn = false;
+    }
     this.writer.exitBlock('');
     this._popBlock();
   }
   this.writer.exitBlock('}');
+  return allCasesReturn;
 }
 MethodGenerator.prototype.visitBlockStatement = function(node) {
   this._pushBlock(false);
   this.writer.enterBlock('{');
+  var returns;
   var $list = node.body;
   for (var $i = 0;$i < $list.length; $i++) {
     var stmt = $list.$index($i);
-    stmt.visit(this);
+    returns = stmt.visit(this);
   }
   this.writer.exitBlock('}');
   this._popBlock();
+  return returns;
 }
 MethodGenerator.prototype.visitLabeledStatement = function(node) {
   this.writer.writeln(('' + node.name.name + ':'));