Fixing division by zero while evaluating constant expression.

Review at http://gwt-code-reviews.appspot.com/435801


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@8040 8db76d5a-ed1c-0410-87a9-c151d255dfc7
diff --git a/dev/core/src/com/google/gwt/dev/jjs/impl/gflow/constants/ExpressionEvaluator.java b/dev/core/src/com/google/gwt/dev/jjs/impl/gflow/constants/ExpressionEvaluator.java
index 6b8f576..47d8064 100644
--- a/dev/core/src/com/google/gwt/dev/jjs/impl/gflow/constants/ExpressionEvaluator.java
+++ b/dev/core/src/com/google/gwt/dev/jjs/impl/gflow/constants/ExpressionEvaluator.java
@@ -133,7 +133,11 @@
         case SUB:
           return new JIntLiteral(x.getSourceInfo(), a - b); 
         case DIV:
-          return new JIntLiteral(x.getSourceInfo(), a / b); 
+          if (b != 0) { 
+            return new JIntLiteral(x.getSourceInfo(), a / b);
+          } else {
+            return null;
+          }
         case EQ:
           return JBooleanLiteral.get(a == b); 
         case NEQ:
diff --git a/dev/core/test/com/google/gwt/dev/jjs/impl/gflow/constants/ExpressionEvaluatorTest.java b/dev/core/test/com/google/gwt/dev/jjs/impl/gflow/constants/ExpressionEvaluatorTest.java
index 14b3444..86ab7a8 100644
--- a/dev/core/test/com/google/gwt/dev/jjs/impl/gflow/constants/ExpressionEvaluatorTest.java
+++ b/dev/core/test/com/google/gwt/dev/jjs/impl/gflow/constants/ExpressionEvaluatorTest.java
@@ -69,6 +69,9 @@
     assertThat("1 + i", "int", "int i; i = 1;").evaluatesInto("<null>");
     assertThat("2 + i", "int", "int i = 1;").evaluatesInto("3");
     assertThat("i + 3", "int", "int i = 1;").evaluatesInto("4");
+    assertThat("i / 2", "int", "int i = 6;").evaluatesInto("3");
+    assertThat("i / 0", "int", "int i = 1;").evaluatesInto("<null>");
+    assertThat("4 / 0", "int", "int i = 0;").evaluatesInto("<null>");
   }
   
   private static class Result {