From bb3eb65015666fc1e9de1f91b9c1589f2346d5ad Mon Sep 17 00:00:00 2001
From: David Glasser <glasser@davidglasser.net>
Date: Wed, 16 Jan 2013 14:59:19 -0500
Subject: [PATCH] Fix output for arrays whose last element is a hole: [1,,]

1529ab96 started to do this (by considering holes to be separate from
"undefined") but it still converted
   [1,,]    (length 2, last element hole, trailing comma)
to
   [1,]     (length 1, trailing comma)

Unfortunately the test suite doesn't really make this clear: the new test here
passes with or without this patch because run-tests.js beautifys the expected
output (in "make_code"), which does the incorrect transformation! If you make
some manual change to arrays.js to make the test fail and see the INPUT and
OUTPUT, then you can see that without this fix, [1,,] -> [1,], and with this fix
it stays [1,,].
---
 lib/output.js           | 5 +++++
 test/compress/arrays.js | 2 ++
 2 files changed, 7 insertions(+)

diff --git a/lib/output.js b/lib/output.js
index 42b3aad9..27a83a43 100644
--- a/lib/output.js
+++ b/lib/output.js
@@ -1007,6 +1007,11 @@ function OutputStream(options) {
             a.forEach(function(exp, i){
                 if (i) output.comma();
                 exp.print(output);
+                // If the final element is a hole, we need to make sure it
+                // doesn't look like a trailing comma, by inserting an actual
+                // trailing comma.
+                if (i === len - 1 && exp instanceof AST_Hole)
+                  output.comma();
             });
             if (len > 0) output.space();
         });
diff --git a/test/compress/arrays.js b/test/compress/arrays.js
index 10fe6eb5..0c3d8ba2 100644
--- a/test/compress/arrays.js
+++ b/test/compress/arrays.js
@@ -1,10 +1,12 @@
 holes_and_undefined: {
     input: {
+        w = [1,,];
         x = [1, 2, undefined];
         y = [1, , 2, ];
         z = [1, undefined, 3];
     }
     expect: {
+        w=[1,,];
         x=[1,2,void 0];
         y=[1,,2];
         z=[1,void 0,3];