Fix output for arrays containing undefined values.

1b6bcca7 was a first attempt at this. That commit made Uglify stop replacing
holes with undefined, but instead it started replacing undefined with
holes. This is slightly problematic, because there is a difference between a
hole and an undefined value. More problematically, it changed [1,undefined] to
[1,] which generally doesn't even parse as a hole (just as a trailing comma), so
it didn't even preserve the length of the array!

Instead, parse holes as their own special AST node which prints invisibly.

1 files changed, 1 insertions, 1 deletions

diff --git a/lib/parse.js b/lib/parse.js
index 5b6820ff..01fbb88f 100644
--- a/lib/parse.js
+++ b/lib/parse.js
@@ -1131,7 +1131,7 @@ function parse($TEXT, options) {
             if (first) first = false; else expect(",");
             if (allow_trailing_comma && is("punc", closing)) break;
             if (is("punc", ",") && allow_empty) {
-                a.push(new AST_Undefined({ start: S.token, end: S.token }));
+                a.push(new AST_Hole({ start: S.token, end: S.token }));
             } else {
                 a.push(expression(false));
             }