From 3ad69fb652f7a364d8d4cf29bb3a37e4a3cc0f63 Mon Sep 17 00:00:00 2001
From: alexlamsl <alexlamsl@gmail.com>
Date: Sat, 25 Mar 2017 01:58:38 +0800
Subject: [PATCH] fix invalid `AST_For.init` Turns out the only place in
 `Compressor` which can generate invalid `AST_For.init` is within
 `drop_unused()`, so focus the fix-up efforts.

supercedes #1652
fixes #1656
---
 lib/compress.js              |  4 +++-
 test/compress/drop-unused.js | 14 ++++++++++++++
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/lib/compress.js b/lib/compress.js
index e13985ee..ab7cca6f 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -1961,6 +1961,9 @@ merge(Compressor.prototype, {
                             return in_list ? MAP.splice(body) : make_node(AST_BlockStatement, node, {
                                 body: body
                             });
+                        } else if (is_empty(node.init)) {
+                            node.init = null;
+                            return node;
                         }
                     }
                     if (node instanceof AST_Scope && node !== self)
@@ -2327,7 +2330,6 @@ merge(Compressor.prototype, {
     };
 
     OPT(AST_For, function(self, compressor){
-        if (is_empty(self.init)) self.init = null;
         if (!compressor.option("loops")) return self;
         if (self.condition) {
             var cond = self.condition.evaluate(compressor);
diff --git a/test/compress/drop-unused.js b/test/compress/drop-unused.js
index 9f3bf77d..fabf8d9f 100644
--- a/test/compress/drop-unused.js
+++ b/test/compress/drop-unused.js
@@ -791,3 +791,17 @@ issue_1583: {
         }
     }
 }
+
+issue_1656: {
+    options = {
+        toplevel: true,
+        unused: true,
+    }
+    beautify = {
+        beautify: true,
+    }
+    input: {
+        for(var a=0;;);
+    }
+    expect_exact: "for (;;) ;"
+}