fix corner case in `reduce_vars` (#4490)

fixes #4489

3 files changed, 30 insertions, 8 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 6c26e8a9..bd98c306 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -9427,8 +9427,7 @@ merge(Compressor.prototype, {
                         }
                     }));
                 } else {
-                    value = fixed.optimize(compressor);
-                    if (value === fixed) value = value.transform(new TreeTransformer(function(node, descend) {
+                    value = fixed.optimize(compressor).transform(new TreeTransformer(function(node, descend) {
                         if (node instanceof AST_Scope) return node;
                         node = node.clone();
                         descend(node, this);
diff --git a/test/compress/hoist_vars.js b/test/compress/hoist_vars.js
index 173aaeaf..82f8ede6 100644
--- a/test/compress/hoist_vars.js
+++ b/test/compress/hoist_vars.js
@@ -158,3 +158,22 @@ issue_4487: {
     }
     expect_stdout: "undefined"
 }
+
+issue_4489: {
+    options = {
+        collapse_vars: true,
+        evaluate: true,
+        hoist_vars: true,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        A = 0;
+        var o = !0 || null;
+        for (var k in o);
+    }
+    expect: {
+        for (var k in !(A = 0));
+    }
+}
diff --git a/test/reduce.js b/test/reduce.js
index 120868fe..e45cfa5d 100644
--- a/test/reduce.js
+++ b/test/reduce.js
@@ -322,7 +322,16 @@ module.exports = function reduce_test(testcase, minify_options, reduce_options)
             }
             else if (node instanceof U.AST_Object) {
                 // first property's value
-                var expr = node.properties[0] instanceof U.AST_ObjectKeyVal && node.properties[0].value;
+                var expr = node.properties[0];
+                if (expr instanceof U.AST_ObjectKeyVal) {
+                    expr = expr.value;
+                } else if (expr instanceof U.AST_Spread) {
+                    expr = expr.expression;
+                } else if (expr && expr.key instanceof U.AST_Node) {
+                    expr = expr.key;
+                } else {
+                    expr = null;
+                }
                 if (expr) {
                     node.start._permute++;
                     CHANGED = true;
@@ -351,11 +360,6 @@ module.exports = function reduce_test(testcase, minify_options, reduce_options)
                     }
                 }
             }
-            else if (node instanceof U.AST_Spread) {
-                node.start._permute++;
-                CHANGED = true;
-                return node.expression;
-            }
             else if (node instanceof U.AST_Switch) {
                 var expr = [
                     node.expression,                         // switch expression