fix corner case in unused (#4850)

fixes #4849

lib/compress.js

@@ -9393,6 +9393,7 @@ merge(Compressor.prototype, {
             var seq = lift_sequence_in_expression(self, compressor);
             if (seq !== self) return seq.optimize(compressor);
         }
+        if (compressor.option("unused")) drop_unused_call_args(self, compressor);
         if (compressor.option("unsafe")) {
             var exp = self.expression;
             if (is_undeclared_ref(exp)) {

test/compress/exponentiation.js

@@ -99,8 +99,8 @@ issue_4664: {
     expect: {
         (function f() {
             new function(a) {
-                console.log(typeof f, 2 ** 30, typeof this);
+                console.log(typeof f, 1073741824, typeof this);
-            }(0, A = 0);
+            }(A = 0);
         })();
     }
     expect_stdout: "function 1073741824 object"

test/compress/spreads.js

@@ -1045,3 +1045,26 @@ issue_4614: {
     expect_stdout: true
     node_version: ">=6"
 }
+
+issue_4849: {
+    options = {
+        reduce_vars: true,
+        unused: true,
+    }
+    input: {
+        while (function() {
+            while (!console);
+        }(new function(a) {
+            console.log(typeof { ...a });
+        }(function() {})));
+    }
+    expect: {
+        while (function() {
+            while (!console);
+        }(function(a) {
+            console.log(typeof { ...function() {} });
+        }()));
+    }
+    expect_stdout: "object"
+    node_version: ">=8"
+}