do not inject IIFE's own arguments into the IIFE when they contain `a…

…wait`. Closes #1489

lib/compress/tighten-body.js

@@ -574,6 +574,14 @@ export function tighten_body(statements, compressor) {
             return found;
         }
 
+        function arg_is_injectable(arg) {
+            if (arg instanceof AST_Expansion) return false;
+            const contains_await = walk(arg, (node) => {
+                if (node instanceof AST_Await) return walk_abort;
+            });
+            if (contains_await) return false;
+            return true;
+        }
         function extract_args() {
             var iife, fn = compressor.self();
             if (is_func_expr(fn)
@@ -582,7 +590,8 @@ export function tighten_body(statements, compressor) {
                 && !fn.pinned()
                 && (iife = compressor.parent()) instanceof AST_Call
                 && iife.expression === fn
-                && iife.args.every((arg) => !(arg instanceof AST_Expansion))) {
+                && iife.args.every(arg_is_injectable)
+            ) {
                 var fn_strict = compressor.has_directive("use strict");
                 if (fn_strict && !member(fn_strict, fn.body))
                     fn_strict = false;

test/compress/collapse_vars.js

@@ -2124,6 +2124,20 @@ iife_2: {
     }
 }
 
+iife_async: {
+    options = { unused: true, collapse_vars: true }
+    input: {
+        (async function(s) {
+            return ((s, a) => s + a)(s, await new Promise(() => {}))
+        })();
+    }
+    expect: {
+        (async function(s) {
+            return ((s, a) => s + a)(void 0, await new Promise(() => {}))
+        })();
+    }
+}
+
 var_defs: {
     options = {
         booleans: true,