fix: ensure delimiter added when scripts merged across async writers

.changeset/purple-cameras-sit.md

@@ -0,0 +1,7 @@
+---
+"marko": patch
+"@marko/compiler": patch
+"@marko/translator-default": patch
+---
+
+Fix an issue where merging scripts (via the out.script api) was not properly inserting delimeters when scripts are added in different async writers.

packages/marko/src/runtime/html/StringWriter.js

@@ -27,7 +27,13 @@ StringWriter.prototype = {
 
   merge: function (otherWriter) {
     this._content += otherWriter._content;
-    this._scripts += otherWriter._scripts;
+
+    if (otherWriter._scripts) {
+      this._scripts = this._scripts
+        ? this._scripts + ";" + otherWriter._scripts
+        : otherWriter._scripts;
+    }
+
     if (otherWriter._data) {
       if (this._data) {
         for (const key in otherWriter._data) {

packages/marko/test/components-server/fixtures/scriptConcat/template.marko

@@ -0,0 +1,17 @@
+import { setImmediate } from "timers";
+static function tick() {
+	return new Promise(resolve => setImmediate(() => setImmediate(resolve)));
+}
+
+<!-- Should merge scripts in the same writer.-->
+$ out.script("console.log('hello')");
+$ out.script("console.log('world')");
+
+<!-- Should merge scripts in different writers.-->
+<await(tick())>
+	<@then>
+		$ out.script("console.log('again')");
+	</>
+</await>
+
+$ out.script("console.log('and again')");

packages/marko/test/components-server/fixtures/scriptConcat/test.js

@@ -0,0 +1,12 @@
+var expect = require("chai").expect;
+
+module.exports = function (helpers, done) {
+  var template = require("./template.marko").default;
+
+  template.render({}, function (err, html) {
+    expect(html.toString()).to.include(
+      "console.log('hello');console.log('world');console.log('again');console.log('and again')"
+    );
+    done();
+  });
+};