Implement lit template parser for limited template formats which extends LitTemplate element

flow-server/src/main/java/com/vaadin/flow/component/polymertemplate/BundleParser.java

@@ -249,12 +249,8 @@ public static Element parseLitTemplateElement(String fileName,
         // template contents.
         if (templateMatcher.find() && templateMatcher.groupCount() == 2) {
             String group = templateMatcher.group(2);
-            // in case greedy match let's truncate the second group (remove
-            // everything after delimiter)
-            int index = group.indexOf(templateMatcher.group(1));
-            if (index >= 0) {
-                group = group.substring(0, index);
-            }
+            group = getNonGreadyTemplateContent(group,
+                    templateMatcher.group(1));
             LOGGER.trace("Found regular Lit template content was {}", group);
 
             templateDocument = Jsoup.parse(group);
@@ -273,6 +269,37 @@ public static Element parseLitTemplateElement(String fileName,
         return null;
     }
 
+    private static String getNonGreadyTemplateContent(String greedyContent,
+            String delimiter) {
+        String templateContent = greedyContent;
+        // in case greedy match let's truncate the second group (remove
+        // everything after delimiter)
+        int index = -1;
+        while (true) {
+            index = greedyContent.indexOf(delimiter, index + 1);
+            if (index < 0) {
+                break;
+            }
+            templateContent = greedyContent.substring(0, index);
+            if (!endsWithEscaped(templateContent)) {
+                break;
+            }
+        }
+        return templateContent;
+    }
+
+    private static boolean endsWithEscaped(String value) {
+        int slashCount = 0;
+        for (int i = value.length() - 1; i >= 0; i--) {
+            if (value.charAt(i) == '\\') {
+                slashCount++;
+            } else {
+                break;
+            }
+        }
+        return slashCount % 2 == 1;
+    }
+
     private static Element tryParsePolymer2(Document templateDocument,
             Matcher noTemplateMatcher) {
         while (noTemplateMatcher.find()

flow-server/src/test/resources/META-INF/VAADIN/config/stats.json

@@ -50,7 +50,7 @@
               ,
               {
                 "name": "./frontend/MyGreedyLitElement.js",
-                "source": "// Import an element\nimport { LitElement, html } from 'lit-element';\n\n// Define an element class\n export class MyGreedyLitElement extends LitElement {\n\n  // Define the element's template\n  render() {\n    return html`\n      <style>\n        :host{ \n          margin: 5px; \n        }\n      \n        .response { margin-top: 10px; } \n      </style>\n   <div>Tag name doesn't match the JS module name<div>inner</div></div>   <div id='test'  class='response'>greedy</div>\n    `;\n static get styles() { return css`:host { background-color: pink } <span>incorrect content</span>`; } }\n}\n\n// Register the element with the browser\ncustomElements.define('my-greedy-element', MyGreedyLitElement);"
+                "source": "// Import an element\nimport { LitElement, html } from 'lit-element';\n\n// Define an element class\n export class MyGreedyLitElement extends LitElement {\n\n  // Define the element's template\n  render() {\n    return html`\n      <style>\n        :host{ \n          margin: 5px; \n        }\n      \n        .response { margin-top: 10px; } \n      </style>\n   <div>\\`Tag name doesn't match the JS module name<div>inner</div></div>   <div id='test'  class='response'>greedy</div>\n    `;\n static get styles() { return css`:host { background-color: pink } <span>incorrect content</span>`; } }\n}\n\n// Register the element with the browser\ncustomElements.define('my-greedy-element', MyGreedyLitElement);"
               }
             ]
         }