fix: move client side frontend resources to META-INF/frontend (#12128)

flow-client/tsconfig.json

@@ -13,12 +13,12 @@
     "noUnusedLocals": true,
     "noUnusedParameters": true,
     "experimentalDecorators": true,
-    "outDir": "target/classes/META-INF/resources/frontend",
+    "outDir": "target/classes/META-INF/frontend",
     "declaration": true,
     "skipLibCheck": true
   },
   "include": [
-    "src/main/resources/META-INF/resources/frontend/**/*.ts"
+    "src/main/resources/META-INF/frontend/**/*.ts"
   ],
   "exclude": []
 }

flow-tests/test-root-context/src/test/java/com/vaadin/flow/ClientResourceIT.java

@@ -0,0 +1,49 @@
+/*
+ * Copyright 2000-2021 Vaadin Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+package com.vaadin.flow;
+
+import java.io.IOException;
+import java.net.HttpURLConnection;
+import java.net.MalformedURLException;
+import java.net.URL;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import com.vaadin.flow.testutil.ChromeBrowserTest;
+
+public class ClientResourceIT extends ChromeBrowserTest {
+
+    @Test
+    public void clientResourcesAreNotExposed() throws IOException {
+        assertResourceIsUnavailable("frontend/VaadinDevmodeGizmo.js.map");
+        assertResourceIsUnavailable("frontend/VaadinDevmodeGizmo.d.ts");
+        assertResourceIsUnavailable("frontend/VaadinDevmodeGizmo.js");
+        assertResourceIsUnavailable("frontend/VaadinDevmodeGizmo.ts");
+    }
+
+    private void assertResourceIsUnavailable(String path) throws IOException {
+        URL url = getResourceURL(path);
+        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
+        int responseCode = connection.getResponseCode();
+        Assert.assertEquals(HttpURLConnection.HTTP_NOT_FOUND, responseCode);
+    }
+
+    private URL getResourceURL(String path) throws MalformedURLException {
+        String url = getRootURL() + "/" + path;
+        return new URL(url);
+    }
+}