Translatable error msg to frontend if new dashboard url already in use (#153501)

homeassistant/components/lovelace/dashboard.py

@@ -287,7 +287,11 @@ class DashboardsCollection(collection.DictStorageCollection):
             raise vol.Invalid("Url path needs to contain a hyphen (-)")
 
         if url_path in self.hass.data[DATA_PANELS]:
-            raise vol.Invalid("Panel url path needs to be unique")
+            raise HomeAssistantError(
+                translation_domain=DOMAIN,
+                translation_key="url_already_exists",
+                translation_placeholders={"url": url_path},
+            )
 
         return self.CREATE_SCHEMA(data)  # type: ignore[no-any-return]
 

homeassistant/components/lovelace/strings.json

@@ -1,4 +1,9 @@
 {
+  "exceptions": {
+    "url_already_exists": {
+      "message": "The URL \"{url}\" is already in use. Please choose a different one."
+    }
+  },
   "services": {
     "reload_resources": {
       "description": "Reloads dashboard resources from the YAML-configuration.",

tests/components/lovelace/test_dashboard.py

@@ -374,7 +374,7 @@ async def test_storage_dashboards(
     assert response["success"]
     assert response["result"] == []
 
-    # Add a wrong dashboard
+    # Add a wrong dashboard (no hyphen)
     await client.send_json(
         {
             "id": 6,
@@ -484,16 +484,36 @@ async def test_storage_dashboards(
     assert response["result"][0]["show_in_sidebar"] is False
     assert response["result"][0]["require_admin"] is False
 
-    # Add dashboard with existing url path
+    # Add a wrong dashboard (missing title)
     await client.send_json(
-        {"id": 14, "type": "lovelace/dashboards/create", "url_path": "created-url-path"}
+        {
+            "id": 14,
+            "type": "lovelace/dashboards/create",
+            "url_path": "path",
+        }
     )
     response = await client.receive_json()
     assert not response["success"]
+    assert response["error"]["code"] == "invalid_format"
+
+    # Add dashboard with existing url path
+    await client.send_json(
+        {
+            "id": 15,
+            "type": "lovelace/dashboards/create",
+            "url_path": "created-url-path",
+            "title": "Another title",
+        }
+    )
+    response = await client.receive_json()
+    assert not response["success"]
+    assert response["error"]["code"] == "home_assistant_error"
+    assert response["error"]["translation_key"] == "url_already_exists"
+    assert response["error"]["translation_placeholders"]["url"] == "created-url-path"
 
     # Delete dashboards
     await client.send_json(
-        {"id": 15, "type": "lovelace/dashboards/delete", "dashboard_id": dashboard_id}
+        {"id": 16, "type": "lovelace/dashboards/delete", "dashboard_id": dashboard_id}
     )
     response = await client.receive_json()
     assert response["success"]