Loki: Improve error message for unescaped \ and add LogQL link to docs (#26136)

* Add custom escaping error message

* Include regex escape error message

* Update docs, add logql link

* Refactor

docs/sources/features/datasources/loki.md

@@ -59,7 +59,7 @@ The new field with the link shown in log details:
 
 ## Querying Logs
 
-Querying and displaying log data from Loki is available via [Explore]({{< relref "../explore" >}}), and with the [logs panel]({{< relref "../../panels/visualizations/logs-panel.md" >}}) in dashboards. Select the Loki data source, and then enter a log query to display your logs.
+Querying and displaying log data from Loki is available via [Explore]({{< relref "../explore" >}}), and with the [logs panel]({{< relref "../../panels/visualizations/logs-panel.md" >}}) in dashboards. Select the Loki data source, and then enter a [LogQL](https://github.com/grafana/loki/blob/master/docs/logql.md) query to display your logs.
 
 ### Log Queries
 

public/app/plugins/datasource/loki/datasource.test.ts

@@ -189,6 +189,33 @@ describe('LokiDatasource', () => {
       expect(dataFrame.meta?.limit).toBe(20);
       expect(dataFrame.meta?.searchWords).toEqual(['foo']);
     });
+
+    test('should return custom error message when Loki returns escaping error', async () => {
+      const customData = { ...(instanceSettings.jsonData || {}), maxLines: 20 };
+      const customSettings = { ...instanceSettings, jsonData: customData };
+      const ds = new LokiDatasource(customSettings, templateSrvMock);
+
+      datasourceRequestMock.mockImplementation(
+        jest.fn().mockReturnValueOnce(
+          Promise.reject({
+            data: 'parse error at line 1, col 6: invalid char escape',
+            status: 400,
+            statusText: 'Bad Request',
+          })
+        )
+      );
+      const options = getQueryOptions<LokiQuery>({
+        targets: [{ expr: '{job="gra\\fana"}', refId: 'B' }],
+      });
+
+      try {
+        await ds.query(options).toPromise();
+      } catch (err) {
+        expect(err.message).toBe(
+          'Error: parse error at line 1, col 6: invalid char escape. Make sure that all special characters are escaped with \\. For more information on escaping of special characters visit LogQL documentation at https://github.com/grafana/loki/blob/master/docs/logql.md.'
+        );
+      }
+    });
   });
 
   describe('When interpolating variables', () => {

public/app/plugins/datasource/loki/datasource.ts

@@ -537,7 +537,11 @@ export class LokiDatasource extends DataSourceApi<LokiQuery, LokiOptions> {
 
     if (err.data) {
       if (typeof err.data === 'string') {
-        error.message = err.data;
+        if (err.data.includes('escape') && target.expr.includes('\\')) {
+          error.message = `Error: ${err.data}. Make sure that all special characters are escaped with \\. For more information on escaping of special characters visit LogQL documentation at https://github.com/grafana/loki/blob/master/docs/logql.md.`;
+        } else {
+          error.message = err.data;
+        }
       } else if (err.data.error) {
         error.message = safeStringifyValue(err.data.error);
       }