loki: better error message when escaping is involved (#50352)

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

@@ -186,4 +186,50 @@ describe('loki backendResultTransformer', () => {
     );
     expect(result.data[0]?.meta?.custom?.error).toBe('Error when parsing some of the logs');
   });
+
+  it('improve loki escaping error message when query contains escape', () => {
+    const response: DataQueryResponse = {
+      data: [],
+      error: {
+        refId: 'A',
+        message: 'parse error at line 1, col 2: invalid char escape',
+      },
+    };
+
+    const result = transformBackendResult(
+      response,
+      [
+        {
+          refId: 'A',
+          expr: '{place="g\\arden"}',
+        },
+      ],
+      []
+    );
+    expect(result.error?.message).toBe(
+      `parse error at line 1, col 2: 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://grafana.com/docs/loki/latest/logql/.`
+    );
+  });
+
+  it('do not change loki escaping error message when query does not contain escape', () => {
+    const response: DataQueryResponse = {
+      data: [],
+      error: {
+        refId: 'A',
+        message: 'parse error at line 1, col 2: invalid char escape',
+      },
+    };
+
+    const result = transformBackendResult(
+      response,
+      [
+        {
+          refId: 'A',
+          expr: '{place="garden"}',
+        },
+      ],
+      []
+    );
+    expect(result.error?.message).toBe('parse error at line 1, col 2: invalid char escape');
+  });
 });

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

@@ -1,4 +1,4 @@
-import { DataQueryResponse, DataFrame, isDataFrame, FieldType, QueryResultMeta } from '@grafana/data';
+import { DataQueryResponse, DataFrame, isDataFrame, FieldType, QueryResultMeta, DataQueryError } from '@grafana/data';
 
 import { getDerivedFields } from './getDerivedFields';
 import { makeTableFrames } from './makeTableFrames';
@@ -101,12 +101,39 @@ function groupFrames(
   return { streamsFrames, metricInstantFrames, metricRangeFrames };
 }
 
+function improveError(error: DataQueryError | undefined, queryMap: Map<string, LokiQuery>): DataQueryError | undefined {
+  // many things are optional in an error-object, we need an error-message to exist,
+  // and we need to find the loki-query, based on the refId in the error-object.
+  if (error === undefined) {
+    return error;
+  }
+
+  const { refId, message } = error;
+  if (refId === undefined || message === undefined) {
+    return error;
+  }
+
+  const query = queryMap.get(refId);
+  if (query === undefined) {
+    return error;
+  }
+
+  if (message.includes('escape') && query.expr.includes('\\')) {
+    return {
+      ...error,
+      message: `${message}. Make sure that all special characters are escaped with \\. For more information on escaping of special characters visit LogQL documentation at https://grafana.com/docs/loki/latest/logql/.`,
+    };
+  }
+
+  return error;
+}
+
 export function transformBackendResult(
   response: DataQueryResponse,
   queries: LokiQuery[],
   derivedFieldConfigs: DerivedFieldConfig[]
 ): DataQueryResponse {
-  const { data, ...rest } = response;
+  const { data, error, ...rest } = response;
 
   // in the typescript type, data is an array of basically anything.
   // we do know that they have to be dataframes, so we make a quick check,
@@ -124,6 +151,7 @@ export function transformBackendResult(
 
   return {
     ...rest,
+    error: improveError(error, queryMap),
     data: [
       ...processMetricRangeFrames(metricRangeFrames),
       ...processMetricInstantFrames(metricInstantFrames),