Loki: Allow regex in `label` derived field (#96609)

* Loki: Allow regex in `label` derived field

* add docs

* change to caution

docs/sources/datasources/loki/configure-loki-data-source.md

@@ -114,9 +114,13 @@ Each derived field consists of the following:
 
 - **Type** - Defines the type of the derived field. It can be either:
 
-  - **Regex**: A regular expression to parse a part of the log message and capture it as the value of the new field. Can contain only one capture group.
+{{% admonition type="caution" %}}
+Using complex regular expressions in either type can impact browser performance when processing large volumes of logs. Consider using simpler patterns when possible.
+{{% /admonition %}}
+
+- **Regex**: A regular expression to parse a part of the log message and capture it as the value of the new field. Can contain only one capture group.
 
-  - **Label**: A label from the selected log line. This can be any type of label - indexed, parsed or structured metadata. The label's value will be used as the value of the derived field.
+- **Label**: A label from the selected log line. This can be any type of label - indexed, parsed or structured metadata. When using this type, the input will match as a regular expression against label keys, allowing you to match variations like `traceid` and `trace_id` with a single regex pattern like `trace[_]?id`. The value of the matched label will be used as the value of the derived field.
 
 - **URL/query** Sets the full link URL if the link is external, or a query for the target data source if the link is internal. You can interpolate the value from the field with the `${__value.raw}` macro.
 

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

@@ -192,4 +192,28 @@ describe('getDerivedFields', () => {
       title: '',
     });
   });
+
+  it('matches label keys using regex when matcherType is label', () => {
+    const df = createDataFrame({
+      fields: [
+        { name: 'labels', values: [{ traceId: 'abc' }, { traceID: 'xyz' }] },
+        { name: 'line', values: ['log1', 'log2'] },
+      ],
+    });
+    const newFields = getDerivedFields(df, [
+      {
+        matcherRegex: 'traceI(d|D)',
+        name: 'traceIdFromLabel',
+        url: 'http://localhost/${__value.raw}',
+        matcherType: 'label',
+      },
+    ]);
+    expect(newFields.length).toBe(1);
+    const traceId = newFields.find((f) => f.name === 'traceIdFromLabel');
+    expect(traceId!.values).toEqual(['abc', 'xyz']);
+    expect(traceId!.config.links![0]).toEqual({
+      url: 'http://localhost/${__value.raw}',
+      title: '',
+    });
+  });
 });

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

@@ -30,10 +30,11 @@ export function getDerivedFields(dataFrame: DataFrame, derivedFieldConfigs: Deri
       if (derivedFieldsGrouped[field.name][0].matcherType === 'label' && labelFields) {
         const label = labelFields.values[i];
         if (label) {
-          // Find the key that matches both, the `matcherRegex` and the label key
-          const intersectingKey = Object.keys(label).find(
-            (key) => derivedFieldsGrouped[field.name][0].matcherRegex === key
-          );
+          // Find the key that matches the regex pattern in `matcherRegex`
+          const intersectingKey = Object.keys(label).find((key) => {
+            const regex = new RegExp(derivedFieldsGrouped[field.name][0].matcherRegex);
+            return regex.test(key);
+          });
 
           if (intersectingKey) {
             field.values.push(label[intersectingKey]);