Fix: Prometheus regex ad-hoc filters w/ wildcards (#16234)

Fixes #14615.

Removes extra escaping for regex filter values when using ad hoc
filters for Prometheus. The extra escaping causes queries with
regex characters to be invalid.

public/app/plugins/datasource/prometheus/datasource.ts

@@ -215,7 +215,7 @@ export class PrometheusDatasource implements DataSourceApi<PromQuery> {
       const { key, operator } = filter;
       let { value } = filter;
       if (operator === '=~' || operator === '!~') {
-        value = prometheusSpecialRegexEscape(value);
+        value = prometheusRegularEscape(value);
       }
       return addLabelToQuery(acc, key, value, operator);
     }, expr);

public/app/plugins/datasource/prometheus/specs/datasource.test.ts

@@ -5,8 +5,8 @@ import {
   alignRange,
   extractRuleMappingFromGroups,
   PrometheusDatasource,
-  prometheusSpecialRegexEscape,
   prometheusRegularEscape,
+  prometheusSpecialRegexEscape,
 } from '../datasource';
 
 jest.mock('../metric_find_query');
@@ -91,6 +91,25 @@ describe('PrometheusDatasource', () => {
       const result = ctx.ds.createQuery(target, { interval: '15s' });
       expect(result).toMatchObject({ expr: 'metric{job="foo",k1="v1",k2!="v2"} - metric{k1="v1",k2!="v2"}' });
     });
+
+    it('should add escaping if needed to regex filter expressions', () => {
+      ctx.templateSrvMock.getAdhocFilters = () => [
+        {
+          key: 'k1',
+          operator: '=~',
+          value: 'v.*',
+        },
+        {
+          key: 'k2',
+          operator: '=~',
+          value: `v'.*`,
+        },
+      ];
+      const result = ctx.ds.createQuery(target, { interval: '15s' });
+      expect(result).toMatchObject({
+        expr: `metric{job="foo",k1=~"v.*",k2=~"v\\\\'.*"} - metric{k1=~"v.*",k2=~"v\\\\'.*"}`,
+      });
+    });
   });
 
   describe('When performing performSuggestQuery', () => {