Escape backslashes in regexps in Loki label browser (#45809, #47039). (#47412)

* Escape backslashes in regexps in Loki label browser (#45809, #47039).

* Escape values in Loki Query Builder.

* Escape more values in Loki Query Builder.

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

@@ -17,3 +17,37 @@ export function shouldRefreshLabels(range?: TimeRange, prevRange?: TimeRange): b
   }
   return false;
 }
+
+// Loki regular-expressions use the RE2 syntax (https://github.com/google/re2/wiki/Syntax),
+// so every character that matches something in that list has to be escaped.
+// the list of meta characters is: *+?()|\.[]{}^$
+// we make a javascript regular expression that matches those characters:
+const RE2_METACHARACTERS = /[*+?()|\\.\[\]{}^$]/g;
+function escapeLokiRegexp(value: string): string {
+  return value.replace(RE2_METACHARACTERS, '\\$&');
+}
+
+// based on the openmetrics-documentation, the 3 symbols we have to handle are:
+// - \n ... the newline character
+// - \  ... the backslash character
+// - "  ... the double-quote character
+export function escapeLabelValueInExactSelector(labelValue: string): string {
+  return labelValue.replace(/\\/g, '\\\\').replace(/\n/g, '\\n').replace(/"/g, '\\"');
+}
+
+export function escapeLabelValueInRegexSelector(labelValue: string): string {
+  return escapeLabelValueInExactSelector(escapeLokiRegexp(labelValue));
+}
+
+export function escapeLabelValueInSelector(labelValue: string, selector?: string): string {
+  return isRegexSelector(selector)
+    ? escapeLabelValueInRegexSelector(labelValue)
+    : escapeLabelValueInExactSelector(labelValue);
+}
+
+export function isRegexSelector(selector?: string) {
+  if (selector && (selector.includes('=~') || selector.includes('!~'))) {
+    return true;
+  }
+  return false;
+}