fix(ui): don't reset regex selection

Fixes #2520

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## [Unreleased]
+
+### Fixed
+
+- Don't reset regex toggle when adding new silence labels #2520
+
 ## v0.77
 
 ### Fixed

ui/src/Components/SilenceModal/SilenceMatch/LabelValueInput.test.tsx

@@ -102,14 +102,14 @@ describe("<LabelValueInput />", () => {
     expect(matcher.isRegex).toBe(false);
   });
 
-  it("selecting one option when matcher.isRegex=true changes it back to false", () => {
+  it("selecting one option when matcher.isRegex=true doesn't change it back to false", () => {
     matcher.isRegex = true;
     const tree = MountedLabelValueInput(true);
     tree.find("input").simulate("change", { target: { value: "f" } });
     expect(matcher.isRegex).toBe(true);
     const options = tree.find("div.react-select__option");
     options.at(0).simulate("click");
-    expect(matcher.isRegex).toBe(false);
+    expect(matcher.isRegex).toBe(true);
   });
 
   it("selecting multiple options forces matcher.isRegex=true", () => {

ui/src/Components/SilenceModal/SilenceMatch/LabelValueInput.tsx

@@ -101,8 +101,6 @@ const LabelValueInput: FC<{
         // force regex if we have multiple values
         if (matcher.values.length > 1 && matcher.isRegex === false) {
           matcher.isRegex = true;
-        } else if (matcher.values.length === 1 && matcher.isRegex === true) {
-          matcher.isRegex = false;
         }
       }}
       hideSelectedOptions