feat: update UI to add hints about implicit ^ and $ (#4667)

This PR updates the UI to reflect the changes to the implicit ^ and $
that we now add. The changes are:

1. Show input adornments for ^ and $ when you create a pattern.
2. Mention that ^ and $ are added implicitly in description.
3. Checks the example you provide against the pattern with added ^ and $
+ adds a test for that.

Points 1 and 2:

![image](https://github.com/Unleash/unleash/assets/17786332/88c610b4-444b-4a83-a50a-4b7639614a86)


## Discussion point:

I have not touched the information about the pattern yet as the PR that
updates that is still in review (#4656), but it would be prudent to also
update that info to make it clearer. I can address that in a follow-up
PR.

frontend/src/component/feature/FeatureNamingPatternInfo/FeatureNamingPatternInfo.tsx

@@ -37,7 +37,7 @@ export const FeatureNamingPatternInfo: React.FC<Props> = ({
             <dl id="feature-naming-pattern-info">
                 <dt>Pattern</dt>
                 <dd>
-                    <code>{featureNaming.pattern}</code>
+                    <code>^{featureNaming.pattern}$</code>
                 </dd>
                 <ConditionallyRender
                     condition={Boolean(featureNaming?.example)}

frontend/src/component/project/Project/ProjectForm/FeatureFlagNamingTooltip.tsx

@@ -4,7 +4,6 @@ import { HelpIcon } from 'component/common/HelpIcon/HelpIcon';
 
 export const FeatureFlagNamingTooltip: FC = () => {
     const X = 'X';
-    const Y = 'Y';
     const nx = 'n{X,}';
     const nxy = 'n{X,Y}';
     return (
@@ -14,7 +13,7 @@ export const FeatureFlagNamingTooltip: FC = () => {
                 <Box>
                     <h3>Enforce a naming convention for feature flags</h3>
                     <hr />
-                    <p>{`eg. ^[A-Za-z0-9]{2}[.][a-z]{4,12}$ matches 'a1.project'`}</p>
+                    <p>{`eg. [A-Za-z0-9]{2}[.][a-z]{4,12} matches 'a1.project'`}</p>
                     <div className="scrollable">
                         <h3>Brackets:</h3>
                         <table>

frontend/src/component/project/Project/ProjectForm/ProjectForm.tsx

@@ -4,7 +4,7 @@ import { StickinessSelect } from 'component/feature/StrategyTypes/FlexibleStrate
 import { ConditionallyRender } from 'component/common/ConditionallyRender/ConditionallyRender';
 import Select from 'component/common/select';
 import { ProjectMode } from '../hooks/useProjectForm';
-import { Box, styled, TextField } from '@mui/material';
+import { Box, InputAdornment, styled, TextField } from '@mui/material';
 import { CollaborationModeTooltip } from './CollaborationModeTooltip';
 import Input from 'component/common/Input/Input';
 import { FeatureTogglesLimitTooltip } from './FeatureTogglesLimitTooltip';
@@ -106,6 +106,10 @@ const StyledFlagNamingContainer = styled('div')(({ theme }) => ({
     '& > *': { width: '100%' },
 }));
 
+const StyledPatternNamingExplanation = styled('div')(({ theme }) => ({
+    'p + p': { marginTop: theme.spacing(1) },
+}));
+
 export const validateFeatureNamingExample = ({
     pattern,
     example,
@@ -118,7 +122,7 @@ export const validateFeatureNamingExample = ({
     if (featureNamingPatternError || !example || !pattern) {
         return { state: 'valid' };
     } else if (example && pattern) {
-        const regex = new RegExp(pattern);
+        const regex = new RegExp(`^${pattern}$`);
         const matches = regex.test(example);
         if (!matches) {
             return { state: 'invalid', reason: 'Example does not match regex' };
@@ -354,8 +358,9 @@ const ProjectForm: React.FC<IProjectForm> = ({
                                 <FeatureFlagNamingTooltip />
                             </Box>
                             <StyledSubtitle>
-                                <p id="pattern-naming-description">
+                                <StyledPatternNamingExplanation id="pattern-naming-description">
-                                    A feature flag naming pattern is a{' '}
+                                    <p>
+                                        Define a{' '}
                                         <a
                                             href={`https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_expressions`}
                                             target="_blank"
@@ -363,20 +368,35 @@ const ProjectForm: React.FC<IProjectForm> = ({
                                         >
                                             JavaScript RegEx
                                         </a>{' '}
-                                    used to enforce feature flag names within
+                                        used to enforce feature flag names
-                                    this project.
+                                        within this project. The regex will be
+                                        surrounded by a leading <code>^</code>{' '}
+                                        and a trailing <code>$</code>.
                                     </p>
                                     <p>
-                                    Leave it empty if you don’t want to add a
+                                        Leave it empty if you don’t want to add
-                                    naming pattern.
+                                        a naming pattern.
                                     </p>
+                                </StyledPatternNamingExplanation>
                             </StyledSubtitle>
                             <StyledFlagNamingContainer>
                                 <StyledInput
                                     label={'Naming Pattern'}
                                     name="feature flag naming pattern"
                                     aria-describedby="pattern-naming-description"
-                                    placeholder="^[A-Za-z]+\.[A-Za-z]+\.[A-Za-z0-9-]+$"
+                                    placeholder="[A-Za-z]+\.[A-Za-z]+\.[A-Za-z0-9-]+"
+                                    InputProps={{
+                                        startAdornment: (
+                                            <InputAdornment position="start">
+                                                ^
+                                            </InputAdornment>
+                                        ),
+                                        endAdornment: (
+                                            <InputAdornment position="end">
+                                                $
+                                            </InputAdornment>
+                                        ),
+                                    }}
                                     type={'text'}
                                     value={featureNamingPattern || ''}
                                     error={Boolean(errors.featureNamingPattern)}

frontend/src/component/project/Project/ProjectForm/validate-feature-naming.test.ts

@@ -47,4 +47,14 @@ describe('validateFeatureNaming', () => {
             expect(result.state).toBe(state);
         }
     );
+
+    test('the pattern gets an implicit leading ^ and trailing $ added', () => {
+        const result = validateFeatureNamingExample({
+            pattern: '[a-z]+',
+            example: 'not.valid',
+            featureNamingPatternError: undefined,
+        });
+
+        expect(result.state).toBe('invalid');
+    });
 });